U.S. patent application number 11/195593 was filed with the patent office on 2005-12-22 for laser apparatus, exposure head, exposure apparatus, and optical fiber connection method.
This patent application is currently assigned to FUJI PHOTO FILM CO., LTD.. Invention is credited to Fujii, Takeshi, Ishikawa, Hiromi, Nagano, Kazuhiko, Okazaki, Yoji, Yamakawa, Hiromitsu.
Application Number | 20050281516 11/195593 |
Document ID | / |
Family ID | 31191849 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050281516 |
Kind Code |
A1 |
Okazaki, Yoji ; et
al. |
December 22, 2005 |
Laser apparatus, exposure head, exposure apparatus, and optical
fiber connection method
Abstract
An optical fiber of a bundled fiber light source is an optical
fiber whose core diameter is uniform but whose emission end
cladding diameter is smaller than an incidence end cladding
diameter thereof, and a light emission region thereof is made
smaller. An angle of luminous flux from this higher luminance
bundled fiber light source, which passes through a lens system and
is incident on a DMD, is smaller, i.e., an illumination NA is made
smaller. Thus, an angle of flux which is incident on a surface that
is to be exposed is smaller. That is, a minute image formation beam
can be obtained without increasing the image formation NA, focal
depth is lengthen.
Inventors: |
Okazaki, Yoji; (Kanagawa,
JP) ; Ishikawa, Hiromi; (Kanagawa, JP) ;
Nagano, Kazuhiko; (Kanagawa, JP) ; Fujii,
Takeshi; (Kanagawa, JP) ; Yamakawa, Hiromitsu;
(Saitama-ken, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJI PHOTO FILM CO., LTD.
|
Family ID: |
31191849 |
Appl. No.: |
11/195593 |
Filed: |
August 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11195593 |
Aug 3, 2005 |
|
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|
10409675 |
Apr 9, 2003 |
|
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6960035 |
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Current U.S.
Class: |
385/96 |
Current CPC
Class: |
G02B 6/08 20130101; G02B
6/2551 20130101; G02B 6/4206 20130101; G02B 6/04 20130101; H01S
3/06708 20130101; G02B 6/4249 20130101; G02B 6/425 20130101; H01S
3/06745 20130101 |
Class at
Publication: |
385/096 |
International
Class: |
G02B 006/255 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2002 |
JP |
2002-108543 |
May 23, 2002 |
JP |
2002-149888 |
Sep 30, 2002 |
JP |
2002-287632 |
Claims
1-18. (canceled)
19. An optical fiber connection method for connecting two optical
fibers with different cladding diameters, the method comprising the
steps of: machining cladding of one end portion of the optical
fiber whose cladding diameter is larger to a diameter substantially
the same as the cladding diameter of the optical fiber whose
cladding diameter is smaller; and fusing the optical fiber whose
cladding diameter is smaller to the one end portion of the optical
fiber that has been machined.
20. An optical fiber connection method for connecting two optical
fibers with different cladding diameters, the method comprising the
steps of: machining cladding of one end portion of the optical
fiber whose cladding diameter is larger to a diameter intermediate
to the cladding diameters of the two optical fibers; and fusing the
optical fiber whose cladding diameter is smaller to the one end
portion of the optical fiber that has been machined.
21. An optical fiber connection method for connecting two optical
fibers with different cladding diameters, the method comprising the
steps of: fusing one end portion of an optical fiber with a
cladding diameter intermediate to the cladding diameters of the two
optical fibers to the optical fiber whose cladding diameter is
larger; and fusing the other end portion of the optical fiber with
the intermediate cladding diameter to the optical fiber whose
cladding diameter is smaller.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a laser apparatus, an
exposure head, and an exposure apparatus, and particularly relates
to a suitable high-brightness laser apparatus which illuminates a
spatial light-modulation element, an exposure head which exposes a
photosensitive material with a laser beam modulated by a spatial
light-modulation element in accordance with image data, and an
exposure apparatus equipped with this exposure head.
[0003] Furthermore, the present invention relates to an optical
fiber connection method and, in particular detail, to a method for
connecting two optical fibers whose cladding diameters differ.
[0004] 2. Description of the Prior Art
[0005] Heretofore, various exposure apparatuses which employ
spatial light modulation elements such as digital micromirror
devices (DMD) have been proposed for carrying out image exposure
with light beams modulated in accordance with image data. An
example of a DMD is a mirror device in which numerous micromirrors,
which alter angles of reflection surfaces thereof in accordance
with control signals, are arranged in a two-dimensional pattern on
a semiconductor support of silicon or the like. An example of an
exposure apparatus that utilizes such a DMD is, as shown in FIG.
15A, structured by a light source 1 which irradiates laser light, a
lens system 2 which collimates the laser light irradiated from the
light source 1, a DMD 3 which is disposed substantially at a
focusing position of the lens system 2, and lens systems 4 and 6
which focus the laser light that has been reflected at the DMD 3
onto a scanning surface 5. In this exposure apparatus, the
respective micromirrors of the DMD 3 are switched on and off by a
control apparatus (not shown), in accordance with control signals
generated in accordance with image data or the like, and modulate
the laser light. Thus, image exposure is carried out by modulated
laser light.
[0006] At the light source 1, a structural unit is plurally
disposed. This structural unit is equipped, as shown in FIG. 29,
with a single semiconductor laser 7, a single multi-mode optical
fiber 8, and a pair of collimator lenses 9. The pair of collimator
lenses 9 focuses laser light irradiated from the semiconductor
laser 7 at an end face of the multi-mode optical fiber 8. The light
source 1 is structured at a bundle-form fiber light source in which
a plurality of the multi-mode optical fibers 8 are bundled.
[0007] Commonly, a laser with an output of around 30 mW
(milliwatts) is employed as the semiconductor laser 7, and an
optical fiber with a core diameter of 50 .mu.m, a cladding diameter
of 125 .mu.m and an NA (numerical aperture) of 0.2 is employed as
the multi-mode optical fiber 8. Accordingly, if an output of around
1 W (watt) is to be obtained, it is necessary to bundle a total of
forty-eight (eight by six) of the multi-mode optical fibers 8 of
the above-described structural units, and a diameter of the light
emission point is about 1 mm.
[0008] However, in a conventional light source, the diameter of a
light emission point becomes larger in the event of bundling and,
consequently, there is a problem in that sufficient depth of focus
cannot be obtained when a high resolution exposure head is to be
structured. Sufficient focal depth cannot be obtained, in
particular, in the case of very high resolution exposure with a
beam diameter of around 1 .mu.m. Moreover, beam blurring occurs at
peripheral edge portions of an area-form exposure beam.
[0009] Further, when a high power output exposure head is
structured with a conventional exposure head, the number of optical
fibers that are bundled increases. Thus, there are problems in
that, not only do costs increase, but diameter of a light emission
point becomes larger, and the illumination NA with respect to the
spatial light modulation element also becomes larger. As a result,
the image formation NA of the image formation beam becomes larger.
Thus, focal depth becomes shallower.
SUMMARY OF THE INVENTION
[0010] The present invention has been devised in the hope of
solving the problems described above. A purpose of the present
invention is to provide a high-brightness laser apparatus that
enables size reduction of the illumination NA with respect to the
spatial light modulation element. Another purpose of the present
invention is to obtain a minute image formation spot without
increasing the image formation NA of the image formation beam, and
to thereby provide an exposure head and exposure apparatus capable
of providing deep focal depth. Yet another purpose of the present
invention is to provide an exposure head and exposure apparatus
with high power outputs and low costs.
[0011] In order to achieve these purposes, a laser apparatus of the
present invention includes a fiber light source which includes an
optical fiber with an incidence end and an emission end, the fiber
light source emitting laser light that enters the incidence end of
the optical fiber from the emission end of the optical fiber,
wherein the optical fiber includes an optical fiber having a
uniform core diameter and a cladding diameter of the emission end
which is smaller than a cladding diameter of the incidence end.
[0012] Because the laser apparatus of the present invention is
equipped with the fiber light source which emits laser light that
has entered through the incidence end of the optical fiber from the
emission end thereof, and utilizes the optical fiber in which the
core diameter is uniform but the cladding diameter of the incidence
end is smaller than the cladding diameter of the emission end, a
light emission portion diameter of the light source can be made
smaller and higher luminance can be provided.
[0013] The fiber light source may, for example, be a fiber light
source with a structure in which a single semiconductor laser is
joined at the incidence end of a single optical fiber. However, a
multiplex laser light source in which a plurality of laser lights
are multiplexed and respectively fed into an optical fiber is
favorable. Higher output can be obtained by employing a multiplex
laser light source. Further, light emission points at emission ends
of optical fibers of a plurality of fiber light sources can be
arranged in an array pattern to form a fiber array light source, or
the respective light emission points can be arranged in the form of
a bundle to form a fiber bundle light source. Even in such cases of
bundling or arraying, the number of optical fibers that are
bundled/arrayed in order to obtain the same light output may be
smaller, and costs are lower. Furthermore, when the number of
optical fibers is small, a light emission region when the optical
fibers are bundled or arrayed can also be made small. In other
words, luminance can be made higher.
[0014] A multiplex laser light source may, for example, be: (1) a
structure which includes a plurality of semiconductor lasers, a
single optical fiber, and a condensing optical system which
condenses laser light emitted from each of the plurality of
semiconductor lasers and focuses the condensed beams at the
incidence end of the optical fiber; (2) a structure which includes
a multi-cavity laser provided with a plurality of light emission
points, a single optical fiber, and a condensing optical system
which condenses laser light emitted from each of the plurality of
light emission points and focuses the condensed beams at the
incidence face of the optical fiber; or (3) a structure which
includes a plurality of multi-cavity lasers, a single optical
fiber, and a condensing optical system which condenses laser light
emitted from each of a plurality of light emission points of the
plurality of multi-cavity lasers and focuses the condensed beams at
the incidence end of the optical fiber.
[0015] From the viewpoint of the diameter of a light emission point
being small, it is preferable if the cladding diameter of the
emission end of the optical fiber is smaller than 125 .mu.m, more
preferably 80 .mu.m or less, and particularly preferably 60 .mu.m
or less. An optical fiber in which the core diameter is uniform and
the cladding diameter of the emission end is smaller than the
cladding diameter of the incidence end may be structured by, for
example, joining a plurality of optical fibers with the same core
diameter and different cladding diameters. Furthermore, when a
plurality of optical fibers are structured to be detachably
connected with a connector or connectors, replacement in a case in
which the light source module is partially damaged or the like is
simple.
[0016] In order to achieve the aforementioned purposes, an exposure
head of the present invention includes: the laser apparatus of the
present invention; a spatial modulation element which modulates
laser light irradiated from the laser apparatus, the spatial
modulation element including numerous pixel portions, light
modulation states of which change in accordance with respective
control signals, the pixel portions being arranged in a
two-dimensional form on a support; and an optical system for
focusing laser light that has been modulated at the pixel portions
on an exposure surface. Further, the exposure apparatus of the
present invention includes: the exposure head of the present
invention; and moving means which moves the exposure head
relatively with respect to the exposure surface.
[0017] In the exposure head of the present invention and the
exposure apparatus of the present invention, the spatial modulation
element modulates the laser light from the laser apparatus and
controls exposure. Because the high-brightness laser apparatus is
provided to serve as the laser apparatus, long focal depth can be
obtained. Furthermore, in a case in which a multiplex laser light
source at which a plurality of laser lights are multiplexed and fed
into respective optical fibers is utilized as the fiber light
source structuring the laser apparatus, high power output can be
obtained. Moreover, even in a case of bundling or arraying, the
number of light fibers need only be small, and lower costs can be
expected.
[0018] As the spatial modulation element, a micromirror device (a
DMD: digital micromirror device) at which a large number of
reflection surfaces, whose angles are adjustable in accordance with
respective control signals, are arranged in a two-dimensional
pattern on a micromirror support (for example, a silicon support)
can be utilized. Further, the spatial modulation element may be
structured with a one-dimensional grating light valve (GLV) whose
structure includes numerous movable grilles and fixed grilles
alternately disposed in parallel. The movable grilles are provided
with ribbon-like reflection surfaces and are movable in accordance
with control signals, and the fixed grilles are provided with
ribbon-like reflection surfaces. Further still, the spatial
modulation element may be structured with a two-dimensional light
valve array in which GLVs are arranged in the form of an array.
Further again, a liquid crystal shutter array whose structure
includes numerous liquid crystal cells, which are capable of
blocking transmitted light in accordance with respective control
signals, arranged in a two-dimensional pattern on a support may be
utilized.
[0019] It is preferable if a microlens array is disposed at an
emission side of the spatial modulation element. The microlens
array is provided with microlenses which are provided in respective
correspondence with pixel portions of the spatial modulation
element and which condense laser light from the respective pixels.
In a case in which a microlens array is disposed thus, the laser
lights that have been modulated at the respective pixel portions of
the spatial modulation element are condensed to correspond with
respective pixels by the microlenses of the microlens array.
Consequently, even in a case in which an exposure area at a surface
to be exposed is enlarged, the size of each of beam spots can be
reduced, and exposure can be carried out with high precision.
[0020] It is also preferable if a collimator lens and a light
intensity distribution-correcting optical system are disposed
between the laser apparatus and the spatial modulation element. The
collimator lens makes luminous flux from the laser apparatus
parallel flux. The light intensity distribution-correcting optical
system converts a flux width at each of emission positions such
that a ratio of a flux width at a peripheral edge portion to a flux
width at a central portion, which is near an optical axis, is
smaller at an emission side of the light intensity
distribution-correcting optical system than at an incidence side
thereof, and corrects a light intensity distribution of the laser
light that has been converted to parallel flux by the collimator
lens so as to be substantially uniform at irradiated faces of the
spatial modulation element.
[0021] As a result of this light intensity distribution-correcting
optical system, in which, for example, light with flux widths that
are the same at the incidence side, at the emission side, the flux
width at the central portion is greater in comparison with the
peripheral edge portion and, conversely, the flux width at the
peripheral edge portion is smaller in comparison with the central
portion. Thus, because flux of the central portion can be brought
to the peripheral edge portion, the spatial modulation element can
be illuminated with light whose light intensity distribution is
substantially uniform, without reducing usage efficiency of the
light as a whole. Consequently, a high quality image can be exposed
at the exposed surface, without the occurrence of exposure
irregularities. Note that, a conventional rod integrator or a
fly-eye lens array may be utilized as the amount distribution
correction optical system.
[0022] The spatial modulation element of the exposure head and
exposure apparatus of the present invention can be controlled with
control signals that are generated in accordance with exposure
information for each of a plurality of the pixel portions whose
number is smaller than the total number of pixel portions arranged
on the support. That is, rather than controlling all of the pixel
portions arranged on the support, a subsection of the pixel
portions can be controlled. Consequently, a transmission rate of
the control signals can be made shorter than in a case in which
control signals are transmitted for all of the pixel portions, and
a modulation rate of the laser light can be made faster. As a
result, high-speed exposure is possible.
[0023] Conventionally, in exposure devices which expose
photosensitive materials with ultraviolet-region laser light
(ultraviolet exposure devices), it has been common to employ gas
lasers, such as argon lasers and the like, and solid lasers with
THG (third harmonics). However, these exposure devices have had
problems in that the devices are large and difficult to maintain,
and exposure speeds are slow. The exposure apparatus of the present
invention can be made to serve as an ultraviolet exposure device by
utilizing a GaN-based (gallium nitride) semiconductor laser with a
wavelength of 350 to 450 nm as the laser apparatus. This
ultraviolet exposure device can be provided with smaller size and
lower cost than the conventional ultraviolet exposure devices.
Moreover, high speed, high accuracy exposure is possible.
[0024] The exposure device of the present invention may be suitably
applied to an optical modelling device in which a light beam
exposes a photo-curable resin to form a three-dimensional model, a
lamination modelling device which sinters a powder with a light
beam to form sintered layers and accumulates the sintered layers to
form a three-dimensional model which is constituted by a sintered
powder body, and the like.
[0025] An optical modelling device may, for example, be provided
with a modelling tank which accommodates a photo-curable resin, a
support table which is for supporting a model and is movable up and
down within the modelling tank, and an exposure head which
includes: a laser apparatus which irradiates laser light; a spatial
modulation element including a large number of pixel portions whose
light modulation states change in accordance with respective
control signals, and which are arranged in a two-dimensional
pattern on a support, and modulate the laser light irradiated from
the laser apparatus; and an optical system which focuses the laser
light that has been modulated by the respective pixel portions onto
a liquid surface of the photo-curable resin accommodated in the
modelling tank. This optical modelling device is also provided with
moving means for moving the exposure head relative to the liquid
surface of the photo-curable resin. If the laser apparatus of the
present invention is utilized in this optical modelling device,
high-speed, high-precision modelling is possible. A specific device
structure is disclosed in Japanese Patent Application No.
2001-274360.
[0026] A lamination modelling device may, for example, be provided
with a modelling tank which accommodates a powder to be sintered by
irradiation of light, a support table which is for supporting a
model and is movable up and down within the modelling tank, and an
exposure head which includes: a laser apparatus which irradiates
laser light; a spatial modulation element including a large number
of pixel portions whose light modulation states change in
accordance with respective control signals, and which are arranged
in a two-dimensional pattern on a support, in accordance with
respective control signals and modulate the laser light irradiated
from the laser apparatus; and an optical system which focuses the
laser light that has been modulated by the respective pixel
portions onto the surface of the powder accommodated in the
modelling tank. This lamination modelling device is also provided
with moving means for moving the exposure head relative to the
surface of the powder. If the laser apparatus of the present
invention is utilized in this lamination modelling device,
high-speed, high-precision modelling is possible. A specific device
structure is disclosed in Japanese Patent Application No.
2001-274351.
[0027] A further purpose of the present invention is to provide a
method capable of reliably joining optical fibers which have a
large difference in external diameters.
[0028] A first optical fiber connection method according to the
present invention is a method for connecting two optical fibers
with different cladding diameters, which method includes the steps
of: machining cladding of one end portion of the optical fiber
whose cladding diameter is larger to a diameter substantially the
same as the cladding diameter of the optical fiber whose cladding
diameter is smaller; and fusing the optical fiber whose cladding
diameter is smaller to the one end portion of the optical fiber
that has been machined.
[0029] A second optical fiber connection method according to the
present invention is similarly a method for connecting two optical
fibers with different cladding diameters, which method includes the
steps of: machining cladding of one end portion of the optical
fiber whose cladding diameter is larger to a diameter intermediate
to the cladding diameters of the two optical fibers; and fusing the
optical fiber whose cladding diameter is smaller to the one end
portion of the optical fiber that has been machined.
[0030] A third optical fiber connection method according to the
present invention is similarly a method for connecting two optical
fibers with different cladding diameters, which method includes the
steps of: fusing one end portion of an optical fiber with a
cladding diameter intermediate to the cladding diameters of the two
optical fibers to the optical fiber whose cladding diameter is
larger; and fusing the other end portion of the optical fiber with
the intermediate cladding diameter to the optical fiber whose
cladding diameter is smaller.
[0031] In the first optical fiber connection method according to
the present invention, the cladding at the one end of the optical
fiber whose cladding diameter is larger is machined to
substantially the same diameter as the cladding diameter of the
optical fiber whose cladding diameter is small, and the optical
fiber whose cladding diameter is smaller is fused to the one end
portion of the optical fiber that has been machined. Thus,
fusion-splicing is applied to two optical fibers which have
substantially the same cladding diameter. Accordingly, the two
optical fibers can be easily and reliably joined without, as in a
case in which two optical fibers whose diameters differ greatly are
joined by fusing, an optical fiber whose external diameter is
smaller being excessively melted or, conversely, an optical fiber
whose external diameter is larger not being melted.
[0032] In the second optical fiber connection method according to
the present invention, the cladding at the one end of the optical
fiber whose cladding diameter is larger is machined to an
intermediate diameter between the cladding diameters of the two
optical fibers, and the optical fiber whose cladding diameter is
smaller is fused to the one end portion of the optical fiber that
has been machined. Thus, fusion-splicing is applied to two optical
fibers whose cladding diameters do not differ greatly. Accordingly,
with this method too, the optical fibers can be easily and reliably
joined without, as in the case in which two optical fibers whose
diameters differ greatly are joined by fusing, the optical fiber
whose external diameter is smaller being excessively melted or,
conversely, the optical fiber whose external diameter is larger not
being melted.
[0033] In the third optical fiber connection method according to
the present invention, the optical fiber whose cladding diameter is
larger and the optical fiber whose cladding diameter is smaller are
joined by fusing via an optical fiber therebetween which has an
intermediate cladding diameter between the cladding diameters of
these two optical fibers. Thus, fusion-splicing is applied to the
optical fiber having the intermediate cladding diameter and the
optical fiber having the larger cladding diameter and
fusion-splicing is applied to the optical fiber having the
intermediate cladding diameter and the optical fiber having the
smaller cladding diameter, without cladding diameters of the pair
of optical fibers in either case differing greatly. Accordingly,
with this method too, the optical fibers can be easily and reliably
joined without, as in the case in which two optical fibers whose
diameters differ greatly are joined by fusing, the optical fiber
whose external diameter is smaller being excessively melted or,
conversely, the optical fiber whose external diameter is larger not
being melted.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a perspective view showing the exterior of an
exposure apparatus relating to a first embodiment of the present
invention.
[0035] FIG. 2 is a perspective view showing a structure of a
scanner of the exposure apparatus relating to the first embodiment
of the present invention.
[0036] FIG. 3A is a plan view showing exposed regions formed at a
photosensitive material.
[0037] FIG. 3B is a view showing an arrangement of exposure areas
due to respective exposure heads.
[0038] FIG. 4 is a perspective view showing schematic structure of
an exposure head of the exposure apparatus relating to the first
embodiment of the invention.
[0039] FIG. 5A is a sectional view, cut in a sub-scanning direction
along an optical axis, showing structure of the exposure head shown
in FIG. 4.
[0040] FIG. 5B is a side view showing a structure of the exposure
head shown in FIG. 4.
[0041] FIG. 6 is a partial enlarged view showing a structure of a
digital micromirror device (DMD).
[0042] FIGS. 7A and 7B are explanatory views for explaining
operation of the DMD.
[0043] FIG. 8A is a plan view showing positions of exposure beams
and scanning lines in a case in which the DMD is not disposed at an
angle.
[0044] FIG. 8B is a plan view showing positions of exposure beams
and scanning lines in a case in which the DMD is disposed at an
angle.
[0045] FIG. 9A is a perspective view showing structure of a fiber
array light source.
[0046] FIG. 9B is a partial enlarged view of the fiber array light
source shown in FIG. 9A.
[0047] FIG. 9C is a plan view showing an arrangement of light
emission points at a laser emission section.
[0048] FIG. 9D is a plan view showing another arrangement of light
emission points at a laser emission section.
[0049] FIG. 10 is a view showing structure of a multi-mode optical
fiber.
[0050] FIG. 11 is a plan view showing structure of a multiplex
laser light source.
[0051] FIG. 12 is a plan view showing structure of a laser
module.
[0052] FIG. 13 is a side view showing structure of the laser module
shown in FIG. 12.
[0053] FIG. 14 is a partial side view showing structure of the
laser module shown in FIG. 12.
[0054] FIG. 15A is a sectional view, cut along the optical axis,
showing depth of focus in a conventional exposure apparatus.
[0055] FIG. 15B is a sectional view, cut along the optical axis,
showing depth of focus in the exposure apparatus relating to the
first embodiment of the invention.
[0056] FIG. 16A is a view showing one row of an employed region of
a DMD.
[0057] FIG. 16B is a view showing another row of the employed
region of the DMD.
[0058] FIG. 17A is a side view showing a case in which the employed
region of the DMD is appropriate.
[0059] FIG. 17B is a sectional view, cut in the sub-scanning
direction along the optical axis, of FIG. 17A.
[0060] FIG. 18 is a plan view for explaining an exposure method for
exposing a photosensitive material with a single cycle of scanning
by a scanner.
[0061] FIGS. 19A and 19B are plan views for explaining an exposure
method for exposing a photosensitive material with a plurality of
cycles of scanning by a scanner.
[0062] FIG. 20 is a perspective view showing structure of a laser
array.
[0063] FIG. 21A is a perspective view showing structure of a
multi-cavity laser.
[0064] FIG. 21B is a perspective view of a multi-cavity laser array
in which multi-cavity lasers are arranged in the form of an
array.
[0065] FIG. 22 is a plan view showing structure of another
multiplex laser light source.
[0066] FIG. 23 is a plan view showing structure of yet another
multiplex laser light source.
[0067] FIG. 24A is a plan view showing structure of still another
multiplex laser light source.
[0068] FIG. 24B is a sectional view, cut along the optical axis, of
FIG. 24A.
[0069] FIGS. 25A, 25B and 25C are views for explaining concepts of
correction by a light intensity distribution-correcting optical
system.
[0070] FIG. 26 is a graph showing a light intensity distribution in
a case in which a light source has a gaussian distribution and
correction of the light intensity distribution is not carried
out.
[0071] FIG. 27 is a graph showing a light intensity distribution
after correction by the light intensity distribution-correcting
optical system.
[0072] FIG. 28A is a sectional view, cut along the optical axis,
showing structure of another exposure head, in which a focusing
optical system is different.
[0073] FIG. 28B is a plan view showing an image which is projected
onto a surface that is to be exposed in a case in which a microlens
array or the like is not employed.
[0074] FIG. 28C is a plan view showing an image which is projected
onto the surface that is to be exposed in a case in which the
microlens array or the like is employed.
[0075] FIG. 29 is a sectional view, cut along the optical axis,
showing structure of a conventional fiber light source.
[0076] FIG. 30 is a perspective view showing schematic structure of
an exposure head of an exposure apparatus relating to a second
embodiment of the invention.
[0077] FIG. 31A is a sectional view, cut along the optical axis,
showing structure of the exposure head shown in FIG. 30.
[0078] FIG. 31B is a side view showing structure of the exposure
head shown in FIG. 31A.
[0079] FIG. 32 is a partial enlarged view showing structure of a
grating light valve (GLV).
[0080] FIGS. 33A and 33B are explanatory views for explaining
operation of the GLV.
[0081] FIG. 34 is a perspective view showing an example in which
the present invention is applied in an optical modelling
device.
[0082] FIG. 35A is a perspective view showing structure of a fiber
bundle light source.
[0083] FIG. 35B is a perspective view showing structure of a
different fiber array light source.
[0084] FIG. 36 is a plan view showing an end face of a laser
emission portion of a bundle-form fiber light source.
[0085] FIGS. 37A and 37B are views for explaining one example of an
optical fiber connection method.
[0086] FIG. 38 is a view for explaining another example of an
optical fiber connection method.
[0087] FIG. 39 is a view for explaining yet another example of an
optical fiber connection method.
[0088] FIG. 40 is a view showing structure of a multi-mode optical
fiber.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0089] Below, embodiments of the present invention will be
described in detail with reference to the drawings.
First Embodiment
[0090] Structure of Exposure Apparatus
[0091] As shown in FIG. 1, an exposure apparatus relating to an
embodiment of the present invention is provided with a flat
board-form stage 152, which sucks and retains a sheet-form
photosensitive material 150 at a surface thereof. Two guides 158,
which extend in a stage movement direction, are provided at an
upper face of a thick board-form equipment pedestal 156, which is
supported by four leg portions 154. The stage 152 is disposed such
that a longitudinal direction thereof is oriented in the stage
movement direction, and is supported by the guides 158 so as to be
movable reciprocally. In the exposure apparatus, an unillustrated
driving apparatus is provided for driving the stage 152 along the
guides 158.
[0092] At a central portion of the equipment pedestal 156, an
inverted `U`-like gate 160 is provided so as to straddle a movement
path of the stage 152. Respective end portions of the inverted
`U`-like gate 160 are fixed at two side faces of the equipment
pedestal 156. Sandwiching the gate 160, a scanner 162 is provided
at one side, and a plurality (for example, two) of detection
sensors 164 are provided at the other side. The detection sensors
164 detect a leading end and a trailing end of the photosensitive
material 150. The scanner 162 and the detection sensors 164 are
respectively mounted at the gate 160, and are fixedly disposed
upward of the movement path of the stage 152. The scanner 162 and
detection sensors 164 are connected to an unillustrated controller
which controls the scanner 162 and detection sensors 164.
[0093] As shown in FIGS. 2 and 3B, the scanner 162 is equipped with
a plurality (for example, fourteen) of exposure heads 166, which
are arranged substantially in a matrix pattern with m rows and n
columns (for example, three rows and five columns). In this
example, in consideration of width of the photosensitive material
150, four of the exposure heads 166 are provided in the third row.
Note that when an individual exposure head, which is arranged in
the m-th row and the n-th column is to be referred to, that
exposure head is denoted as exposure head 166.sub.mn.
[0094] Exposure areas 168 covered by the exposure heads 166 have
rectangular shapes with short sides thereof in a sub-scanning
direction. Consequently, in accordance with movement of the stage
152, band-form exposed regions 170 are formed on the photosensitive
material 150 at the respective exposure heads 166. Note that when
an exposure area formed by an individual exposure head, which is
arranged in the m-th row and the n-th column, is to be referred to,
that exposure area is denoted as exposure area 168.sub.mn.
[0095] As shown in FIGS. 3A and 3B, in each row, the respective
exposure heads, which are arranged in a line, are disposed to be
offset by a predetermined interval in a row arrangement direction
(which interval is an integer multiple (two in the present
embodiment) of the long dimension of the exposure areas), such that
the band-form exposed regions 170 will be lined up without gaps
therebetween in a direction intersecting the sub-scanning
direction. Thus, a portion that cannot be exposed between exposure
area 168.sub.11 and exposure area 168.sub.12 of the first row can
be exposed by exposure area 168.sub.21 of the second row and
exposure area 168.sub.31 of the third row.
[0096] As shown in FIGS. 4, 5A and 5B, at each of the exposure
areas 166.sub.11 to 166.sub.mn, a digital micromirror device (DMD)
50 is provided to serve as a spatial modulation element for
modulating an incident light beam at each of pixels in accordance
with image data. The DMD 50 is connected with an unillustrated
controller, which is provided with a data processing section and a
mirror driving control section. At the data processing section of
this controller, on the basis of inputted image data, driving
signals are generated for driving control of each micromirror in a
region of the DMD 50 at the corresponding exposure head 166 which
region is to be controlled. The regions that are to be controlled
are described later. The mirror driving control section controls
the angle of a reflection surface of each micromirror of the DMD 50
at the corresponding exposure head 166, on the basis of the control
signals generated at the image data processing section. Control of
the angles of the reflection faces is described later.
[0097] At a light incidence side of the DMD 50, a fiber array light
source 66, a lens system 67 and a mirror 69 are disposed in this
order. The fiber array light source 66 is equipped with a laser
emission section in which emission end portions (light emission
points) of optical fibers are arranged in a row along a direction
corresponding to the direction of the long sides of the exposure
area 168. The lens system 67 corrects laser light that is emitted
from the fiber array light source 66, and focuses the light on the
DMD. The mirror 69 reflects the laser light that has been
transmitted through the lens system 67 toward the DMD 50.
[0098] The lens system 67 is structured with a single pair of
combination lenses 71, which make the laser light that has been
emitted from the fiber array light source 66 parallel, a single
pair of combination lenses 73, which correct the laser light that
has been made parallel such that a light intensity distribution is
uniform, and a condensing lens 75 that focuses the laser light
whose light intensity distribution has been corrected on the DMD.
The combination lenses 73 have the functions of, in the direction
of arrangement of the laser emission ends, broadening portions of
luminous flux that are close to an optical axis of the lenses and
narrowing portions of the luminous flux that are distant from the
optical axis, and in a direction intersecting this direction of
arrangement, transmitting the light unaltered. Thus, the laser
light is corrected such that the light intensity distribution is
uniform. Here, an example of means for correcting distribution of
the light intensity has been shown. However, conventionally known
means for making the distribution of the light intensity uniform,
such as rod integrator, fly-eye lens array or the like, may be
used.
[0099] Lens systems 54 and 58 are disposed at a light reflection
side of the DMD 50. The lens systems 54 and 58 focus the laser
light that has been reflected at the DMD 50 on a scanning surface
(a surface that is to be exposed) 56 of the photosensitive material
150. The lens systems 54 and 58 are disposed such that the DMD 50
and the surface to be exposed 56 have a conjugative
relationship.
[0100] As shown in FIG. 6, at the DMD 50, very small mirrors
(micromirrors) 62, which are supported by support columns, are
disposed on an SRAM cell (memory cell) 60. The DMD 50 is a mirror
device which is structured with a large number (for example, 600 by
800) of these extremely small mirrors, which structure picture
elements (pixels), arranged in a checkerboard pattern. At each
pixel, the micromirror 62 is provided so as to be supported at an
uppermost portion of the support column. A material with high
reflectivity, such as aluminum or the like, is applied by vapor
deposition on the surface of the micromirror 62. Here, the
reflectivity of the micromirror 62 is at least 90%. An SRAM cell 60
with CMOS silicon gates, which is fabricated by a usual
semiconductor memory production line, is disposed directly under
the micromirror 62, with the support column, which includes a hinge
and a yoke, interposed therebetween. The whole of this structure is
monolithic (integrated).
[0101] When digital signals are written to the SRAM cell 60 of the
DMD 50, the micromirrors 62 supported at the support columns are
inclined, about a diagonal of the micromirror 62, within a range of
.+-..alpha..degree. (for example, +.+-.10.degree.), relative to the
side of the support at which the DMD 50 is disposed. FIG. 7A shows
a state in which the micromirror 62 is inclined at
+.alpha..degree., which is an `ON` state, and FIG. 7B shows a state
in which the micromirror 62 is inclined at -.alpha..degree., which
is an `OFF` state. Accordingly, as a result of control of the
inclinations of the micromirrors 62 at the pixels of the DMD 50 in
accordance with image signals, as shown in FIG. 6, light that is
incident at the DMD 50 is reflected in directions of inclination of
the respective micromirrors 62.
[0102] FIG. 6 shows a portion of the DMD 50 enlarged, and shows an
example of a state in which the micromirrors 62 are controlled to
+.alpha..degree. and -.alpha..degree.. The ON-OFF control of the
respective micromirrors 62 is carried out by the unillustrated
controller connected to the DMD 50. A light-absorbing body (which
is not shown) is disposed in the direction in which light beams are
reflected by the micromirrors 62 that are in the OFF state.
[0103] It is preferable if the DMD 50 is disposed to be slightly
inclined, such that a short side thereof forms a predetermined
angle .theta. (for example, 1.degree. to 5.degree.) with the
sub-scanning direction. FIG. 8A shows scanning tracks of reflected
light images (exposure beams) 53 formed by the micromirrors in a
case in which the DMD 50 is not inclined. FIG. 8B shows scanning
tracks of the exposure beams) 53 in the case in which the DMD 50 is
inclined.
[0104] At the DMD 50, a large number (for example, 800) of
micromirrors are arranged in a long side direction to form a
micromirror row, and a large number (for example, 600) of these
micromirror rows are arranged in a short side direction. As shown
in FIG. 8B, when the DMD 50 is inclined, a pitch P2 of scanning
paths (scanning lines) of the exposure beams 53 from the
micromirrors is tighter than a pitch P1 of scanning lines in the
case in which the DMD 50 is not inclined. Thus, resolution can be
greatly improved. However, because the angle of inclination of the
DMD 50 is very small, a scanning width W2 in the case in which the
DMD 50 is inclined is substantially the same as a scanning width W1
in the case in which the DMD 50 is not inclined.
[0105] The same scanning line will be superposingly exposed by
different micromirror rows (multiple exposure). As a consequence of
this multiple exposure, exposure positions can be controlled in
very fine amounts, and high accuracy exposure can be implemented.
Further, by control in very fine amounts of exposure positions at
boundary lines between the plurality of exposure heads arranged in
a main scanning direction, joins without steps can be formed.
[0106] Instead of inclining the DMD 50, the micromirrors may be
disposed in a staggered pattern in which the micromirror rows are
shifted by predetermined intervals in the direction intersecting
the sub-scanning direction, and the same effects can be
obtained.
[0107] As shown in FIG. 9A, the fiber array light source 66 is
equipped with a plurality (for example, six) of laser modules 64.
At each of the laser modules 64, one end of a multi-mode optical
fiber 30 is connected. At the other end of the multi-mode optical
fiber 30, an optical fiber 31, whose core diameter is the same as
that of the multi-mode optical fiber 30 and whose cladding diameter
is smaller than that of the multi-mode optical fiber 30, is
connected. As shown in FIG. 9C, emission end portions of the
multi-mode optical fibers 31 (light emission points) are arranged
in a single row along the main scanning direction, which intersects
the sub-scanning direction, to structure a laser emission portion
68. Note that the light emission points may be arranged in two rows
along the main scanning direction, as shown in FIG. 9D.
[0108] As is shown in FIG. 9B, the emission end portions of the
optical fibers 31 are inserted between a pair of support plates 65,
which have flat faces.
[0109] In this example, because the emission ends of the optical
fibers 31 with small cladding diameters are arranged in a single
row without gaps therebetween, some of the multi-mode optical
fibers 30, which are each between two of the multi-mode optical
fibers 30 that are adjacent at the section with large cladding
diameters, are piled up on the adjacent two of the multi-mode
optical fibers 30. The emission end of the optical fiber 31 that is
joined to the multi-mode optical fiber 30 that is piled up is
arranged so as to be sandwiched between the two emission ends of
the multi-mode optical fibers 31 that are joined to the two
multi-mode optical fibers 31 that are adjacent at the section with
large cladding diameters.
[0110] These optical fibers, as shown in FIG. 10, for example, can
be obtained by coaxially joining 1 to 30 cm lengths of the optical
fibers 31 with small diameters to distal end portions, at the laser
light emission side, of the multi-mode optical fibers 30 with large
cladding diameters. The two types of optical fiber are joined by
fusing incidence end faces of the optical fibers 31 to emission end
faces of the multi-mode optical fibers 30 such that central axes of
the pairs of fibers coincide. As described above, a diameter of a
core 31 a of the optical fiber 31 has the same magnitude as a
diameter of a core 30a of the multi-mode optical fiber 30.
[0111] A short-strip optical fiber, at which the optical fiber
whose cladding diameter is smaller is fused to an optical fiber
whose length is short and whose cladding diameter is larger, may be
joined at the emission end of the multi-mode optical fiber 30 via a
ferrule, an optical connector or the like. Because the joining is
carried out using the connector or the like so as to be detachable,
replacement of a peripheral end portion, in a case in which the
optical fiber whose cladding diameter is small has been damaged or
the like, is simple and costs required for maintenance of the
exposure head can be reduced. Hereafter, the optical fiber 31 may
on occasions be referred to as an exposure end portion of the
multi-mode optical fiber 30.
[0112] As the multi-mode optical fiber 30 and the multi-mode
optical fiber 31, any of step index-type optical fibers, graded
index-type optical fibers and multiplex-type optical fibers can be
used. For example, a step index-type optical fiber produced by
Mitsubishi Cable Industries, Ltd. can be used. In the present
embodiment, the multi-mode optical fiber 30 and the optical fiber
31 are step index-type optical fibers. The multi-mode optical fiber
30 has cladding diameter=125 .mu.m, core diameter=25 .mu.m, NA=0.2,
and transmittance of an end face coating=99.5% or more. The optical
fiber 31 has cladding diameter=60 .mu.m, core diameter=25 .mu.m,
and NA=0.2.
[0113] Commonly, with laser light in the infrared region,
propagation losses increase as the cladding diameter of an optical
fiber becomes smaller. Therefore, suitable cladding diameters are
determined in accordance with a wavelength range of laser light.
However, the shorter the wavelength, the smaller the propagation
losses. Thus, with laser light with a wavelength of 405 nm, emitted
from a GaN-based semiconductor laser, propagation losses are barely
increased at all in a case in which a cladding thickness ((cladding
diameter--core diameter)/2) is around half that for a case of
propagating infrared light in an 800 nm wavelength region or around
a quarter that for a case of propagating infrared light in a 1.5
.mu.m wavelength region, the latter of which is used for
communications. Accordingly, the cladding diameter can be reduced
to 60 .mu.m. Therefore, by utilizing, in place of the infrared
laser, a GaN-based semiconductor laser, which is a shorter
wavelength light source, enables to make the cladding diameter can
be reduced to a value substantially the same as the core diameter.
Thus, by arranging the optical fibers having a small cladding in an
array, or in other words, by disposing the optical fibers having a
diameter substantially the same as the core diameter in an array it
becomes highly possible to obtain a very high-brightness light
source.
[0114] However, the cladding diameter of the optical fiber 31 is
not limited to 60 .mu.m. An optical fiber which is employed in a
conventional fiber light source has a cladding diameter of 125
.mu.m. However, because focal depth becomes deeper as the cladding
diameter become smaller, it is preferable if the cladding diameter
is 80 .mu.m or less, more preferably 60 .mu.m or less, and even
more preferably 40 .mu.m or less. On the other hand, given that the
core diameter needs to be at least 3 to 4 .mu.m, it is preferable
that the cladding diameter of the optical fiber 31 is at least 10
.mu.m.
[0115] The laser module 64 is structured by a multiplexed laser
light source (fiber light source) shown in FIG. 11. This multiplex
laser light source is structured with a plurality (for example,
seven) of chip-form lateral multi-mode or single-mode GaN-based
semiconductor lasers LD1, LD2, LD3, LD4, LD5, LD6 and LD7,
collimator lenses 11, 12, 13, 14, 15, 16 and 17, a single
condensing lens 20, and one of the multi-mode optical fibers 30.
The GaN-based semiconductor lasers LD1 to LD7 are fixedly arranged
on a heat block 10. The collimator lenses 11 to 17 are provided in
correspondence with the GaN-based semiconductor lasers LD1 to LD7,
respectively. The number of semiconductor lasers is not limited to
seven. As many as twenty semiconductor lasers may be fed into a
multi-mode optical fiber with cladding diameter=60 .mu.m, core
diameter=50 .mu.m and NA=0.2. Thus, a light intensity required from
the exposure head can be realized, and/or the number of optical
fibers can be further reduced.
[0116] The GaN-based semiconductor lasers LD1 to LD7 all have a
common oscillation wavelength (for example, 405 nm), and a common
maximum output (for example, 100 mW with multi-mode lasers, 30 mW
with single-mode lasers). For the GaN-based semiconductor lasers
LD1 to LD7, lasers can be utilized which are provided with an
oscillation wavelength different from the above-mentioned 405 nm,
in a wavelength range of 350 nm to 450 nm.
[0117] As shown in FIGS. 12 and 13, the above-described multiplex
laser light source, together with other optical elements, is
accommodated in a box-like package 40 a top of which is opened. The
package 40 is provided with a package lid 41 prepared so as to
close the opening of the package 40. After an air removal
treatment, sealed gas is introduced inside the package and the
opening of the package 40 is closed by the package lid 41. Thus,
the above-described multiplex laser light source is hermetically
sealed in a closed space (sealed space) formed by the package 40
and the package lid 41.
[0118] A baseplate 42 is fixed at a lower face of the package 40.
The heat block 10, a condensing lens holder 45 and a fiber holder
46 are attached at an upper face of the baseplate 42. The
condensing lens holder 45 holds the condensing lens 20. The fiber
holder 46 holds an incidence end portion of the multi-mode optical
fiber 30. An opening is formed in a wall face of the package 40,
and the emission end portion of the multi-mode optical fiber 30 is
passed through this opening and led out to the outside of the
package.
[0119] A collimator lens holder 44 is attached at a side face of
the heat block 10, and holds the collimator lenses 11 to 17.
Openings are formed in a lateral wall face of the package 40.
Wiring 47, which supplies driving current to the GaN-based
semiconductor lasers LD1 to LD7, is passed through these openings
and led out to outside the package.
[0120] Note that in FIG. 13, in order to avoid complexity of the
drawing, of the plurality of GaN-based semiconductor lasers, only
the GaN-based semiconductor laser LD7 is marked with a reference
numeral, and of the plurality of collimator lenses, only the
collimator lens 17 is marked with a reference numeral.
[0121] FIG. 14 shows front face configurations of attachment
portions of the collimator lenses 11 to 17. Each of the collimator
lenses 11 to 17 has a long, narrow, cut-down shape with parallel
flat faces defining a region that includes an optical axis of a
circular-form lens which is provided with an aspherical surface.
The collimator lenses with this long, narrow shape can be formed,
for example, by molding-formation of resin or optical glass. The
collimator lenses 11 to 17 are closely disposed in a direction of
arrangement of light emission points of the GaN-based semiconductor
lasers LD1 to LD7 (the left-right direction in FIG. 14) such that
the longitudinal directions of the collimator lenses 11 to 17 cross
the direction of arrangement of the light emission points at right
angles.
[0122] As the GaN-based semiconductor lasers LD1 to LD7, lasers may
be employed which are provided with an active layer with a light
emission width of 2 .mu.m, and which respectively emit laser beams
B1 to B7 in forms which widen at angles of, for example, 10.degree.
and 30.degree. with respect, respectively, to a direction parallel
to the active layers and a direction perpendicular to the active
layers. These GaN-based semiconductor lasers LD1 to LD7 are
disposed such that the light emission points are lined up in a
single row in the direction parallel to the active layers.
[0123] Accordingly, the laser beams B1 to B7 emitted from the
respective light emission points are incident, respectively, on the
collimator lenses 11 to 17 having the long, narrow forms described
above, in states in which the direction for which the spreading
angle of the beam, which is greater, is greater coincides with the
longitudinal direction of the lens and the direction in which the
spreading angle is smaller coincides with a width direction (a
direction intersecting the longitudinal direction at right angles).
Specifically, the width of each of the collimator lenses 11 to 17
is 1.1 mm and the length thereof is 4.6 mm, and the laser beams B1
to B7 incident thereat have beam diameters in the horizontal
direction and the vertical direction of 0.9 mm and 2.6 mm,
respectively. Further, each of the collimator lenses 11 to 17 has a
focal length f1=3 mm, NA=0.6 and lens arrangement pitch=1.25
mm.
[0124] The condensing lens 20 is cut away in a long, narrow shape
with parallel flat faces defining a region that includes an optical
axis of a circular-form lens which is provided with an aspherical
surface, and is formed in a shape which is long in the direction of
arrangement of the collimator lenses 11 to 17 (i.e., the horizontal
direction) and short in a direction perpendicular thereto. The
condensing lens 20 has a focal length f2=23 mm and NA=0.2. Since
the wavelength is about 400 nm, a minute spot diameter that
sufficiently enables joining with high efficiency for a core
diameter of 50 .mu.m can be obtained. The condensing lens 20 is
also formed by, for example, molding-formation of resin or optical
glass.
[0125] Operation of the Exposure Apparatus
[0126] Next, operation of the exposure apparatus described above
will be explained.
[0127] In the exposure heads 166 of the scanner 162, the respective
laser beams B1, B2, B3, B4, B5, B6 and B7, which are emitted in
divergent forms from the respective GaN-based semiconductor lasers
LD1 to LD7 that structure the multiplex laser light source of the
fiber array light source 66, are converted to parallel light by the
corresponding collimator lenses 11 to 17. The laser beams B1 to B7
that have been collimated are focused by the condensing lens 20,
and converge at the incidence end face of the core 30a of the
multi-mode optical fiber 30.
[0128] In the present example, a condensing optical system is
structured by the collimator lenses 11 to 17 and the condensing
lens 20, and a multiplexing optical system is structured by the
condensing optical system and the multi-mode optical fiber 30.
Thus, the laser beams B1 to B7 focused by the condensing lens 20 as
described above enter the core 30a of the multi-mode optical fiber
30, are propagated in the optical fiber, multiplexed to a single
laser beam B, coupled at the emission end portion of the multi-mode
optical fiber 30, and emitted from the optical fiber 31.
[0129] In each laser module, a coupling efficiency of the laser
beams B1 to B7 into the multi-mode optical fiber 30 is 0.85.
Therefore, in a case in which the respective outputs of the
GaN-based semiconductor lasers LD1 to LD7 are 30 mW, the
multiplexed laser beam B can be obtained with an output of 180 mW
(=30 mW.times.0.85.times.7) from each of the optical fibers 31
arranged in the array pattern. Accordingly, output of the laser
emission portion 68 in which six of the optical fibers 31 are
arranged in the array pattern is approximately 1 W (=180
mW.times.6).
[0130] At the laser emission portion 68 of the fiber array light
source 66, high-brightness light emission points as described above
are arranged in a single row along the main scanning direction.
Because a conventional fiber light source, in which laser light
from a single semiconductor laser is focused at a single optical
fiber, has low output, a desired output cannot be obtained without
arranging these conventional light sources in a large number of
rows. However, because the multiplex laser light source employed in
the present embodiment has high power output, a desired output can
be obtained with only a small number of rows, for example, one
row.
[0131] For example, in a conventional fiber light source, in which
semiconductor lasers are joined with optical fibers in a one-to-one
relationship, lasers with outputs of around 30 mW (milliwatts) are
commonly employed as the semiconductor lasers, and multi-mode
optical fibers with core diameter 50 .mu.m, cladding diameter 125
.mu.m, and NA (numerical aperture) 0.2 are employed as the optical
fibers. Therefore, if an output of around 1 W (watt) is to be
obtained, forty-eight (8.times.6) multi-mode optical fibers must be
bundled. Thus, from a light emission region with an area of 0.62
mm.sup.2 (0.675 mm by 0.925 mm), luminance of this laser emission
portion 68 is 1.6.times.10.sup.6 W/m.sup.2, and luminance from each
optical fiber is 3.2.times.10.sup.6 W/m.sup.2.
[0132] In contrast, in the present embodiment, an output of
approximately 1 W can be provided by six multi-mode optical fibers,
as described above. Thus, from a light emission region of the laser
emission portion 68 with an area of 0.0081 nm.sup.2 (0.325
mm.times.0.025 mm), luminance of the laser emission portion 68 is
123.times.10.sup.6 W/m.sup.2. Thus, a luminance about eighty times
higher than in the conventional case can be expected. Furthermore,
the luminance from each optical fiber is 90.times.10.sup.6
W/m.sup.2. Thus, a luminance around twenty-eight times higher than
in the conventional case can be expected. As described above, a
light source having a high-brightness can be obtained.
Particularly, since a shorter wavelength light source such as a
GaN-based light source can be utilized, a minute spot can be
obtained even at the same condensing NA (i.e., fiber incident NA),
and a fiber light source and a fiber array or bundle having a
higher luminance can be obtained. As a result, since the laser
light has a shorter wavelength, the image formation beam can be
formed in a minute spot, and thus, high energy density and strong
photon energy can be obtained. Due to these two effects, the light
source may be utilized not only for chemical alteration, such as
photochemical polymerization, but for broad applications, such as
sintering, annealing and metal machining which use physical
alteration.
[0133] Further, since the light source is a high-brightness light
source, a minute image formation beam can be secured even by a
small image formation NA, and even in digital exposure using a
spatial light modulation element, an illumination NA for the
spatial light modulation element can be made smaller. As a result,
the size of the spatial light modulation element can be reduced,
and transmission speed or light-switching speed can be easily
improved, and high speed and high precision exposure can be carried
out.
[0134] Furthermore, by utilizing a semiconductor laser, photon cost
can be greatly reduced. Further, since turning the light source ON
and OFF can be easily carried out and life of the light source can
be lengthen, the light source can be made maintenance free, and
reduction in cost of the light source sufficient to allow broad
application thereof can be realized for the first time.
[0135] Moreover, an optical fiber is easy to handle and easy to
replace. Therefore, the light source can be utilized for various
uses.
[0136] Now, a difference in focal depth between the conventional
exposure head and the exposure head of the present embodiment will
be described with reference to FIGS. 15A and 15B. A diameter in the
sub-scanning direction of the light-emitting region of the
bundle-form fiber light source of the conventional exposure head is
0.675 mm, whereas the diameter in the sub-scanning direction of the
light-emitting region of the fiber array light source of the
exposure head of the present embodiment is 0.025 mm. As shown in
FIG. 15A, with the conventional exposure head, because the
light-emitting region of the light source 1 (the bundle-form fiber
light source) is large, the angle of luminous flux incident on the
DMD 3 is large. Hence, the angle of luminous flux incident on the
scanning surface 5 is large. Consequently, the beam diameter is
susceptible to broadening with respect to a condensing direction
(displacement in a direction of focusing).
[0137] In contrast, as shown in FIG. 15B, with the exposure head of
the present embodiment, the diameter in the sub-scanning direction
of the light-emitting region of the fiber array light source 66 is
smaller. Hence, the angle of luminous flux that has passed through
the lens system 67 and is incident on the DMD 50 is smaller.
Consequently, the angle of luminous flux incident on the scanning
surface 56 is smaller. That is, the focal depth is longer. In this
example, the diameter in the sub-scanning direction of the
light-emitting region is about a thirtieth that in the conventional
case, and a focal depth substantially corresponding to the
diffraction limit can be obtained. Accordingly, the present
embodiment is excellent for exposure with very fine spots. The
effect on the focal depth is particularly remarkable when the light
intensity required from the exposure head is large, which is
useful. In this example, the size of one pixel as projected on the
exposure surface is 10 .mu.m by 10 .mu.m. Note that, although the
DMDs are reflection-type spatial modulation elements, FIGS. 15A and
15B are expanded views, for the purpose of explaining optical
relationships.
[0138] Image data corresponding to an exposure pattern is inputted
at the unillustrated controller connected to the DMD 50, and is
temporarily stored in a frame memory in the controller. This image
data is data which represents a density of each pixel structuring
an image with a binary value (whether or not a dot is to be
recorded).
[0139] The stage 152, at which the surface of the photosensitive
material 150 is sucked and attached, is moved along the guides 158
at a constant speed by the driving apparatus, from an upstream side
of the gate 160 to a downstream side thereof. When the stage 152 is
passing under the exposure areas 168, and the leading end of the
photosensitive material 150 has been detected by the detection
sensors 164 attached at the gate 160, the image data stored in the
frame memory is read out as a plurality of line portion units in
sequence, and control signals for each of the exposure heads 166
are generated on the basis of the image data read from the data
processing section. Hence, the micromirrors of the DMDs 50 at the
respective exposure heads 166 are respectively switched on and off
by the mirror driving control section on the basis of the control
signals that have been generated.
[0140] When laser light is irradiated from the fiber array light
source 66 to the DMD 50, if a micromirror of the DMD 50 is in the
ON state, the reflected laser light is focused on the surface to be
exposed 56 of the photosensitive material 150 by the lens systems
54 and 58. Thus, the laser light irradiated from the fiber array
light source 66 is turned on or off at each pixel, and the
photosensitive material 150 is exposed in a unit with a number of
pixels substantially the same as the number of pixels employed at
the DMD 50 (the exposure area 168). Furthermore, as the
photosensitive material 150 is moved together with the stage 152 at
the constant speed, the photosensitive material 150 is scanned in a
direction opposite to the stage movement direction by the scanner
162, and the strip-form exposed regions 170 are formed at the
respective exposure heads 166.
[0141] As shown in FIGS. 16A and 16B, at the DMD 50 in the present
embodiment, 600 micromirror rows, in each of which 800 of the
micromirrors are arranged in the main scanning direction, are
arranged in the sub-scanning direction. However, control by the
controller so as to drive only a portion of the micromirror rows
(for example, 800 micromirrors by 100 rows) is possible.
[0142] Micromirror rows that are disposed at a central portion of
the DMD 50 may be employed, as shown in FIG. 16A, and micromirror
rows that are disposed at an end portion of the DMD 50 may be
employed, as shown in FIG. 16B. Further, in a case in which defects
have occurred at some of the micromirrors, the micromirror rows
that are to be employed may be suitably changed in accordance with
the situation, by employing micromirror rows in which defects have
not occurred, or the like.
[0143] There is a limit to a data processing speed of the DMD 50,
and a modulation rate for one line is determined in proportion to
the number of pixels employed. Thus, the modulation rate for one
line can be accelerated by employing only a portion of the
micromirror rows. Further, in the case of an exposure method in
which the exposure head is continuously moved relative to the
exposure surface, there is no need to employ all pixels in the
sub-scanning direction.
[0144] For example, in a case in which only 300 of the 600 rows of
micromirrors are employed, modulation is possible at twice the rate
for one line as in a case in which all 600 lines are employed.
Further, in a case in which only 200 of the 600 rows of
micromirrors are employed, modulation is possible three times as
quickly for one line as in the case of employing all 600 lines.
Specifically, a region which is 500 mm in the sub-scanning
direction can be exposed in 17 seconds. Furthermore, in a case in
which only 100 lines are employed, modulation for one line can be
done six times as quickly. That is, a region which is 500 mm in the
sub-scanning direction can be exposed in 9 seconds.
[0145] The number of micromirror rows that are employed, that is,
the number of micromirrors arranged in the sub-scanning direction,
is preferably at least 10 and at most 200, and is more preferably
at least 10 and at most 100. An area corresponding to one
micromirror, which corresponds to one pixel, is 15 .mu.m.times.15
.mu.m. Therefore, when an employed region of the DMD 50 is reduced,
it is preferable that this region is at least 12 mm by 150 .mu.m
and at most 12 mm by 3 mm, and more preferably at least 12 mm by
150 .mu.m and at most 12 mm by 1.5 mm.
[0146] If the number of micromirrors that are employed is within
the ranges described above, the laser light that is irradiated from
the fiber array light source 66 can be made substantially parallel
by the lens system 67 and irradiated at the DMD 50, as shown in
FIGS. 17A and 17B. It is preferable if an irradiated region of the
DMD 50 which is irradiated with the laser light substantially
coincides with the region of the DMD 50 that is employed. If the
irradiated region is larger than the employed region, then usage
efficiency of the laser light will fall.
[0147] There is a requirement that the diameter in the sub-scanning
direction of the light beam that is focused on the DMD 50 is made
smaller by the lens system 67, in accordance with the number of
micromirrors arranged in the sub-scanning direction. Thus, if the
number of micromirror rows that are employed is less than 10, the
angle of the luminous flux incident at the DMD 50 will be large,
and the focal depth of the light beam at the surface to be exposed
56 will be shallow, which is not preferable. In addition, the
number of micromirror rows that are employed is preferable to be
less than 200 or less from the viewpoint of modulation rate. Note
that, although the DMD is a reflection-type spatial modulation
element, FIGS. 17A and 17B are expanded views, for the purpose of
explaining optical relationships.
[0148] When sub-scanning of the photosensitive material 150 by the
scanner 162 has been completed and the trailing end of the
photosensitive material 150 has been detected by the detection
sensors 164, the stage 152 is driven back along the guides 158 by
the unillustrated driving apparatus, to a start point at an
upstream-most side of the gate 160, and is again moved along the
guides 158, at a constant speed, from the upstream side to the
downstream side of the gate 160.
[0149] As has been described above, the exposure apparatus of the
present embodiment is provided with an exposure head in which a
fiber array light source, at which emission end portions (light
emission points) of optical fibers of a multiplex laser light
source are arranged in an array pattern, irradiates a spatial
modulation element. At this fiber array light source, because
cladding diameters of emission ends of the optical fibers are set
to be smaller than cladding diameters of incidence ends thereof,
light emission portion diameters are smaller and a fiber array
light source with a higher luminance can be provided. Consequently,
an exposure head and exposure apparatus featuring a deep focal
depth can be realized. For example, in a case of very high
resolution exposure with a beam diameter of 1 .mu.m or less and a
resolution of 0.1 .mu.m or less, a long focal depth can be
obtained, and beam blurring at peripheral edge portions of an
area-type exposure beam can be suppressed. Thus, high-speed,
high-precision exposure is possible. Accordingly, the exposure
apparatus of the present embodiment can be employed even for thin
film transistor (TFF) exposure processes and the like, which
require high resolution.
[0150] Further, because a multiplex laser light source in which a
plurality of laser lights are multiplexed and fed into an optical
fiber is used, output at the emission end of the optical fiber is
greater, and exposure with a high power output is possible. Further
still, because the output of each fiber light source is greater,
the number of fiber light sources required for providing a desired
output is smaller, and reducing in costs of the exposure apparatus
can be provided.
[0151] Further yet, the exposure apparatus of the present
embodiment is provided with a DMD in which 600 micromirror rows are
arranged in the sub-scanning direction with 800 micromirrors being
arranged in the main scanning direction in each of the micromirror
rows. However, by a controller controlling so as to drive only some
of the micromirror rows, a modulation rate for one line can be made
faster than in a case in which all of the micromirror rows are
driven. Thus, exposure at high speed is possible.
Second Embodiment
[0152] An exposure apparatus relating to a second embodiment
utilizes grating light valves (GLV) as spatial light modulation
elements which are employed at respective exposure heads. The GLVs
are one kind of MEMS-type (microelectro-mechanical systems) spatial
light modulation elements (SLM: spatial light modulator), and are
reflective diffraction grating-type spatial light modulation
elements. Other structures are the same as in the exposure
apparatus relating to the first embodiment. Accordingly,
descriptions thereof will be omitted.
[0153] As shown in FIGS. 30, 31A and 31B, each of the exposure
heads 166.sub.11 to 166.sub.mn is provided with a GLV 300 whose
shape is long in a predetermined direction (a linear form), to
serve as a spatial light modulation element for modulating the
incident light beam at each of the pixels in accordance with the
image data. At a light incidence side of the GLV 300, similarly to
the first embodiment, the fiber array light source 66, the lens
system 67 and the mirror 69 are disposed in this order.
[0154] The linear-form GLV 300 is disposed such that a long
direction thereof is parallel with the direction of arrangement of
the optical fibers of the fiber array light source 66, and
reflection faces of ribbon-form microbridges of the GLV 300 are
substantially parallel to the reflection face of the mirror 69. The
GLV 300 is connected to an unillustrated controller which controls
the GLV 300.
[0155] At the GLV 300, as shown in FIG. 32, a large number (for
example, 6,480) of microbridges 209, which are provided with
ribbon-form reflection surfaces, are arranged in parallel on a long
strip-form form support 203, which is formed of silicon or the
like. At the GLV 300, a large number of slits 211 are formed
between adjacent microbridges 209. Ordinarily, one pixel is
structured by a row of a plurality (for example, six) of the
microbridges 209. If it is assumed that each pixel is structured by
a row of six microbridges, then exposure of 1,080 pixels is
possible with the 6,480 microbridges.
[0156] As shown in FIGS. 33A and 33B, at each microbridge 209, a
reflection electrode film 209b is formed on a surface of a flexible
beam 209a. The beam 209a is formed of silicon nitride (SiN.sub.x)
or the like, and the reflection electrode film 209b is formed of a
single-layer metallic film of aluminum (or gold, silver, copper or
the like). Each of the reflection electrode films 209b is connected
to a power source by unillustrated wiring, via an unillustrated
switch.
[0157] Now, a principle of operation of the GLV 300 will be briefly
described. In a state in which voltage is not applied, the
microbridge 209 has a predetermined spacing distance from the
support 203. When a voltage is applied between the microbridge 209
and the support 203, a static electricity attraction force is
generated between the microbridge 209 and the support 203 by
induced static charge, and the microbridge 209 flexes to the
support 203 side thereof. Then, when the application of voltage is
stopped, this flexure is released and the microbridge 209 reverts
elastically, thus separating from the support 203. Accordingly, by
disposing microbridges to which voltage is applied and microbridges
to which voltage is not applied alternately, a diffraction grating
can be formed by the application of voltages.
[0158] FIG. 33A shows a case in which voltage is not applied to a
row of microbridges of a pixel unit, and the pixel unit is in an
`OFF` state. In the OFF state, the heights of reflection surfaces
of the microbridge 209 are all the same, optical path differences
in reflected light are not generated, and the reflected light is
reflected normally. In other words, diffracted light only of the
zero-th order can be obtained. Alternatively, FIG. 33B shows a case
in which voltages are applied to the microbridge row of the pixel
unit, and the pixel unit is in an `ON` state. Note that the voltage
is only applied to every second microbridge 209. In the ON state,
according to the principle described above, central portions of the
microbridges 209 are flexed, and a reflection surface with
alternating steps is formed. In other words, a diffraction grating
is formed. When laser light is made incident on this reflection
surface, an optical path difference is generated between light that
is reflected from the microbridges 209 that are flexed and light
that is reflected from the microbridges 209 that are not flexed.
Thus, light with a diffraction order of .+-.1 is emitted in a
predetermined direction.
[0159] Accordingly, in accordance with control signals from the
unillustrated controller, voltages are applied to drive the
microbridge rows for the respective pixels of the GLV 300 for
control between the ON and OFF states. Thus, laser light that is
incident at the GLV 300 is modulated at each pixel and diffracted
in the predetermined direction.
[0160] At the light reflection side of the GLV 300, that is, at the
side to which the diffracted light (zero-th order diffracted light
and .+-.1st order diffracted light) is emitted, the lens systems 54
and 58, which focus the diffracted light onto the scanning surface
(surface to be exposed) 56 are disposed such that the GLV 300 and
the surface to be exposed 56 have a conjugative relationship.
Furthermore, the ribbon-form reflection surfaces of the GLV 300 are
disposed in advance to be inclined at a predetermined angle (for
example, 45.degree.) with respect to the optical axis of the lens
system 54, such that the diffracted light is incident at the lens
system 54.
[0161] In FIGS. 31A and 31B, the zero-th order diffraction light is
represented by broken lines and the .+-.1st order diffraction light
is represented by solid lines. The zero-th order diffraction light
from the GLV 300 is focused only in the longitudinal direction of
the GLV by the lens system 54. Accordingly, a shading plate 55 with
a long strip form, which is for eliminating the zero-th order
diffraction light from the optical path to the scanning surface 56
is disposed between the lens system 54 and the lens system 58 such
that the longitudinal direction of the shading plate 55 intersects
the longitudinal direction of the GLV 300.
[0162] The lens system 54 condenses the diffracted light that is
incident thereat in the longitudinal direction of the GLV 300, and
makes the light parallel in the sub-scanning direction. The long
strip-form shading plate 55, which is for eliminating the zero-th
order diffracted light from the optical path to the scanning
surface 56, is disposed at a focusing point of the zero-th order
diffracted light between the lens system 54 and the lens system 58,
such that the longitudinal direction of the shading plate 55
intersects the longitudinal direction of the GLV at right angle. As
a result, the zero-th order diffracted light alone is selectively
removed.
[0163] In this exposure head, image data corresponding to an
exposure pattern is inputted to the unillustrated controller
connected to the GLV 300, and control signals are generated on the
basis of this image data. Each pixel unit of the microbridges of
the GLV 300 at each exposure head is switched on or off on the
basis of the generated control signals. As a result, the
photosensitive material 150 is exposed in a unit with a number of
pixels substantially the same as the number of pixels at the GLVs
300. Thus, with sub-scanning due to movement of the stage 152, the
strip-form exposed regions are respectively formed by the exposure
heads.
[0164] In the exposure apparatus of the present embodiment, because
the GLV 300 is a long strip-form spatial light modulation element
whose width in a short direction thereof is narrow, it is difficult
to illuminate the GLV 300 efficiently. However, as in the first
embodiment, the high-brightness fiber array light source, at which
the emission end portions of the optical fibers of the multiplex
laser light source are arranged in an array pattern, is utilized at
a light source for illuminating the GLV, and the cladding diameters
of the emission ends of the optical fibers are smaller than the
cladding diameters of the incidence ends thereof. Therefore, the
sub-scanning direction diameter of the beam emitted from the laser
emission portion 68 is small, and an angle of luminous flux that
has passed through the lens system 67 and the like and is incident
on the GLV 300 is small. Thus, the GLV 300 can be illuminated with
high efficiency and a long depth of focus can be provided.
Moreover, because the multiplex laser light source is utilized,
exposure with a high power output is possible and a lower cost
exposure apparatus can be provided.
[0165] Next, variant examples of the exposure apparatus described
above will be described.
[0166] Application of the Exposure Apparatus
[0167] The exposure apparatus described above may be suitably
utilized for application to, for example, exposure of a dry film
resist (DFR) in a process for fabricating a printed wiring board
(PWB), formation of a color filter in a process for fabricating a
liquid crystal display (LCD), exposure of a DFR in a process for
fabricating a TFT, exposure of a DFR in a process for fabricating a
plasma display panel (PDP), and the like.
[0168] Further, the exposure apparatus described above may also be
employed for various types of laser machining, such as laser
ablation for vaporizing, dispersing or the like and hence removing
a portion of a material by laser irradiation, and for sintering,
lithography and the like. Because the exposure apparatus described
above has high power output and is capable of exposing at high
speed with a deep depth of focus, the exposure apparatus can be
employed for fine-detail machining by laser ablation or the like.
For example, instead of carrying out developing processing to
prepare a PWB, the exposure apparatus described above may be
employed for removing a resist in accordance with a pattern by
ablation, or for forming a pattern in a PWB by direct ablation
without using a resist. Further still, for a lab-on-a-chip, in
which mixing, reaction, separation, detection and the like of
numerous fluids are integrated at a glass or plastic chip, the
exposure apparatus described above can be employed for forming very
small flow channels with groove widths of tens of microns.
[0169] In particular, because the exposure apparatus described
above utilizes the GaN-based semiconductor lasers in the fiber
array light sources, the exposure apparatus can be favorably
employed for the above-mentioned laser processes. Specifically,
GaN-based semiconductor lasers can be driven with short pulses, and
sufficient power can be provided even for laser ablation and the
like. Further, because these are semiconductor lasers, unlike solid
state lasers in which driving speeds are low, rapid driving with a
cycling frequency of around 10 MHz is possible, and high-speed
exposure is possible. Further still, because metals have high
optical absorptivities for laser light with a wavelength in the
vicinity of 400 nm, and readily convert such laser light to heat
energy, laser ablation or the like can be carried out rapidly.
[0170] In a case of exposing a liquid resist which is to be
employed for TFT patterning, a liquid resist which is to be
employed for patterning a color filter or the like, it is
preferable that the material to be exposed is exposed in a nitrogen
atmosphere, in order to prevent a reduction in sensitivity
(desensitization) due to oxygen inhibition. Consequent to such
exposure in a nitrogen atmosphere, oxygen inhibition of
photopolymerization reactions is inhibited, sensitivity of the
resist is raised, and rapid exposure is possible.
[0171] With the exposure apparatus described above, any of photon
mode photosensitive materials, which are directly recorded with
information by exposure, and heat mode photosensitive materials, in
which heat is generated by exposure and information is recorded
thereby, may be employed. In cases in which photon mode
photosensitive materials are employed, GaN-based semiconductor
lasers, wavelength-conversion solid state lasers and the like are
employed as the laser apparatus, and in cases in which heat mode
photosensitive materials are employed, AlGaAs-based semiconductor
lasers (infrared lasers) and solid state lasers are employed as the
laser apparatus.
[0172] Other Spatial Modulation Elements
[0173] For the first embodiment described above, examples of
driving only a portion of the DMD micromirrors were described.
However, a long, thin DMD may be utilized in which a large number
of micromirrors, whose reflection surface angles can be
respectively altered in accordance with control signals, are
arranged in a two-dimensional pattern on a support whose length in
a direction corresponding to a predetermined direction is longer
than a length thereof in a direction intersecting the predetermined
direction. When such a DMD is utilized, because the number of
micromirrors whose reflection surface angles are to be controlled
is smaller, modulation rates can be similarly increased.
[0174] For the first and second embodiments described above,
exposure heads which are provided with DMDs or GLVs as spatial
modulation elements have been described. However, for example, MEMS
(microelectro-mechanical systems) type spatial modulation elements
(SLM: spatial light modulator), optical elements (PLZT elements),
liquid crystal shutters (FLC) and the like, which modulate
transmitted light by electro-optical effects, and spatial
modulation elements other than MEMS types may be utilized. In these
cases too, a pixel portion which is a subsection of all of the
pixels that are arranged on a support may be employed. Thus,
modulation rates per pixel and per main scanning line can be made
faster, and the same effects as above can be provided.
[0175] Herein, MEMS is a general term for Microsystems in which
micro-size sensors, actuators and control circuits are integrated
by micro-machining technology based on IC fabrication processes.
MEMS type spatial modulation elements means spatial modulation
elements which are driven by electro-mechanical operations by
utilization of static electric forces.
[0176] Another Exposure Method
[0177] As shown in FIG. 18, the whole surface of the photosensitive
material 150 may be exposed by a single cycle of scanning in a
direction X by the scanner 162, the same as in the embodiments
described above. Alternatively, as shown in FIGS. 19A and 19B,
scanning and displacement may be repeated such that, after the
photosensitive material 150 has been scanned in the direction X by
the scanner 162, the scanner 162 is displaced by one step in a
direction Y and scanning is again carried out in the direction X.
Thus, the whole surface of the photosensitive material 150 can be
exposed by a plurality of scans. Note that in this example the
scanner 162 is equipped with eighteen of the exposure heads
166.
[0178] Other Laser Devices (Light Sources)
[0179] For the embodiments described above, examples in which the
fiber array light sources that are utilized are equipped with
pluralities of multiplex laser light sources have been described.
However, the laser apparatus is not limited to a fiber array light
source in which multiplexed laser light sources are arranged. For
example, a fiber array light source may be utilized in which fiber
light sources which are each equipped with a single optical fiber,
which emits laser light inputted from a single semiconductor laser
having one light emission point, are arrayed.
[0180] Further, for the embodiments described above, an example in
which the multiplex laser light source that is utilized is provided
with a laser array in which, as shown in FIG. 20, the plurality
(for example, seven) of chip-form semiconductor lasers LD1 to LD7
are arranged on a heat block 100, has been described. However, the
multiplex laser light source is not limited to a laser light source
which multiplexes laser light emitted from a plurality of chip-form
semiconductor lasers.
[0181] As shown in FIG. 21A, a chip-form multi-cavity laser 110 in
which a plurality (for example, five) of light emission points 110a
are arranged in a predetermined direction is known. For example, as
shown in FIG. 22, a multiplex laser light source in which this
multi-cavity laser 110 is provided may be utilized. This multiplex
laser light source is structured with the multi-cavity laser 110, a
single multi-mode optical fiber 130 and a condensing lens 120. The
multi-cavity laser 110 may be structured with, for example, a
GaN-based laser diode with an oscillation wavelength of 405 nm.
[0182] In comparison with cases in which chip-form semiconductor
lasers are arranged, the multi-cavity laser 110 can be arranged
with better positional accuracy of the light emission points. As a
result, the laser beams emitted from the respective light emission
points are easier to multiplex. However, if the number of light
emission points is large, deformation of the multi-cavity laser 110
is likely to occur during laser fabrication. Therefore, it is
preferable if the number of the light emission points 110a is not
more than five.
[0183] In the structure described above, laser beams B, which are
emitted respectively from the plurality of light emission points
110a of the multi-cavity laser 110, are condensed by the condensing
lens 120 and inputted to a core 130a of the multi-mode optical
fiber 130. The laser lights that have been inputted to the core
130a are propagated in the optical fibers, multiplexed into a
single beam, and emitted.
[0184] The plurality of light emission points 110a of the
multi-cavity laser 110 may be lined up within a breadth that is
substantially the same as a core diameter of the multi-mode optical
fiber 130. As the condensing lens 120, a convex lens with a focal
length substantially the same as the core diameter of the
multi-mode optical fiber 130, a rod lens which collimates the beams
emitted from the multi-cavity laser 110 only in a dimension which
is orthogonal to active layers of the multi-cavity laser 110, or
the like may be utilized. By lining up the light emission points
110a and using such a lens, a coupling efficiency of the laser
beams B into the multi-mode optical fiber 130 can be raised.
[0185] Further, as shown in FIG. 21B, a multi-cavity laser array
can be utilized in which a plurality of the multi-cavity lasers 110
are arranged on the heat block 100 in the same direction as the
arrangement direction of the light emission points 110a of each of
these chips. As shown in FIG. 23, a structure of a multiplex laser
array may be provided with a laser array 140 in which a plurality
(for example, nine) of the multi-cavity lasers 110 are arranged
with a constant spacing therebetween on a heat block 111. The
plurality of multi-cavity lasers 110 are arranged in the same
direction as the direction of arrangement of the light emission
points 110a of each chip, and fixed.
[0186] The structure of this multiplex laser array includes the
laser array 140, a plurality of lens arrays 114, a single rod lens
113, the single multi-mode optical fiber 130 and the condensing
lens 120. The plurality of lens arrays 114 is disposed in
correspondence with the multi-cavity lasers 110. The rod lens 113
is disposed between the laser array 140 and the plurality of lens
arrays 114. The lens arrays 114 are provided with pluralities of
microlenses corresponding to the light emission points of the
multi-cavity lasers 110.
[0187] In the structure described above, each of laser beams B that
are respectively emitted from the plurality of light emission
points 110a of the plurality of multi-cavity lasers 110 are
condensed in a predetermined direction by the rod lens 113, and
then made parallel by the respective microlenses of the lens arrays
114. Laser beams L that have been made parallel are condensed by
the condensing lens 120 and inputted into the core 130a of the
multi-mode optical fiber 130. The laser light that has been fed in
to the core 130a is propagated in the optical fiber, multiplexed to
a single beam, and emitted.
[0188] Still another example of a multiplex laser light source will
be illustrated. In this multiplex laser light source, as shown in
FIGS. 24A and 24B, a heat block 182, which is L-shaped in a section
cut in the direction of an optical axis, is mounted on a
substantially rectangular heat block 180. An accommodation space is
formed between the two heat blocks. At an upper face of the
L-shaped heat block 182, a plurality (for example, two) of the
multi-cavity lasers 110, in which pluralities (for example, five)
of the light emission points are arranged in an array pattern, are
arranged with constant spacing in a direction the same as the
direction of arrangement of the light emission points 110a of each
chip, and fixed.
[0189] A recess is formed in the substantially rectangular heat
block 180. A plurality (for example, two) of the multi-cavity
lasers 110, in which pluralities (for example, five) of the light
emission points are arranged in an array pattern, are disposed on a
recess side of an upper face of the heat block 180, such that the
light emission points thereof are disposed in the same vertical
plane as the light emission points of the laser chips that are
disposed at the upper face of the heat block 182.
[0190] A collimation lens array 184, in which collimator lenses are
arranged in correspondence with the light emission points 110a of
each chip, is disposed at a laser light emission side of the
multi-cavity lasers 110. The collimation lens array 184 is disposed
such that a longitudinal direction of each collimator lens
coincides with a direction in which spreading angles of the laser
beams are large (a fast axis direction) and the width direction of
the each collimator lens coincides with a direction in which the
spreading angles are small (a slow axis direction). Accordingly,
because the collimator lenses are arrayed and integrated, a spatial
utilization rate of the laser light can be improved, and higher
output can be provided by the multiplexed laser light source.
Moreover, the number of components can be reduced and costs can be
lowered.
[0191] The single multi-mode optical fiber 130 and the condensing
lens 120 are disposed at a laser light emission side of the
collimation lens array 184. The condensing lens 120 condenses and
focuses the laser beams onto the incidence end of the multi-mode
optical fiber 130.
[0192] In the structure described above, respective laser beams,
which are emitted from the pluralities of light emission points
110a of the plurality of multi-cavity lasers 110 disposed on the
heat blocks 180 and 182, are converted to parallel light by the
collimation lens array 184, condensed by the condensing lens 120,
and made to be incident on the core 130a of the multi-mode optical
fiber 130. The laser light that is incident at the core 130a is
propagated in the optical fiber, multiplexed into a single beam,
and emitted.
[0193] Because, in this multiplex laser light source, the
multi-cavity lasers are disposed at a plurality of levels and the
collimator lenses are arrayed as described above, a particularly
high power output can be expected. When this multiplexed laser
light source is utilized, a fiber array light source, a bundled
fiber light source or the like with even higher luminance can be
structured. Thus, this multiplex laser light source is particularly
favorable for use as the fiber light source structuring the laser
light source of the exposure apparatus of the present
invention.
[0194] The multiplex laser light source described above is
accommodated in a casing, and a laser module in which an emission
end portion of the multi-mode optical fiber 130 is led out from the
casing can be structured.
[0195] For the embodiments described above, examples have been
described in which another optical fiber, which has the same core
diameter as the multi-mode optical fiber but a smaller cladding
diameter than the multi-mode mode optical fiber, is joined at the
emission end of the multi-mode optical fiber of the multiplex laser
array, and the fiber array light source is thus designed to have a
higher luminance. However, for example, as shown in FIGS. 35A and
35B, the multi-mode optical fibers 30 may be employed with cladding
diameters of 125 .mu.m, 80 .mu.m, 60 .mu.m or the like, and without
joining other optical fibers at the emission ends thereof. When
such optical fibers with small cladding diameters are employed and
two or three of the fiber light sources at which numerous beams are
multiplexed are arrayed as shown in FIG. 35B or bundled as shown in
FIG. 35A, the light emission points can be brought close together,
as a point-like light source. Consequently, structure of the
optical system that is used in this light source is simple.
Accordingly, this light source can be structured with a low cost,
high functionality optical system.
[0196] FIG. 36 shows end faces (a light emission portion) of the
laser emission portion 68 of FIG. 35A. The multi-mode optical
fibers 30 are bundled such that adjacent the optical fibers are as
close to each other as possible. Because, as described above,
cladding diameters of the multi-mode optical fibers 30 are all 125
.mu.m, the size of the light emission portion is about 0.375 mm by
0.25 mm. Further, as described above, the output of the laser
emission portion 68 is about 1 W. Thus, in comparison with a
conventional bundled fiber light source, the same laser output can
be provided with about one-seventh the number of fibers, about
one-third the light emission portion diameter, and about one-tenth
the light emission region area.
[0197] Accordingly, because the number of multi-mode optical fibers
(the number of laser modules) can be reduced, a lowering in costs
of the light source can be expected. Further, by reducing the
number of optical fibers, the light emission portion diameter can
be made smaller. Thus, a luminance about ten times higher can be
expected.
[0198] As mentioned above, an example in which a plurality of
optical fibers with different cladding diameters are joined into an
optical fiber in which the cladding diameter of the emission end is
smaller than the cladding diameter of the incidence end has been
described. However, it is also possible to structure the optical
fibers such that the cladding diameter gets smaller from the
incidence end to the emission end gradually.
[0199] Light Amount Distribution-Correcting Optical System
[0200] In the embodiments described above, a light intensity
distribution-correcting optical system formed of a single pair of
combination lenses is used at the exposure head. The light
intensity distribution-correcting optical system converts an
optical flux width at each of emission positions such that a ratio
of a flux width at a peripheral edge portion to a flux width at a
central portion, which is near an optical axis, is smaller at an
emission side of the light intensity distribution-correcting
optical system than at an incidence side thereof, and corrects the
light intensity distribution such that a light intensity
distribution at irradiated surfaces of the DMD or the like is
substantially uniform when the parallel flux from the light source
is irradiated at the DMD. Operation of this light intensity
distribution-correcting optical system will be described.
[0201] First, as shown in FIG. 25A, a case in which the overall
luminous flux widths (total flux widths) H0 and H1 of incidence
luminous flux and emission luminous flux are the same is described.
In FIG. 25A, the portions indicated by the reference numerals 51
and 52 represent, virtually, an incidence plane and an emission
plane of the light intensity distribution-correcting optical
system.
[0202] In the light intensity distribution-correcting optical
system, luminous flux widths h0 of luminous flux that is incident
at a central portion near to an optical axis Z1, and luminous flux
width h1 of luminous flux that is incident at a peripheral edge
portion are set to be the same (h0=h1). The light intensity
distribution-correcting optical system implements operations on the
luminous flux widths h0 and h1 at the incidence side, which are
equal, so as to expand the luminous flux width h0 for the incident
flux of the central portion and, conversely, to contract the
luminous flux width h1 for the incident light of the peripheral
edge portion. That is, for a width h10 of emission luminous flux of
the central portion and a width h11 of emission luminous flux of
the peripheral edge portion, h11 is made to be less than h10.
Represented as a ratio of flux widths, at the emission side, a
ratio of the luminous flux width at the peripheral edge portion to
the luminous flux width at the central portion, (h11/h10) is
smaller than the ratio (h1/h0=1) at the incidence side (i.e.,
h11/h10<1).
[0203] When the luminous flux widths are converted in this manner,
the flux at central portions, at which the luminous flux
distribution is usually large, can be shifted to peripheral edge
portions, at which light intensities are usually insufficient.
Thus, the light intensity distribution can be made uniform at the
irradiated surfaces without a drop in efficiency of utilization of
the light as a whole. The degree to which the luminous flux is made
uniform is such that, for example, unevenness of light intensities
inside an effective region is within 30%, and preferably within
20%.
[0204] Operation and effects of this light intensity
distribution-correcting optical system are the same in a case in
which the overall flux width changes between the incidence side and
the emission side (see FIGS. 25B and 25C).
[0205] FIG. 25B shows a case in which the overall flux width H0 at
the incidence side is "contracted" to a width H2 and emitted
(H0>H2). In this case too, the light intensity
distribution-correcting optical system acts on the light which has
flux widths at the incident side h0 and h1, which are equal, to
make the flux width h10 of the central portion at the emission side
greater in comparison to the peripheral edge portion and, in
contrast, to make the flux width h11 of the peripheral edge portion
smaller in comparison to the central portion. In terms of a
contraction ratio of the flux, the light intensity
distribution-correcting optical system implements operation such
that a contraction ratio relative to the incident luminous flux is
smaller at the central portion than at the peripheral edge portion
and a contraction ratio relative to the incident luminous flux is
larger at the peripheral edge portion than at the central portion.
In this case too, the ratio of the flux width at the peripheral
edge portion to the flux width at the central portion (h11/h10) is
smaller than the ratio (h1/h0=1) at the incidence side (i.e.,
h11/h10<1).
[0206] FIG. 25C shows a case in which the overall flux width H0 at
the incidence side is "expanded" to a width H3 and emitted
(HO<H3). In this case too, the light intensity
distribution-correcting optical system acts on the light which has
flux widths at the incident side h0 and h1, which are equal, to
make the flux width h10 of the central portion at the emission side
greater in comparison to the peripheral edge portion and, in
contrast, to make the flux width h11 of the peripheral edge portion
smaller in comparison to the central portion. In terms of an
expansion ratio of the flux, the light intensity
distribution-correcting optical system implements operation such
that an expansion ratio relative to the incident luminous flux is
greater at the central portion than at the peripheral edge portion,
and an expansion ratio relative to the incident luminous flux is
smaller at the peripheral edge portion than at the central portion.
In this case too, the ratio of the flux width at the peripheral
edge portion relative to the flux width at the central portion
(h11/h10) is smaller than the ratio (h11/h0=1) at the incidence
side (i.e., h11/h10<1).
[0207] Thus, the light intensity distribution-correcting optical
system changes the luminous flux widths at each emission position,
and makes ratios of luminous flux widths at peripheral edge
portions to luminous flux widths at central portions, which are
close to the optical axis Z1, smaller at the emission side than at
the incidence side. Thus, at the emission side, light that has flux
widths that are equal at the incidence side has flux widths at
central portions that are greater than at peripheral edge portions,
and flux widths at the peripheral edge portions become smaller than
at the central portions. Hence, the flux of the central portions
can be shifted towards the peripheral edge portions, and a luminous
flux cross-section whose light intensity distribution has been made
uniform can be formed without bringing down light usage efficiency
of the optical system as a whole.
[0208] Next, one example of specific lens data of the combination
lenses that are employed as the light intensity
distribution-correcting optical system will be illustrated. In this
example, lens data is illustrated for a case in which, as in cases
in which the light source is a laser array light source, the light
intensity distribution of a cross-section of emitted flux is a
gaussian distribution. Now, in a case in which a single
semiconductor laser is connected to the incidence end of a
single-mode optical fiber, the light intensity distribution of
emitted flux from the optical fiber will be a gaussian
distribution. This is also applicable in cases such as the present
embodiments. Furthermore, this is also applicable to a case in
which light intensities at central portions, which are close to the
optical axis, are greater than light intensities at peripheral edge
portions because the core diameter of a multi-mode optical fiber
has been made smaller, approaching the structure of a single-mode
optical fiber, or the like.
[0209] Basic lens data is shown in the following table 1.
1TABLE 1 Basic Lens Data Si ri di Ni (surface (radius of (surface
separation) (refractive number) curvature) (mm) index) 01
aspherical 5.000 1.52811 surface 02 8 50.000 03 8 7.000 1.52811 04
aspherical surface
[0210] As can be seen from table 1, the single pair of combination
lenses is structured by two aspherical-faced lenses with rotational
symmetry. If a face at the light incidence side of a first lens,
which is disposed at the light incidence side of the pair, is
considered to be a first face, and a face at the emission side of
the first lens considered to be a second face, the first face has
an aspherical surface form. If a face at the light incidence side
of a second lens, which is disposed at the light emission side of
the pair, is considered to be a third face and a face at the light
emission side of the second lens is considered to be a fourth face,
the fourth face has an aspherical surface form.
[0211] In table 1, surface number Si represents the number of the
i-th surface (i=1 to 4), radius of curvature ri represents the
radius of curvature of the i-th surface, and surface distance di
represents a surface spacing, on the optical axis, between the i-th
surface and the (i+1)-th surface. The dimension of surface distance
di is millimeter (mm). Refractive index Ni represents the value of
an index of refraction, for wavelength 405 nm, of the optical
element at which the i-th surface is provided.
[0212] Aspherical surface data of the first and fourth surfaces is
shown in the following table 2.
2TABLE 2 Aspherical Surface Data First Surface Fourth Surface C
-1.4098E-02 -9.8506E-03 K -4.2192E+00 -3.6253E+01 a3 -1.0027E-04
-8.9980E-05 a4 3.0591E-05 2.3060E-05 a5 -4.5115E-07 -2.2860E-06 a6
-8.2819E-09 8.7661E-08 a7 4.1020E-12 4.4028E-10 a8 1.2231E-13
1.3624E-12 a9 5.3753E-16 3.3965E-15 a10 1.6315E-18 7.4823E-18
[0213] The aspherical surface data shown above represents factors
in the following formula (A), which represents aspherical surface
forms. 1 Z = C 2 1 + 1 - K ( C ) 2 + i = 3 10 ai i ( A )
[0214] Each of the factors in the above formula (A) is defined as
follows.
[0215] Z: length (mm) of a vertical line descending, in a plane
tangential to an apex point of the aspherical surface (a flat plane
pependicular to the optical axis), from a point on the aspherical
surface which is positioned at a height p from the optical axis
[0216] .rho.: distance from the optical axis (mm)
[0217] K: a coefficient of conicality
[0218] C: a rate of curvature near the axis (1/r, r being a
near-axis radius of curvature)
[0219] ai: an i-th aspherical surface coefficient (i=3 to 10)
[0220] In the numerical values shown in table 2, the symbol "E"
signifies that the number following the E represents a decimal
exponent, and that the number preceding the E is to be multiplied
by a value represented by the decimal exponent. For example,
"1.0E-2" represents 1.0.times.10.sup.-2.
[0221] FIG. 27 shows a light intensity distribution of illumination
light provided by the single pair of combination lenses illustrated
in table 1 and table 2 above. The horizontal axis shows
co-ordinates from the optical axis, and the vertical axis shows
light intensity ratios (%). For comparison, FIG. 26 shows a light
intensity distribution of illumination light in a case in which the
correction is not carried out (a gaussian distribution). As can be
seen from FIGS. 26 and 27, because the correction is carried out by
the light intensity distribution-correcting optical system, a light
intensity distribution which is substantially uniform in comparison
to the case in which the correction is not carried out can be
obtained. Thus, exposure with uniform laser light that is free of
unevenness can be carried out without reducing the efficiency of
utilization of the light in the exposure head.
[0222] An example of a light intensity distribution correcting
optical system has been shown. However, conventionally known means,
such as a rod integrator, a fly-eye lens array or the like may be
used.
[0223] Another Imaging Optical System
[0224] In the first embodiment described above, two groups of
lenses are disposed to serve as an imaging optical system at the
light reflection side of the DMD employed in the exposure head.
However, a coupling optical system which widens and focuses the
laser light may be disposed thereat. By widening the
cross-sectional area of optical flux lines reflected by the DMD, an
exposure area at the surface to be exposed (an imaging region) can
be enlarged to a desired size.
[0225] For example, as shown in FIG. 28A, the exposure head may be
structured with the DMD 50, an illumination apparatus 144, lens
systems 454 and 458, a microlens array 472, an aperture array 476,
and lens systems 480 and 482. The illumination apparatus 144
illuminates laser light onto the DMD 50. The lens systems 454 and
458 widen and focus laser light that has been reflected at the DMD
50. A large number of microlenses 474 are disposed at the microlens
array 472, in respective correspondence with the pixels of the DMD
50. The aperture array 476 is provided with a large number of
apertures 478 in respective correspondence with the microlenses of
the microlens array 472. The lens systems 480 and 482 focus laser
light that has been transmitted through the apertures onto the
surface to be exposed 56.
[0226] In this exposure head, when laser light is irradiated from
the illumination apparatus 144, the cross-sectional area of
luminous flux lines reflected in the `ON` direction by the DMD 50
is enlarged to a magnification (for example, .times.2) by the lens
systems 454 and 458. The enlarged laser light is condensed in
accordance with the pixels of the DMD 50 by the microlenses of the
microlens array 472, and is passed through the corresponding
apertures of the aperture array 476. The laser light that has
passed through the apertures is imaged on the surface to be exposed
56 by the lens systems 480 and 482.
[0227] In this imaging optical system, because the laser light that
has been reflected by the DMD 50 is enlarged to a certain
magnification by the enlarging lens systems 454 and 458 and then
projected on the surface to be exposed 56, the overall image region
becomes larger. Here, if the microlens array 472 and the aperture
array 476 is not disposed in the system, then, as shown in FIG.
28B, a one-pixel size (spot size) of each beam spot BS that is
projected onto the surface to be exposed 56 will have a size
corresponding to the size of an exposure area 468, and an MTF
(modulation transfer function) characteristic representing
sharpness of the exposure area 468 will fall.
[0228] In contrast, in the case in which the microlens array 472
and aperture array 476 are disposed in the system, the laser light
that has been reflected by the DMD 50 is condensed in
correspondence with the pixels of the DMD 50 by the microlenses of
the microlens array 472. As a result, as shown in FIG. 28C, even
though the exposure area is enlarged, the spot size of each beam
spot BS can be shrunk to a desired size (for example, 10 .mu.m by
10 .mu.m). Thus, the reduction of the MTF characteristic can be
prevented, and high precision exposure can be carried out. Note
that the exposure area 468 is inclined because the DMD 50 is
disposed at an angle so as to eliminate gaps between pixels.
[0229] Moreover, even if the beams are broadened by aberration of
the microlenses, the beams can be smoothed by the apertures such
that the spot sizes on the surface to be exposed 56 have a certain
size. In addition, by this transmission through the apertures
provided in correspondence with the pixels, crosstalk between
adjacent pixels can be prevented.
[0230] By employing the illumination apparatus 144 as a
high-brightness light source in the same way as in the embodiments
described above, the angle of flux that is incident on the
microlenses of the microlens array 472 from the lens system 458 is
made small. Thus, incidence of portions of the flux at neighboring
pixels can be prevented. Thus, a high extinction ratio can be
realized. The extinction ratio could also be further improved by
making the aperture diameters smaller to cut excess light, but
light intensity losses would be large. In contrast, in the present
example the extinction ratio can be improved without increasing
light intensity losses.
[0231] Another Structure of Connected Optical Fibers
[0232] With FIG. 10, an example has been described in which the
incidence end face of the optical fiber 31 is fused and joined at
the emission end face of the multi-mode optical fiber 30. However,
as shown in FIG. 40, it is also possible to form a small diameter
portion 30c at a distal end portion of the laser light emission
side of the multi-mode optical fiber 30 whose cladding diameter is
large, and to coaxially join the optical fiber 31, with a small
cladding diameter and a length of 100 mm to the small diameter
portion 30c. A connection method for this optical fiber is
described next.
[0233] As the multi-mode optical fiber 30 and the optical fiber 31,
any of step index-type optical fibers, graded index-type optical
fibers and multiplex-type optical fibers can be used. For example,
step index-type optical fibers produced by Mitsubishi Cable
Industries, Ltd. can be utilized. In the present embodiment, the
multi-mode optical fiber 30 and the multi-mode optical fiber 31 are
step index-type optical fibers. For the multi-mode optical fiber
30, cladding diameter=125 .mu.m, core diameter=50 .mu.m, NA=0.2,
and transmittance of the end face coating=99.5% or more. For the
optical fiber 31, cladding diameter=60 .mu.m, core diameter=50
.mu.m, and NA=0.2.
[0234] Optical Fiber Connection Methods
[0235] Conventionally, since the tapered region of the cladding
could not be obtained for a sufficient length, the tapered region
included only the distal end of the cladding. Accordingly, it was
difficult to closely dispose the claddings to arrange the claddings
in a array or a bundle, and to obtain a high-brightness light
source. Furthermore, since it was difficult to arrange the cladding
diameters evenly, it was difficult to form a uniform fiber
array.
[0236] Accordingly, connecting separate optical fibers, whose
cladding diameters are smaller, to distal ends of optical fibers
that are usually employed for light propagation, and bundling
portions of these optical fibers whose cladding diameters are
smaller has been considered. Conventionally, to connect two optical
fibers in such a manner, electric discharge-type fusion-splicing
devices, which fuse and splice end portions of two optical fibers
which have been coaxially aligned, are widely used.
[0237] However, in a case in which two optical fibers having a
large difference in external diameters (cladding diameters) thereof
are fusion-spliced in this manner, if electric discharge conditions
are specified such that the thicker of the optical fibers is
suitably melted, the thinner of the optical fibers is excessively
melted and the distal end thereof becomes rounded. Hence, the two
optical fibers cannot be suitably fusion-spliced. Conversely, if
the electric discharge conditions are specified such that the
thinner of the optical fibers is suitably melted, the electrical
discharge is weak, and the thicker of the optical fibers is not
melted. Consequently, in this case too, the two optical fibers
cannot be tightly contacted and suitably fusion-spliced.
Specifically, in cases depending on this conventional method,
losses of the order of 1 dB may occur at the connection portion,
and a connection efficiency may be limited to around 80%.
[0238] According to a connection method described below, two
optical fibers having a large difference in external diameter can
be reliably connected. This optical fiber connection method will be
described with reference to FIGS. 37A and 37B. A present example,
as shown in FIGS. 37A and 37B, is an example in which the distal
end portion of the multi-mode optical fiber 30, whose external
diameter (cladding diameter) is 125 .mu.m, is connected with the
multi-mode optical fiber 31 whose external diameter (cladding
diameter), being 60 .mu.m, is smaller. As an example, the
multi-mode optical fiber 30 is a step index-type optical fiber, in
which the core 30a is covered with a cladding 30b, whose refraction
index is lower than that of the core 30a. Similarly, at the
multi-mode optical fiber 31, the core 31a is covered with a
cladding 31b, whose refraction index is lower than that of the core
31a.
[0239] At the multi-mode optical fiber 30, cladding diameter=125
.mu.m, core diameter=50 .mu.m, NA=0.2, and transmittance of the end
face coating=99.5% or more. At the multi-mode optical fiber 31,
cladding diameter=60 .mu.m, core diameter=50 .mu.m, and NA=0.2.
[0240] First, as shown in FIG. 37A, mechanical machining such as
grinding or the like is applied to the cladding 30b at the distal
end portion of the core 30a. Thus, the small diameter portion 30c
is formed with a length of the order of around 100 mm. The external
diameter of this small diameter portion 30c is 60 .mu.m, the same
as the cladding diameter of the multi-mode optical fiber 31.
[0241] Next, as shown in FIG. 37B, at the distal end of the small
diameter portion 30c described above, the multi-mode optical fiber
31, whose external diameter is the same as portion 30c, is
fusion-spliced in a state in which the core axes of the small
diameter portion 30c and the multi-mode optical fiber 31 are
coaxially aligned with one another. For this fusion, an ordinary
electric discharge-type fusion-splicing device which is used for
fusing such optical fibers may be used. Examples of such optical
fiber fusion-splicing devices include a compact direct core
monitoring optical fiber fusion splicer SUMIOFCAS TYPE-37, from
Sumitomo Electric Industries, Ltd., and the like.
[0242] In the method described above, the small diameter portion
30c is formed at the distal end portion of the multi-mode optical
fiber 30, and then the optical fiber 31 having the same external
diameter as the small diameter portion 30c is fusion-spliced
thereto. Therefore, the two optical fibers 30 and 31 can be
connected simply and reliably without, as in cases of fusing and
connecting two optical fibers whose external diameters differ
greatly, the external diameter of the optical fiber 31 whose
external diameter is smaller being excessively melted or,
conversely, the external diameter of the optical fiber 30 whose
external diameter is larger not being melted. Specifically, losses
at the connection portion of the two optical fibers 30 and 31 can
be suppressed to around 0.05 dB, and a connection efficiency of 99%
can be realized.
[0243] As described later, a plurality of optical fibers in which
the two optical fibers 30 and 31 are connected are prepared, and
the distal end portions of the optical fibers 31 thereof are
bundled for employment. Here, because the small diameter portions
30c of the distal end portions of the multi-mode optical fibers 30
are not bundled, a mechanical machining precision that is required
at the small diameter portions 30c is not particularly high, and
the small diameter portions 30c can accordingly be formed with
ease.
[0244] Next, another optical fiber connection method will be
described, with reference to FIG. 38. In FIG. 38, the same
reference numerals are applied to elements that are the same as
elements in FIG. 37, and descriptions thereof that are not
particularly necessary will be omitted (and the same applies
hereafter).
[0245] In this example, a small diameter portion 30c' with a length
of, for example, around 100 mm, is formed by applying mechanical
machining, such as grinding or the like, to the cladding 30b at the
distal end portion of the multi-mode optical fiber 30. The external
diameter of this small diameter portion 30c' is set to 80 .mu.m,
which is a little greater than the 60 .mu.m cladding diameter of
the multi-mode optical fiber 31. Next, the distal end of the small
diameter portion 30c' is fusion-spliced with the multi-mode optical
fiber 31, whose external diameter is a little smaller than that of
the small diameter portion 30c', in a state in which the core
diameters of the small diameter portion 30c' and the multi-mode
optical fiber 31 are coaxially aligned with one another.
[0246] In the above-described case too, the two optical fibers 30
and 31 can be connected simply and reliably without, as in a case
of fusing and connecting the multi-mode optical fiber 31 directly
to the distal end portion of the multi-mode optical fiber 30 in
which case the external diameters of the two optical fibers differ
greatly, the optical fiber 31 whose external diameter is smaller
being excessively melted or, conversely, the optical fiber 30 whose
external diameter is larger not being melted.
[0247] Next, yet another optical fiber connection method will be
described, with reference to FIG. 39. In this example, first, the
distal end portion of the multi-mode optical fiber 30 is
fusion-spliced with a multi-mode optical fiber 32 having an
external diameter of 80 .mu.m, which is smaller than the external
diameter of the multi-mode optical fiber 30 and larger than the
external diameter of the multi-mode optical fiber 31. Then the
distal end portion of the multi-mode optical fiber 32 with the
intermediate diameter is fusion-spliced with the multi-mode optical
fiber 31 whose external diameter is smaller than that of the
multi-mode optical fiber 32.
[0248] As described above, when the multi-mode optical fiber 32
whose external diameter does not differ greatly from that of the
multi-mode optical fiber 30 is fusion-spliced to the multi-mode
optical fiber 30, the external diameter of the optical fiber 32
whose external diameter is smaller is not excessively melted and,
conversely, the optical fiber 30 whose external diameter is larger
does not fail to be melted. Further, when the multi-mode optical
fiber 31 whose external diameter does not differ greatly from that
of the multi-mode optical fiber 32 is fusion-spliced to the
multi-mode optical fiber 32, the external diameter of the optical
fiber 31 whose external diameter is smaller is not excessively
melted and, conversely, the optical fiber 32 whose external
diameter is larger does not fail to be melted. As a result, the two
optical fibers 30 and 31 can be easily and reliably connected.
[0249] Conversely to the above, the multi-mode optical fiber 30 and
multi-mode optical fiber 32 may be fusion-spliced after the optical
fiber 31 and multi-mode optical fiber 32 have been fusion-spliced.
In this case too, the same effects as described above are
obtained.
[0250] Application Examples
[0251] The exposure apparatus of the present invention may be
suitably applied to an optical modelling device in which a light
beam exposes a photo-curable resin to form a three-dimensional
model, a lamination modelling device which sinters a powder with a
light beam to form sintered layers and accumulates the sintered
layers to form a three-dimensional model which is formed by a
sintered powder body, and the like.
[0252] For example, FIG. 34 shows structure of an optical modelling
device in which the present invention is applied. This optical
modelling device is provided with a tank 556 whose top opens. A
photocurable resin 550 is accommodated in the tank 556. A flat
board-like ascending/descending stage 552 is disposed in the tank
556. This ascending/descending stage 552 is supported by a support
portion 554 which is disposed outside the tank 556. A female screw
portion 554A is provided at the support portion 554. This female
screw portion 554A is screwingly engaged with a lead screw 555
which is driven to rotate by an unillustrated driving motor. The
ascending/descending stage 552 ascends and descends in accordance
with the rotation of the lead screw 555.
[0253] Above a liquid surface of the ascending/descending stage 552
accommodated in the tank 556, a box-like scanner 562 is disposed
with long sides thereof oriented in a direction of short sides of
the tank 556. The scanner 562 is supported by two support arms 560,
which are attached at two side faces in a short side direction of
the scanner 562. The scanner 562 has the same structure as the
scanners in the embodiments described above, is provided with a
plurality of exposure heads, and is connected to an unillustrated
controller which controls the exposure heads.
[0254] Respective guides 558, which extend in a longitudinal
direction, are provided at two side faces in a long side direction
of the tank 556. Lower end portions of the two support arms 560 are
attached at these guides 558 so as to be reciprocally movable along
the longitudinal direction. In this optical modelling device, an
unillustrated driving apparatus is provided for moving the support
arms 560 and the scanner 562 along the guides 558.
[0255] In this optical modelling device, the scanner 562 is moved
at a constant speed along the guides 558, from an upstream side to
a downstream side in the longitudinal direction, by the
unillustrated driving apparatus. In accordance with the movement of
the scanner 562 at the constant speed, the liquid surface of the
photocurable resin 550 is scanned, and a strip-form cured region is
formed by each recording head. When curing of a portion
corresponding to one layer by one cycle of sub-scanning by the
scanner 562 has been completed, the scanner 562 is returned along
the guides 558 by the unillustrated driving device to a start point
at an upstream-most side. Then the lead screw 555 is rotated by the
unillustrated driving motor, and the ascending/descending stage 552
descends by a predetermined amount. Thus, the cured portion of the
photocurable resin 550 is submerged below the liquid surface, and
the liquid-form photocurable resin 550 fills the space above the
cured portion. Hence, the sub-scanning is carried out by the
scanner 562 repeatedly. In this manner, exposure (curing) by the
sub-scanning and lowering of the stage is carried out repeatedly
and, by accumulating the cured portions, a three-dimensional model
is formed. Because the high-brightness laser apparatus of the
present invention is utilized at the exposure heads of the scanner
562, deep focal depth can be obtained. Thus, modelling can be
carried out with high-speed and high accuracy.
[0256] According to the present invention, a high-brightness laser
apparatus is provided. Further, when an exposure apparatus and/or
exposure head of the present invention utilizes this
high-brightness laser apparatus, an effect that deep depth of focus
can be obtained is additionally produced. Further still, in the
case of an area-type exposure beam, an effect that beam blurring at
peripheral edge portions can be suppressed is provided. Further
yet, in a case in which a multiplex laser light source is utilized
as the high-brightness laser apparatus, an effect that the exposure
apparatus and exposure head can be designed for higher output and
lower costs is obtained.
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