U.S. patent application number 10/359206 was filed with the patent office on 2003-07-31 for method of making diffraction grating device, diffraction grating device, and apparatus for making the same.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Hashimoto, Ken, Inoue, Akira, Ohmura, Masaki.
Application Number | 20030140656 10/359206 |
Document ID | / |
Family ID | 18276711 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030140656 |
Kind Code |
A1 |
Hashimoto, Ken ; et
al. |
July 31, 2003 |
Method of making diffraction grating device, diffraction grating
device, and apparatus for making the same
Abstract
The present invention relates to a method of making a
diffraction grating device, in which an optical waveguide is
irradiated, by way of a phase grating, with light capable of
inducing a refractive index modulation in an optical waveguide
region of the optical waveguide so as to form a diffraction grating
in the optical waveguide region. In the present invention, when
modulating the refractive index of the optical waveguide region of
an optical fiber, the intensity of refractive index modulation
inducing light emitted from a laser light source so as to irradiate
the phase grating is adjusted according to individual positions on
the phase grating. Alternatively, the scanning speed of a mirror
scanned by a stage is adjusted according to the individual
positions on the phase grating. Here, the amount of irradiation of
refractive index modulation inducing light at each position on the
phase grating is adjusted so as to cancel the diffraction
efficiency distribution of phase grating. The present invention can
make a diffraction grating device having a desirable characteristic
even when the diffraction efficiency distribution of phase grating
deviates from its desirable distribution.
Inventors: |
Hashimoto, Ken;
(Yokohama-shi, JP) ; Inoue, Akira; (Yokohama-shi,
JP) ; Ohmura, Masaki; (Yokohama-shi, JP) |
Correspondence
Address: |
McDermott, Will & Emery
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD.
Osaka
JP
|
Family ID: |
18276711 |
Appl. No.: |
10/359206 |
Filed: |
February 6, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10359206 |
Feb 6, 2003 |
|
|
|
09722048 |
Nov 27, 2000 |
|
|
|
6519389 |
|
|
|
|
Current U.S.
Class: |
65/378 ; 385/37;
430/290 |
Current CPC
Class: |
G02B 6/02152 20130101;
G02B 6/02138 20130101 |
Class at
Publication: |
65/378 ; 385/37;
430/290 |
International
Class: |
G02B 006/34 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 1999 |
JP |
P1999-334378 |
Claims
What is claimed is:
1. A method of making a diffraction grating device, in which an
optical waveguide is irradiated, by way of a phase grating, with
refractive index modulation inducing light capable of inducing a
refractive index modulation in an optical waveguide region of said
optical waveguide so as to form a diffraction grating in said
optical waveguide region, said method comprising: a diffraction
efficiency distribution measuring step of measuring a diffraction
efficiency distribution of said phase grating; and a refractive
index modulating step of irradiating said optical waveguide with
said refractive index modulation inducing light by way of said
phase grating with an amount of irradiation of said refractive
index modulation inducing light at each position on said phase
grating being adjusted according to said diffraction efficiency
distribution measured in said diffraction efficiency distribution
measuring step, so as to modulate a refractive index of said
optical waveguide region.
2. A method of making a diffraction grating device according to
claim 1, wherein said diffraction efficiency distribution measuring
step is carried out prior to said refractive index modulating
step.
3. A method of making a diffraction grating device according to
claim 1, wherein said diffraction efficiency distribution measuring
step is carried out simultaneously with said refractive index
modulating step; and wherein said amount of irradiation of
refractive index modulation inducing light at each position on said
phase grating is feedback-controlled according to said diffraction
efficiency distribution of phase grating measured in said
diffraction efficiency distribution measuring step.
4. A method of making a diffraction grating device according to
claim 1, wherein said refractive index modulation inducing light is
made incident on said phase grating while being scanned in a
longitudinal direction of said optical waveguide in said refractive
index modulating step, and the intensity of said refractive index
modulation inducing light irradiating each position on said phase
grating is adjusted upon said scanning.
5. A method of making a diffraction grating device according to
claim 1, wherein said refractive index modulation inducing light is
made incident on said phase grating while being scanned in a
longitudinal direction of said optical waveguide in said refractive
index modulating step, and the scanning speed of said refractive
index modulation inducing light irradiating each position on said
phase grating is adjusted upon said scanning.
6. A diffraction grating device made by the method of making a
diffraction grating device according to claim 1.
7. An apparatus for making a diffraction grating device, in which
an optical waveguide is irradiated, by way of a phase grating, with
refractive index modulation inducing light capable of inducing a
refractive index modulation in an optical waveguide region of said
optical waveguide so as to form a diffraction grating in said
optical waveguide region, said apparatus comprising: diffraction
efficiency distribution measuring means for measuring a diffraction
efficiency distribution of said phase grating; and refractive index
modulating means for irradiating said optical waveguide with said
refractive index modulation inducing light by way of the phase
grating with an amount of irradiation of said refractive index
modulation inducing light at each position on said phase grating
being adjusted according to said diffraction efficiency
distribution measured by said diffraction efficiency distribution
measuring means, so as to modulate a refractive index of said
optical waveguide region.
8. An apparatus for making a diffraction grating device according
to claim 7, wherein said diffraction efficiency distribution
measuring means measures said diffraction efficiency distribution
of said phase grating before said refractive index modulating means
irradiates said phase grating with said refractive index modulation
inducing light.
9. An apparatus for making a diffraction grating device according
to claim 7, wherein said diffraction efficiency distribution
measuring means measures said diffraction efficiency distribution
of said phase grating at the same time when said refractive index
modulating means irradiates said phase grating with said refractive
index modulation inducing light; and wherein said refractive index
modulating means feedback-controls said amount of irradiation of
refractive index modulation inducing light at each position on said
phase grating according to said diffraction efficiency distribution
of phase grating measured by said diffraction efficiency
distribution measuring means.
10. An apparatus for making a diffraction grating device according
to claim 7, wherein said refractive index modulating means
comprises: irradiating means for making said refractive index
modulation inducing light incident on said phase grating while
scanning said refractive index modulation inducing light in a
longitudinal direction of said optical waveguide; and irradiation
intensity adjusting means for adjusting the intensity of said
refractive index modulation inducing light irradiating each
position on said phase grating when said refractive index
modulation inducing light is scanned by said irradiating means.
11. An apparatus for making a diffraction grating device according
to claim 7, wherein said refractive index modulating means
comprises: irradiating means for making said refractive index
modulation inducing light incident on said phase grating while
scanning said refractive index modulation inducing light in a
longitudinal direction of said optical waveguide; and scanning
speed adjusting means for adjusting the scanning speed of said
refractive index modulation inducing light irradiating each
position on said phase grating when said refractive index
modulation inducing light is scanned by said irradiating means.
12. An apparatus for making a diffraction grating device, in which
a diffraction grating is made in an optical waveguide region of an
optical waveguide, said apparatus comprising: a light source for
emitting refractive index modulation inducing light capable of
inducing a refractive index modulation in said optical waveguide
region; a phase grating for diffracting said refractive index
modulation inducing light emitted from said light source; a mirror
for reflecting said refractive index modulation inducing light
emitted from said light source so as to make said refractive index
modulation inducing light incident on said phase grating; a moving
unit for moving said mirror along a longitudinal direction of said
optical waveguide; and a speed control unit for controlling,
according to a diffraction efficiency distribution of said phase
grating, the moving speed of said mirror moved by said moving
unit.
13. An apparatus for making a diffraction grating device, in which
a diffraction grating is made in an optical waveguide region of an
optical waveguide, said apparatus comprising: a light source for
emitting refractive index modulation inducing light capable of
inducing a refractive index modulation in said optical waveguide
region; a phase grating for diffracting said refractive index
modulation inducing light emitted from said light source; a mirror
for reflecting said refractive index modulation inducing light
emitted from said light source so as to make said refractive index
modulation inducing light incident on said phase grating; a moving
unit for moving said mirror along a longitudinal direction of said
optical waveguide; and an irradiation intensity control unit for
controlling the irradiation intensity of said refractive index
modulation inducing light emitted from said light source.
14. An apparatus for making a diffraction grating device according
to claim 12 or 13, further comprising a light-receiving device
provided so as to sandwich said phase grating between said
light-receiving device and said mirror.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of making a
diffraction grating device in which an optical waveguide is
irradiated, by way of a phase grating, with light capable of
inducing a refractive index modulation in an optical waveguide
region of the optical waveguide so as to form a diffraction grating
in the optical waveguide region; the diffraction grating device
made by this method; and an apparatus for making the same.
[0003] 2. Related Background Art
[0004] Diffraction grating device has diffraction grating formed in
optical waveguide region of optical waveguide (encompassing both
optical fiber and planar optical waveguide) and is used as optical
filter and the like. Such a diffraction grating device is
manufactured as follows. Namely, by way of a phase grating, an
optical waveguide is irradiated with a predetermined wavelength of
light capable of inducing a refractive index modulation (which is
ultraviolet light in general, and will hereinafter be referred to
as "refractive indexmodulation inducing light"). Then, interference
fringes of the refractive index modulation inducing light are
generated in an optical waveguide region of the optical waveguide.
Hence, the refractive index at a predetermined part of the optical
waveguide region provided with the interference fringes is
modulated, whereby a diffraction grating is formed.
[0005] Here, laser light emitted from a light source such as a KrF
laser light source, which outputs the refractive index modulation
inducing light, has a luminous flux diameter smaller than the
length of the diffraction grating to be manufactured. As a
consequence, a diffraction grating having a desirable length is
made when the refractive index modulation inducing light is made
incident on the phase grating while being scanned in a longitudinal
direction of the optical waveguide.
SUMMARY OF THE INVENTION
[0006] The inventors have studied the conventional technique
mentioned above and, as a result, have found a problem as follows.
Namely, when making a diffraction grating, e.g., when making a
uniform diffraction grating, a phase grating having a uniform
diffraction efficiency distribution within a plane should be used.
However, since the diffraction efficiency distribution of phase
grating is not always set uniformly within a plane, a nonuniform
diffraction grating may be made even if a uniform diffraction
grating is intended to be made. Thus, the above-mentioned
conventional technique has been problematic in that diffraction
grating having desirable characteristics cannot be made if the
diffraction efficiency distribution of a phase grating deviates
from its desirable distribution.
[0007] For overcoming the above-mentioned problem, it is an object
of the present invention to provide a method of making a
diffraction grating device which can make a diffraction grating
having a desirable characteristic even when the diffraction
efficiency distribution of phase grating deviates from a desirable
distribution, the diffraction grating device made by this method,
and an apparatus for making the same.
[0008] The present invention provides a method of making a
diffraction grating device, in which an optical waveguide is
irradiated, by way of a phase grating, with refractive index
modulation inducing light capable of inducing a refractive index
modulation in an optical waveguide region of the optical waveguide
so as to form a diffraction grating in the optical waveguide
region; the method comprising: (1) a diffraction efficiency
distribution measuring step of measuring a diffraction efficiency
distribution of the phase grating; and (2) a refractive index
modulating step of irradiating the optical waveguide with the
refractive index modulation inducing light by way of the phase
grating with an amount of irradiation of the refractive index
modulation inducing light at each position on the phase grating
being adjusted according to the diffraction efficiency distribution
measured in the diffraction efficiency distribution measuring step,
so as to modulate a refractive index of the optical waveguide
region.
[0009] Preferably, in the method of making a diffraction grating
device in accordance with the present invention, the diffraction
efficiency distribution measuring step is carried out prior to the
refractive index modulating step. Alternatively, it is preferred
that the diffraction efficiency distribution measuring step be
carried out simultaneously with the refractive index modulating
step, and that the amount of irradiation of refractive index
modulation inducing light at each position on the phase grating be
feedback-controlled according to the diffraction efficiency
distribution of phase grating measured in the diffraction
efficiency distribution measuring step.
[0010] In the method of making a diffraction grating device in
accordance with the present invention, it is preferred that the
refractive index modulation inducing light be made incident on the
phase grating while being scanned in a longitudinal direction of
the optical waveguide in the refractive index modulating step, and
that the intensity of the refractive index modulation inducing
light irradiating each position on the phase grating be adjusted
upon the scanning.
[0011] In the method of making a diffraction grating device in
accordance with the present invention, it is preferred that the
refractive index modulation inducing light be made incident on the
phase grating while being scanned in a longitudinal direction of
the optical waveguide in the refractive index modulating step, and
that the scanning speed of the refractive index modulation inducing
light irradiating each position on the phase grating be adjusted
upon the scanning.
[0012] The present invention provides a diffraction grating device
made by the above-mentioned method of making a diffraction grating
device.
[0013] The present invention provides an apparatus for making a
diffraction grating device, in which an optical waveguide is
irradiated, by way of a phase grating, with refractive index
modulation inducing light capable of inducing a refractive index
modulation in an optical waveguide region of the optical waveguide
so as to form a diffraction grating in the optical waveguide
region; the apparatus comprising: (1) diffraction efficiency
distribution measuring means for measuring a diffraction efficiency
distribution of the phase grating; and (2) refractive index
modulating means for irradiating the optical waveguide with the
refractive index modulation inducing light by way of the phase
grating with an amount of irradiation of the refractive index
modulation inducing light at each position on the phase grating
being adjusted according to the diffraction efficiency distribution
measured by the diffraction efficiency distribution measuring
means, so as to modulate a refractive index of the optical
waveguide region.
[0014] Preferably, in the apparatus for making a diffraction
grating device in accordance with the present invention, the
diffraction efficiency distribution measuring means measures the
diffraction efficiency distribution of the phase grating before the
refractive index modulating means irradiates the phase grating with
the refractive index modulation inducing light. Alternatively, it
is preferred that the diffraction efficiency distribution measuring
means measure the diffraction efficiency distribution of phase
grating at the same time when the refractive index modulating means
irradiates the phase grating with the refractive index modulation
inducing light, and that the refractive index modulating means
feedback-control the amount of irradiation of refractive index
modulation inducing light at each position on the phase grating
according to the diffraction efficiency distribution of phase
grating measured by the diffraction efficiency distribution
measuring means.
[0015] In the apparatus for making a diffraction grating device,
the refractive index modulating means may comprise irradiating
means for making the refractive index modulation inducing light
incident on the phase grating while scanning the refractive index
modulation inducing light in a longitudinal direction of the
optical waveguide, and irradiation intensity adjusting means for
adjusting the intensity of the refractive index modulation inducing
light irradiating each position on the phase grating when the
refractive index modulation inducing light is scanned by the
irradiating means.
[0016] In the apparatus for making a diffraction grating device,
the refractive index modulating means may comprise irradiating
means for making the refractive index modulation inducing light
incident on the phase grating while scanning the refractive index
modulation inducing light in a longitudinal direction of the
optical waveguide, and scanning speed adjusting means for adjusting
the scanning speed of the refractive index modulation inducing
light irradiating each position on the phase grating when the
refractive index modulation inducing light is scanned by the
irradiating means.
[0017] The present invention provides an apparatus for making a
diffraction grating device, in which a diffraction grating is made
in an optical waveguide region of an optical waveguide, the
apparatus comprising: (1) a light source for emitting refractive
index modulation inducing light capable of inducing a refractive
index modulation in the optical waveguide region; (2) a phase
grating for diffracting the refractive index modulation inducing
light emitted from the light source; (3) a mirror for reflecting
the refractive index modulation inducing light emitted from the
light source so as to make the refractive index modulation inducing
light incident on the phase grating; (4) a moving unit for moving
the mirror along a longitudinal direction of the optical waveguide;
and (5) an irradiation intensity control unit for controlling the
irradiation intensity of the refractive index modulation inducing
light emitted from the light source.
[0018] The present invention provides an apparatus for making a
diffraction grating device, in which a diffraction grating is made
in an optical waveguide region of an optical waveguide, the
apparatus comprising: (1) a light source for emitting refractive
index modulation inducing light capable of inducing a refractive
index modulation in the optical waveguide region; (2) a phase
grating for diffracting the refractive index modulation inducing
light emitted from the light source; (3) a mirror for reflecting
the refractive index modulation inducing light emitted from the
light source so as to make the refractive index modulation inducing
light incident on the phase grating; (4) a moving unit for moving
the mirror along a longitudinal direction of the optical waveguide;
and (5) a speed control unit for controlling, according to a
diffraction efficiency distribution of the phase grating, the
moving speed of the mirror moved by the moving unit.
[0019] The apparatus for making a diffraction grating device in
accordance with the present invention may further comprise a
light-receiving device provided so as to sandwich the phase grating
between the light-receiving device and the mirror.
[0020] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present invention.
[0021] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a diagram schematically showing the apparatus for
making a diffraction grating device in accordance with a first
embodiment;
[0023] FIG. 2 is a view showing how the diffraction efficiency
distribution of a phase grating is measured by the apparatus for
making a diffraction grating device in accordance with the first
embodiment;
[0024] FIG. 3A is a graph showing the diffraction efficiency
distribution of a phase grating for a first case;
[0025] FIG. 3B is a graph showing a distribution of amount of
irradiation of refractive index modulation inducing light with
respect to the phase grating for the first case;
[0026] FIG. 3C is a graph showing the degree of refractive index
modulation in an optical waveguide region of an optical fiber for
the first case;
[0027] FIG. 4A is a graph showing the diffraction efficiency
distribution of a phase grating for a second case;
[0028] FIG. 4B is a graph showing a distribution of amount of
irradiation of refractive index modulation inducing light with
respect to the phase grating for the second case;
[0029] FIG. 4C is a graph showing the degree of refractive index
modulation in an optical waveguide region of an optical fiber for
the second case;
[0030] FIG. 5A is a graph showing the diffraction efficiency
distribution of the phase grating for a third case;
[0031] FIG. 5B is a graph showing a distribution of amount of
irradiation of refractive index modulation inducing light with
respect to the phase grating for the second case;
[0032] FIG. 5C is a graph showing the degree of refractive index
modulation in an optical waveguide region of an optical fiber for
the third case;
[0033] FIG. 6 is a diagram schematically showing a diffraction
efficiency distribution measuring unit for measuring the
diffraction efficiency distribution of a phase grating; and
[0034] FIG. 7 is a diagram schematically showing the apparatus for
making a diffraction grating device in accordance with a second
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] In the following, embodiments of the present invention will
be explained in detail with reference to the accompanying drawings.
In the explanation of drawings, constituents identical to each
other will be referred to with numerals or letters identical to
each other, without repeating their overlapping descriptions.
Though the following explanation mainly relates to cases where an
optical fiber is employed as an optical waveguide, it is similarly
applicable to planar optical waveguides formed on planar
substrates.
[0036] To begin with, a first embodiment of the method of making a
diffraction grating device in accordance with the present
invention, diffraction grating device made by this method, and
apparatus for making the same will be explained.
[0037] FIG. 1 is a diagram schematically showing an apparatus 10
for making a diffraction grating device in accordance with the
first embodiment. This apparatus 10 comprises a laser light source
11, a slit 12, a mirror 13, a stage 14 equipped with a motor 14a, a
phase grating 15, and a control unit 16 for controlling the
apparatus 10. This apparatus 10 is configured such that an optical
fiber (optical waveguide) 90 to be formed with a diffraction
grating is disposed directly under the phase grating 15.
[0038] The optical fiber 90 has a core region 91 located at the
center thereof, and a cladding region 92 surrounding the core
region 91. Though the light guided through the optical fiber 90
propagates while being confined in the core region 91, a part of
the energy of light also exists in the cladding region 92 in the
vicinity of the core region 91. Namely, the optical waveguide
region of the optical fiber 90 is constituted by the core region 91
and the part of cladding region 92 in the vicinity of the core
region 91. While the optical fiber 90 is mainly composed of silica
glass, the optical waveguide region (at least the core region 91)
is doped with GeO.sub.2. As a consequence, if the optical fiber 90
is irradiated with refractive index modulation inducing light, then
the refractive index of the region doped with GeO.sub.2 is
modulated according to the intensity of irradiation.
[0039] The laser light source 11 is a light source for outputting
the refractive index modulation inducing light. As the light
source, an excimer laser light source (e.g., KrF laser light source
or the like) capable of emitting ultraviolet laser light is
suitably used. Preferably, the intensity of refractive index
modulation inducing light emitted from the laser light source 11 is
variable.
[0040] Of the refractive index modulation inducing light outputted
from the laser light source 11, the part entering an opening 12A of
the slit 12 passes therethrough so as to be made incident on the
mirror 13. The mirror 13 reflects the refractive index modulation
inducing light passed through the opening 12A of slit 12, so as to
make it incident on the phase grating 15. The mirror 13 can be
moved in the longitudinal direction of the optical fiber 90 by the
stage 14 having the motor 14a. When the mirror 13 is moved as such,
the refractive index modulation inducing light can be made incident
on the phase grating 15 while being scanned in the longitudinal
direction of the optical fiber 90.
[0041] The phase grating 15 is formed with projections and
depressions having a predetermined period on the side (where the
optical fiber 90 is placed) opposite from the side on which the
refractive index modulation inducing light reflected by the mirror
13 is incident, and diffracts the incident refractive index
modulation inducing light. Also, the phase grating 15 forms
interference fringes of outputted (+)first-order diffracted light
and (-)first-order diffracted light, whereby a refractive index
modulating area corresponding to these interference fringes is
formed in the optical waveguide region of optical fiber 90. The
optical fiber 90 in which the refractive index modulating area is
formed in the optical waveguide region acts a diffraction grating
device.
[0042] The control unit 16 is constituted by a microcomputer, a
memory, and the like. The control unit 16 is electrically connected
to the light source 11, so as to control the intensity of
refractive index modulation inducing light emitted from the light
source 11. Also, the control unit 16 is electrically connected to
the motor 14a of stage 14, so as to control the moving speed of
mirror 13.
[0043] In the method of making a diffraction grating device in
accordance with this embodiment, the diffraction efficiency
distribution of phase grating 15 is initially measured, and then a
refractive index modulating area 94 is formed in the optical
waveguide region of optical fiber 90 with the amount of irradiation
of refractive index modulation inducing light at each position of
the phase grating 15 being adjusted according to the measured
diffraction efficiency distribution of phase grating 15. When
measuring the diffraction efficiency distribution of phase grating
15, as shown in FIG. 2, the respective intensities of zero-order
light, (+)first-order light, and (-)first-order light outputted
from the phase grating 15 are measured by means of light-receiving
devices 6 to 8 or the like in the apparatus 10 for making the
diffraction grating device shown in FIG. 1 while the mirror 13 is
moved in the longitudinal direction of optical fiber 90 by the
stage 14 in the state without the optical fiber 90. Then, the
diffraction efficiency distribution of phase grating 15 is
determined according to the individual intensities. In this
embodiment, the apparatus 10 for making a diffraction grating
device may comprise the light-receiving devices 6 to 8.
[0044] When making the diffraction grating 94 in the optical
waveguide region of optical fiber 90, the intensity of refractive
index modulation inducing light emitted from the laser light source
11 so as to be made incident on the phase grating 15 is adjusted by
the control unit 16 according to individual positions on the phase
grating 15. Alternatively, the motor 14a of stage 14 is controlled
by the control unit 16, so as to regulate the moving speed of
mirror 13, such that the scanning speed of mirror 13 is adjusted
according to the individual positions on the phase grating 15.
Thus, the amount of irradiation of the refractive index modulation
inducing light at each position of the phase grating 15 is
adjusted. Here, the amount of irradiation of the refractive index
modulation inducing light with respect to the phase grating 15 is
adjusted so as to cancel the diffraction efficiency distribution of
phase grating 15.
[0045] FIGS. 3A, 4A, and 5A are graphs showing respective
diffraction efficiency distributions of the phase grating 15 for
first to third cases. FIGS. 3B, 4B, and 5B are graphs showing
respective distributions of amount of irradiation of refractive
index modulation inducing light with respect to the phase grating
15 for these cases. FIGS. 3C, 4C, and 5C are graphs showing
respective degrees of refractive index modulation in the optical
waveguide region of optical fiber 90 for these cases.
[0046] In the first case, as shown in FIG. 3A, the diffraction
efficiency of phase grating 15 is the highest in the vicinity of
the center of the phase grating 15 in the longitudinal direction
thereof and decreases toward its marginal areas. Here, the amount
of irradiation of refractive index modulation inducing light with
respect to the phase grating 15 is adjusted so as to become uniform
in the longitudinal direction as shown in FIG. 3B. Then, the degree
of refractive index modulation in the optical waveguide region of
optical fiber 90 is the highest in the vicinity of the center of
the phase grating 15 in the longitudinal direction thereof and
decreases toward its marginal areas as shown in FIG. 3C, thus
becoming nonuniform.
[0047] As shown in FIG. 4A, the diffraction efficiency of phase
grating 15 is the highest in the vicinity of the center of the
phase grating 15 in the longitudinal direction thereof and
decreases toward its marginal areas in the second case as well.
However, unlike the first case, the amount of irradiation of
refractive index modulation inducing light with respect to the
phase grating 15 in the second case is adjusted so as to cancel the
diffraction efficiency distribution of phase grating 15, i.e., so
as to become the lowest in the vicinity of the center in the
longitudinal direction thereof and increase toward its marginal
areas as shown in FIG. 4B. As a consequence, the degree of
refractive index modulation in the optical waveguide region of
optical fiber 90 becomes longitudinally uniform as shown in FIG.
4C.
[0048] In the third case, the diffraction efficiency of phase
grating 15 is the lowest in the vicinity of the center in the
longitudinal direction thereof and increases toward its marginal
areas as shown in FIG. 5A. The amount of irradiation of refractive
index modulation inducing light with respect to the phase grating
15 in the third case is adjusted so as to cancel the diffraction
efficiency distribution of phase grating 15, i.e., so as to become
the highest in the vicinity of the center in the longitudinal
direction thereof and decrease toward its marginal areas as shown
in FIG. 5B. As a consequence, the degree of refractive index
modulation in the optical waveguide region of optical fiber 90
becomes longitudinally uniform as shown in FIG. 5c.
[0049] The diffraction efficiency distribution of phase grating 15
may be measured by means of the apparatus 10 for making a
diffraction grating device shown in FIGS. 1 and 2, or a diffraction
efficiency distribution measuring unit separate therefrom. FIG. 6
is a schematic diagram showing a diffraction efficiency
distribution measuring unit 20 for measuring the diffraction
efficiency distribution of phase grating 15.
[0050] The diffraction efficiency distribution measuring unit 20
comprises a stage 21 mounting the phase grating 15 and having a
motor 21a for moving the latter; a mirror 22 for causing the
refractive index modulation inducing light outputted from the laser
light source 11 to be incident on the phase grating 15; acondenser
lens 23; and light-receiving devices 24 to 26 for measuring the
respective intensities of zero-order light, (+)first-order
diffracted light, and (-)first-order diffracted light outputted
from the phase grating 15.
[0051] In the diffraction efficiency distribution measuring
apparatus 20, the refractive index modulation inducing light
outputted from the laser light source 11 is reflected by the mirror
22 and then is collected by the condenser lens 23, so as to
irradiate the phase grating 15 mounted on the stage 21. The
intensity of the zero-order light generated along with the
irradiation of the phase grating 15 with the refractive index
modulation inducing light is measured by the light-receiving device
24, the intensity of thus generated (+)first-order diffracted light
is measured by the light-receiving device 25, and the intensity of
thus generated (-)first-order diffracted light is measured by the
light-receiving device 26. As the intensity of each diffracted
light is measured while the phase grating 15 is moved by the stage
21, the diffraction efficiency distribution of phase grating 15 is
determined.
[0052] The diffraction efficiency distribution measuring apparatus
20 may use other laser light sources in place of the laser light
source 11 for outputting the refractive index modulation inducing
light, and the diffraction efficiency distribution of phase grating
15 at the wavelength of refractive index modulation inducing light
may be determined according to the diffraction efficiency
distribution of phase grating 15 measured by use of these other
laser light sources.
[0053] In this embodiment, as in the foregoing, the diffraction
efficiency distribution of phase grating 15 is initially measured,
and then diffraction grating 94 is formed in the optical waveguide
region of optical fiber 90 with the amount of irradiation of
refractive index modulation inducing light at each position of the
phase grating 15 being adjusted according to the measured
diffraction efficiency distribution of phase grating 15. As a
consequence, even when the diffraction efficiency of phase grating
15 is not uniform within a plane, a diffraction grating device
having a desirable characteristic can be made.
[0054] A second embodiment of the method of making a diffraction
grating device in accordance with the present invention,
diffraction grating device made by this method, and apparatus for
making the same will now be explained.
[0055] FIG. 7 is a diagram schematically showing an apparatus 30
for making a diffraction grating device in accordance with the
second embodiment. The apparatus 30 for making a diffractiong
rating device in accordance with this embodiment further comprises
light-receiving devices 31 to 33 in addition to the apparatus 10
for making a diffraction grating device in accordance with the
first embodiment.
[0056] Each of the light-receiving devices 31 to 33 is provided so
as to sandwich the phase grating 15 between the mirror 13 and the
respective light-receiving device, so that the optical fiber 90 is
set between the phase grating 15 and the light-receiving devices 31
to 33. The light-receiving device 31 measures the intensity of the
zero-order light generated along with the irradiation of phase
grating 15 with the refractive index modulation inducing light. The
light-receiving device 32 measures the intensity of the
(+)first-order diffracted light generated along with the
irradiation of phase grating 15 with the refractive index
modulation inducing light. The light-receiving device 33 measures
the intensity of the (-)first-order diffracted light generated
along with the irradiation of phase grating 15 with the refractive
index modulation inducing light. Thus, the diffraction efficiency
distribution of phase grating 15 is determined according to the
intensities of light received by the light-receiving devices 31 to
33.
[0057] In this embodiment, the diffraction efficiency distribution
of phase grating 15 is measured at the same time when the
refractive index of optical waveguide region in the optical fiber
90 is modulated, and the amount of irradiation of refractive index
modulation inducing light at each position of the phase grating 15
is feedback-controlled according to thus measured diffraction
efficiency distribution of phase grating 15.
[0058] Namely, when measuring the diffraction efficiency
distribution of phase grating 15, the diffraction grating is formed
in the optical waveguide region of optical fiber 90 while the
mirror 13 is moved in the longitudinal direction of optical fiber
90 by the stage 14 in the state where the optical fiber 90 is set
between the phase grating 15 and the light-receiving devices 31 to
33 in the apparatus 30 for making a diffraction grating device
shown in FIG. 7. At the same time, the respective intensities of
the zero-order light, (+)first-order light, and (-)first-order
light outputted from the phase grating 15 are received by the
light-receiving devices 31 to 33, and the diffraction efficiency
distribution of phase grating 15 is determined according to thus
received light intensities.
[0059] When forming the diffraction grating 94, the light source 11
is controlled by the control unit 16, such that the intensity of
the refractive index modulation inducing light emitted from the
laser light source 11 so as to be made incident on the phase
grating 15 is adjusted according to the individual positions on the
phase grating 15. Alternatively, the motor 14a of stage 14 is
controlled by the control unit 16, so as to regulate the moving
speed of mirror 13, such that the scanning speed of mirror 13 is
adjusted according to the individual positions on the phase grating
15. Here, the amount of irradiation of refractive index modulation
inducing light at each position on the phase grating 15 is
feedback-controlled according to the measured diffraction
efficiency distribution of phase grating 15 so as to cancel the
diffraction efficiency distribution of phase grating 15.
[0060] In this embodiment, the relationship among the diffraction
efficiency distribution of phase grating 15, the distribution of
amount of irradiation of refractive index modulation inducing light
with respect to the phase grating 15, and the degree of refractive
index modulation is similar to that explained with reference to
FIGS. 3A to 3C, 4A to 4C, and 5A to 5C in the first embodiment.
[0061] In this embodiment, as in the foregoing, the diffraction
efficiency distribution of phase grating 15 is measured at the same
time when the diffraction grating 94 is formed in the optical
waveguide region of optical fiber 90, and the amount of irradiation
of refractive index modulation inducing light at each position of
the phase grating 15 is feedback-controlled according to thus
measured diffraction efficiency distribution of phase grating 15.
As a consequence, even when the diffraction efficiency of the phase
grating 15 is not uniform within a plane, a diffraction grating
device having a desirable characteristic can be made. In
particular, a diffraction grating device having a desirable
characteristic can be made in this embodiment even when the
intensity of the refractive index modulation inducing light emitted
from the laser light source 11 is unstable.
[0062] Here, when a plurality of signals at intervals of 0.4 nm
(approximately equivalent to 50 GHz) are made incident on a fiber
grating, there is a correlation between the value of reflection
(side lobe) of the spectrum at a wavelength separated by 2 channels
(0.8 nm) or more from the center wavelength of the fiber grating
and the amount of fluctuation in diffraction efficiency of a phase
grating used for making the fiber grating. Therefore, using a phase
grating whose amount of fluctuation of zero-order diffraction
efficiency is 0.35, the inventors studied the side lobe in each of
a fiber grating made with the fluctuation of diffraction efficiency
being corrected by the method of making a diffraction grating
device in accordance with this embodiment and a fiber grating made
without correcting the fluctuation of diffraction efficiency. The
result indicates that, while the side lobe of the fiber grating
made without correcting the fluctuation of diffraction efficiency
is as much as about -22 dB, the side lobe of the fiber grating made
with the fluctuation of diffraction efficiency being corrected is
-28 dB or less, thereby improving a characteristic. The value of
-28 dB or less is on a par with that of a side lobe obtained when
the amount of fluctuation of zero-order diffraction efficiency is
0.01 or less.
[0063] Without being restricted to the above-mentioned embodiments,
the present invention can be modified in various ways. For example,
while the above-mentioned embodiments relate to the making of a
diffraction grating device in which the degree of refractive index
modulation in the optical waveguide region of optical fiber 90 is
longitudinally uniform, the same also applies to the making of a
diffraction grating device in which the degree of refractive index
modulation has a predetermined distribution which is not
longitudinally uniform.
[0064] Though the above-mentioned embodiments relate to the case
where the optical waveguide is an optical fiber, the same also
applies to planar optical waveguides formed on planar
substrates.
[0065] Also, in addition to or in place of the respective
intensities of zero-order light, (+)first-order diffracted light,
and (-)first-order diffracted light, the respective intensities of
(+)second-order diffracted light and (-)second-order diffracted
light may be measured, so as to control the amount of irradiation
of refractive index modulation inducing light according to these
intensities.
[0066] According to the present invention, as explained in detail
in the foregoing, the diffraction efficiency distribution of a
phase grating is measured by diffraction efficiency distribution
measuring means in a diffraction efficiency distribution measuring
step. Then, in a refractive index modulating step, the amount of
irradiation of refractive index modulation inducing light at each
position on the phase grating is adjusted by refractive index
modulating means according to thus measured diffraction efficiency
distribution of phase grating, whereby a refractive index
modulating area is formed in the optical waveguide region of an
optical waveguide. Thus, even when the diffraction efficiency
distribution of phase grating deviates from its desirable
distribution, a diffraction grating device having a desirable
characteristic is made.
[0067] From the invention thus described, it will be obvious that
the invention may be varied in many ways. Such variations are not
to be regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended for inclusion within the scope of
the following claims.
* * * * *