U.S. patent application number 09/966916 was filed with the patent office on 2003-04-03 for apparatus and method for making a lens on the end of an optical waveguide fiber.
Invention is credited to Wagner, Robert S..
Application Number | 20030062345 09/966916 |
Document ID | / |
Family ID | 25512046 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030062345 |
Kind Code |
A1 |
Wagner, Robert S. |
April 3, 2003 |
APPARATUS AND METHOD FOR MAKING A LENS ON THE END OF AN OPTICAL
WAVEGUIDE FIBER
Abstract
The present invention relates to an apparatus and method for
making a lens on the end of an optical waveguide fiber. The
apparatus includes a laser, wherein the laser emits a laser beam.
The apparatus further includes a beam expander disposed to receive
the laser beam, whereby the beam expander increases the diameter of
the laser beam, thereby producing an expanded laser beam. The
apparatus further includes a first aperture disposed within the
expanded laser beam, wherein the first aperture blocks a portion of
the expanded laser beam, and a second aperture disposed within the
expanded laser beam, wherein the second aperture blocks a portion
of the expanded laser beam. The apparatus further includes a first
mirror disposed in the path of the expanded laser beam wherein the
first mirror redirects the expanded laser beam. The apparatus
further includes a focusing mirror disposed to receive the expanded
laser beam, wherein the focusing mirror focuses the expanded laser
beam thereby forming a heat zone. The apparatus further includes a
first positioner disposed to selectively position at least a
portion of a lens preform within the heat zone, and a second
positioned disposed to selectively position at least a portion of
an optical waveguide fiber within the heat zone.
Inventors: |
Wagner, Robert S.; (Corning,
NY) |
Correspondence
Address: |
CORNING INCORPORATED
SP-TI-3-1
CORNING
NY
14831
|
Family ID: |
25512046 |
Appl. No.: |
09/966916 |
Filed: |
September 28, 2001 |
Current U.S.
Class: |
219/121.69 ;
219/121.74; 219/121.83 |
Current CPC
Class: |
G02B 6/2552 20130101;
G02B 6/262 20130101; B23K 26/04 20130101; B23K 26/066 20151001 |
Class at
Publication: |
219/121.69 ;
219/121.74; 219/121.83 |
International
Class: |
B23K 026/38; B23K
026/03; B23K 026/06 |
Claims
What is claimed is:
1. An apparatus for making a lens on the end of an optical
waveguide fiber comprising: a laser, wherein said laser emits a
laser beam; a beam expander disposed to receive the laser beam,
whereby said beam expander increases the diameter of the laser
beam, thereby producing an expanded laser beam; a first aperture
disposed within said expanded laser beam, wherein said first
aperture blocks a portion of said expanded laser beam; a second
aperture disposed within said expanded laser beam, wherein said
second aperture blocks a portion of said expanded laser beam; a
first mirror disposed in the path of said expanded laser beam
wherein said first mirror redirects said expanded laser beam; a
focusing mirror disposed to receive said expanded laser beam,
wherein said focusing mirror focuses said expanded laser beam
thereby forming a heat zone; a first positioner disposed to
selectively position at least a portion of a lens preform within
said heat zone; and a second positioned disposed to selectively
position at least a portion of an optical waveguide fiber within
said heat zone.
2. The apparatus of claim 1 further including a controller; wherein
said controller is coupled to said first positioned, whereby said
controller activates said first positioner to selectively position
said at least a portion of said lens preform within said heat zone;
wherein said controller is coupled to said second positioner,
whereby said controller activates said second positioner to
selectively position said at least a portion of said optical
waveguide fiber within said heat zone; wherein said controller is
coupled to said laser, whereby said controller adjust the output
power of said laser.
3. The apparatus of claim 2 wherein said controller includes: a
first camera, wherein the field of view of said first camera
includes said heat zone; a second camera disposed perpendicular to
said first camera, wherein the field of view of said second camera
includes said heat zone; wherein said first camera and said second
camera are disposed radially with respect to said expanded laser
beam; and wherein said first and second cameras are located in a
plane perpendicular to said expanded laser beam.
4. The apparatus of claim 3 wherein said controller further
includes: a digital computer coupled to said first camera and said
second camera, wherein said digital computer receives a first image
from said first camera and a second image from said second camera
and wherein said digital computer uses said first and second images
to control said first and second positioners thereby locating said
lens preform and said optical waveguide fiber in a predetermined
relationship to one another.
5. A method of making a lens on the end of an optical fiber
comprising the steps of: providing an optical waveguide fiber, the
optical waveguide fiber having at least one end; providing a lens
preform; coupling the lens preform to the at least one end, thereby
forming a junction; determining the volume of the lens to be
formed; determining the length of the lens preform that corresponds
to the determined volume; removing the portion of the lens preform
that is in excess of the volume of the lens to be formed; and
forming the lens.
6. The method of claim 5 wherein the diameter of the lens preform
is greater than the diameter of the optical waveguide fiber.
7. The method of claim 5 wherein the volume of the lens to be
formed is calculated according to the formula: 5 V lens = [ 4 3 R c
3 + r 2 ( L fl - R c ) ] ,where L.sub.fl is the desired overall
length of the lens, R.sub.c is the desired front surface radius of
curvature and r is the cross-sectional radius of the lens
preform.
8. The method of claim 7 wherein the length of the cylindrical
glass fiber that corresponds to the determined volume is
L.sub.start and L.sub.start is calculated according to the formula:
6 L start = ( 4 3 R c 3 ) r 2 + ( L fl - 2 R c ) .
9. The method of claim 5, wherein the step of providing a
cylindrical glass fiber includes the step of providing a
cylindrical silica glass fiber.
10. The method of claim 5 wherein the steps of: determining the
volume of the lens to be formed; determining the length of the lens
preform that corresponds to the determined volume; and removing the
portion of the lens preform that is in excess of the volume of the
lens to be formed, thereby producing an endface on the lens
preform; are preformed prior to the step of coupling the
lenspreform to the at least one end.
11. The method of claim 5 wherein the step of forming the lens
includes the step of forming an aspherical lens.
12. The method of claim 5 wherein the step of forming the lens
includes the step of forming an spherical lens.
13. The method of claim 12 wherein the step of forming the
spherical lens includes the steps of: providing a heat source;
heating the endface of the lens preform; and moving the junction a
distance toward the heat source.
14. The method of claim 13 wherein the distance is a melt back
displacement D.sub.MB estimated by the equation 7 D MB = 4 3 R c 3
r 2 - 2 R c ,where R.sub.c is the desired front surface radius of
curvature and r is the cross-sectional radius of the lens
preform.
15. The method of claim 5 wherein the step of forming the lens
includes the step of forming an ball lens.
16. The method of claim 5 further including the step of
characterizing the lens.
17. The method of claim 16 wherein the step of characterizing the
lens includes the step of measuring the geometry of the lens.
18. The method of claim 17 further includes the step of comparing
the measured geometry of the lens to a desired lens geometry.
19. The method of claim 18 further including the step of adjusting
the output of the heat source.
20. The method of claim 19, wherein the heat source is a laser and
the step of adjusting the output of the heat source includes
adjusting the output power of the laser.
21. The method of claim 18 further including the step of adjusting
the melt back displacement.
22. The method of claim 18 further including the step of adjusting
the taper cut displacement.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to lenses for
optical waveguide fibers, and particularly to an apparatus and
method of making lenses for optical waveguide fibers.
[0003] 2. Technical Background
[0004] Advances in optical communications have generated
significant need for optical components that involve light being
transmitted to or from an optical fiber through free-space to
interact with or pass through one or more optical device. A wide
variety of passive and active optical devices exist, some simple
examples including thin-film filters or birefringent elements, and
some of the more complex being large scale three-dimensional switch
fabrics. Other uses for free-space optical components include
injecting light from a laser diode into an optical fiber,
transmitting light through free-space from one optical fiber to
another (such as an amplifier fiber) or projecting light from an
optical fiber to a detector.
[0005] In optical components utilizing free-space transmission of
light (sometimes called micro-optic components), the light beam is
often either expanded and collimated into approximately parallel
rays from the exposed end of an optical fiber, or conversely
focused from an expanded beam into a narrower beam capable of being
injected into the end of the optical fiber at a desired angle of
incidence. While other functions may be performed on the light beam
exiting or entering an optical fiber, collimating and focusing are
the functions that are most commonly encountered in micro-optic
components.
[0006] In order to accomplish the collimating or focusing functions
within the specifications required for optical communications,
cylindrically-shaped gradient-index (GRIN) lenses employing
graduated radial refractive index profiles have become the most
prevalent conventional alternative. However, commercially-available
GRIN lenses are expensive, difficult to manufacture, and present
certain disadvantages in assembling, aligning, and tuning the
optical components.
[0007] Several other approaches to fabricating collimating or
focusing lenses for optical components are known. Axial GRIN
lenses, molded polymer and glass lenses having spherical and
aspherical lens surfaces, composite or complex lens elements,
optical fibers having integral lenses formed by processes such as
thermal expansion or diffusion, and ball lenses are among the many
alternatives.
[0008] Thus there exits a need for a method of making lower cost
precision lenses for optical components.
SUMMARY OF THE INVENTION
[0009] One aspect of the invention is an apparatus for making a
lens on the end of an optical waveguide fiber. The apparatus
includes a laser, wherein the laser emits a laser beam. The
apparatus further includes a beam expander disposed to receive the
laser beam, whereby the beam expander increases the diameter of the
laser beam, thereby producing an expanded laser beam. The apparatus
further includes a first aperture disposed within the expanded
laser beam, wherein the first aperture blocks a portion of the
expanded laser beam, and a second aperture disposed within the
expanded laser beam, wherein the second aperture blocks a portion
of the expanded laser beam. The apparatus further includes a first
mirror disposed in the path of the expanded laser beam wherein the
first mirror redirects the expanded laser beam. The apparatus
further includes a focusing mirror disposed to receive the expanded
laser beam, wherein the focusing mirror focuses the expanded laser
beam thereby forming a heat zone. The apparatus further includes a
first positioner disposed to selectively position at least a
portion of a lens preform within the heat zone, and a second
positioned disposed to selectively position at least a portion of
an optical waveguide fiber within the heat zone.
[0010] In another aspect, the present invention includes method for
making a lens on the end of an optical waveguide fiber. The method
includes the step of providing an optical waveguide fiber, the
optical waveguide fiber having at least one end. The method further
includes the steps of providing a lens preform and of coupling the
lens preform to the at least one end, thereby forming a junction.
The method further includes the steps of determining the volume of
the lens overview or framework for understanding the nature and
character of the invention as it is claimed. The accompanying
drawings are included to provide a further understanding of the
invention, and are incorporated into and constitute a part of this
specification. The drawings illustrate various embodiments of the
invention, and together with the description serve to explain the
principles and operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic diagram of an apparatus embodiment of
the present invention;
[0012] FIG. 2 is a cross section of a partially blocked laser beam
in accordance with the present invention.
[0013] FIG. 3 is a perspective view of one embodiment of a flat
mirror used in the apparatus of FIG. 1;
[0014] FIG. 4 is a cross sectional view of the flat mirror if FIG.
3;
[0015] FIG. 5 is a perspective view of an alternative embodiment of
the flat mirror shown in FIG. 3;
[0016] FIG. 6 is a cross sectional view of a spherical mirror
embodiment of the focusing mirror used in the apparatus of FIG.
1;
[0017] FIG. 7 is a cross sectional view of a conical mirror
embodiment of the focusing mirror used in the apparatus of FIG.
1;
[0018] FIG. 8 is a top plan view of the conical mirror of FIG.
7;
[0019] FIG. 9 is a cross sectional view of a multi-conical mirror
embodiment of the focusing mirror used in the apparatus of FIG.
1;
[0020] FIG. 10 is a top plan view of the multi-conical mirror of
FIG. 9;
[0021] FIG. 10A is a graphical representation of the typical energy
density as a function of length in the heat zone of the apparatus
of FIG. 1 when the focusing mirror is a conical mirror;
[0022] FIG. 10B is a graphical representation of the typical energy
density as a function of length in the heat zone of the apparatus
of FIG. 1 when the focusing mirror is a multi-conical mirror;
[0023] FIG. 11 is a side elevation view of the lens preform and
optical waveguide fiber acted upon by the apparatus of FIG. 1 prior
to alignment and forming the lens;
[0024] FIG. 12 is a flowchart showing the fabrication steps of one
embodiment of the present invention in block diagram form;
[0025] FIG. 13 is a flow chart showing the fabrication steps of one
embodiment of the lens forming step of FIG. 12; and
[0026] FIG. 14 is a side elevation view of one embodiment of a
fiber holder used in the apparatus of FIG. 1; and
[0027] FIG. 15 is an enlarged fragmentary view of a portion of the
fiber holder shown in FIG. 14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Whenever possible, the
same reference numerals will be used throughout the drawings to
refer to the same or like parts.
[0029] One embodiment of the present invention is an apparatus for
making lenses on the end of an optical waveguide fiber is shown in
FIG. 1 and is designated generally throughout by the reference
numeral 10.
[0030] The present invention for an apparatus 10 for making lenses
on the end of an optical waveguide fiber includes a laser 12, such
as, for example a 10W CO.sub.2 laser having a wavelength of 10.6
.mu.m. The laser is coupled to a controller 14 that controls the
duration and power of the laser beam 16. In one embodiment the
laser 12 emits a laser beam 16 having a spot size of 3 mm. It will
be apparent to those skilled in the pertinent art, however, that
the spot size of the laser beam 16 and output power of the laser 12
are design choices that may very with the optics used in the
apparatus 10 or with the desired lens geometry.
[0031] The apparatus 10 also includes a beam expander 18 disposed
to expand the spot size of the laser beam 14. The beam expander 18
emits an expanded laser beam 20 having a decreased energy density.
In one embodiment of the present invention, the beam expander is a
4.times. beam expanded and increases the spot size of the laser
beam 16 from about 3 mm to about 12 mm.
[0032] A first aperture 22 and a second aperture 24 are disposed in
the path of the expanded laser beam 20. The first and second
apertures 22, 24 are orthogonal to the expanded laser beam 20 and
to one another. The first and second apertures 22, 24 block a
cruciform section of the expanded laser beam 20. Preferably, the
center of the cruciform section of the expanded laser beam 20 that
is blocked by the first and second apertures 22, 24 is coincident
with the center of the expanded laser beam 20. FIG. 2 shows cross
section of the expanded laser beam 20 at the plane 26. The blocked
cruciform section of the expanded laser beam 20 is useful in
balancing the energy distribution of to the expanded laser beam 20.
Returning to FIG. 1, the first and second apertures 22, 24 may be,
for example, stainless steel rods with a diameter of about 1.5
mm.
[0033] The apparatus 10 also includes a flat mirror 28. The flat
mirror 28 is inclined at an angle of about 45 degrees with respect
to the axis 30 of the expanded laser beam 20. The flat mirror 28
may be, for example, a copper mirror. FIG. 3 and FIG. 4 show one
possible embodiment of the flat mirror 28. The flat mirror 28 is
adapted to allow an optical waveguide fiber 48, such as for example
a SMF-28.TM. optical waveguide fiber, available from Corning
Incorporated of Corning, N.Y., USA, to pass through the flat mirror
28. Preferably, the flat mirror 28 is configured with an opening
32, such as, for example a hole or slot, that allows the optical
waveguide fiber 48 to positioned in the center of the reflected
laser beam 34. Preferably, the opening for optical waveguide fiber
48 in the flat mirror 28 is located in the mirror so as to fall
within the blocked portion of the expanded laser beam 20.
[0034] The apparatus 10 also includes a fiber feed mechanism 72.
The fiber feed mechanism 72 is positioned above the flat mirror 28
and feeds the optical waveguide fiber 48 through the opening 32.
The fiber feed mechanism 72 is capable of moving the optical
waveguide fiber 48 in reciprocal motion parallel to the axis of the
reflected laser beam 34 as indicated by the arrow 74. The fiber
feed mechanism 72 is also capable of moving the optical waveguide
fiber 48 in a plane transverse to the axis of the reflected laser
beam 34. The fiber feed mechanism 72 may include a fiber holder 78.
In one embodiment, as shown in FIG. 14 and FIG. 15, the fiber
holder 78 is vacuum device that uses suction to hold the end of the
optical waveguide fiber 48. The fiber holder 78 includes a tube 94,
as shown in FIG. 15, the end of the tube 94 is notched to receive
the optical waveguide fiber 48. Suction holds the optical waveguide
fiber 48 against a reference surface 96. The fiber holder 78
provides a way to securely hold the optical waveguide fiber 48
while at the same time inhibiting damage to the fiber while the
position of the optical waveguide fiber 48 is being
manipulated.
[0035] In one embodiment the fiber feed mechanism 72 includes a
positioning stage capable of translation in three orthogonal
directions (X, Y, Z) and three actuators for driving the
positioning stage. The positioner stage is located so that the X-Y
plane of the positioner stage is transverse to the reflected laser
beam 34 and preferably the reflected laser beam 34 is orthogonal to
the X-Y plane of the positioner stage. The optical waveguide fiber
48 is mounted to the positioner, such as, for example a Newport 562
position stage, available from Newport Corporation of Irvine,
Calif., USA. Two actuators, such as, for example, Newport 850G
closed loop Precision Actuators, available from Newport Corporation
of Irvine, Calif., USA, drive the positioning stage in the X and Y
directions. A third actuator, such as, for example a commercially
available, stepper motor or servo having a 0.1 .mu.m step may be
used to drive the positioner stage in the Z direction, thereby
allowing the optical waveguide fiber 48 to be brought into contact
with a lens preform 30. The displacement of the actuators and hence
the position of the optical waveguide fiber 48 is controlled by a
controller 76 that will be described in more detail below.
[0036] Returning to FIG. 1, the lens preform 30 is secured by a
clamp 36 to a positioning stage 38 capable of translation along
three (3) orthogonal axes (X, Y, Z), such as, for example a Newport
562 position stage, available from Newport Corporation of Irvine,
Calif., USA. The positioning stage 38 is located so that the X-Y
plane of the positioner stage is transverse to the expanded laser
beam 20 and preferably the reflected laser beam 34 is orthogonal to
the X-Y plane of the positioner stage. Two actuators, such as, for
example, Newport 850G closed loop Precision Actuators, available
from Newport Corporation of Irvine, Calif., USA, drive the
positioning stage in the X and Y directions. This allows the lens
preform 30 to be positioned within the reflected laser beam 34. A
third actuator, such as, for example a commercially available,
stepper motor or servo having a 0.1 .mu.m step may be used to drive
the positioner stage in the Z direction
[0037] In an alternative embodiment, as shown in FIG. 5, the flat
mirror 28 includes a groove 39 machined into the reflective
surface. The groove 39 replaces the second aperture 26 while still
producing an expanded laser beam with a centrally located cruciform
section removed from the beam.
[0038] Returning to FIG. 1, the apparatus 10 also includes a
focusing mirror 42. The focusing mirror 42 is an axisymmetric
focusing mirror that focuses the expanded laser beam to a heat zone
44. The focusing mirror 42 includes an opening 46 sized to allow a
lens preform 30, such as for example a glass rod to pass through
the focusing mirror 42. The lens preform 30 is a glass body, such
as, for example a cylinder of glass. The shape of the preform
depends upon the final geometry of the lens to be formed and may be
any geometric cross-section, such as, for example circular,
triangular, rectangular, hexagonal, octagonal, annular, C-shaped,
V-shaped, or H-shaped. The lens preform 30 may be, for example, a
glass rod, such as, for example a silica glass rod having a
diameter in the range from about 100 .mu.m to about 350 .mu.m. The
lens preform 30 has a chemical composition chosen to allow the lens
preform to be coupled to the optical waveguide fiber and have a
desired refractive index so that lens formed on the end of the
optical waveguide fiber will have desirable geometric and optical
characteristics. Preferably, the opening 46 is disposed to allow
the lens preform 30 to be positioned coincident with the axis of
symmetry of the focusing mirror 42.
[0039] The focusing mirror 42 may be, for example, a spherical
mirror, a parabolic mirror, a conical mirror or a multi-conical
mirror. FIG. 6 shows a cross sectional view of a spherical mirror
embodiment of the focusing mirror 42. FIG. 7 shows a cross
sectional view of a conical mirror embodiment of the focusing
mirror 42, while FIG. 8 is a top plan view of the conical mirror
embodiment of the focusing mirror 42. An example of a multi-conical
mirror is shown in FIG. 9 and FIG. 10. The choice of the type of
mirror to use as the focusing mirror 42 depends upon the desired
dimensions and energy distribution of the heat zone 44. For a
spherical mirror, the size of the heat zone 44 is independent of
the size of the reflected laser beam 34. When the focusing mirror
42 is a spherical mirror, the energy density of the heat zone 44 is
dependent upon the surface finish of the spherical mirror. For
example if the energy density of the heat zone 44 is too great, it
may be reduced by increasing the surface roughness of the spherical
mirror. Conversely, if the if the energy density of the heat zone
44 is too low, it may be increased by decreasing the surface
roughness of the spherical mirror. The size of the heat zone 44
from a spherical mirror is very small, the spherical mirror
essentially focuses the reflected laser beam 34 to a single
point.
[0040] For conical and multi-conical mirrors, such as, for example
those shown in FIGS. 7, 8, 9, and 10, the size of the heat zone 44
depends upon the size of the reflected laser beam 34. As shown in
FIG. 10A, a conical mirror focuses a laser beam coincident with the
axis of symmetry of the mirror into a heat zone 44 having a uniform
energy density over a discrete length. For example, for a laser
beam with a diameter of 12 mm and a conical mirror with a cone
angle of about 143 degrees, the heat zone 44 has a length of about
3 mm. The type of focusing mirror 42 used in important in being
able to tailor the energy density throughout the heat zone 44.
[0041] FIG. 9 is a cross-sectional view of a multi-conical mirror
46 that may be used as the focusing mirror 42. The multi-conical
mirror 46 shown in FIG. 9 and FIG. 10 includes 4 conical surfaces
49, 50, 52, 54. The first conical surface 49 has a base diameter 56
of about 0.348 inch and a cone angle .alpha..sub.1 of about 120
degrees. The second conical surface 50 has a base diameter 58 of
about 0.252 inch and a cone angle .alpha..sub.2 of about 136
degrees. The third conical surface 52 has a base diameter 60 of
about 0.142 inch and a cone angle .alpha..sub.3 of about 156
degrees. The fourth conical surface 54 has a base diameter 62 of
about 0.080 inch and a cone angle .alpha..sub.4 of about 166
degrees. This particular arrangement of base diameters and cone
angles, in conjunction with a laser beam 14 mm in diameter incident
upon the multi-conical mirror 46, results in a heat zone 44 of 1 mm
in length and an axial energy distribution profile as shown in FIG.
10B. The multi-conical mirror 46 shown in FIG. 9 and FIG. 10 also
includes a slot 64. The slot 64 is about 0.040 inch wide and
extends about 0.060 inch past the center of the multi-conical
mirror 46. The multi-conical mirror 46 is made of Tellurium Copper.
As shown in FIG. 9 and FIG. 10 the multi-conical mirror 46 includes
a cylindrical potion 66 having a diameter D.sub.1 of about 0.800
inch and a height of about 0.345 inch. The multi-conical mirror 46
also includes a mounting ring 68 having a diameter D.sub.2 of about
1.000 inch and a thickness 70 of about 0.050 inch.
[0042] As will be appreciated by those of ordinary skill in the
optical arts, the number of conical surfaces as well as the size
and cone angles of the conical surfaces are all variables that may
be changed individually or in combination to produce a heat zone 44
of desirable dimension and energy distribution for a particular
application.
[0043] The size and shape of the first and second apertures 24, 26
and the optical characteristics of the focusing mirror 42 control
the shape of the lens. In some optical applications for example it
may be desirable to have a lens that has different radii of
curvature in orthogonal directions, such as, for example when
optically coupling an optical waveguide fiber to the elliptical
beam from a laser diode.
[0044] Returning to FIG. 1, the apparatus 10 also includes a
positioning stage 38. The positioning stage 38 is positioned below
the focusing mirror 42 and feeds the optical waveguide fiber 48
through the opening 46. The positioning stage 38 is capable of
moving the lens preform 30 in reciprocal motion parallel to the
axis of symmetry of the focusing mirror 42 as indicated by the
arrow 74. The positioning stage 38 is also capable of moving the
optical waveguide fiber 48 in a plane transverse to the axis of
symmetry of the focusing mirror 42.
[0045] In one embodiment the fiber feed mechanism 72 includes a
positioning stage capable of translation in three orthogonal
directions (X, Y, Z) and three actuators for driving the
positioning stage. The positioner stage is located so that the X-Y
plane of the positioner stage is transverse to the expanded laser
beam 20 and preferably the expanded laser beam 20 is orthogonal to
the X-Y plane of the positioner stage. The optical waveguide fiber
48 is mounted to the positioner, such as, for example a Newport 562
position stage, available from Newport Corporation of Irvine,
Calif., USA. Two actuators, such as, for example, Newport 850G
closed loop Precision Actuators, available from Newport Corporation
of Irvine, Calif., USA, drive the positioning stage in the X and Y
directions. A third actuator, such as, for example a commercially
available, stepper motor or servo having a 0.1 .mu.m step may be
used to drive the positioner stage in the Z direction, thereby
allowing the optical waveguide fiber 48 to be brought into contact
with the lens preform 30. The displacement of the actuators and
hence the position of the optical waveguide fiber 48 is controlled
by a controller 76. The controller 76 is connected to the
positioning stage 38 and the fiber feed mechanism 72. The
controller 76 aligns the lens preform 30 and the optical waveguide
fiber 48 with one another.
[0046] The controller 76 includes a first camera 78 and a second
camera 80. The first and second cameras 78, 80 may be, for example,
NTSC analog cameras, such as, for example Dage MTI CCD-100 cameras
available DAGE-MTI Incorporated of Michigan City, Ind. The first
and second cameras 78, 80 are located such that the heat zone 44 is
substantially centered within the respective field of views of
first and second cameras 78, 80. Preferably the first and second
cameras 78, 80 are coplanar with one another and are located so
that their respective fields of view are approximately orthogonal
to one another. Additionally, although not required, it is
preferable that the plane in which the first and second cameras 78,
80 are located is perpendicular to the expanded laser beam 20.
[0047] The first and second cameras 78, 80 each transmit a digital
image to a digital computer 82. An example of a digital image
transmitted by either the first or second camera 78, 80 is shown in
FIG. 11. The digital computer 82 uses a edge detection algorithm,
such as for example a SORBEL algorithm to identify the edges 83,
84, 86 of the lens preform 30 and the edges 88, 90, 92 optical
waveguide fiber 72.
[0048] After the edges 83, 84, 86, 88, 90, 92 are detected the
digital computer 80 determines the physical location of the edges
82, 84, 86, 88, 90, 92 with respect to a predetermined coordinate
system. A mode filter algorithm has proven useful in reliably
determining the location of the edges 83, 84, 86, 88, 90, 92 within
the reference coordinate system. Once the location of the edges 83,
84, 86, 88, 90, 92 within the reference coordinate system are
determined the digital computer 80 directs the positing stage 38
and fiber feed mechanism 72 to move the lens preform 30 and the
optical waveguide fiber 48 into alignment with one another. The
lens preform 30 is then fused to the optical waveguide fiber 48 and
if necessary cut to length. The lens preform 30 is moved into the
heat zone 44 and a lens is formed by melting the lens preform 30
and allowing the surface tension of the melted lens preform 30 to
form the lens.
[0049] After the lens is formed, the digital computer 82 uses
images from the first and second cameras 78, 80 to preform a
geometric analysis of the lens, determining the radii of curvature
in two orthogonal directions.
[0050] In an alternative embodiment, a third digital camera (not
shown) is used to provide another view of the lens which the
digital computer 82 uses to characterize the lens.
[0051] Another embodiment of the method for making lenses of the
present invention is shown in FIG. 2 and is designated generally
throughout by the reference numeral 100.
[0052] The present invention for a method 100 of making a lens on
the end of an optical waveguide fiber includes the step 102 of
providing an optical waveguide fiber, such as, for example
SMF-28.TM. single mode optical waveguide fiber, available from
Corning Incorporated of Corning, N.Y. The method 100 further
includes the step 104 of providing a lens preform. The lens preform
is a glass body, such as, for example a cylinder of glass. The
shape of the preform depends upon the final geometry of the lens to
be formed and may be any geometric cross-section, such as, for
example circular, triangular, rectangular, hexagonal, octagonal,
annular, C-shaped, V-shaped, or H-shaped.
[0053] The lens preform has a chemical composition chosen to allow
the lens preform to be coupled to the optical waveguide fiber and
have a desired refractive index so that lens formed on the end of
the optical waveguide fiber will have desirable geometric and
optical characteristics. The lens preform may, for example, be a
silica glass fiber having a diameter from about 100 .mu.m to about
300 .mu.m when the optical waveguide fiber is SMF-28.TM. single
mode optical waveguide fiber.
[0054] The method 100 further includes the step 106 of coupling the
lens preform to the optical waveguide fiber. The lens preform may
be coupled to the optical waveguide fiber by fusing the lens
preform to the optical waveguide fiber. The lens preform may be
fused to the optical waveguide fiber by conventional electrode arc
fusion splicing techniques. Alternatively a laser, such as, for
example, a CO.sub.2 laser may be used to splice the lens preform to
the optical waveguide fiber.
[0055] The method 100 further includes the step 108 of determining
the volume of the lens to be formed. For example, for a lens having
a desired overall length L.sub.fl and a front surface radius of
curvature R.sub.c , when the lens preform is circular in
cross-section the total volume of the lens, V.sub.lens, is
calculated according to equation 1. It should be noted that
equation 1 only provides an estimation of the volume of the desired
lens. 1 V lens = r 2 ( L fl - 2 R c ) + 4 3 R c 3 ( 1 )
[0056] where, r is the cross-sectional radius of the lens
preform.
[0057] The method 100 further includes the step 110 of determining
the length of the lens preform that corresponds to the estimated
volume of the desired lens. For a cylindrical lens preform, the
starting length, L.sub.start, may be estimated according to
equation 2. 2 L start = ( 4 3 R c 3 ) r 2 + ( L fl - 2 R c ) ( 2
)
[0058] As will be appreciated by those skilled in the pertinent
art, for the starting length may be calculated by employing the
appropriate geometric formulas.
[0059] The method 100 further includes the step 112 of cutting the
lens preform to length. The step 112 of cutting the lens preform to
length produces and endface on the lens preform. The lens preform
may be cut to length using a mechanical fiber cleaver or a laser.
When a laser is used in the step 106 to couple the lens preform to
the optical waveguide fiber, either the lens preform moved or the
laser beam is redirected so that the lens preform is sufficiently
heated, at the distance equal to the starting length, L.sub.start,
from the junction of the lens preform to the optical waveguide
fiber, so that melting of the lens preform is initiated and surface
tension pulls the glass apart, thus completing the cut. As will be
appreciated by those skilled in the pertinent art, more than one
laser beam may be used, such as, for example two laser beams of
equal powerdirected to opposite sides of the lens preform.
Alternatively, a precut lens preform may be used thus removing the
need to cut the lens preform to length after coupling the lens
preform to the optical waveguide fiber.
[0060] The method 100 further includes the step 114 of forming the
lens. The step of forming the lens may include the step 116 of
measuring the distance from the junction of the lens preform and
the optical waveguide fiber to the end of the lens preform. Based
upon this measured distance, the necessary relative movement
between the heat source and junction, and the power setting of the
heat source that are required to form a desired lens shape may be
estimated. If a precut lens preform is used the step 116 of
measuring the distance from the junction of the lens preform and
the optical waveguide fiber to the end of the lens preform may be
omitted.
[0061] The step 114 of forming the lens of the method 100 may
further include the step 118 providing a heat source, such as, for
example a laser. The step 114 includes the step of applying heat to
the endface of the lens preform, thereby melting the endface of the
lens preform. The surface tension of the glass forms a curved front
surface. The step 118 of applying heat to the endface of the lens
preform may also include the step 120 of decreasing the distance
between the heat source and the junction of the lens preform and
the optical waveguide fiber. The distance between the heat source
and the junction of the lens preform and the optical waveguide
fiber may be decreased by moving the junction relative while the
heat source remains stationary or by moving the heat source while
the junction remains stationary. The amount that distance between
the heat source and the junction of the lens preform and the
optical waveguide fiber must be decreased by to form the lens is
the melt back distance, D.sub.MB. The melt back distance is
estimated by equating the volume of the lens preform to be formed
into the lens to the volume of the lens. For example, when the lens
preform is cylindrical and the lens is spherical the the volume of
the lens preform required to form the lens is denoted by
V.sub.cylinder and volume of the formed lens is denoted by
V.sub.sphere.V.sub.cylinder may be calculated using equation 3,
where L.sub.MB if the length of the melt back.
V.sub.cylinder=.pi..multidot.r.sup.2.multidot.L.sub.MB (3)
[0062] V.sub.sphere may be calculated according to equation 4. 3 V
sphere = 4 3 R c 3 ( 4 )
[0063] The length of the melt back, L.sub.MB, is unknown and is
determined by setting V.sub.cylinder equal to V.sub.sphere and
solving for L.sub.MB, which yields equation 5. 4 L MB = ( 4 3 R c 3
) r 2 ( 5 )
[0064] The melt back distance D.sub.MB is calculated by
substituting this value of L.sub.MB into equation 6.
D.sub.MB=L.sub.MB-2.multidot.R.sub.c (6)
[0065] The step 114 of forming the lens of the method 100 may
further include the step 122 of measuring the geometric properties,
specifically the radius of curvature, R.sub.c, and length of the
lens element, L.sub.measured, as the lens as formed.
[0066] The step 114 of forming the lens of the method 100 may
further include the step 124 of using the measured values of the
lens length, L.sub.measured, and radius of curvature, R.sub.c, as
input data for a control algorithm that controls the power of the
heat source P and the relative displacement between the heat source
and the junction of the lens preform and the optical waveguide
fiber for the formation of the next lens.
[0067] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *