U.S. patent application number 10/625905 was filed with the patent office on 2005-01-27 for optical connector assembly.
Invention is credited to Maj, Tomasz, Rolston, David Robert Cameron.
Application Number | 20050018974 10/625905 |
Document ID | / |
Family ID | 34080288 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050018974 |
Kind Code |
A1 |
Rolston, David Robert Cameron ;
et al. |
January 27, 2005 |
Optical connector assembly
Abstract
A method and apparatus is disclosed for enabling a coupling of
at least one optical fiber with an optoelectronic device. The
apparatus comprises at least one v-groove for receiving at least
one optical fiber. A first end of the apparatus is then polished at
a predetermined angle in order to enable an optical coupling with
the optoelectronic device.
Inventors: |
Rolston, David Robert Cameron;
(Beaconsfield, CA) ; Maj, Tomasz; (Montreal,
CA) |
Correspondence
Address: |
OGILVY RENAULT
1981 MCGILL COLLEGE AVENUE
SUITE 1600
MONTREAL
QC
H3A2Y3
CA
|
Family ID: |
34080288 |
Appl. No.: |
10/625905 |
Filed: |
July 24, 2003 |
Current U.S.
Class: |
385/83 ;
385/137 |
Current CPC
Class: |
G02B 6/4214 20130101;
G02B 6/4204 20130101; G02B 6/4221 20130101; G02B 6/4249
20130101 |
Class at
Publication: |
385/083 ;
385/137 |
International
Class: |
G02B 006/36 |
Claims
We claim:
1. A method for manufacturing an optical connector assembly,
comprising: preparing a sealed assembly comprising at least one
embedded optical fiber; polishing an end of said sealed assembly at
a predetermined angle to enable a coupling of said optical fiber to
an optical device using a total internal reflection to a planar
coupling surface located on said sealed assembly; buffing at least
said planar coupling surface of said assembly; placing said
coupling surface on said optical device with said coupling surface
abutting a planar window of said optical device; and using
references on said optical device and said assembly to adjust a
position of said assembly on said window to achieve said
coupling.
2. The method as claimed in claim 1, wherein said preparing said
assembly comprises: providing a substrate having at least one
V-groove; inserting an optical fiber in each of the at least one
V-groove provided in the assembly; providing a coating substance
over at least one part of said assembly, in the vicinity of the at
least one V-groove; and sealing the optical fiber in each of the at
least one V-groove provided in the assembly using the coating
substance and a sheet material provided over said assembly surface
to create a sealed assembly.
3. The method as claimed in claim 2, further comprising the step of
removing said sheet material.
4. The method as claimed in claim 2, wherein said sheet material is
transparent, further comprising the step of partially removing said
sheet material.
5. The method as claimed in claim 1, wherein said buffing
comprising removing a portion of a cladding of said optical fiber
in said assembly, a core of said fiber being essentially adjacent
said edge of said assembly, said adjusting comprising observing a
position of said core near said edge on said window so as to
position said core over a corresponding optical element of said
device.
6. The method as claimed in claim 5, wherein the object of
observation is a fiducial mark or etching on said edge on said
window.
7. The method as claimed in claim 1, wherein the coating substance
is light activated, further comprising the step of light activating
the light activated substance.
8. The method as claimed in claim 2, wherein the sheet material is
a transparent sheet material, said coupling surface being on said
sheet material.
9. The method as claimed in claim 2, wherein said at least one
v-groove comprises a plurality of fibers inserted in a plurality of
parallel V-grooves.
10. The method as claimed in claim 7, wherein the at least one
V-groove are etched in silicon.
11. The method as claimed in claim 1, wherein said preparing
comprises using a plastic-molding technique to embed said at least
one fiber in said substrate.
12. The method as claimed in claim 1, wherein the step of placing
said coupling surface over said optical device with said coupling
surface abutting a window of said optical device comprises the
providing of a transparent sheet of material between said coupling
surface and said window of said optical device.
13. The method as claimed in claim 10, wherein the sheet material
comprises at least one microlens, said at least one microlens
enhancing said coupling between said optical device and said
assembly.
14. The method as claimed in claim 10, wherein a microlens is
provided on the sheet material at a distance that will enable a
capture of all light originating from a corresponding optical fiber
and collimate all the light to the optical device.
15. The method as claimed in claim 1, wherein said polishing
further comprises providing a reflective coating to replace said
total internal reflection.
16. An optical connector comprising: a sealed assembly comprising
at least one channel, each said channel receiving an optical
waveguide extending in a lengthwise direction, and having a beveled
end at which said waveguide terminates, wherein light from said
waveguide is reflected at said end for lateral coupling; a layer of
transparent material disposed between said channel and a side of
said connector, said layer including a planar optical coupling
surface; and a microlens positioned on said optical coupling
surface to focus light communicated between said waveguide and an
optical device.
17. The connector as claimed in claim 16, wherein said at least one
channel comprises a plurality of parallel channels.
18. The connector as claimed in claim 16, wherein said beveled end
is exposed, said light from said waveguide being reflected by total
internal reflection.
19. The connector as claimed in claim 16, wherein said waveguide is
an optical fiber.
20. An optical connector comprising: a substrate having at least
one optical fiber embedded near one side of said substrate; said
substrate having a beveled end at which said fiber terminates at a
leading edge thereof, wherein light from said fiber is reflected at
said end for coupling on said one side; and said optical fiber
having a portion of a cladding removed on said one side to
facilitate coupling of said core once alignment between said core
and an optical device has been accomplished.
21. The connector as claimed in claim 20, wherein said substrate
comprises a chip member comprising at least one V-groove on one
side, an optical fiber being bonded in each said V-groove.
22. The connector as claimed in claim 21, wherein said at least one
V-groove comprises a plurality of parallel V-grooves.
23. The connector as claimed in claim 20, wherein said beveled end
is exposed, said light from said waveguide being reflected by total
internal reflection.
24. The connector as claimed in claim 20, wherein said cladding is
removed on said one side.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is the first application filed for the present
invention. This application is related to commonly assigned
co-pending applications filed herewith bearing agent docket numbers
16005-2US entitled "Optical Ferrule" and 16005-3US entitled
"Encapsulated Optical Package", the specifications of which are
hereby incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to the field of optical connecting
devices. More precisely, this invention relates to methods and
apparatus for connecting optical fibers to optoelectronic
devices.
BACKGROUND OF THE INVENTION
[0003] The optical coupling of light emitted, absorbed or altered
by optoelectronic (OE) devices, such as photodetectors, light
emitting diodes (LED's), lasers, and vertical cavity surface
emitting lasers (VCSEL), with optical waveguides, such as optical
fibers and planar waveguides, is well known in conventional
photonics. One technique that is known involves cutting an optical
fiber at a 45 degree bevel so that light is exchanged between the
fiber and an OE device at a side of the fiber. The bevel surface
may be coated to be more reflective, or it may be left exposed so
as to reflect light by total internal reflection (TIR).
[0004] The cost of manufacturing such waveguide-to-device couplings
is determined by the ease of preparing the both the waveguide (e.g.
fiber) and the OE device for the step of coupling, and then
performing the coupling itself in a manner that ensures an
efficient transfer of optical signal without introduction of
noise.
[0005] An optoelectronic chip, containing a device such as a
vertical cavity surface emitting laser (VCSEL), is typically
mounted in an electronic package where the direction of the light
from the VCSEL is perpendicular (normal) to the surface of both the
chip itself and the surface on which the electronic package has
been placed. Electronic packages are typically placed on large 2-D
flat printed circuit boards (PCBs), and these PCBs are typically
stacked within a chassis with very narrow gaps between the PCBs.
This type structure requires that all the connections to and from
the PCB enters and leaves from the PCB's edge, called the
card-edge. Since the light from the VCSEL is emitted perpendicular
to the PCB, a method is required to direct the light off the edge
of the PCB, and hence parallel to the flat surface of the PCB. The
typical method used to achieve card-edge connections with light is
to use a flexible-PCB bent at 90-degrees where one face of the
flexible-PCB connects to the main PCB and the other face has the
optoelectronic chip where the light from the VCSEL is directed
parallel to the surface of the main PCB. The light is then
butt-coupled into an optical fiber.
[0006] The bevel coupling method allows the optoelectronic chip to
be placed in the conventional packages where the light is directed
perpendicular to the PCB. The optical fiber is then beveled at
45-degrees and placed over the light beam such that the light is
reflected at 90-degrees and propagates parallel to the PCB within
the optical fiber. This method allows more conventional packaging
and reduces the alignment tolerance because the length of the
optical fiber is essentially laid over the flat surface of the
PCB.
[0007] Several patents use 45-degree beveled optical fiber as the
core of their assemblies as well. U.S. Pat. No. 4,092,061 granted
May 30, 1978, U.S. Pat. No. 6,250,820 granted Jan. 26, 2001, U.S.
Pat. No. 6,315,464 granted Nov. 13, 2001 and U.S. Pat. No.
6,389,202 granted May 14, 2002 all describe assemblies that have
beveled optical fiber tips located over (or under) optoelectronic
devices. The alignment procedures for these types of assemblies are
complicated. These methods typically involve micro-solder ball
re-flow, flip-chip alignment and/or precisely machined parts, which
require significant resources and materials.
[0008] The concept of creating a completely integrated assembly
that holds both the optoelectronic devices and the waveguides has
also been proposed in U.S. Pat. No. 4,611,886 granted Sep. 16,
1986. It describes a method of using a molded housing that carries
a glass-plate with a beveled end, which is aligned using etched
grooves in the molded housing that match the chip carrier. This
technique may be adequate for large area optoelectronics, but would
not be a suitable alignment methodology for small devices such as
VCSELs.
[0009] Another assembly proposed in U.S. Pat. No. 4,756,590 granted
Jul. 12, 1988 describes a method of using a 45-degree
bevel-polished silicon v-groove sandwich of optical fibers that has
optoelectronic devices glued over the bevel in line with the
optical fibers. In the principal embodiment, the optical fibers are
held in a block that is polished and beveled. The block is
typically made from two silicon v-groove chips that sandwich the
optical fibers between them. By polishing the end of the sandwich
at 45-degrees and then applying a metallic mirror, the light is
forced to reflect at 90-degrees and travel perpendicularly from the
optical fibers through one of the silicon v-groove chips. It is,
however, unclear how any measureable amount of light (for example:
1-milliwatt of 850-nm wavelength light--typical of a vcsel) can
pass through a silicon v-groove chip since silicon is opaque. U.S.
Pat. No. 4,756,590 also teaches the removal of part of one silicon
v-groove chip by polishing until the longitudinal sides near the
tips of the optical fibers are exposed. This is to allow closer
access to the core of the optical fiber at the tip.
[0010] Finally, U.S. Pat. No. 4,756,590 describes that the
optoelectronic devices must be glued against the silicon v-groove
ferrule above the optical fiber in a face-down orientation. This
completely rules-out a VCSEL chip since the vertical cavity laser
would be damaged if bonded up-side-down, not to mention that the
wirebond connections are made on the same surface as the vertical
cavity laser and it would be physically impossible to wirebond to
the VCSEL chip in such an orientation.
SUMMARY OF THE INVENTION
[0011] It is an object of the invention to provide an optical
connector.
[0012] It is another object of the invention to provide a method
for connecting a fiber to an optical or optoelectronic device.
[0013] It is another object of the invention to provide a method
for adjusting a fiber with respect to an optical device.
[0014] This invention relates to the optical coupling of light
emitted, absorbed or altered by optoelectronic devices (such as
photodetectors, light emitting diodes, lasers, vertical cavity
surface emitting lasers (VCSEL), etc.) with optical waveguides
(such as optical fibers, planar waveguides, etc.). The invention
facilitates the coupling procedure by using mechanical assemblies
to hold the waveguides in contact with the optoelectronic devices.
These assemblies do not require any other coupling agent, such as
lenses, but must be sufficiently close in order to maximize the
coupling efficiency into (or out of) the waveguide (optical fiber).
Both assemblies are particularly amenable to a one-step alignment
process involving the planar-on-planar (or stacked) 2-D alignment
of the waveguide assembly with an optoelectronic assembly. The
assemblies are stacked on top of each other and viewed from above
to simultaneously observe features on both the waveguide assembly
and the optoelectronic assembly. The alignment process involves
sliding the two assemblies (waveguide assembly and optoelectronic
assembly) with respect to each other on their co-incident 2-D
surfaces. This procedure can be done passively (without energizing
the optoelectronic assembly), and requires only one alignment step
to be performed. This is contrary to other methods described in the
prior art that use mechanical constraints, such as extra grooves,
stop-walls, stand-offs, precision machining or precise
pick-and-place methods to align waveguides to optoelectronic
devices. It also supercedes older methods that rely on large
optoelectronic devices to overcome slight misalignments of the
optical fiber.
[0015] The essential aspect of the waveguide assembly described
below is the 45-degree bevel at the tips of the waveguides (optical
fiber). This feature allows for side-coupling of light into the
core of the waveguide (optical fiber) by using the 45-degree bevel
as a mirror surface. The light is initially directed at 90-degrees
to the longitudinal direction of the optical fiber and travels
through the cladding towards the center of the beveled tip. Total
internal reflection at the 45-degree beveled tip forces the light
to reflect at 90-degrees and couple along the longitudinal axis of
the optical fiber. A metallic reflection coating can be applied to
the beveled tip with an appropriate metal to enhance the coupling
into the optical fiber. One of the earliest references of the
45-degree beveling of optical fiber can be found in U.S. Pat. No.
4,130,343 granted Dec. 19, 1978. In this patent, a single optical
fiber is beveled at 45-degrees and placed in-contact over a single
optoelectronic device. The embodiment described in this document
uses this now common approach but improves the alignment
method.
[0016] The embodiment in this document uses only one silicon
v-groove chip and has a sacrificial sheet material (such as a glass
plate) bonded over the optical fibers to keep them in place. The
sheet material can be later thinned or removed completely by means
such as chemical etching or mechanical polishing. The key aspect of
removing the sheet material (glass plate) is to allow the beveled
tips of the optical fibers to be observed. This is an essential
part of the alignment procedure since the fiber tips must be well
aligned with the optoelectronic devices as described earlier.
[0017] The embodiment in this document claims that the entire cover
sheet can be removed and the entire longitudinal length of the
optical fibers are exposed. Furthermore, the longitudinal length of
the optical fibers may even be slightly over-polished into the
cladding of the optical fibers to obtain an even closer proximity
to the core.
[0018] In accordance with a first aspect of the invention, there is
provided a method for manufacturing an optical connector assembly,
comprising providing an assembly comprising at least one V-groove,
inserting an optical fiber in each of the at least one V-groove
provided in the assembly; providing a coating substance over at
least one part of the assembly, in the vicinity of the at least one
V-groove, sealing the optical fiber in each of the at least one
V-groove provided in the assembly using the coating substance and a
sheet material provided over the assembly surface to create a
sealed assembly, polishing an end of the sealed assembly at a
predetermined angle to enable a coupling of the optical fiber to an
optical device using a total internal reflection to a planar
coupling surface located on the sealed assembly, buffing at least
the planar coupling surface of the assembly, placing the coupling
surface on the optical device with the coupling surface abutting a
planar window of the optical device, and adjusting a position of
the assembly on the window to achieve the coupling.
[0019] According to a further broad aspect of the invention, there
is provided an optical connector comprising a sealed assembly
having at least one channel, each channel receiving an optical
waveguide extending in a lengthwise direction, and having a beveled
end at which the waveguide terminates, wherein light from the
waveguide is reflected at the beveled end for lateral coupling, a
layer of transparent material disposed between the channel and a
side of the connector, the layer including a planar optical
coupling surface, and a microlens positioned on the optical
coupling surface to focus light communicated between the waveguide
and an optical device.
[0020] According to yet a further broad aspect of the invention,
there is provided an optical connector comprising a chip member
having at least one V-groove on one side, an optical fiber bonded
in each V-groove, and a beveled end at which the fiber terminates
at a leading edge thereof, wherein light from the fiber is
reflected at the beveled end for lateral coupling, and the optical
fiber having some of its cladding removed on one lateral side to
facilitate a greater optical coupling to the core once the core and
optical device are aligned.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Further features and advantages of the present invention
will become apparent from the following detailed description, taken
in combination with the appended drawings, in which:
[0022] FIG. 1 is a 3D perspective view which shows four optical
fibers;
[0023] FIGS. 2a,b are a 3D perspective view and a front view which
show an assembly which comprises four parallel optical fiber
v-grooves;
[0024] FIGS. 3a,b are a 3D perspective view and a front view of an
intermediate assembly which comprises four parallel optical fibers
each located in one of the optical fiber v-grooves and an epoxy
located on the four parallel optical fibers;
[0025] FIGS. 4a,b are a 3D perspective view and a front view of the
intermediate assembly where a glass plate is used to flatten the
epoxy;
[0026] FIGS. 5a,b are a 3D perspective view and a front view of the
intermediate assembly where a protective epoxy is further added at
each end of the assembly;
[0027] FIGS. 6a,b are a 3D perspective view and a front view of the
intermediate assembly where a front beveled face has been polished
and a back flat face has been polished;
[0028] FIGS. 7a,b are a 3D perspective view and a front view which
shows the intermediate assembly where the glass plate has been
polished away;
[0029] FIG. 8 is a profile view of the preferred embodiment of the
optical connector assembly;
[0030] FIGS. 9a,b are a first perspective view of the front face of
the optical connector assembly where a perfect polish has been done
and a second perspective view of the front face of another
over-polished connector assembly;
[0031] FIGS. 10a,b,c,d are a 3D perspective view, a top view, a
side view and a back view of another embodiment of the invention
where the connected assembly is plastic-micro molded;
[0032] FIG. 11 is a 3D perspective view of the other embodiment of
the invention where four optical fibers are inserted;
[0033] FIG. 12 is a 3D perspective view of the other embodiment of
the invention where epoxy is used to fix the four optical
fibers;
[0034] FIG. 13 is a 3D perspective view of the other embodiment of
the invention where a front beveled face has been polished;
[0035] FIG. 14 is a 3D perspective view of the other embodiment of
the invention where the bottom of the assembly has been flat
polished to exposed the optical fibers;
[0036] FIG. 15 is a 3D perspective view which shows an optical
ferrule in the vicinity of an optoelectronic device;
[0037] FIGS. 16a,b are a 3D perspective view and a top view of an
optical ferrule seated on a transparent material located between
the optical ferrule and an optoelectronic chip;
[0038] FIGS. 17a,b are another 3D perspective view and top view of
an optical ferrule seated on a transparent material located between
the optical ferrule and an optoelectronic chip which the optical
ferrule is closer to the optoelectronic chip;
[0039] FIGS. 18a,b are a 3D perspective view and top view of an
optical ferrule seated on a transparent material enabling an
optical coupling between the optical ferrule and the optoelectronic
chip;
[0040] FIG. 19 is a side view of the optical ferrule seated on the
transparent material which shows the optical coupling between the
optical ferrule and the optoelectronic chip;
[0041] FIG. 20 is a top view of a transparent substrate which
comprises four patterned microlenses;
[0042] FIG. 21 is a 3D perspective view of an optical ferrule
seated on a transparent material enabling an optical coupling
between the optical ferrule and the optoelectronic chip where the
transparent material comprises patterned microlenses;
[0043] FIGS. 22a,b are a zoom-in of a side view and a front view of
the optical coupling using patterned microlenses; and
[0044] FIG. 23 is a side view of an optical ferrule seated on a
transparent material enabling an optical coupling between the
optical ferrule and the patterned microlenses.
[0045] It will be noted that throughout the appended drawings, like
features are identified by like reference numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0046] The parallel optical connector is a mechanical structure
used to connect a parallel optical fiber ribbon to an array of
optoelectronic devices, such as a vertical cavity surface emitting
laser (VCSEL), or photodetector array.
[0047] The parallel optical connector consists of a structure to
rigidly hold optical fibers in the same plane and pitched from each
other at 250-microns. One end of the structure is polished at a
45-degree angle to create a reflective glass-air interface at the
fiber tips. This interface can reflect light at 90-degrees by
either total internal reflection (TIR) when the glass-air interface
is preserved, or by depositing a reflective metal layer on the
exposed tips of the fiber. The reflective metal layer may be made
of gold, silver, etc.
[0048] Light directed at the 45-degree tips of the optical fiber
will be reflected and coupled into the optical fiber orthogonal to
the initial direction. In this situation, light will pass though
the side of the optical fiber, through the cladding and reflect off
the 45-degree tip, due to TIR or the metallic surface, into the
core of the optical fiber. Conversely, when light is already in the
core and traveling towards the 45-degree polished tip, it reflects
off the 45-degree tip, due to TIR or the metallic surface, and is
directed normal to the optical fiber passing through the cladding
and out of the side of the optical fiber.
[0049] The opposite end of the structure has the optical fibers
leave as a parallel ribbon cable.
[0050] Primary Embodiment--Silicon V-Groove
[0051] The parallel optical connector is comprised of 6 elements,
one of which is used as a sacrificial element and is not present in
the final assembly. The elements are described as: a silicon
v-groove chip, optically transparent epoxy, protective epoxy,
parallel optical fiber ribbon, an evaporated metal layer, and a
sacrificial cover plate. The sacrificial cover plate is typically
made of glass.
[0052] A parallel optical fiber ribbon (2) typically has several
optical fibers (6) within protective polymer jackets (4) that keep
them roughly pitched at 250-microns, however this is not precise.
The end portions, approximately 2-cm long, of the protective
polymer jackets of the optical fiber ribbon (6) are stripped and
clean--using standard means--to produce 2-cm long segments of
separated parallel optical fibers (i.e. only the glass), still
roughly pitched at 250-microns but not touching each other. The
segment of bare optical fiber remains part of the ribbon cable, as
shown in FIG. 1.
[0053] The silicon v-groove chip (8) is on the order of
1-cm.times.1-cm.times.0.2-cm in dimensions and has been chemically
etched on one of the large surfaces to produce v-shaped grooves in
the silicon (10), as shown in FIG. 2.
[0054] The process of creating v-grooves in crystalline silicon is
well known and described in the literature. The v-groove structure
is used in this case to maintain two essential features. A first
essential feature is that the optical fibers must be pitched from
each other at precisely 250-microns, while a second essential
feature is that the optical fibers must remain in precisely the
same plane.
[0055] In this description, the v-groove dimensions are made such
that the optical fibers form a three-point contact with the sides
of the v-grooves.
[0056] The v-groove chip, the optical fiber, the transparent
optical epoxy and the cover plate are now assembled together to
form the ferrule. A small quantity of transparent epoxy (12) is
placed in the center of the v-grooves (10) on the chip (8) in FIG.
3a,b. The bare optical fibers are then carefully placed in the
v-grooves with one end protruding past the silicon chip by
.about.2-mm and the other end still connected to the ribbon cable.
A cover plate, approximately 1-cm.times.1-cm.times.0.1-cm (14), is
then placed over the optical fibers in the v-grooves and pressed
together to sandwich the optical fibers in place in FIG. 4a,b. The
epoxy is either heat, time or UV-cured. Note that the exact
placement and the size of the cover plate are unimportant as long
as the cover plate is larger than the silicon chip.
[0057] Once the epoxy joining the cover plate to the silicon chip
has hardened, the tips of the optical fibers, within the v-grooves,
are coated with a small amount of epoxy (16) to protect them during
the polishing process. The side where the optical fibers lead out
of the chip and continue on as a ribbon cable have epoxy placed
around the bare optical fiber near the chip as well so that the
assembly is more robust during polishing, as shown in FIG.
5a,b.
[0058] The ferrule is then placed on a polishing machine such that
it is held at a 45-degree angle to the surface of the polisher with
the corner of the silicon chip polishing first and progressively
towards the cover plate. This creates the 45-degree angled polish
of the optical fibers (18), as shown in FIG. 6a,b. Standard lapping
and polishing techniques must be applied, including progressively
finer grits of polishing paper, correct timing, appropriate slurry
mixtures, and a method of holding the parts in a rigid manner.
[0059] A thin metallic coating can be applied to the 45-degree
beveled surface to create a mirrored surface on the inside region
of the optical fiber. The metallic coating can be made of gold,
silver, etc.
[0060] The rest of this application will assume no metallic
coating, but there is no difference to the procedure if one is
included at this point.
[0061] To remove the cover plate, several methods could be used.
The cover plate could be made of a material that would not adhere
to the epoxy or silicon v-groove chip. The plate could then be
mechanically removed after the epoxy had secured the optical fibers
in place. This may or may not result in a suitable optically flat
surface, and polishing (buffing) still might be required. The cover
plate might also be made of a material that could be chemically
dissolved, leaving the fibers, epoxy and glue unaffected. This also
may or may not result in a suitable optically flat surface, and
polishing (buffing) still might be required.
[0062] The preferred method will assume that the cover plate must
be removed by polishing. The ferrule is then placed on a polishing
machine such that the large exposed surface of the cover plate is
in contact with the polishing surface. The cover plate is then
lapped and polished until it has been completely worn away leaving
only the polished flat surface of the silicon chip and optical
fibers embedded in optical epoxy within the v-grooves (20), as
shown in FIG. 7a,b. A to-scale profile view of the connector (23a)
is provided in FIG. 8.
[0063] During the polishing step to remove the cover plate, an
over-polish can be applied to the surface (20). Over-polishing
creates a flat side along the outside the optical fibers in the
v-grooves (22). This is advantageous because it allows the light to
be coupled closer to the core of the optical fiber, resulting in
higher coupling efficiency. The over-polish also allows a more
flexible tolerance during the polishing step; a distance of between
0 to 25-microns can be polished into the optical fiber's cladding
before damaging the core, as shown in FIG. 9b.
[0064] During the polishing step to remove the cover plate, an
under-polish can also be applied to the surface (20). An
under-polish simply leaves some thickness of the cover plate in
tact and over the optical fibers. If the cover plate is glass, this
can be done to help with optical distance requirements to a lens or
other type structures.
[0065] Alternative Embodiment--Molded Plastic
[0066] The structure used to hold the optical fibers may be
fabricated from other materials and other assembly methods could be
used. The mechanical structure that holds the optical fibers in the
same plane and pitched 250-microns from each other can be based on
precision micro-molding techniques of plastic.
[0067] This version of the parallel optical connector is comprised
of 3 elements. The elements are described as: an injection-molded
plastic ferrule, optically transparent epoxy, and parallel optical
fiber ribbon.
[0068] The plastic ferrule is a piece that is on the order of
1-cm.times.1-cm.times.0.3-cm in size (24). It is a hollow plastic
box with one side open into which the optical fibers are inserted.
The opposite side has a linear array of 125-micron diameter holes
pitched at 250-microns. The holes bore into the plastic
approximately 0.05-cm and are used to align the tips of the optical
fiber (23). Inside the box, a flat surface is used to keep the
optical fibers equal or higher than the array of holes. The others
interior sides of the box are tapered towards the array of holes to
better guide the fibers into the holes during their insertion (26).
The plastic ferrule has one or more injection openings in which to
inject epoxy (25), as shown in FIG. 10a,b,c,d.
[0069] A similar parallel optical fiber ribbon, as shown in FIG. 1,
is also used for the plastic molded embodiment.
[0070] The array of bare optical fibers is inserted into the
plastic ferrule from the open end (26). The fibers are pushed
through the holes and protrude from the end of the plastic ferrule,
as shown in FIG. 11.
[0071] Transparent epoxy (27) is then injected into the injection
openings (25) and the optical fibers are pushed and pulled back and
forth to ensure that the epoxy has well coated all the fibers
within the array of holes. Epoxy is then applied to the outside of
the array of holes where the optical fibers are protruding. The
epoxy is then cured by heat, time, or UV light, as shown in FIG.
12.
[0072] The ferrule is then placed on a polishing machine such that
it is held at a 45-degree angle to the surface of the polisher with
the corner of the facet containing the array of holes polishing
first (28) and progressively towards a plane below the optical
fibers such that the optical fibers have been completely beveled at
45-degrees (29), as shown in FIG. 13. Standard lapping and
polishing techniques must be applied, including progressively finer
grits of polishing paper, correct timing, appropriate slurry
mixtures, and a method of holding the parts in a rigid manner.
[0073] Again, a metallic coating can be applied to the 45-degree
beveled surface. Although the rest of this document will assume no
metallic coating is used.
[0074] The plastic ferrule is then placed on a polishing machine
such that the larger exposed surface (30) is in contact with the
polishing surface. The larger area is lapped and polished until the
sides of the optical fibers have been exposed from end to end, as
shown in FIG. 14.
[0075] Again, over-polishing of the large flat surface (30) can be
advantageous at this point.
[0076] Applications
[0077] The complete connector described above and shown in FIG. 8
can be used in applications involving the direct coupling of light
from a micro-laser, such as a VCSEL, into an optical fiber.
Conversely, coupling light out of an optical fiber onto a
photodetector, such as a PIN diode, can also be done. The connector
can also be used to couple light into optical elements, such as a
micro-lens array.
[0078] The main attributes of the coupling method are:
[0079] 1) The simplified alignment obtained by stacking and then
aligning using two co-planar surfaces.
[0080] 2) The ability to precisely position the parallel optical
connector over another component by direct observation above the
two parts using the 45-degree bevel to simultaneously observe both
the optical fiber tips and the component below.
[0081] The polished surface allows a co-planar and stackable
alignment procedure. This reduces the number of mechanical degrees
of freedom from 6 to only 3; lateral-x, lateral-y and rotational-z.
The 45-degree bevel allows both the connector and the target to be
observed simultaneously without disturbing the components. A slight
offset may result because the beveled tips of the optical fibers do
not allow direct viewing through them. However, other
edge-features, such as the edges of the v-grooves, can be used to
locate the fibers over the chip. Extra v-grooves without optical
fibers or other fiducial markings that can be observed on the
beveled side of the ferrule may also be included to help with
alignment registration between the ferrule and the part in contact
with the ferrule. This is similar to methods employed with mask
alignment in photolithographic processes used to produce
microchips, although with much less stringent alignment accuracy.
Thus it will be appreciated that the object of observation during
alignment need not be the fiber core(s) near the edge of the
assembly on the coupling window and covering the visibility of the
VCSELs or other optoelectronic devices, but another fiducial mark
or etching on the assembly edge matched with a mark on the coupling
window.
[0082] Coupling to an Optoelectronic Device
[0083] The parallel optical connector can be connected to any
optoelectronic device (32) that emits light orthogonal to the
direction of the optical fibers in the ferrule, as shown in FIG.
15. However, when the ferrule is aligned with an optoelectronic
device that has a flat, co-planar window above its active region,
the full advantage of the alignment aspects described above can be
realized.
[0084] The following describes a typical alignment procedure:
[0085] The packaged optoelectronic chip consists of a substrate
(31), trace lines, wirebonds, a chip (32) with light emitting
devices (33), and a method of providing a flat, co-planar optical
window above the active region of the optoelectronic chip (34), as
described in co-pending US patent application entitled
"Encapsulated Optical Package", bearing attorney docket number
16005-3US.
[0086] The parallel optical connector, shown in FIG. 8, is first
placed directly over the flat, co-planar window of the
optoelectronic chip, as shown in FIG. 16, with a reasonably
accurate position.
[0087] An observing microscope or magnifying camera is placed
directly above the two parts to simultaneously view the chip and
the ferrule positions.
[0088] The ferrule is then moved laterally in the x-axis, laterally
in the y-axis and rotated about z-axis until the centers of the
optical fibers are directly over top of the center of the lasers,
as shown in FIGS. 16a,b and 17a,b. This procedure may use an
automated or manual micropositioner and also may require that the
microscope magnification and depth of focus be occasionally
adjusted. These adjustments depend greatly on the desired
accuracy.
[0089] Once the ferrule is in place (35) over the emitting lasers
(33) as shown in FIG. 18a,b, the ferrule can be epoxied in place. A
profile view of the connector aligned over a packaged
optoelectronic chip is shown in FIG. 19. The optoelectronic package
also shows the relative placement of wirebonds (37) and trace lines
(36).
[0090] Coupling to an Optical Element--Microlenses
[0091] Although the previous embodiments do not specify the use of
multimode or single mode optical fiber, the physical structure of
the previous embodiments imply the use of a relative large optical
target such as a multimode optical fiber core of 62.5-microns. In
this application where a lens structure is used, a smaller target,
such as a single-mode optical fiber core of only 8-microns
(effective field diameter), is possible. The lens structure focuses
the light into a smaller spot closer to the diameter of the
single-mode optical fiber core.
[0092] The identical procedure can be used to align the connector
with an optical element such as an array of microlenses. What will
be described is when the connector is to be aligned to a linear
array of patterned Fresnel microlenses (38).
[0093] The linear microlens array (38) will contain the same number
of lenses, as there are optical fibers in the connector. They are
placed on the bottom of a glass plate (39), as shown in FIG. 20,
that has a thickness that will allow each lens to capture all the
light from their respective optical fiber and collimate the light.
Any appropriate optical system can then be constructed subsequent
to this first lens.
[0094] Similar to the previous explanation, the parallel optical
connector, as shown in FIG. 8, is first placed directly over the
flat, co-planar glass plate on the opposite side from the lenses,
as shown in FIG. 21, with a reasonably accurate, but random,
position.
[0095] Once the ferrule is in place (35) over the emitting lasers
(33) as shown in FIG. 18a,b, the ferrule can be epoxied in place. A
profile view of the connector aligned over a packaged
optoelectronic chip is shown in FIG. 19. The optoelectronic package
also shows the relative placement of wirebonds (37) and trace lines
(36).
[0096] Coupling to an Optical Element--Microlenses
[0097] Although the previous embodiments do not specify the use of
multimode or single mode optical fiber, the physical structure of
the previous embodiments imply the use of a relative large optical
target such as a multimode optical fiber core of 62.5 microns. In
this application where a lens structure is used, a smaller target
such as a single-mode optical fiber core of only 8-microns
(effective field diameter), is possible. The lens structure focuses
the light into a smaller spot closer to the diameter of the
single-mode optical fiber core
[0098] The identical procedure can be used to align the connector
with an optical element such as an array of microlenses. What will
be described is when the connector is to be aligned to a linear
array of patterned Fresnel microlenses (38).
[0099] The linear microlens array (38) will contain the same number
of lenses, as there are optical fibers in the connector. They are
placed on the bottom of a glass plate (39), as shown in FIG. 20,
that has a thickness that will allow each lens to capture all the
light from their respective optical fiber and collimate the light.
Any appropriate optical system can then be constructed subsequent
to this first lens.
[0100] Similar to the previous explanation, the parallel optical
connector, as shown in FIG. 8, is first placed directly over the
flat, co-planar glass plate on the opposite side from the lenses,
as shown in FIG. 21, with a reasonably accurate, but random,
position.
[0101] An observing microscope or magnifying camera is placed
directly above the two parts to simultaneously view the glass plate
with the microlenses and the ferrule positions.
[0102] The ferrule is then moved laterally in the x-axis, laterally
in the y-axis and rotated about z-axis until the centers of the
optical fibers are directly over top of the center of the
microlenses.
[0103] Once the ferrule is in place, the connector can be epoxied
in place. A close-up of the side and front views of the tips of the
optical fibers aligned over the microlens array is shown in FIG.
22a,b. The dashed lines (40) indicate the rays of light that are
being coupled into (or out of) the optical fibers. A to-scale side
view of the ferrule located over the micro-lens array is shown in
FIG. 23.
[0104] If the depth of focus used to view both the ferrule and the
microlens array is too great, other techniques can be used to
maintain one imaging plane, such as: the illumination of the
microlens plate from behind using collimated light to produce
focused spots essentially at the beveled tips of the optical
fibers. The spots and the tips of the optical fibers can then be
viewed simultaneously.
[0105] The embodiments of the invention described above are
intended to be exemplary only. The scope of the invention is
therefore intended to be limited solely by the scope of the
appended claims.
* * * * *