U.S. patent application number 16/140006 was filed with the patent office on 2019-06-06 for axial alignment of a lensed fiber in a grooved assembly.
The applicant listed for this patent is Skorpios Technologies, Inc.. Invention is credited to Daming Liu, John Zyskind.
Application Number | 20190170953 16/140006 |
Document ID | / |
Family ID | 55969660 |
Filed Date | 2019-06-06 |
United States Patent
Application |
20190170953 |
Kind Code |
A1 |
Liu; Daming ; et
al. |
June 6, 2019 |
AXIAL ALIGNMENT OF A LENSED FIBER IN A GROOVED ASSEMBLY
Abstract
A v-groove assembly is used to edge couple a lensed fiber (e.g.,
an optical fiber made of silica) with a waveguide in a photonic
chip. The v-groove assembly is made from fused silica. Fused silica
is used to so that an adhesive (e.g., epoxy resin) used in bonding
the lensed fiber to the v-groove assembly and/or bonding the
v-groove assembly to the photonic chip can be cured, at least
partially, by light.
Inventors: |
Liu; Daming; (Tucson,
AZ) ; Zyskind; John; (Albuquerque, NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Skorpios Technologies, Inc. |
Albuquerque |
NM |
US |
|
|
Family ID: |
55969660 |
Appl. No.: |
16/140006 |
Filed: |
September 24, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15136229 |
Apr 22, 2016 |
10107976 |
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16140006 |
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14857580 |
Sep 17, 2015 |
9348094 |
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15136229 |
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62136504 |
Mar 21, 2015 |
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62136503 |
Mar 21, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/30 20130101; G02B
6/4225 20130101; G02B 6/3692 20130101; G02B 6/4239 20130101; G02B
6/3652 20130101; G02B 6/4202 20130101; G02B 6/4243 20130101; G02B
6/3636 20130101; G02B 6/4226 20130101; G02B 6/4214 20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42; G02B 6/30 20060101 G02B006/30; G02B 6/36 20060101
G02B006/36 |
Claims
1. (canceled)
2. A method for optically coupling an optical fiber to a
semiconductor waveguide, the method comprising: providing an
optical assembly for connecting the optical fiber to the
semiconductor waveguide, the optical assembly comprising: a
v-groove assembly comprising: a base; a lid; a v-groove; and a
facet, wherein the facet is for bonding the v-groove assembly to an
optical chip; the optical fiber is positioned in the v-groove
between the base and the lid; and epoxy bonding the optical fiber
to the base and the lid, wherein the epoxy is, at least partially,
cured using light; providing the optical chip, wherein the optical
chip comprises the semiconductor waveguide; aligning the v-groove
assembly with the optical chip so that the optical fiber aligns
with the semiconductor waveguide; applying adhesive between the
facet of the v-groove assembly and the optical chip so that the
adhesive contacts both the facet of the v-groove assembly and the
optical chip after the v-groove assembly is aligned with the
optical chip; and irradiating the adhesive to, at least partially,
cure the adhesive.
3. The method of claim 2, further comprising: After irradiating the
adhesive, applying additional adhesive; curing, at least partially,
the additional adhesive with light; and curing, with heat, the
additional adhesive.
4. The method of claim 2, further comprising bonding the facet of
the v-groove assembly to an edge facet of the optical chip.
5. The method of claim 2, further comprising using a gripper that
mechanically holds the v-groove assembly to align the v-groove
assembly with the optical chip.
6. The method of claim 5, wherein the gripper holds the v-groove
assembly by the lid during alignment of the v-groove assembly with
the optical chip and during irradiating the adhesive to, at least
partially, cure the adhesive.
7. The method of claim 2, further comprising using feedback from a
diode on the optical chip to align the v-groove assembly with the
optical chip, wherein the diode detects light coupled from the
optical fiber into the semiconductor waveguide.
8. The method of claim 2, further comprising using ultraviolet
light to, at least partially, cure the adhesive.
9. The method of claim 2, further comprising transmitting light
through the v-groove assembly to irradiate the adhesive.
10. The method of claim 2, wherein a thickness of the adhesive
between the facet of the v-groove assembly and the optical chip,
after aligning the v-groove assembly with the optical chip and
before irradiating the adhesive, is from seven to ten microns.
11. A system for coupling light from a chip to an optical network,
the system comprising: a v-groove assembly comprising: a base; a
lid; a v-groove; and a facet; an optical fiber bonded in the
v-groove assembly between the base and the lid, wherein the optical
fiber is bonded in the v-groove by an epoxy cured by ultraviolet
light; and the chip having a waveguide, wherein the chip is bonded
to the facet of the v-groove assembly by an adhesive so that an end
of the optical fiber aligns with the waveguide of the chip.
12. The system of claim 11, wherein: the chip comprises a
substrate, an insulating layer, and a device layer; the waveguide
of the chip is formed in the device layer; and the device layer is
crystalline silicon.
13. The system of claim 11, wherein the adhesive is an epoxy
resin.
14. The system of claim 11, wherein the v-groove assembly is bonded
to an edge facet of the chip.
15. The system of claim 11, wherein the v-groove assembly is made
of fused silica.
16. A method for optically coupling an optical fiber to a
semiconductor waveguide, the method comprising: providing an
optical assembly for connecting the optical fiber to the
semiconductor waveguide, the optical assembly comprising: a
v-groove assembly comprising: a base; a lid; a v-groove; and a
facet, wherein the facet is for bonding the v-groove assembly to an
optical chip; the optical fiber is positioned in the v-groove
between the base and the lid; and epoxy bonding the optical fiber
to the base and the lid, wherein the epoxy is, at least partially,
cured using light; providing the optical chip, wherein the optical
chip comprises the semiconductor waveguide; aligning the v-groove
assembly with the optical chip so that the optical fiber aligns
with the semiconductor waveguide; applying adhesive between the
facet of the v-groove assembly and the optical chip so that the
adhesive contacts both the facet of the v-groove assembly and the
optical chip after the v-groove assembly is aligned with the
optical chip; irradiating the adhesive to, at least partially, cure
the adhesive; applying additional adhesive; and curing, at least
partially, the additional adhesive.
17. The method of claim 16, wherein curing the additional adhesive
comprises curing with light and heat.
18. The method of claim 16, wherein aligning the v-groove assembly
with the optical chip places the facet of the v-groove assembly no
more than ten microns away from the optical chip.
19. The method of claim 16, wherein the v-groove assembly is made
of fused silica and the semiconductor waveguide is made of
crystalline silicon.
20. The method of claim 16, further comprising using a diode on the
optical chip to align the v-groove assembly with the optical
chip.
21. The method of claim 16, wherein the adhesive contacts an edge
facet of the optical chip.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/136,229, filed on Apr. 22, 2016, entitled
"Axial Alignment of a Lensed Fiber in a Grooved Assembly," which
application is a divisional of U.S. patent application Ser. No.
14/857,580, filed on Sep. 17, 2015, entitled "Axial Alignment of a
Lensed Fiber in a Silica V-Groove," now U.S. Pat. No. 9,348,094,
issued on May 24, 2016, which application claims priority to U.S.
Provisional Application No. 62/136,504, filed on Mar. 21, 2015, and
U.S. Provisional Application No. 62/136,503, filed on Mar. 21,
2015, the disclosures of which are incorporated by reference for
all purposes.
BACKGROUND
[0002] Silicon integrated circuits have dominated the development
of electronics, and many technologies based upon silicon processing
have been developed over the years. Their continued refinement led
to nano-scale feature sizes that can be important for making metal
oxide semiconductor CMOS (complementary metal-oxide semiconductor)
circuits. Silicon can be used as an optical medium, particularly
for light having a wavelength of about 1.55 microns (m). Light
having a wavelength of 1.55 .mu.m is often used for fiber-optic
telecommunication systems.
[0003] Some silicon devices have both electronic and optical
components.
BRIEF SUMMARY OF THE INVENTION
[0004] This application relates to coupling optical waveguides.
More specifically, and without limitation, to coupling an optical
fiber with a semiconductor waveguide, such as a waveguide made in
silicon.
[0005] A v-groove assembly is used to edge couple a lensed fiber
(e.g., an optical fiber made of silica) with a waveguide in a
photonic chip. For example the lensed fiber is butt-coupled to the
photonic chip. The v-groove assembly is made from fused silica
(e.g., by diamond dicing and/or etching). Fused silica is used so
that resin used in bonding the lensed fiber to the v-groove
assembly, and/or bonding the v-groove assembly to the photonic
chip, can be cured, at least partially, by light (e.g., ultraviolet
(UV) light used to cure the resin). In some embodiments, the
photonic chip comprises silicon, and the waveguide comprises a
crystalline-silicon core (e.g., the crystalline-silicon core being
formed from a device layer of a silicon-on-insulator wafer). In
some embodiments, photonic chips comprising other materials are
used (e.g., II-VI and/or III-V compounds; including GaAs and/or InP
and related compounds). In some embodiments, the photonic chip
comprises two semiconductor materials. The photonic chip comprises
an edge facet where the waveguide terminates and is coupled with
the lensed fiber.
[0006] In some embodiments, a method for aligning an optical fiber
with a v-groove assembly is described. A facet of the v-groove
assembly is placed next to a mirror. A first end of the optical
fiber is placed in a v-groove of the v-groove assembly, wherein the
v-groove assembly comprises a base and a lid. The lid is placed
over the optical fiber so that the optical fiber is between the
base and the lid. An adhesive is applied to the v-groove assembly
and/or the optical fiber for bonding the optical fiber to the
v-groove assembly. A second end of the optical fiber is connected
to a splitter, wherein the splitter is optically coupled with an
optical source and a detector. Light of a first wavelength is
transmitted from the optical source, through the splitter, to the
optical fiber, and out the optical fiber through a tip of the first
end of the optical fiber. With the mirror, light of the first
wavelength is reflected back from the tip of the optical fiber back
into the optical fiber through the tip. Light of the first
wavelength is transmitted from the tip to the detector through the
splitter. Feedback is received from the detector. A distance
between the tip of the optical fiber and the mirror is adjusted
based on feedback from the detector. The adhesive is at least
partially cured using light of a second wavelength passing through
the lid, after adjusting the distance between the tip of the
optical fiber and the mirror.
[0007] In some embodiments, the lid is made of fused silica; the
base is made of fused silica; light of the first wavelength is
infrared light and light of the second wavelength is ultraviolet
light; adjusting the distance between the tip of the optical fiber
and the mirror includes moving the optical fiber in an axial
direction to optimize received power at the detector; the chip
comprises crystalline silicon and/or III-V material; and/or the
adhesive is an epoxy resin configured to be at least partially
cured by ultraviolet light. In some embodiments, the method further
comprises bonding the v-groove assembly to a chip, after at least
partially curing the adhesive.
[0008] A system for aligning an optical fiber with a v-groove
assembly is described. The system comprises the optical fiber. The
optical fiber has a first end and a second end; and the first end
comprises a tip. The system comprises the v-groove assembly. The
v-groove assembly comprises a base; a lid, wherein the first end of
the optical fiber is between the base and the lid; and a facet for
bonding to a chip, wherein the first end of the optical fiber is
placed between the base and the lid such that the facet extends
beyond the of the optical fiber. The system comprises an optical
source, detector, and splitter. The splitter is coupled with the
second end of the optical fiber, the optical source, and the
detector. The system comprises a mirror for reflecting light from
the optical source traveling out of the tip of the optical fiber
back into the tip of the optical fiber and to the detector.
[0009] In some embodiments, in the system for aligning an optical
fiber with a v-groove assembly, the optical source emits infrared
light, the system further comprises a lamp, the lamp emits
ultraviolet light, and/or the system further comprises an adhesive,
at least partially cured by ultraviolet light, used to bond the
optical fiber to the base and the lid; the v-groove assembly
further comprises a v-groove, the optical fiber is in the v-groove,
and the v-groove does not extend to the facet; the system further
comprises an optical circulator or an optical isolator between the
optical source and the splitter; the detector is a power meter; the
lid is made of fused silica; and/or the base is made of fused
silica.
[0010] An optical assembly for connecting an optical fiber to a
semiconductor waveguide is described. The optical assembly
comprises a v-groove assembly and adhesive. The v-groove assembly
comprises a base; a lid; a v-groove; and a facet, wherein the facet
is for bonding the v-groove assembly to a chip. The optical fiber
in the v-groove, positioned between the base and the lid. The
adhesive bonds the optical fiber to the base and the lid, wherein
the adhesive is, at least partially, cured using light. In some
embodiments, the base and/or the lid comprise fused silica. In some
embodiments, the lid consists of fused silica.
[0011] Further areas of applicability of the present disclosure
will become apparent from the detailed description provided
hereinafter. It should be understood that the detailed description
and specific examples, while indicating various embodiments, are
intended for purposes of illustration only and are not intended to
necessarily limit the scope of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 depicts a perspective view of an embodiment an
optical adapter using a v-groove assembly.
[0013] FIG. 2 depicts a perspective view of an embodiment of a
portion of the v-groove assembly.
[0014] FIG. 3 depicts a top view of an embodiment of the v-groove
assembly aligned with a chip.
[0015] FIG. 4 depicts an embodiment of an alignment station.
[0016] FIG. 5 depicts a flowchart of an embodiment of a process for
aligning an optical fiber in the v-groove assembly with a waveguide
in a chip.
[0017] FIG. 6 depicts a simplified schematic top view of an
embodiment of an alignment system.
[0018] FIG. 7 depicts a simplified front view of an embodiment of a
v-groove assembly during working-distance alignment.
[0019] FIG. 8 depicts a simplified front view of another embodiment
of a v-groove assembly.
[0020] FIG. 9 depicts a simplified view of a further embodiment of
a v-groove assembly.
[0021] FIG. 10 depicts a flowchart of an embodiment of a process
for aligning an optical fiber in the v-groove assembly.
[0022] FIG. 11 depicts a flowchart of an embodiment of a process
for connecting an optical fiber, which is bonded to a v-groove
assembly, with a photonic chip.
[0023] In the appended figures, similar components and/or features
may have the same reference label. Further, various components of
the same type may be distinguished by following the reference label
by a dash and a second label that distinguishes among the similar
components. If only the first reference label is used in the
specification, the description is applicable to any one of the
similar components having the same first reference label
irrespective of the second reference label.
DETAILED DESCRIPTION
[0024] The ensuing description provides preferred exemplary
embodiment(s), and is not intended to limit the scope,
applicability, or configuration of the disclosure. Rather, the
ensuing description of the preferred exemplary embodiment(s) will
provide those skilled in the art with an enabling description for
implementing a preferred exemplary embodiment. It is understood
that various changes may be made in the function and arrangement of
elements without departing from the spirit and scope as set forth
in the appended claims.
[0025] In some embodiments, an optical fiber is optically coupled
to a waveguide in a chip (in some embodiments the chip is also
referred to as a photonic chip or optical chip) using a v-groove
assembly. For example, the waveguide is crystalline silicon etched
in a device layer of a silicon-on-insulator substrate. The v-groove
assembly is made of silica. For example, the v-groove assembly is
made by dicing, machining, grinding, etching, and/or polishing
fused silica. Silica (SiO2) is used because silica is optically
transparent to ultraviolet (UV) light in some forms. The optical
fiber is bonded to the v-groove assembly using a resin cured by UV
light, and/or the v-groove assembly is bonded to the chip using a
resin cured by UV light. Forming the v-groove assembly from silica
allows UV light to pass through parts of v-groove assembly for
curing the resin.
[0026] Referring to FIG. 1, a perspective view of an embodiment an
optical adapter 100 is shown. The optical adapter 100 optically
couples a waveguide on a chip to a fiber-optics network. The
optical adapter 100 comprises an optical fiber 104, a v-groove
assembly 108, and a receptacle 112. A first end 114 of the optical
fiber 104 is attached to the v-groove assembly 108, and a second
end 115 of the optical fiber 104 is attached to the receptacle
112.
[0027] In some embodiments, the optical fiber 104 is made of silica
(e.g., Corning SMF-28 Ultra or similar fibers). The optical fiber
104 comprises a tip 116 at the first end 114 of the optical fiber
104. In some embodiments, the tip 116 is lensed (e.g., a tapered
tip) for focusing light exiting the tip 116 of the optical fiber
104. In some embodiments, the optical fiber 104 has an ultra-high
numerical aperture (NA). For example, ultra-high NA fibers have
NA.gtoreq.0.25. In some embodiments, 0.5.gtoreq.NA.gtoreq.0.25.
[0028] The first end 114 of the optical fiber 104 is secured to the
v-groove assembly 108. A lid 120 of the v-groove assembly 108
covers the optical fiber 104 to secure the optical fiber 104 in the
v-groove assembly 108. An adhesive that is cured by UV light (e.g.,
an epoxy resin, and/or UV/thermal curable, low-shrinkage epoxy
resin) is used to secure the optical fiber 104 to the v-groove
assembly 108.
[0029] In some embodiments, the second end 115 of the optical fiber
104 is connected to the receptacle 112. In some embodiments, the
second end 115 of the optical fiber is fusion spliced to a fiber
network. In some embodiments, the receptacle 112 is shaped as an LC
connector (e.g., complying with IEC (International Electrotechnical
Commission) standard 61754-20). The receptacle 112 allows for more
simple and/or convenient optical connection to an optical network
(e.g., for connecting to an intranet or to the Internet) than
splicing optical fibers.
[0030] FIG. 2 depicts a perspective view of an embodiment of a
portion of the v-groove assembly 108. The v-groove assembly 108
comprises the lid 120, and a base 202. The base 202 comprises a
v-groove 204 and one or more facets 208. In FIG. 2, the base 202
comprises a first facet 208-1 and a second facet 208-2. The first
facet 208-1 is to one side of the v-groove 204 and the second facet
208-2 is to another side of the v-groove 204. The facets 208 are
for bonding the v-groove assembly 108 to a chip.
[0031] The first end 114 of the optical fiber 104 is placed in the
v-groove 204, and the lid 120 is placed over the optical fiber 104.
The facets 208 extend beyond, in an axial direction, the v-groove
204 for bonding to a chip. The axial direction is a direction along
an axis of the optical fiber 104 (e.g., direction of beam
propagation). A lateral direction is orthogonal to the axial
direction; and the lateral direction can be further subdivided into
a vertical direction and a horizontal direction. The tip 116 of the
optical fiber 104 extends past the v-groove 204, axially. In some
embodiments, the facets 208 extend past the v-groove 204 so that an
adhesive used to bond the v-groove assembly 108 to the chip is not
as likely to cover the tip 116 of the optical fiber 104. In some
embodiments, the v-groove 204 comprises two bonding facets 208 to
provide structural support when securing the v-groove assembly 108
to the photonic chip. The bonding facets 208 extend past the
v-groove 204 a first length 212. In some embodiments, the first
length 212 is between 100 and 300 .mu.m and/or 225 and 275 .mu.m
(e.g., 150, 200, 250, or 300 .mu.m).
[0032] FIG. 3 depicts a top view of an embodiment of the v-groove
assembly 108 aligned with a chip 308. The chip 308 comprises a
waveguide 312 (e.g., a semiconductor waveguide made of crystalline
silicon). An adhesive 316 is used to bond the v-groove assembly 108
to the chip 308. The adhesive 316 is applied to the bonding facet
208 of the v-groove assembly 108 and to an edge facet 320 of the
chip 308.
[0033] In some embodiments, the chip 308 comprises and/or is
optically coupled with a receiver (e.g., photodiode). In some
embodiments, the waveguide 312 is optically coupled with the
receiver. In some embodiments, the chip 308 comprises one or more
other chips (e.g., III-V chips for a gain medium) as described in
U.S. application Ser. No. 14/509,914, filed on Oct. 8, 2014, which
is incorporated by reference. The v-groove assembly 108 is aligned
by applying adhesive 316 to the bonding facet 208 (or to the edge
facet 320 of the chip 308, or both), and the v-groove assembly 108
is roughly aligned with the chip 308 (e.g., bringing the v-groove
assembly 108 near the edge facet 320 of the chip 308). Light is
transmitted through the optical fiber 104 and into the waveguide
312. A gripper holding the v-groove assembly 108 is adjusted to
position the tip 116 of the optical fiber 104 in relation to the
waveguide 312 to optimize optical transmission from the optical
fiber 104 into the waveguide 312 (e.g., the receiver registers a
maximum power; a percentage of maximum power, e.g., >90%, 95%;
or a predetermined threshold power). In some embodiments, the
v-groove assembly 108 is actively aligned (e.g., using a
computerized system). In some embodiments, a thickness of the
adhesive 316 before a first cure is equal to or less than 10, 8, or
7 .mu.m. In some embodiments, the bonding facets 208 are polished
and the thickness of the epoxy resin before the first cure is equal
to or less than 5 .mu.m (e.g., separation of the bonding facet from
the edge facet is equal to or less than 5 .mu.m). In some
embodiments, the bonding facets 208 are pitted and/or roughened for
an adhesive 316 to better adhere to. In some embodiments, a
thickness of the adhesive 316 before the first cure is 7-10 .mu.m,
because results from bonding show 7-10 .mu.m forms a stable bond,
which is sufficient for some applications. In some embodiments, the
waveguide 312 has a height (vertical) and/or width (horizontal)
equal to or less than 12, 10, 8, 5, 2, 1.7, 1.6, or 1.5 .mu.m. In
some embodiments, the waveguide has a height (vertical) and/or
width (horizontal) greater than 1.0 or 1.5 .mu.m for improved
coupling with the optical fiber 104 (e.g., with a tapering
waveguide). In some embodiments, only one dimension (e.g., a
lateral dimension) is adjusted by the gripper holding the v-groove
assembly 108. For example, a vertical height (i.e., into and out of
the page of FIG. 3) is determined by a height of the v-groove 204
of the v-groove assembly 108; an axial distance (along a direction
of beam propagation of the optical fiber 104) between the tip 116
of the optical fiber 104 and the edge facet 320 of the chip 308 is
determined by a distance between the tip 116 of the optical fiber
104 and the bonding facet 208. In some embodiments, the bonding
facet 208 is placed to touch the edge facet 320 of the chip 308,
and then the v-groove assembly is moved away from the edge facet
320 of the chip 308 a predetermined distance (e.g., 7-10 .mu.m)
before adhesive 316 is applied between the bonding facet 208 and
the edge facet 320.
[0034] After the tip 116 of the optical fiber 104 is aligned to the
waveguide 312 of the chip 308 (e.g., by the gripper holding the
v-groove assembly 108), a first cure of the adhesive 316 is
performed (e.g., by irradiating the adhesive 316 with light). In
some embodiments, the adhesive 316 is an epoxy resin cured with
ultraviolet (UV) light (e.g., light having a wavelength between 100
nm and 400 nm, or between 250 and 400 nm). In some embodiments, the
v-groove assembly 108 is made of fused silica, which is made
transparent to UV light, so that UV light can be shined through the
v-groove assembly 108 to cure the adhesive 316 that is between the
bonding facet 208 of the v-groove assembly 108 and the edge facet
320 of the chip 308. In some embodiments, the v-groove assembly 108
is made of silica having greater than 60% or 70% transmission for
wavelengths from 250 nm to 400 nm, or from 300 nm to 400 nm (e.g.,
UV-grade silica and/or broadband silica). It is noted that
crystalline silicon has low transmission (e.g., <20%) for
wavelengths less than 900 nm. In some embodiments, additional epoxy
resin is added after the first cure (e.g., to sides and/or other
surfaces of the v-groove assembly 108), and a second cure is
performed where the additional epoxy resin is cured with UV light.
In some embodiments, two steps of curing epoxy resin is used
because the first cure is used to set alignment of the v-groove,
wherein using less epoxy resin has less shrinkage during UV cure.
And the second cure, with the additional epoxy resin, is used to
add more epoxy resin to form a more robust bond between the
v-groove assembly 108 and the chip 308. After the second cure (or
in some embodiments after the first cure if the second cure is not
used), a thermal cure is performed. The thermal cure further
hardens the epoxy resin.
[0035] In some embodiments, coupling arrangement between the
optical fiber 104 and the waveguide 312 shown in FIG. 3 is compact,
which reduces space on a printed circuit board assembly (PCBA).
Further, coupling loss during adhesive 316 cure is reduced and
reliability is improved.
[0036] FIG. 4 depicts an embodiment of an alignment station 400.
The alignment station 400 comprises a gripper 404 and a PCBA mount
408. The PCBA mount 408 secures a PCBA 412. The PCBA 412 comprises
a first chip 308-1 and a second chip 308-2. The gripper 404 is used
to align the v-groove assembly 108 with the first chip 308-1 or the
second chip 308-2. In some embodiments, mechanical controls 416 are
used to move the gripper 404. In some embodiments, electrical
connections 420 are used to automate alignment of the v-groove
assembly 108 with the chip 308. Such a system has demonstrated
robust, high coupling efficiency alignment. In some embodiments, a
sub mount is used instead of the PCBA 412.
[0037] FIG. 5 depicts a flowchart of an embodiment of a process 500
for aligning the optical fiber 104, which is in the v-groove
assembly 108, with the chip 308. The process 500 for aligning the
optical fiber 104 with the chip 308 begins in step 504 with loading
the PCBA 412 (or a sub mount) on the PCBA mount 408. In some
embodiments, the PCBA 412 is loaded on the PCBA mount 408 after
chip(s) 308 and/or wire bonding are added to the PCBA 412. The
gripper 404 picks up the v-groove assembly 108 (e.g., by the lid
120 of the v-groove assembly 108) and actively aligns the v-groove
assembly 108 with the chip 308, step 508. In some embodiments,
alignment involves providing active lateral and/or active axial
(longitudinal) alignment. For reliability, and/or to minimize
movement during adhesive 316 curing, in some embodiments, thickness
of the adhesive 316 for butt-bonding between the v-groove assembly
108 and the chip 308 is reduced (e.g., <10 .mu.m). In some
embodiments, an initial-alignment position is established. After an
initial alignment, the v-groove assembly 108 is moved, using the
gripper 404, away from the chip 308. In step 512, adhesive 316 is
applied to the v-groove assembly 108 (e.g., bonding facets 208). In
some embodiments, a first amount of epoxy resin (e.g., a portion of
adhesive 316) is applied to the bonding facet(s) 208 of the
v-groove assembly 108. The v-groove assembly 108 is moved back to
the initial-alignment position using the gripper 404 (e.g.,
automatically using the gripper 404 and electrical connections 420
after the first amount of epoxy resin is applied). In some
embodiments, a final alignment is performed. In some embodiments, a
first cure of the adhesive 316 is performed, wherein the first cure
at least partially cures the first amount of epoxy resin between
the bonding facet 208 and the edge facet 320 of the chip 308 (e.g.,
UV curing by shining UV light through the v-groove assembly 108,
such as through the bonding facet 208). In some embodiments, a
second amount of epoxy resin (e.g., a portion of adhesive 316) is
applied to the v-groove assembly 108 and/or the chip 308. In some
embodiments, a second cure of the adhesive 316 is performed to
further secure the v-groove assembly 108 to the chip 308 and/or the
PCBA 412 (e.g., the adhesive is a two-step adhesive, which is
thermally cured after UV curing). In some embodiments, the adhesive
316 is thermally cured after UV curing. In some embodiments,
additional assembly of the PCBA 412 is performed after a UV curing
and/or a thermal curing of the adhesive 316.
[0038] In some embodiments, using a v-groove assembly 108 bonded to
the chip 308 holds the optical fiber 104 with high stability for
optical coupling; the fused silica optical properties enable UV
curing of the adhesive 316 (e.g., epoxy resin) between the v-groove
assembly 108 and the chip 308. Shifting of the tip 116 of the
optical fiber 104 during UV curing and/or thermal curing is small
(e.g., is less than 0.5, 0.4, 0.3, 0.2, or 0.1 .mu.m, in each of
the three directions); and/or directly bonding the v-groove
assembly 108 to the edge facet 320 of the chip 308 makes a stable
bond when temperature varies. In some embodiments, a similar design
can be applied to discrete optics coupling. For example, an optical
assembly is formed that holds a discrete optical element (e.g., a
lens). The optical assembly has facets for bonding to a photonic
chip similar to the bonding facets 208 of the v-groove assembly
108. The optical assembly is then bonded to the photonic chip
(e.g., similarly as the v-groove assembly 108 is bonded to the chip
308). Because of a larger working distance that discrete optical
elements normally have, a geometry with discrete optics would not
likely be as compact as for a lensed fiber. However, attachment of
an optical mount directly to the edge facet 320 of the chip 308
would still provide a more compact geometry and a direct attachment
of the discrete optical element to the chip 308, minimizing
movement during curing and from thermal effects, and/or improving
reliability.
[0039] In a previous approach by the applicant (and not admitted by
the applicant to be prior art), a discrete lens plus a fiber
collimator was used. Fiber output was collimated using a pigtailed
collimator. A discrete lens coupled light into a waveguide (e.g.,
waveguide 312 on the chip 308). Some embodiments of this disclosure
differ in that a lensed fiber is directly coupled to the waveguide
(e.g., without a collimator and/or discrete lens); a v-groove
assembly 108 is used to hold the optical fiber 104; the v-groove
assembly 108 is attached directly to the chip 308 (e.g., by epoxy);
higher optimal coupling efficiency during alignment is achieved;
less movement during epoxy resin curing is achieved; improved final
coupling efficiency is achieved; higher reliability is achieved;
reduced temperature dependence of coupling efficiency due to
thermal expansion due to compact geometry and/or limited epoxy
thickness is achieved; and/or reduced board real estate is
achieved.
[0040] Referring next to FIG. 6, a simplified schematic top view of
an embodiment of an alignment system 600 is shown. The alignment
system 600 is used to align and bond the optical fiber 104 to the
v-groove assembly 108. The alignment system 600 comprises the
optical fiber 104, the base 202 of the v-groove assembly 108, an
optical source 604, an optical isolator 606, a splitter 608, a
mirror 612, a detector 616, and a lamp 620.
[0041] The optical source 604 is a laser, LED, or RCLED
(resonant-cavity LED) emitting light of a first wavelength (e.g.,
light centered at a first wavelength). In some embodiments, the
first wavelength is between 1000 nm and 1800 nm or between 1300 nm
and 1600 nm (e.g., having a peak intensity at 1550 nm). The optical
isolator 606 passes light traveling from the optical source 604,
and attenuates and/or blocks light from being transmitted to the
optical source 604. The optical source 604 is optically coupled
with the splitter 608, with the optical isolator 606 being between
the optical source 604 and the splitter 608. The splitter 608 is
optically coupled with the second end 115 of the optical fiber 104.
For example, the splitter 608 is optically coupled with the
receptacle 112 of the optical adapter 100.
[0042] The base 202 of the v-groove assembly 108 shown in FIG. 6 is
similar to the base 202 of the v-groove assembly 108 show in FIG.
3. The lid 120 of the v-groove assembly 108 is not shown in FIG. 6.
The bonding facet 208 of the base 202 of the v-groove assembly 108
is placed next to the mirror 612. In some embodiments, the bonding
facet 208 touches the mirror. In some embodiments, the bonding
facet 208 is placed close to the mirror 612, but not touching the
mirror (e.g., less than 1, 2, 5, 7, or 10 .mu.m away from the
mirror).
[0043] The optical fiber 104 is placed in the v-groove 204 of the
base 202 of the v-groove assembly 108. The tip 116 of the optical
fiber 104 is directed towards the mirror 612. Adhesive is applied
to the optical fiber 104 and/or the base 202 of the v-groove
assembly 108 (e.g., to the v-groove 204, to an interface between
the base 202 and the lid 120, and/or placing the lid 120 over the
base 202, at least partially covering the optical fiber 103, and
adhesive is applied between the optical fiber 104 and the lid 120,
such that capillary action brings the adhesive into interfaces
between the lid 120, the optical fiber 104, and/or the base 202).
In some embodiments, adhesive is applied to the lid 120 of the
v-groove assembly 108. In some embodiments, the adhesive applied to
the optical fiber 104 and/or the base 202 of the v-groove assembly
108 is similar to the adhesive 316 applied between the bonding
facet 208 and the edge facet 320 in FIG. 3. The bonding facet 208
helps orient the direction of beam propagation from the optical
fiber 104 to be orthogonal a surface of the mirror 612, because the
bonding facet 208 is orthogonal to a length of the v-groove 204.
The lid 120 is placed over the v-groove 204, at least partially
covering the optical fiber 104. The adhesive applied to the optical
fiber and/or the base 202 of the v-groove assembly 108 is not cured
until after aliment of the optical fiber 104 in the v-groove
assembly 108. The bonding facet 208 is not bonded to the mirror
612.
[0044] The splitter 608 is optically coupled with the detector 616.
In some embodiments, the detector 616 is a power meter. Light of
the first wavelength is transmitted from the optical source 604,
through the splitter 608 and into the optical fiber 104. Light of
the first wavelength is then transmitted out the tip 116 of the
optical fiber 104, to the mirror 612, and reflected back into the
tip 116 of the optical fiber 104. Light of the first wavelength
then travels from the tip 116 to the splitter 608 and to the
detector 616.
[0045] A distance, which is referred to as a working distance 624,
separates the tip 116 of the optical fiber 104 from the mirror 612.
The optical fiber 104 is moved longitudinally (in an axial
direction), within the v-groove 204, to adjust the working distance
624. The tip 116 of the optical fiber 104 is lensed. As the working
distance 624 approaches a focal length of the lens of the tip 116,
optical power at the detector 616 increases because more optical
power is being reflected back into the optical fiber 104. The
working distance 624 is optimized (e.g., to have power above a
predetermined threshold, or a percentage of maximum). In some
embodiments, after the working distance 624 is optimized, the
optical fiber 104 is then advanced so that the tip 116 goes toward
the mirror 612 (i.e., reducing the working distance 624) a
predetermined distance corresponding to an expected thickness of
adhesive 316 between the bonding facet 208 and the edge facet 320
(e.g., 1-10 .mu.m).
[0046] After the working distance 624 is set, adhesive applied to
the lid 120, the optical fiber 104, and/or the base 202 of the
v-groove assembly 108 is at least partially cured using a light
source of a second wavelength. In the alignment system 600, the
lamp 620 is used as the light source of the second wavelength. The
lid 120 is made of fused silica because fused silica transmits UV
light. The lamp 620 emits UV light that is transmitted through the
lid 120 to at least partially cure the adhesive applied to the
optical fiber 104 and/or the base 202 of the v-groove assembly
108.
[0047] In some embodiments, an epoxy resin is placed on the
v-groove assembly 108 and/or the optical fiber 104 before alignment
so that the fiber 104 can be fixed in position after optimization.
In some embodiments, the lid 120 serves to retain and protect the
optical fiber 104 and/or serve as a handle for gripper 404 to hold
the v-groove assembly 108 for lateral and/or axial alignment with
the chip 308. In some embodiments, adhesive applied to the v-groove
assembly 108 and/or the optical fiber 104 is also thermally cured.
In some embodiments, the adhesive applied to the v-groove assembly
and/or the optical fiber 104 has a first, initial cure followed by
additional adhesive and a second cure. In some embodiments, the
second cure is followed by a heat cure.
[0048] In some embodiments, once a set working distance 624 is
known, then subsequent fibers can be positioned in v-groove
assemblies 108 using a microscope and eyepiece (reticle scale). In
some embodiments, in place of the splitter 608 and the isolator
606, an optical circulator may be used. In some embodiments, the
lid 120, the v-groove 204, and/or the bonding facets 208 are made
of fused silica. In some embodiments, the lid 120 is fused silica
for curing epoxy resin that secures the lid 120 to other portions
of the v-groove assembly 108 and/or to the optical fiber 104.
[0049] FIG. 7 depicts a simplified front view of an embodiment of a
v-groove assembly 108 during working-distance alignment. The
v-groove assembly comprises the v-groove 204, a first bonding facet
208-1, a second bonding facet 208-2, and the lid 120. The tip 116
of the optical fiber 104 is shown between the lid 120 and the
v-groove 204. Adhesive 704 between the lid 120 and the v-groove 204
bonds the optical fiber 104 to the v-groove assembly 108. In some
embodiments, the adhesive 704 is used to bond the lid 120 to the
base 202 of the v-groove assembly 108. In some embodiments,
additional adhesive is used to bond the lid 120 to the base 202 of
the v-groove assembly 108 (e.g., sides of the lid 120).
[0050] Referring next to FIGS. 8 and 9, FIGS. 8 and 9 depict
additional embodiments of the v-groove assembly 108. FIG. 8 depicts
a simplified front view of an embodiment of a v-groove assembly
108. FIG. 8 is similar to FIG. 7, except instead of having the
first bonding facet 208-1 and the second bonding facet 208-2, the
v-groove assembly 108 in FIG. 8 has only one bonding facet 208.
[0051] FIG. 9 depicts a simplified view of an embodiment of a
v-groove assembly 900. The v-groove assembly 900 comprises a base
902 and a lid 920. The lid 920 comprises a v-groove 904. The base
902 comprises a bonding facet 908. An optical fiber 104 is placed
between the base 902 and the lid 920. The base 902 further
comprises a recess formed by a floor 912 and walls 916. The recess
helps prevent adhesive from getting on the tip 116 of the optical
fiber 104.
[0052] FIG. 10 depicts a flowchart of an embodiment of a process
1000 for aligning an optical fiber 104 in the v-groove assembly
(e.g., v-groove assembly 108 or 900). The process 1000 for aligning
an optical fiber 104 in the v-groove assembly 108 begins in step
1004 by placing a facet (e.g., bonding facet 208) of the v-groove
assembly next to a mirror (e.g., mirror 612). In some embodiments,
placing the bonding facet 208 next to the mirror 612 means the
bonding facet 208 contacts the mirror 612. In some embodiments,
placing the bonding facet 208 next to the mirror 612 means the
bonding facet 208 is close to, but not contacting, the mirror 612
(e.g., less than 15, 10, or 5 .mu.m from the mirror 612). In some
embodiments, the bonding facet 208 does not contact the mirror 612
in order to compensate for an estimated thickness of adhesive 316
for bonding the v-groove assembly 108 to the chip 308.
[0053] In step 1008, the first end 114 of the optical fiber 104 is
placed in the v-groove 204 of the v-groove assembly 108. The lid
120 is placed on the base 202 of the v-groove assembly 108,
covering at least a portion of the first end 114 of the optical
fiber 104. The optical fiber 104 is between the base 202 of the
v-groove assembly 108 and the lid 120 of the v-groove assembly 108.
Then adhesive 704 (e.g. an epoxy resin) is applied between the
optical fiber 104 and the lid 120. Capillary action draws the
adhesive into an interface between the lid 120, the optical fiber
104, and/or the base 202. In step 1012, the second end 115 of the
optical fiber 104 is connected to the splitter 608.
[0054] In step 1016, light of a first wavelength is transmitted
from the optical source 604, through the splitter 608, and to the
first end 114 of the optical fiber 104. In some embodiments, light
of the first wavelength is transmitted through an optical isolator
606 positioned between the source 604 and the splitter 608. In some
embodiments, the light of the first wavelength is infrared (e.g.,
between 1250 nm and 1600 nm). Light of the first wavelength is
transmitted out of the first end 114 of the optical fiber 104
through the tip 116 of the optical fiber 104.
[0055] In step 1020, light of the first wavelength transmitted out
of the first end 114 of the optical fiber 104 through the tip 116
of the optical fiber 104 reflects off the mirror 612 and back into
the first end 114 of the optical fiber 104 through the tip 116 of
the optical fiber 104. Reflected light of the first wavelength from
the mirror 612 travels from first end 114 of the optical fiber 104,
to the second end 115 of the optical fiber 104, to the splitter
608, and from the splitter 608 to the detector 616. The isolator
606 is used to keep light from reflecting back into the source
604.
[0056] In step 1024, a distance (e.g., the working distance 624) is
adjusted between the tip 116 of the optical fiber 104 and the
mirror 612 based on feedback from the detector 616. For example,
the detector 616, in some embodiments, is a power meter. The tip
116 of the optical fiber 104 is moved axially (e.g., toward or away
from the mirror 612) and a power reading of the detector 616
changes. Power increases as the working distance 624 approaches a
focal length of the tip 116 (e.g., a lensed fiber). Power decreases
as the working distance 624 departs from the focal length of the
tip 116 of the optical fiber 104.
[0057] Once the working distance 624 is adjusted based on feedback
from the detector 616, adhesive 704 in the v-groove 204 is cured
using lamp 620. To cure the adhesive 704 in the v-groove, light of
a second wavelength (e.g., UV light), is transmitted through the
lid 120 to cure the adhesive 704 in the v-groove 204, step 1028.
Since the lid 120 is made of fused silica, UV light can penetrate
through the lid 120 to cure the adhesive 704 in the v-groove 204.
Thus the optical fiber 104 can be aligned with, and bonded to, in
the v-groove assembly 108 accurately and/or with less risk of
altering alignment of the optical fiber 104 during curing than
previous bonding techniques (e.g., alignment can be done before
curing).
[0058] In some embodiments, the bonding facet 208 contacts the
mirror 612 and adjusting the working distance 624 includes moving
the tip 116 of the optical fiber 104 toward the mirror 612 to
compensate for an estimated thickness of adhesive 316 for bonding
the v-groove assembly 108 to the chip 308.
[0059] FIG. 11 depicts a flowchart of an embodiment of a process
1100 for bonding a v-groove assembly 108, which is bonded to an
optical fiber 104, to a chip 308. In some embodiments, the chip 308
comprises silicon (e.g., a silicon-on-insulator (SOI) wafer having
a waveguide in a device layer of the SOI wafer). The process 1100
for bonding the v-groove assembly 108 to the chip 308 begins in
step 1104 where a v-groove assembly 108 is provided. For example,
the optical adapter 100, comprising the receptacle 112, optical
fiber 104, and v-groove assembly 108, is provided.
[0060] An adhesive (e.g., adhesive 316, such as an epoxy resin) is
applied to a facet (e.g., bonding facet 208) of the v-groove
assembly 108, step 1108. In some embodiments, adhesive 316 is
applied to the edge facet 320 in addition to, or in lieu of,
applying adhesive 316 to the v-groove assembly 108. In some
embodiments, applying adhesive 316 to the v-groove assembly
comprises applying adhesive 316 to the edge facet 320 of the chip
308 and bringing the v-groove assembly 108 near the edge facet 320
so that adhesive 316 touches the bonding facet 208.
[0061] In step 1112, the v-groove assembly 108 is aligned with the
chip 308. For example, the optical fiber 104, bonded to the
v-groove assembly 108, is aligned with the waveguide 312 of the
chip 308. In some embodiments, the gripper 404 is used to align the
v-groove assembly 108 with the chip 308 (e.g., by holding the lid
120 of the v-groove assembly 108). In some embodiments, light from
the optical fiber 104, which is coupled into the waveguide 312, is
used in aligning the v-groove assembly 108 with the chip 308. For
example, the waveguide 312 couples light from the optical fiber 104
to a photodetector (either on the chip 308, such as a PIN diode
formed in the device layer of the SOI wafer, or off the chip 308).
Feedback from the photodetector is used to align the optical fiber
104 to the waveguide 312.
[0062] In step 1116, the adhesive 316 is cured. In some
embodiments, the adhesive 316 is an epoxy resin and is cured with
UV light (e.g., similar to lamp 620 producing light of a second
wavelength). In some embodiments, light of the second wavelength is
transmitted through the v-groove assembly 108 (e.g., and through
the bonding facet 208). Light of the second wavelength is
transmitted through the v-groove assembly 108 because the v-groove
assembly 108 is made of fused silica, which is transparent to UV
light. In some embodiments, a second cure is performed after a
first cure (e.g., see discussion relating to FIG. 3). In some
embodiments, transmitting light of the second wavelength through
the v-groove assembly 108 is done so that the gripper 404 can hold
the v-groove assembly 108 in place after alignment and during cure
so that the optical fiber 104 remains aligned with the waveguide
312. In some embodiments, the term "v-groove" is used as a generic
term for a groove configured to position an optical fiber in a
material, and may include shapes such as a `v`, a trench (e.g.,
flat sides), and `u`-shaped grooves, depending on fabrication
(e.g., trenches, in some embodiments, are easier to cut or etch in
fused silica than a `v`; in some embodiments, a v-groove is cut or
etched if the base 202 is made of crystalline material and etching
can be done by etching on a crystalline plane).
[0063] The specific details of particular embodiments may be
combined in any suitable manner without departing from the spirit
and scope of embodiments of the invention. However, other
embodiments of the invention may be directed to specific
embodiments relating to each individual aspect, or specific
combinations of these individual aspects.
[0064] The above description of exemplary embodiments of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form described, and many modifications and
variations are possible in light of the teaching above. The
embodiments were chosen and described in order to explain the
principles of the invention and its practical applications to
thereby enable others skilled in the art to utilize the invention
in various embodiments and with various modifications as are suited
to the particular use contemplated.
[0065] For example, in some embodiments, the waveguide 312 of the
chip 308 comprises a taper to more efficiently couple light into
the waveguide 312. In some embodiments, the waveguide 312 has
rectangular cross section. In some embodiments, the waveguide is a
ridge waveguide. In some embodiments, the mirror 612 comprises
multilayers. In some embodiments, the mirror 612 comprises metal.
In some embodiments, the mirror 612 is a block (e.g., a flat piece
of metal).
[0066] In some embodiments, a tip 116 other than a lensed fiber is
used (e.g., flat, cleaved end of a fiber). In some embodiments, the
optical fiber 104 is aligned to a device other than the waveguide
312 of the chip 308. For example, the tip 116 of the optical fiber
104 could be aligned to a photodiode or a laser in the chip 308. In
some embodiments, the lid 120 and/or the base 202 of the v-groove
assembly are made of other material transparent to UV light (e.g.,
the lid 120 is made of quartz or UV-grade sapphire).
[0067] In some embodiments, the chip 308 comprises a light source
(e.g., is made of III-V material as a gain medium for a laser).
Light is coupled from the chip 308 to the optical fiber 104.
[0068] Also, it is noted that the embodiments may be described as a
process which is depicted as a flowchart, a flow diagram, a data
flow diagram, a structure diagram, or a block diagram.
[0069] Although a flowchart may describe the operations as a
sequential process, many of the operations can be performed in
parallel or concurrently. In addition, the order of the operations
may be re-arranged. A process is terminated when its operations are
completed, but could have additional steps not included in the
figure. A process may correspond to a method, a function, a
procedure, a subroutine, a subprogram, etc.
[0070] A recitation of "a", "an", or "the" is intended to mean "one
or more" unless specifically indicated to the contrary.
[0071] All patents, patent applications, publications, and
descriptions mentioned here are incorporated by reference in their
entirety for all purposes. None is admitted to be prior art.
* * * * *