U.S. patent application number 15/880462 was filed with the patent office on 2018-05-31 for hermetic optical subassembly.
The applicant listed for this patent is NANOPRECISION PRODUCTS, INC.. Invention is credited to Jeremy BURKE, Rand DANNENBERG, Robert Ryan VALLANCE.
Application Number | 20180149817 15/880462 |
Document ID | / |
Family ID | 58667611 |
Filed Date | 2018-05-31 |
United States Patent
Application |
20180149817 |
Kind Code |
A1 |
VALLANCE; Robert Ryan ; et
al. |
May 31, 2018 |
HERMETIC OPTICAL SUBASSEMBLY
Abstract
A hermetic optical subassembly includes an optical bench having
a mirror directing optical signals to/from an optical waveguide, a
carrier supporting a photonic device, and an intermediate optical
bench having a mirror directing optical signals between the
photonic device and the optical bench. The optical bench and the
intermediate optical bench optically aligns the photonic device to
the waveguide along a desired optical path. In one embodiment, the
photonic device is an edge emitting laser (EML). The mirror of the
optical bench may be passively aligned with the mirror of the
intermediate optical bench. The assembled components are
hermetically sealed. The body of the optical benches are preferably
formed by stamping a malleable metal material to form precise
geometries and surface features. In a further aspect, the hermetic
optical subassembly integrates a multiplexer/demultiplexer, for
directing optical signals between a single optical fiber and a
plurality of photonic devices.
Inventors: |
VALLANCE; Robert Ryan;
(Newbury Park, CA) ; BURKE; Jeremy; (Los Angeles,
CA) ; DANNENBERG; Rand; (Newbury Park, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NANOPRECISION PRODUCTS, INC. |
El Segundo |
CA |
US |
|
|
Family ID: |
58667611 |
Appl. No.: |
15/880462 |
Filed: |
January 25, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15333184 |
Oct 24, 2016 |
9880366 |
|
|
15880462 |
|
|
|
|
15236390 |
Aug 12, 2016 |
9864145 |
|
|
15333184 |
|
|
|
|
15077816 |
Mar 22, 2016 |
|
|
|
15236390 |
|
|
|
|
62245878 |
Oct 23, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4215 20130101;
G02B 6/4249 20130101; G02B 6/4257 20130101; H04B 10/501 20130101;
G02B 6/3652 20130101; G02B 6/3881 20130101; G02B 6/4214 20130101;
G02B 6/4251 20130101; G02B 6/29367 20130101; G02B 6/3696 20130101;
G02B 6/4255 20130101; G02B 6/2938 20130101; G02B 6/423
20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42; H04B 10/50 20130101 H04B010/50; G02B 6/293 20060101
G02B006/293; G02B 6/38 20060101 G02B006/38 |
Claims
1. A hermetic optical subassembly, comprising: a first optical
bench supporting an optical fiber, and comprising at least one
first mirror defined by stamping a first malleable metal stock
material; a second optical bench comprising at least one second
mirror defined by stamping a second malleable metal stock material;
a carrier supporting at least one photonic device, wherein the
optical fiber, the first mirror, the second mirror and the photonic
device are in optical alignment, and the first mirror and the
second mirror directs an optical signal between the photonic device
and the optical fiber, and wherein the first optical bench, the
second optical bench and the carrier are coupled to form a hermetic
package.
Description
PRIORITY CLAIM
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/333,184 filed on Oct. 24, 2016, which:
[0002] (1) claims the priority of U.S. Provisional Patent
Application No. 62/245,878 filed on Oct. 23, 2015; [0003] (2) is a
continuation-in-part of U.S. patent application Ser. No. 15/236,390
filed on Aug. 12, 2016, now U.S. Pat. No. 9,864,145; and [0004] (3)
is a continuation-in-part of U.S. patent application Ser. No.
15/077,816 filed on Mar. 22, 2016.
[0005] These applications are fully incorporated by reference as if
fully set forth herein. All publications noted below are fully
incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
Field of the Invention
[0006] The present invention relates to optical subassemblies,
particularly to hermetically sealed optical subassemblies.
Description of Related Art
[0007] There are many advantages of transmitting light signal via
optical fiber waveguides and the use thereof is diverse. Single or
multiple fiber waveguides may be used simply for transmitting
visible light to a remote location. Complex telephony and data
communication systems may transmit multiple specific optical
signals. The data communication systems involve devices that couple
fibers in an end-to-end relationship, including optoelectronic or
photonic devices that include optical and electronic components
that source, detect and/or control light, converting between light
signals and electrical signals, to achieve high speed and high
capacity data communication capabilities.
[0008] In an optical communication system, components on the
transmission side are typically packaged in a transmitter optical
subassembly (TOSA), and components on the receiving side are
typically packaged in a receiver optical subassembly (ROSA). For
bidirectional signal transmission along a single optical fiber,
components are packaged in a bidirectional optical subassembly
(BOSA).
[0009] Heretofore, the TOSA consists of a laser diode (e.g., a
distributed feedback (DFB) laser), optical interface, monitor
photodiode, metal and/or plastic housing, and electrical interface.
Depending upon the required functionality and application, other
components may be present as well including filter elements and
isolators. It is used to convert an electrical signal into an
optical signal that is coupled into an optical fiber. The ROSA
consists of a photodiode, optical interface, metal and/or plastic
housing, and electrical interface. Depending upon the required
functionality and application, other components may be present as
well including trans impedance amplifiers. It is used to receive an
optical signal from a fiber and convert it back into an electrical
signal. A BOSA consists of a TOSA, a ROSA and a WDM filter so that
it can use bidirectional technology to support two wavelengths on
each optical fiber.
[0010] For the TOSA, semiconductor lasers used in fiber optics
industry are small, sensitive devices. They are typically a few
hundred microns long, with tiny pads for cathode and anode that
need wire bonding for electrical connection. It is generally
necessary to strictly regulate the operating temperature of the
laser in order to stabilize the wavelength of the light; this is
typically done using a thermoelectric cooler (TEC). Moreover, to
couple the light generated by them into an optical fiber, focusing
lenses with tight alignment tolerances are needed. Because of these
delicacies, proper packaging is a crucial aspect.
[0011] With the TOSA, an optical subassembly fulfills several
functions. It provides a stable mechanical platform for the laser
chip along with the necessary electrical interconnects. Inside the
TOSA, the interconnects are wirebonded to the laser's cathode and
anode. Practical TOSAs may include a number of other electronic
parts, such as power monitoring diodes, TEC coolers, and external
modulators. The laser diode (and any additional device) is mounted
on a substrate.
[0012] In assembling a TOSA package, the laser is aligned with an
optical fiber so as to provide sufficient coupling efficiency. The
laser and the optical fiber may also need to be aligned with lenses
disposed therebetween. It is often difficult and challenging to
align all of the optical components to each other since
three-dimensional alignment is typically required. In addition, for
a variety of applications, it is desirable to hermetically seal the
opto-electronic devices within the housing of the TOSA package, to
protect the components from corrosive media, moisture and the
like.
[0013] Heretofore, in a hermetically sealed package, the
opto-electronic components (receiver and/or transmitter and
associated optical elements and electronic hardware) are contained
in an opto-electronic package. The optical fiber is introduced from
outside the housing of the opto-electronic package, through an
opening provided in the housing wall. The end of the optical fiber
is optically coupled to the opto-electronic components held within
the housing. A feedthrough element supports the portion of the
optical fiber through the wall opening. Since the package of the
opto-electronic package must be hermetically sealed as whole, the
feedthrough element must be hermetically sealed, so that the
electro-optic components within the opto-electronic package housing
are reliably and continuously protected from the environment.
[0014] Heretofore, hermetic feedthrough is in the form of a
cylindrical opening in the package housing defining a relatively
large clearance through which a section of the optical fiber
passes. A sealing material such as glass frit or metal solder is
applied to seal the clearance space between the optical fiber and
the housing. Given the large clearance between the housing and the
optical fiber and the use of sealant material and its clearance
(i.e., a layer of material between the external fiber wall and the
inside wall of the housing), the housing does not support the
optical fiber with precise positional alignment with respect to the
components inside housing. The end of the optical fiber is required
to be positioned by a ferrule or other alignment feature that is
optically aligned with the opto-electronic components provided in
the package. To optically couple the input/output of the optical
fiber to the opto-electronic components in the package, optical
elements such as lenses and mirrors are required to collimate
and/or focus light from a light source (e.g., a laser) into the
input end of the optical fiber (or to collimate and/or focus light
from the output end of the optical fiber to the receiver). To
achieve acceptable signal levels, the end of the optical fiber must
be precisely aligned at high tolerance to the transmitters and
receivers, so the optical fiber is precisely aligned to the optical
elements supported with respect to the transmitters and/or
receivers.
[0015] It can be appreciated that for a TOSA, the connection and
optical alignment of the optical fiber with respect to a
transmitter must be assembled and the components must be fabricated
with sub-micron precision. In the past, it has been challenging for
TOSAs to be economical produced in a fully automated, high-speed
process. Similar challenges apply to ROSA and BOSA.
[0016] U.S. Patent Application Publication No. US2016/0274318A1,
commonly assigned to the assignee of the present invention,
discloses an optical bench subassembly including an integrated
photonic device. Optical alignment of the photonic device with the
optical bench can be performed outside of an optoelectronic package
assembly before attaching thereto. The photonic device is attached
to a base of the optical bench, with its optical input/output in
optical alignment with the optical output/input of the optical
bench. The optical bench supports an array of optical fibers in
precise relationship to a structured reflective surface. The
photonic device is mounted on a submount to be attached to the
optical bench. The photonic device may be actively or passively
aligned with the optical bench. After achieving optical alignment,
the submount of the photonic device is fixedly attached to the base
of the optical bench.
[0017] What is needed is an improved hermetic optical subassembly,
which reduces package size, and improves manufacturability,
throughput, optical alignment tolerance, ease of use, functionality
and reliability at reduced costs. The present invention improves on
the invention disclosed in U.S. Patent Application Publication No.
US2016/0274318A1.
SUMMARY OF THE INVENTION
[0018] The present invention provides an improved hermetic optical
subassembly structure to facilitate optical alignment of components
within the subassembly, which overcomes the drawbacks of the prior
art. The present invention provides a hermetic subassembly
comprising three main structural components, including a first
optical bench that directs optical signals to/from an optical
waveguide, a carrier supporting at least one opto-electronic or
photonic device (e.g., a laser or a photodiode), and a second,
intermediate, optical bench that directs optical signals between
the photonic device and the first optical bench. When assembled,
the intermediate optical bench aligns the carrier to the first
optical bench, such that the photonic device and the waveguide are
optically aligned along a desired optical path.
[0019] In one embodiment, the first optical bench supports an
optical component in the form of an optical wave guide (e.g., an
optical fiber). In a more specific embodiment, the body of the
first optical bench defines an alignment structure in the form of
at least one groove to precisely support the end section of an
optical fiber. An optical element (e.g., a lens, a prism, a
reflector, a mirror, etc.) is provided in precise relationship to
the end face of the optical fiber. In a further embodiment, the
optical element comprises a structured reflective surface (e.g.,
planar reflective, convex reflective, or concave reflective (e.g.,
an aspherical mirror surface)). The reflective surface is optically
aligned with the optical axis of the optical fiber along the
desired optical path.
[0020] In one embodiment, the photonic device is mounted on the
substrate of the carrier. In one embodiment, the photonic device
comprises at least one edge emitting laser (EML). A
thermos-electric cooler (TEC) is provided between the EML and the
carrier substrate for cooling the EML. The carrier may be provided
with circuits, electrical contact pads, circuit components (e.g., a
driver for the EML), and other components and/or circuits
associated with the operation of the photonic device.
[0021] The intermediate optical bench includes a structured
reflective surface (e.g., planar reflective, convex reflective, or
concave reflective (e.g., an aspherical mirror surface)) that
directs optical signals between the carrier and the first optical
bench. A planar surface of the intermediate optical bench is
attached to the first optical bench with the reflective surfaces
optically aligned to each other along the desired optical path. The
body of the intermediate optical bench is attached to the carrier
with the reflective surface optically aligned with the photonic
device (i.e., its optical axis) along the desired optical path.
[0022] Accordingly, after assembly, optical signals can be directed
between the photonic device and the waveguide via the reflective
surface of the first optical bench and the reflective surface of
the intermediate optical bench.
[0023] The reflective surface of the first optical bench may be
passively aligned with the reflective surface of the intermediate
optical bench (e.g., relying on alignment surface features and/or
indicia provided on first optical bench and/or the intermediate
optical bench. In addition, the photonic device may be passively
aligned to the reflective surface of the intermediate optical
bench. Alternatively, the photonic device and the optical bench may
be actively aligned by passing an optical signal between the
reflective surface in the intermediate optical bench and the
photonic device. The photonic device can be activated to allow for
active alignment. After achieving optical alignment, the carrier of
the photonic device is fixedly attached to the body of the
intermediate optical bench. The optical benches and the carrier are
structured to be hermetically sealed against each other to form a
hermetic package.
[0024] The body of the first and second optical benches are
preferably formed by stamping a malleable stock material (e.g., a
metal stock), to form precise geometries and features of the
optical benches (including reflective surfaces, optical fiber
alignment grooves, etc.). By using a stamped single-solid-body for
each of the benches, the optical components that are not stamped
(e.g., fibers, ball lens) can be aligned passively using alignment
features defined within the stamped benches. The stamped optical
bench will minimize the number of components that need to be
actively aligned, reducing production costs and increasing yield
and throughput.
[0025] In another embodiment of the present invention, the optical
bench is structured to support multiple waveguides (e.g., multiple
optical fiber), and structured reflective surfaces (e.g., an array
of mirrors), to work with an array of photonic devices mounted on a
carrier.
[0026] In a further aspect of the present invention, the hermetic
optical subassembly of the present invention integrates
multiplexers/demultiplexers (Mux/Demux), for directing optical
signals between a single optical fiber and a plurality of photonic
devices.
[0027] In Summary, the present invention provides a hermetic
optical subassembly, comprising: a first optical bench supporting
an optical fiber, and comprising at least one first mirror defined
by stamping a first malleable metal stock material; a second
optical bench comprising at least one second mirror defined by
stamping a second malleable metal stock material; a carrier
supporting at least one photonic device, wherein the optical fiber,
the first mirror, the second mirror and the photonic device are in
optical alignment, and the first mirror and the second mirror
directs an optical signal between the photonic device and the
optical fiber, and wherein the first optical bench, the second
optical bench and the carrier are coupled to form a hermetic
package. Further, the present invention provides wherein the first
optical bench further comprising a multiplexer that combines a
plurality of input optical signals each having a different
wavelength into a single output optical signal to be directed to
the optical fiber, wherein the photonic device comprises a
plurality of transmitters each providing an optical signal of a
different wavelength, wherein the first optical bench comprises a
plurality of first mirrors and the second optical bench comprises a
plurality of second mirrors corresponding to the plurality of first
mirrors and corresponding to the plurality of transmitters, and
wherein corresponding transmitter, first mirror and second mirror
are in optical alignment, and corresponding first mirror and
corresponding second mirror directs corresponding optical signal
provided by corresponding transmitter to the multiplex. The
multiplexer comprises a filter block supported on the first optical
bench, wherein the filter block combines the optical signals
provided by the respective transmitters into the single output
signal to be directed at the optical fiber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] For a fuller understanding of the nature and advantages of
the invention, as well as the preferred mode of use, reference
should be made to the following detailed description read in
conjunction with the accompanying drawings. In the following
drawings, like reference numerals designate like or similar parts
throughout the drawings.
[0029] FIG. 1A is a perspective diagram of a quad small-form-factor
pluggable (QSFP) transceiver module incorporating a hermetic
optical subassembly, in accordance with one embodiment of the
present invention; FIG. 1B is another view of FIG. 1A with
shading.
[0030] FIG. 2A is a sectional view of the hermetic optical
subassembly of FIG. 1, FIG. 2B is another view of FIG. 2A with
shading.
[0031] FIGS. 3A to 3E illustrate the structure of the first optical
bench in the hermetic optical subassembly, in accordance with one
embodiment of the present invention.
[0032] FIGS. 4A to 4D illustrate the structure of the second,
intermediate, optical bench in the hermetic optical subassembly, in
accordance with one embodiment of the present invention.
[0033] FIGS. 5A and 5B illustrate the structure of the carrier
including the photonic devices, in accordance with one embodiment
of the present invention.
[0034] FIGS. 6A to 6C illustrate the hermetic optical subassembly
as assembled with its components.
[0035] FIGS. 7A to 7D depict exemplary dimensions of the hermetic
optical subassembly and installation thereof in the QSFP
module.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] This invention is described below in reference to various
embodiments with reference to the figures. While this invention is
described in terms of the best mode for achieving this invention's
objectives, it will be appreciated by those skilled in the art that
variations may be accomplished in view of these teachings without
deviating from the spirit or scope of the invention.
[0037] The present invention provides an improved hermetic optical
subassembly structure to facilitate optical alignment of components
within the subassembly, which overcomes the drawbacks of the prior
art. The present invention provides a hermetic subassembly
comprising three main structural components, including a first
optical bench that directs optical signals to/from an optical
waveguide, a carrier supporting an opto-electronic or photonic
device (e.g., a laser or a photodiode), and a second, intermediate,
optical bench that directs optical signals between the photonic
device and the first optical bench. When assembled, the
intermediate optical bench aligns the carrier to the first optical
bench, such that the photonic device and the waveguide are
optically aligned along a desired optical path.
[0038] Various embodiments of the present invention incorporate
some of the inventive concepts developed by the Assignee of the
present invention, nanoPrecision Products, Inc., including various
proprietary including optical bench subassemblies for use in
connection with optical data transmissions, including the concepts
disclosed in the patent publications discussed below, which have
been commonly assigned to the Assignee.
[0039] For example, U.S. Patent Application Publication No.
US2013/0322818A1 discloses an optical coupling device for routing
optical signals, which is in the form of an optical bench having a
stamped structured surface for routing optical data signals. The
optical bench comprising a metal base having a structured surface
defined therein, wherein the structured surface has a surface
profile that bends, reflects, and/or reshapes an incident light.
The base further defines an alignment structure, which is
configured with a surface feature to facilitate precisely
positioning an optical component (e.g., an optical fiber) on the
base in precise optical alignment with the structured surface to
allow light to be transmitted along a defined path between the
structured surface and the optical component, wherein the
structured surface and the alignment structure are integrally
defined on the base by stamping a malleable metal material to form
an optical bench.
[0040] U.S. Patent Application Publication No. US2015/0355420A1
further discloses an optical coupling device for routing optical
signals for use in an optical communications module, in particular
an optical coupling device in the form of an optical bench, in
which defined on a metal base is a structured surface having a
surface profile that bends, reflects and/or reshapes an incident
light. An alignment structure is defined on the base, configured
with a surface feature to facilitate positioning an optical
component (e.g., an optical fiber) on the base in optical alignment
with the structured surface to allow light to be transmitted along
a defined path between the structured surface and the optical
component. The structured surface and the alignment structure are
integrally defined on the base by stamping a malleable metal
material of the base. The alignment structure facilitates passive
alignment of the optical component on the base in optical alignment
with the structured surface to allow light to be transmitted along
a defined path between the structured surface and the optical
component.
[0041] U.S. Patent Application Publication No. US2013/0294732A1
further discloses a hermetic optical fiber alignment assembly
having an integrated optical element, in particular a hermetic
optical fiber alignment assembly including an optical bench that
comprises a metal ferrule portion having a plurality of grooves
receiving the end sections of optical fibers, wherein the grooves
define the location and orientation of the end sections with
respect to the ferrule portion. The assembly includes an integrated
optical element for coupling the input/output of an optical fiber
to optoelectronic devices in an optoelectronic module. The optical
element can be in the form of a structured reflective surface. The
end of the optical fiber is at a defined distance to and aligned
with the structured reflective surface. The structured reflective
surfaces and the fiber alignment grooves can be formed by stamping
a malleable metal to define those features on a metal base.
[0042] U.S. Pat. No. 7,343,770 discloses a novel precision stamping
system for manufacturing small tolerance parts. Such inventive
stamping system can be implemented in various stamping processes to
produce the devices disclosed in the above-noted patent
publications. These stamping processes involve stamping a stock
material (e.g., a metal blank), to form the final overall geometry
and geometry of the surface features at tight (i.e., small)
tolerances, including reflective surfaces having a desired geometry
in precise alignment with the other defined surface features.
[0043] U.S. Patent Application Publication No. US2016/0016218A1
further discloses a composite structure including a base having a
main portion and an auxiliary portion of dissimilar metallic
materials. The base and the auxiliary portion are shaped by
stamping. As the auxiliary portion is stamped, it interlocks with
the base, and at the same time forming the desired structured
features on the auxiliary portion, such as a structured reflective
surface, optical fiber alignment features, etc. With this approach,
relatively less critical structured features can be shaped on the
bulk of the base with less effort to maintain a relatively larger
tolerance, while the relatively more critical structured features
on the auxiliary portion are more precisely shaped with further
considerations to define dimensions, geometries and/or finishes at
relatively smaller tolerances. The auxiliary portion may include a
further composite structure of two dissimilar metallic materials
associated with different properties for stamping different
structured features. This stamping approach improves on the earlier
stamping process in U.S. Pat. No. 7,343,770, in which the stock
material that is subjected to stamping is a homogenous material
(e.g., a strip of metal, such as Kovar, aluminum, etc.) The
stamping process produces structural features out of the single
homogeneous material. Thus, different features would share the
properties of the material, which may not be optimized for one or
more features. For example, a material that has a property suitable
for stamping an alignment feature may not possess a property that
is suitable for stamping a reflective surface feature having the
best light reflective efficiency to reduce optical signal
losses.
[0044] U.S. Pat. No. 8,961,034 discloses a method of producing a
ferrule for supporting an optical fiber in an optical fiber
connector, comprising stamping a metal blank to form a body having
a plurality of generally U-shaped longitudinal open grooves each
having a longitudinal opening provided on a surface of the body,
wherein each groove is sized to securely retain an optical fiber in
the groove by clamping the optical fiber. The optical fiber is
securely retained in the body of the ferrule without the need for
additional fiber retaining means.
[0045] International Patent Application No. PCT/US2016/046936 (PCT
Publication No. WO/2017/027864) discloses a
multiplexer/demultiplexer (Mux/Demux) subassembly includes a
stamped optical bench, which includes an array of stamped
reflective surfaces for redirecting optical signals. Alignment
features and components of the Mux/Demux subassembly are integrally
formed on a stamped optical bench, defining a desired optical path
with optical alignment at tight tolerances. The optical bench is
formed by stamping a malleable stock material (e.g., a metal
stock), to form precise geometries and features of the optical
bench.
[0046] The above inventive concepts are incorporated by reference
herein, and will be referred below to facilitate disclosure of the
present invention. The present invention is disclosed in connection
with exemplary embodiments of hermetic transmitter optical
subassemblies (TOSA's), which include Mux/Demux. It is understood
that the present invention may be adapted to hermetic optical
subassemblies for other applications (e.g., ROSA, BOSA), with or
without Mux/Demux.
[0047] FIG. 1A is a perspective diagram of a quad small-form-factor
pluggable (QSFP) module 100 incorporating a hermetic optical
subassembly 10, in accordance with one embodiment of the present
invention; FIG. 1B is another view of FIG. 1A with shading. The
QSFP is a full-duplex optical transceiver module with four
independent transmit and receive channels. It is designed to
replace four single-channel small-form-factor pluggable (SFP) and
in a package only about 30% larger than the standard SFP. To equip
a QSFP and similar transceivers requiring multiple wavelengths, a
small Mux and/or DeMux device is very important. The hermetic
optical subassembly 10 of the present invention provides a small
footprint, broad operating wavelength range, enhanced impact
performance, lower cost, and easier manufacturing process.
[0048] FIG. 2A is a sectional view of the hermetic optical
subassembly of FIG. 1, FIG. 2B is another view of FIG. 2A with
shading. These sectional views illustrate the optical path defined
by the hermetic optical subassembly 10. Specifically, in the
illustrated embodiment, the hermetic optical subassembly is a
TOSA.
[0049] The hermetic optical subassembly 10 includes three main
structural components, including a first optical bench 11 that
directs optical signals to/from an optical waveguide (e.g., an
optical fiber 20), a carrier 13 supporting at least one photonic
device 22 (e.g., an electrically modulated, edge-emitting laser
(EML)), and a second, intermediate, optical bench 12 that directs
optical signals between the photonic device 22 and the optical
bench 11. When assembled, the intermediate optical bench 12 aligns
the carrier 13 to the optical bench 11, such that the photonic
device 22 and the optical fiber 20 are optically aligned along a
desired optical path L. Specifically, optical signal from the
photonic device 22 is reshaped and turned (redirected) by the micro
mirror 31 on the intermediate optical bench 12 towards the micro
mirror 21 on the optical bench 11, which in turn reshape and/or
redirect the optical signal towards the optical fiber 20 (though a
ball lens 17).
[0050] FIGS. 3A to 3E illustrate the structure of the optical bench
11 in the hermetic optical subassembly 10, in accordance with one
embodiment of the present invention. FIG. 3A shows the structure of
the optical bench 11 without the reflective surfaces 21 (shown in
FIG. 3C) and the components for the Mux/Demux (e.g., filter block
with thin-film filters and a reflective film; see discussions below
in connection with FIG. 3E). FIG. 3B is a section view taken alone
line 3B-3B in FIG. 3A. The optical bench 11 serves as a "cover" for
the overall hermetic optical subassembly 10. Defined on the body of
the optical bench 11 are a through opening 14 adjacent a recess 15,
a dimple 16 (e.g., a spherical or tetrahedral depression) to
support a ball lens 17 (see FIG. 3D), and a groove 18 in a cavity
68 for aligning the optical fiber 20 (see FIG. 3D). FIG. 3C
illustrates a block 19 in the shape of a plug or rivet, which is
provided with a plurality of micro mirrors or structured reflective
surfaces 21. In this particular illustrated embodiment, there are
four micro mirrors 21 corresponding to four EML's (see FIGS. 3E, 5A
and 5B). The geometry of the micro mirrors 21 may conform to planar
reflective, convex reflective, or concave reflective (e.g., an
aspherical mirror surface). For example, in the illustrated
embodiment, the micro mirrors 21 may be generally aspherical
convex. The block 19 fits into the opening 14 in the body of the
optical bench 11 (as will be explained later, the shape of the
block 19 is formed in place in the optical bench 11 by a stamping
operation, instead of it being separately formed and inserted into
the opening 14).
[0051] Referring to FIG. 3D, the optical bench 11 is complete with
the micro mirrors 21, and the components for the Mux/Demux
(actually in this embodiment of TOSA, it is a Mux 23). Referring
also to FIG. 3E, the components and optical paths in the Mux 23 is
schematically illustrated, in accordance with one embodiment of the
present invention. In the illustrated embodiment, the Mux 23 is
configured for input signals of four different wavelengths to be
combined (i.e., multiplexed) into a single output signal (in
reverse, a single input signal can be split (demultiplexed) into
four output signals of different wavelengths). The Mux 23 includes
a transparent block 24 having an array of thin film filters 25
(there are four filters 25 in this embodiment, each having a
particular transmissive wavelength to allow optical signal from
respective EML 22 of the respective wavelength to pass through) and
a mirror 26 (e.g., a reflective coating) provided on opposing
surfaces. The Mux 23 is supported in the recess 15 in the body of
the optical bench 11, between the micro mirrors 21 and the ball
lens 17 and optical fiber 20, with each micro mirror 21 positioned
corresponding to a thin film filter 25.
[0052] In a multiplexing operation, optical signals reflected from
the micro mirrors 21 (which originated from the outputs of the
EML's 22 via micro mirror 31) are passed through the respective
filters 25, and the signals are reflected within the transparent
block 24 between the thin film filters 25 and the mirror 26, with
the thin film filters reflecting all signals that do not correspond
to the respective the transmission wavelengths. As a result, the
optical signals are effectively combined into a single output
signal to the optical fiber 20. The ball lens 17 focus this output
signal onto the end face of the optical fiber to improve optical
coupling. The particular illustrated optical paths in FIG. 3E were
configured in prior art systems, except that none of those systems
incorporates the type of optical subassembly in accordance with the
present invention. As shown, the "desired optical path L" would
include various input optical paths from the EML'ss 22. (In a
demultiplexer operation, the optical paths are in reverse.)
[0053] In accordance with one embodiment of the present invention,
the array of micro mirrors 21, and some or all of the alignment
features for the optical fiber 20, the ball lens 17, and the
components of the Mux 23 may be integrally formed on the body of
the optical bench 11 by stamping, so as to define the desired
optical path, with optical alignment at tight tolerances. These
features may be integrally formed in a single stamping operation,
after the body of the optical bench 11 is first provided with the
recess 15, opening 14 and cavity 68 (e.g., from an earlier stamping
operation) as shown in FIG. 3A.
[0054] In the illustrated embodiment, the stamped optical bench 11
supports the filter block 24 (having the thin film filters 25 and
mirror 26), the lens 17, and the optical fiber 20. The body of the
optical bench 11 defines an alignment structure in the form of the
groove 18 to precisely support the end section of the optical fiber
20. The body of the optical bench 11 also defines the slot 16
(e.g., a spherical or tetrahedral depression) to support the ball
lens 17 (or a reflector, a mirror, etc.) in precise relationship to
the end face of the optical fiber 20, and further an additional
alignment feature (e.g., a step in the recess 15, not shown) for
accurately, and passively, aligning the filter block 14 along the
desired optical path. The optical element comprising the array of
structured reflective surfaces (e.g., micro mirrors 21, which may
be planar reflective or concave reflective (e.g., an aspherical
mirror surface)) is stamped formed with the appropriate geometries
for routing optical signals along the desired optical path L.
[0055] As shown in FIG. 3C, the block 19 having the micro mirrors
21 is shown alone after stamp forming. In actual stamping
operation, before the micro mirror features are formed by stamping,
a metallic "rivet", e.g., made from a soft material such as
aluminum, is inserted into the opening 14 in the body of the
optical bench 11. Other surface features on the optical bench 11
may also be formed together after inserting the aluminum rivet into
the opening 14 in the body of the optical bench 11. For example,
the aluminum rivet is stamped with the desired surface features
shown along with some of the other features (e.g., the groove 18
for receiving a section of the optical fiber 20; alignment features
65a to 65c on planar surface 61; see FIG. 3D). This "rivet" type
stamping approach and its features and benefits are disclosed in
U.S. Patent Application Publication No. US2016/0016218A1, which has
been commonly assigned to the Assignee of the present invention.
Details of such stamping process is not discussed herein, but
incorporated by reference herein.
[0056] The aluminum rivet is easily formable by stamping, and it
has high reflectance in the wavelength range adopted in
telecommunications and data communications. The material of the
body of the optical bench 11 may be Kovar. Specifically, in the
above described embodiments, pure aluminum is chosen for the rivet
for forming the optical bench because it is relatively softer, and
more malleable/ductile than Kovar chosen for the body of the
optical bench 11, to obtain the desired geometries, dimensions
and/or finishes of critical features (e.g., the micro mirrors 21)
at the optical bench 11. The harder and stronger frame material
(e.g., Kovar) is chosen to form structures that require the
integrity of a harder material, but stamping the harder base
material would require larger forces and result in more springback,
requiring multiple hits of the stamping punch to obtain the desire
shape (especially for deeper profiles such as a deep recess), which
may result in relatively higher tolerances. In contrast, the
relatively softer material chosen for stamping the micro mirrors 21
requires less stamping forces and results in less springback,
requiring relatively fewer hits (e.g., just one hit) of the
stamping punch to obtain the final stamped part. Hence, micro
features such as micro mirrors 21 can be stamped on the optical
bench 11 with very tight dimensional tolerances. The harder body
material of the optical bench 11 also functions as part of the die,
which partially shapes the block 19 to define the micro mirror 21
during stamping operation. The coefficient of thermal expansion for
Kovar material also closely matches the coefficient of thermal
expansion of most semiconductor and glass materials so that
temperature changes induce minimal misalignment between the
components. Furthermore, the melting temperatures of the metallic
optical bench are sufficiently high to allow for compatibility with
soldering processes that are commonly used in electronic and
photonic packaging. Optionally, an optical coating may be deposited
onto the stamped micro mirrors 21 to increase reflectivity.
[0057] While the above embodiment makes use of a ball lens 17 to
focus output light from the Mux 23 to the optical fiber 20, instead
of a ball lens 17, a micro mirror (not shown) may be stamped formed
on the body of the optical bench 11, to focus output optical signal
from the Mux 23 to the optical fiber 20.
[0058] If at least the micro mirrors 21 and the fiber alignment
groove 18 are stamped in a single stroke by the same tool when
forming the optical bench 11, the alignment precision between the
optical fiber 20 and the array of micro mirrors 21 could be on the
order of 200 nanometers. This provides completely passive alignment
sufficient for single-mode optics, thus avoiding the tedious and
more complex active alignment practice in the prior art. If the
other alignment features for the ball lens 17 and the filter block
24 are also integrally stamped in a single step along with the
micro mirrors 21 and the fiber alignment groove 2, further accurate
passive alignment of these components are also possible.
[0059] An alternate embodiment of a Mux (and Demux) optical bench
subassembly is disclosed in International Patent Application No.
PCT/US2016/046936 (PCT Publication No. WO/2017/027864), which may
be adapted and replace the optical bench 11 in the hermetic optical
subassembly of the present invention.
[0060] In view of the above disclosure, it can be seen that the
stamped optical Mux subassembly in accordance with the present
invention uses a stamped optical alignment platform that uses
non-stamped thin-film filters to combine multiple sources of
different wavelengths (via a stamped reflector) into a single beam
and inject it into an optical fiber. By using stamped micro mirror
arrays in combination with thin-film bandpass filters as part of
the optical system to do the optical signal splitting/combining,
the mirrors and the alignment optical bench will be a stamped
single-solid-body, and all of the optical components that are not
stamped (fibers, thin film filters, possible ball lenses) can be
aligned passively using features defined within the stamped optical
bench. The stamped optical bench will minimize the number of
components that need to be actively aligned, reducing production
costs and increasing yield and throughput.
[0061] A Mux/Demux having a stamped optical bench could have
similar or smaller overall size and configuration, and similar or
smaller footprint, compared to a prior art Mux/Demux using, e.g., a
silicon optical bench. Stamped optical benches could be configured
to have a smaller footprint and overall size than silicon optical
benches. A stamped optical bench can effectively simplify the
configuration of a silicon optical bench without compromising the
desired defined optical path.
[0062] The Mux/Demux subassembly on the optical bench 11 discussed
above is suited for single-mode, or multi-mode, and the sources may
be fibers, or grating couplers, or VCSEL's, or DFB lasers. The
receiver for the light output may be any kind of light sensitive
detector, or any kind of fiber, or grating couplers, or any kind of
waveguide. The Mux/Demux may involve coarse wavelength division
multiplexing (CWDM) or dense wavelength division multiplexing
(DWDM), and involve any number of wavelengths or channels, beyond
the four channels illustrated in the embodiments.
[0063] FIGS. 4A to 4D illustrate the structure of the second,
intermediate, optical bench 12 in the hermetic optical subassembly
10, in accordance with one embodiment of the present invention.
FIG. 4A shows the structure of the optical bench 12 without the
micro mirrors 21 (shown in FIG. 4C). FIG. 4B is a section view
taken alone line 4B-4B in FIG. 4A. The optical bench 12 serves as
an intermediate adaptor to couple (as will be further discussed
below, hermetically couple) the carrier 13 having the photonic
devices and the optical bench 11 to form the overall hermetic
optical subassembly 10. Defined on the body of the optical bench 12
is a through opening 34 in a recess 35 adjacent two prongs 36. The
through hole is flanked by the main body of the optical bench 12,
and a cross-member 33 between the prongs 36. A small through-hole
67 is provided at a corner of the planar surface 62, at a location
matching the location of the cavity 68 in the optical bench 11, for
inserting hermetic sealing material to seal the optical fiber
section (as will be explained later below).
[0064] FIG. 4C illustrates a block 29 in the shape of a plug or
rivet, which is provided with a plurality of micro mirrors or
structured micro mirrors 31. In this particular illustrated
embodiment, there are four micro mirrors 31 corresponding to the
four EML's (see FIGS. 3E, 5A and 5B). The geometry of the micro
mirrors 21 may conform to planar reflective, convex reflective, or
concave reflective (e.g., an aspherical mirror surface). For
example, in the illustrated embodiment, the micro mirrors 21 may be
generally aspherical concave. Referring also to FIG. 5B, the output
of the EML 22 does not cast a round beam spot, but instead an oval
beam spot with fast and slow axes. Accordingly, the micro mirrors
21 and 31 have geometry that reshapes the oval beam into a round
beam and turn the beam towards the filter 24 in the cover optical
bench 11. The block 29 fits into the opening 34 in the body of the
optical bench 12 (as will be explained later, and similar to the
block 19 in the optical bench 11, the shape of the block 29 is
formed in place in the optical bench 12 by a stamping operation,
instead of it being separately formed and inserted into the opening
34).
[0065] Referring to FIG. 4D, the optical bench 12 is complete with
the micro mirrors 31. In accordance with one embodiment of the
present invention, the array of micro mirrors 31, and passive
alignment features (e.g., alignment indicia and windows,
protrusions and/or recesses, schematically represented by dotted
squares 65a to 65c in FIGS. 3D and 4D) complementarily provided on
the facing planar surfaces 61 and 62 for passively aligning the
optical benches 11 and 12, may be integrally formed on the body of
the optical bench 12 by stamping, so as to define the desired
optical path, with optical alignment at tight tolerances. These
features may be integrally formed in a single stamping operation,
after the body of the optical bench 12 is first provided with the
prongs 36, the recess 35, the opening 34 and the opening 67 (e.g.,
from an earlier stamping operation) as shown in FIG. 4A.
[0066] As shown in FIG. 4C, the block 29 having the micro mirrors
31 is shown alone after stamp forming. In actual stamping
operation, before the micro mirror features are formed by stamping,
a metallic "rivet", e.g., made from a soft material such as
aluminum, is inserted into the opening 34 in the body of the
optical bench 12 (which could be made of Kovar). Other surface
features on the optical bench 12 may also be formed together after
inserting the aluminum rivet into the opening 34 in the body of the
optical bench 12. For example, the aluminum rivet is stamped with
the desired surface features shown along with some of the other
features (e.g., passive alignment features 65 for aligning with the
optical bench 11). Optionally, an optical coating may be deposited
onto the stamped micro mirrors 31 to increase reflectivity.
[0067] This "rivet" type stamping approach and its features and
benefits are disclosed in U.S. Patent Application Publication No.
US2016/0016218A1, which has been commonly assigned to the Assignee
of the present invention. Details of such stamping process is not
discussed herein, but incorporated by reference herein. The design
considerations using this approach is similar to those in
connection with stamp forming the optical bench 11, and they will
not be repeated here.
[0068] FIGS. 5A and 5B illustrate the structure of the carrier 13
including the photonic device 22, in accordance with one embodiment
of the present invention. The carrier 13 serves as a "base" of the
overall hermetic optical subassembly 10, for mounting the hermetic
optical subassembly 10 onto, e.g., a standard "QFSP28" board 50
shown in FIG. 1A. The carrier 13 supports a thermoelectric cooler
(TEC) 41, on which at least one photonic device is supported (in
this embodiment, the photonic device includes four EML's of
different wavelengths). Cooling of EML's is essential for proper
operation of the EML's. The EML's are mounted on a sub-carrier
(e.g., in a chip on carrier (COC) configuration) on top of the TEC
41. The temperature of the carrier and hence the EML's need to be
regulated to control the wavelength of the optical signal output of
the EML's. The carrier 13 may be provided with circuits, electrical
contact pads, circuit components (e.g., drivers for the EML's), and
other components and/or circuits associated with the operation of
the EML's.
[0069] It is noted that preferably, the electrical traces should be
coplanar with the lasers to improve signal integrity. As can be
seen from FIGS. 1A, 2A, 6A and 6c, the carrier 13 includes a block
43 having a vertically extending wall 44. Patterned electrical
traces 47 are provided through and/or below the wall 44, so that
sections 45 and 46 of the traces 47 are exposed beyond both sides
of the wall 44. The traces 45 provide for electrical access to the
hermetic optical subassembly 10, or wire bonding to other
components outside the hermetic optical subassembly 10, and the
traces 46 provide for wire bonding to the EML's. The traces are
substantially coplanar with the EML's. Given the distal surface of
the block 44 and the wall 44 of the carrier 13 are exposed to
external environment, the material of the carrier 13 should be
chosen to be a hermetic material with the electrical traces 47
running there-through. The carrier 13 may be made of hermetic
materials such as Aluminum Nitrite (AlN), high temperature cofired
ceramic (HTCC) or low temperature cofired ceramic (LTCC), which are
good hermetic packaging material due to its desirable electrical
properties, high mechanical strength and good thermal conductivity.
These materials are non-electrically conductive or electrically
insulating, so as to be able to support the traces 47, as compared
to the optical benches 11 and 12, which are made of metal
material(s).
[0070] With the optical bench 11, the intermediate optical bench 12
and the carrier 13 pre-assembled as respectively shown in FIG. 3D,
FIG. 4D and FIG. 5A, the optical bench 11 is first attached to the
intermediate optical bench 12. The planar surface 62 (see FIG. 4D)
of the intermediate optical bench 12 is mated to the planar surface
61 (see FIG. 3D) of the optical bench 11, so that the reflective
surfaces 21 and 31 are optically aligned to each other along the
desired optical path L. As noted above, passive alignment of the
optical benches 11 and 12 may be achieved by making use of the
alignment features 65a to 65b provided on the facing planar
surfaces 61 and 62 of the optical benches 11 and 12, respectively.
The optical benches 11 and 12 may be fixedly attached by soldering,
brazing, or laser welding along the perimeter of the mating
surfaces to provide hermetic joints. A hermetic sealing material,
such as a glass solder, is inserted into the opening 67 to fill the
cavity 68 in the optical bench 11 (see FIGS. 2A and 3D), so as to
hermetically seal the feedthrough section of the optical fiber 20.
Hermetic sealing may further be based on the teaching of U.S.
Patent Application Publication No. US2013/0294732A1. After
hermetically assembling the first and second optical benches 11 and
12 and the carrier together, a hermetic package is formed.
[0071] After assembling the optical benches 11 and 12, the
preassembled carrier 13 shown in FIG. 5A is aligned and attached to
the front of and below the intermediate optical bench 12. The
adjoining mating surfaces are hermetically sealed, e.g., by
soldering. The photonic device 22 may be passively aligned to the
reflective surfaces 31 of the intermediate optical bench 12 (e.g.,
by providing additional passive alignment surface features on the
mating surfaces of the carrier 13 and the optical bench 12 (not
shown). Alternatively, the photonic device 22 and the intermediate
optical bench 12 may be actively aligned by passing an optical
signal between the reflective surfaces 31 in the intermediate
optical bench 12 and the photonic device 22. The photonic device 22
can be activated to allow for active alignment. After achieving
optical alignment, the carrier 13 having the photonic device 22 is
fixedly attached to the base of the intermediate optical bench. The
optical benches and the carrier are structured to be hermetically
sealed against each other. The resultant structure of the hermetic
optical subassembly would include a 3-tier structure, including the
top optical bench 11, the intermediate optical bench 12 and the
bottom carrier 13.
[0072] FIG. 6C is a sectional view illustrating the hermetic
optical subassembly 10 after assembly as discussed above. The base
of the carrier 13 is shown attached to the QSFP28 board 50. The
pigtail end of the optical fiber 20 may be terminated in a ferrule
(not shown) in an optical connector to provide a connection to an
external optical fiber.
[0073] After assembly, optical signals can be directed between the
photonic device 22 (e.g., EML's) and the optical fiber 20 via the
reflective surface 31 of the intermediate optical bench 12 and the
reflective surface 21 of the optical bench 11. In the illustrated
embodiment, there are four EML's, which output signal are
multiplexed through the Mux 23 in the optical bench 11. Given the
nature of EML's, their output is parallel to the carrier on which
the EML's are mounted. Accordingly, the output signals would be
transmitted horizontally, which need to be turned upwards to the
level of the Mux 23 and optical fiber 20. The micro mirrors 31
serves to reshape and turn or fold the output signal, which is then
collimated before passing through the Mux 23 to be focused at the
optical fiber 20. In the past, EML's were not effectively used in
TOSA, given the difficulties in obtaining an acceptable optical
path. In the illustrated embodiments, the output signals from the
EML's are substantially parallel to the input signal to the optical
fiber 20 (at least in a vertical direction). With the use of two
sets of reflective surfaces, the desired optical effect and optical
path can be achieved while maintaining the overall height of the
hermetic optical subassembly to a minimum. With the stamped optical
benches, it is now possible to incorporate a multiplexer into the
hermetic TOSA (or a de-multiplexer in a hermetic ROSA). The smaller
and more compact construction improves reliability and preserves
optical alignment by reducing the magnitude of thermal expansion
due to temperature changes while operating the laser or due to heat
from other module components.
[0074] FIGS. 7A to 7D depict exemplary dimensions of the hermetic
optical subassembly and installation thereof in the QSFP module.
(All dimension shown in mm.)
[0075] In accordance with the present invention discussed above, it
can be seen that a hermetic optical subassembly can be configured
with a small form factor, which can be manufacture using high
throughput stamping processes. More specifically, the present
invention provides a hermetic TOSA having a small package size,
with improved manufacturability, throughput, optical alignment
tolerance, ease of use, functionality and reliability at reduced
costs.
[0076] While the invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made without departing from the spirit, scope,
and teaching of the invention. Accordingly, the disclosed invention
is to be considered merely as illustrative and limited in scope
only as specified in the appended claims.
* * * * *