U.S. patent application number 16/268765 was filed with the patent office on 2020-08-06 for transmitter optical subassembly arrangement with vertically-mounted monitor photodiodes.
The applicant listed for this patent is Applied Optoelectronics, Inc.. Invention is credited to Kai-Sheng LIN, Kevin LIU, Hsiu-Che WANG.
Application Number | 20200251879 16/268765 |
Document ID | 20200251879 / US20200251879 |
Family ID | 1000004970236 |
Filed Date | 2020-08-06 |
Patent Application | download [pdf] |
United States Patent
Application |
20200251879 |
Kind Code |
A1 |
LIN; Kai-Sheng ; et
al. |
August 6, 2020 |
TRANSMITTER OPTICAL SUBASSEMBLY ARRANGEMENT WITH VERTICALLY-MOUNTED
MONITOR PHOTODIODES
Abstract
The present disclosure is generally directed to a multi-channel
TOSA with vertically-mounted MPDs to reduce TOSA housing dimensions
and improve RF driving signal quality. In more detail, a TOSA
housing consistent with the present disclosure includes at least
one vertical MPD mounting surface that extends substantially
transverse relative to a LD mounting surface, with the result being
that a MPD coupled to the vertical MPD mounting surface gets
positioned above an associated LD coupled to the LD mounting
surface. The vertically-mounted MPD thus makes regions adjacent an
LD that would otherwise be utilized to mount an MPD available for
patterning of conductive RF traces to provide an RF driving signal
to the LD. The conductive RF traces may therefore extend below the
vertically-mounted MPD to a location that is proximate the LD to
allow for relatively short wire bonds therebetween.
Inventors: |
LIN; Kai-Sheng; (Sugar Land,
TX) ; WANG; Hsiu-Che; (Rosenberg, TX) ; LIU;
Kevin; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Optoelectronics, Inc. |
Sugar Land |
TX |
US |
|
|
Family ID: |
1000004970236 |
Appl. No.: |
16/268765 |
Filed: |
February 6, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 5/0014 20130101;
H01S 5/4087 20130101; H01S 5/4012 20130101; H01S 5/02415 20130101;
H01S 5/02236 20130101 |
International
Class: |
H01S 5/022 20060101
H01S005/022; H01S 5/024 20060101 H01S005/024; H01S 5/00 20060101
H01S005/00; H01S 5/40 20060101 H01S005/40 |
Claims
1. A transmitter optical subassembly (TOSA) module, the TOSA module
comprising: a laser diode (LD) mounting surface; at least a first
LD disposed on the LD mounting surface, the first LD having a
back-side emission surface for emitting a portion of optical power
along a first optical path; a base portion comprising a feedthrough
device, the feedthrough device providing a vertical MPD mounting
surface; and a first MPD disposed on the vertical MPD mounting
surface, the first MPD having a light receiving region optically
aligned with the first LD via the first optical path based at least
in part on the vertical MPD mounting surface extending
substantially transverse relative to the LD mounting surface such
that the first optical path intersects with the light receiving
region of the first MPD.
2. The TOSA module of claim 1, further comprising: a housing having
a plurality of sidewalls that define a cavity, the LD mounting
surface being disposed in the cavity; and wherein the feedthrough
device is configured to at least partially be disposed in the
cavity of the housing, and wherein a first end of the feedthrough
device provides an electrical coupling region to electrically
couple to an optical module substrate to receive a radio frequency
(RF) driving signal to drive the first LD, and a second end of the
feedthrough device defines the vertical MPD mounting surface, the
vertical MPD mounting surface being disposed in the cavity.
3. The TOSA module of claim 2, wherein the cavity of the housing is
hermetically sealed to prevent ingress of contaminants.
4. The TOSA module of claim 2, wherein at least one sidewall of the
plurality of sidewalls of the housing provides a thermoelectric
cooler (TEC) mounting section, and wherein the TOSA provides: a
thermoelectric cooler (TEC) arrangement mounted to the TEC mounting
section; and a LD submount disposed on the TEC arrangement, the LD
submount being in thermal communication with the TEC arrangement,
and wherein the LD submount provides the LD mounting surface.
5. The TOSA module of claim 1, further comprising a plurality of
transmit (TX) radio frequency (RF) traces, the TX RF traces being
disposed on a surface of the base that extends away from the
vertical mounting surface along a direction that is substantially
parallel with the LD mounting surface.
6. The TOSA module of claim 5, wherein the plurality of TX RF
traces are disposed below the MPD when mounted to the vertical MPD
mounting surface to allow the plurality of TX RF traces to extend
towards the LD mounting surface, and wherein a portion of the
plurality of TX RF traces are disposed adjacent the LD mounting
surface.
7. The TOSA module of claim 1, further comprising a second LD
disposed on the LD mounting surface and a second MPD disposed on
the vertical MPD mounting surface, the second LD being configured
to emit an associated channel wavelength different from that of the
first LD, and wherein the second LD and second MPD are optically
aligned via a second optical path such that the second optical path
extends from a back-side emission surface of the second LD and
intersects with a light receiving region of the second MPD.
8. The TOSA module of claim 7, further comprising a multiplexing
arrangement, the multiplexing arrangement having at least first and
second input ports optically aligned with the first and second
optical paths, respectively, to receive and combine channel
wavelengths emitted by the first and second LDs into a multiplexed
optical signal for output via an output port.
9. The TOSA module of claim 8, wherein the multiplexing arrangement
includes an arrayed waveguide grating AWG to multiplex the received
channel wavelengths, and wherein AWG provides the output port and
passes the multiplexed optical signal on to a transmit waveguide
coupled to the output port.
10. The TOSA module of claim 8, wherein the first and second input
ports of the multiplexing arrangement are angled relative to the
light emitting region of the first and second LDs such that
incident channel wavelengths received along the first and second
optical paths intersect at an angle of about 8 degrees to prevent
back reflection.
11. (canceled)
12. A method for optically coupling monitor photodiodes (MPDs) to
corresponding laser diodes (LDs) in a multi-channel optical
transceiver (TOSA) housing, the method comprising: mounting at
least one MPD to a vertical MPD mounting surface provided by a
feedthrough device; patterning a plurality of conductive traces on
to one or more surfaces of the feedthrough device; and inserting
the feedthrough device into a cavity of the TOSA housing to bring
the plurality of conductive traces into close proximity with the
LDs in the TOSA, wherein inserting the feedthrough device into the
cavity causes each of the at least one MPDs mounted to the vertical
MPD mounting surface to optically couple with a back-side emission
surface of each corresponding LD.
13. The method of claim 12, further comprising introducing an inert
gas into the cavity to form a hermetic seal.
14. The method of claim 12, further comprising introducing wire
bonds between the LDs and the plurality of conductive traces after
insertion of the feedthrough device into the cavity of the TOSA
housing.
15. The method of claim 12, wherein patterning the plurality of
conductive traces includes disposing each conductive trace of the
plurality of conductive traces on to a surface that extends below
the vertical MPD mounting surface.
16. A multi-channel optical transceiver module comprising: a
printed circuit board assembly (PCBA); a multi-channel transmitter
optical subassembly (TOSA) arrangement coupled to the PCBA, the
TOSA arrangement comprising: a laser diode (LD) mounting surface;
at least a first LD disposed on the LD mounting surface, the first
LD having a back-side emission surface for emitting a portion of
optical power along a first optical path; a base portion comprising
a feedthrough device, the feedthrough device providing a vertical
MPD mounting surface; a first MPD disposed on the vertical MPD
mounting surface, the first MPD having a light receiving region
optically aligned with the first LD via the first optical path
based at least in part on the vertical MPD mounting surface
extending substantially transverse relative to the LD mounting
surface such that the first optical path intersects with the light
receiving region of the first MPD; and a multi-channel receiver
optical subassembly arrangement.
17. The multi-channel optical transceiver of claim 16, wherein the
TOSA arrangement further comprises: a TOSA housing having a
plurality of sidewalls that define a cavity, the LD mounting
surface being disposed in the cavity; and wherein the feedthrough
device is configured to at least partially be disposed in the
cavity of the TOSA housing, and wherein a first end of the
feedthrough device provides an electrical coupling region to
electrically couple to an optical module substrate to receive a
radio frequency (RF) driving signal to drive the first LD, and a
second end of the feedthrough device defines the vertical MPD
mounting surface, the vertical MPD mounting surface being disposed
in the cavity of the TOSA housing.
18. The multi-channel optical transceiver of claim 17, wherein the
cavity of the TOSA housing is hermetically sealed to prevent
ingress of contaminants.
19. The multi-channel optical transceiver of claim 17, wherein at
least one sidewall of the plurality of sidewalls of the TOSA
housing provides a thermoelectric cooler (TEC) mounting section,
and wherein the TOSA provides: a thermoelectric cooler (TEC)
arrangement mounted to the TEC mounting section; and a LD submount
disposed on the TEC arrangement, the LD submount being in thermal
communication with the TEC arrangement, and wherein the LD submount
provides the LD mounting surface.
20. The multi-channel optical transceiver of claim 16, further
comprising a plurality of transmit (TX) radio frequency (RF)
traces, the TX RF traces being disposed on a surface of the base
portion that extends away from the vertical mounting surface along
a direction that is substantially parallel with the LD mounting
surface, and wherein the TX RF traces are disposed below the MPD
when mounted to the vertical MPD mounting surface to allow the TX
RF traces to extend towards the LD mounting surface.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to optical communications,
and more particularly, to a transmitter optical subassembly (TOSA)
arrangement having vertically-mounted monitor photodiodes to reduce
housing dimensions and improve radio frequency (RF) drive signal
quality.
BACKGROUND INFORMATION
[0002] Optical transceivers are used to transmit and receive
optical signals for various applications including, without
limitation, internet data center, cable TV broadband, and fiber to
the home (FTTH) applications. Optical transceivers provide higher
speeds and bandwidth over longer distances, for example, as
compared to transmission over copper cables. The desire to provide
higher transmit/receive speeds in increasingly space-constrained
optical transceiver modules has presented challenges, for example,
with respect to thermal management, insertion loss, RF driving
signal quality and manufacturing yield.
[0003] Optical transceiver modules generally include one or more
transmitter optical subassemblies (TOSAs) for transmitting optical
signals. TOSAs can include one or more lasers to emit one or more
channel wavelengths and associated circuitry for driving the
lasers. Some optical applications, such as long-distance
communication, can require TOSAs to include hermetically-sealed
housings with arrayed waveguide gratings, temperature control
devices, laser packages and associated circuitry disposed therein
to reduce loss and ensure optical performance. However, the
inclusion of hermetically-sealed components increases manufacturing
complexity, cost, and raises numerous non-trivial challenges within
space-constrained housings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] These and other features and advantages will be better
understood by reading the following detailed description, taken
together with the drawings wherein:
[0005] FIG. 1 is a block diagram of a multi-channel optical
transceiver module, consistent with embodiments of the present
disclosure.
[0006] FIG. 2 is a perspective view of an optical transceiver
module consistent with embodiments of the present disclosure.
[0007] FIG. 3 is a side view of the optical transceiver module of
FIG. 2 in accordance with an embodiment of the present
disclosure.
[0008] FIGS. 4-5 collectively show an example TOSA arrangement
suitable for use in the optical transceiver module of FIGS. 2-3, in
accordance with an embodiment of the present disclosure.
[0009] FIG. 6 is a top view of the example TOSA arrangement of
FIGS. 4-5, consistent with embodiments of the present
disclosure.
[0010] FIG. 7 shows an enlarged portion of a cavity of the example
TOSA arrangement of FIGS. 4-6, in accordance with an embodiment of
the present disclosure.
[0011] FIG. 8A is a side view of the example TOSA arrangement of
FIGS. 4-7, in accordance with an embodiment of the present
disclosure.
[0012] FIG. 8B is a cross-sectional view of the example TOSA
arrangement of FIG. 5 taken along line 8B-8B, in accordance with an
embodiment of the present disclosure.
[0013] FIG. 9 is another example TOSA arrangement suitable for use
in the optical transceiver module of FIGS. 2-3, in accordance with
an embodiment of the present disclosure.
[0014] FIG. 10 shows an existing approach to registering optical
power of a laser arrangement.
DETAILED DESCRIPTION
[0015] As discussed above, some TOSAs can reach optical
transmission distances of up to 10 km or more. Such TOSAs may be
suitable for use in C form-factor pluggable (CFP), CFP2, CFP4 and
quad small form-factor pluggable (QSFP) applications. In general,
such TOSAs include a hermetic-sealed package (or housing) with an
LC receptacle (or other suitable port) for optical coupling. The
hermetic-sealed package can house laser packages, e.g.,
electro-absorption modulator integrated lasers (EMLs), power
monitors photodiodes (PDs), thermoelectric coolers (TECs), an
optical multiplexer such as an arrayed waveguide grating (AWG) for
multiplexing multiple channel wavelengths, and electrical
interconnects such as flexible printed circuit boards, and optical
interconnects such as fiber stubs. Hermetic-sealed packages can
include cavities specifically designed to house such components in
a manner that optimizes the space constraints and promotes thermal
communication. However, manufacturing hermetic-sealed packages with
the dimensions necessary to fit the components of the light engine
increases manufacturing cost and complexity.
[0016] One component in such TOSAs that can result in increased
cost and complexity is monitor photodiodes (MPDs). MPDs can be used
to monitor optical power of a corresponding laser diode. However,
existing approaches tend to position MPDs behind, in front of, or
otherwise adjacent an associated laser diode. In some cases, MPDs
are mounted to the same substrate as the associated LD. For
example, FIG. 10 shows one example of laser arrangement 1000
whereby a sidewall of a TOSA housing 1004 supports a substrate 1002
(or submount), and the substrate 1002 and/or the surface of the
TOSA housing 1004 supports LD 1008 and the MPD 1006. One position
utilized for registering optical power from an LD by an MPD 1006 is
directly behind the LD 1008 to receive a small portion of optical
power 1011 emitted by the LD 1008 backwards away from a transmit
(TX) waveguide, e.g., an optical fiber. Another position includes
mounting the MPD 1006 below or otherwise in front of the LD 1008 to
directly receive the optical power 1010 emitted by the LD 1008.
[0017] In either case, the TOSA housing 1004 must be dimensioned to
accommodate the position of the MPD 1006, with the result being an
overall increase in housing length along dimension D. This results
in two significant challenges for TOSA designs. First, the position
of the MPD, e.g., behind the LD 1008, can require that interconnect
circuitry such as wire bonds 1014 that extend from the laser diode
driver (LDD) 1012 to the LD 1008 must be lengthened to route
over/around the MPD 1006. Extending and routing the wire bonds 1014
in this fashion can result in time-of-flight (TOF) delays and
impedance matching issues as well as worse RF performance. Second,
increasing the overall length can increase the overall volume of
the TOSA housing cavity and the complexity in the manufacture of
the TOSA. In scenarios where hermetically-sealed housings are
utilized, this can result in a significantly higher cost and time
per unit to manufacture, which can ultimately reduce yield.
[0018] Thus, the present disclosure is generally directed to a
multi-channel TOSA with vertically-mounted MPDs to reduce TOSA
housing dimensions and improve RF driving signal quality. In more
detail, a TOSA housing consistent with the present disclosure
includes at least one vertical MPD mounting surface that extends
substantially transverse relative to a LD mounting surface, with
the result being that a MPD coupled to the vertical MPD mounting
surface gets positioned above an associated LD coupled to the LD
mounting surface. The vertically-mounted MPD thus makes regions
adjacent an LD that would otherwise be utilized to mount an MPD
available for patterning of conductive RF traces to provide an RF
driving signal to the LD. The conductive RF traces may therefore
extend below the vertically-mounted MPD to a location that is
proximate the LD to allow for relatively short wire bonds
therebetween.
[0019] In a specific example embodiment, the vertical MPD mounting
surface may be provided at least in part by a feedthrough device of
the TOSA housing. The feedthrough device can be configured to be at
least partially disposed in a hermetically-sealed cavity of the
TOSA housing to provide electrical connectivity to optical
components therein. The feedthrough device may also provide a
conductive trace mounting surface that extends substantially
transverse relative to the vertical MPD mounting surface for
purposes of patterning the above-discussed conductive RF traces.
Accordingly, an MPD may be securely mounted to the feedthrough
device prior to insertion of the feedthrough device into a TOSA
housing. Likewise, the conductive RF traces and other associated
circuitry (e.g., filtering capacitors, conductive direct current
(DC) traces, and so on) may be patterned/disposed when the
feedthrough device is outside of the TOSA housing. Thus, insertion
of the feedthrough device within the TOSA housing can result in the
vertically-mounted MPD being passively optically aligned with an
associated LD, and the conductive RF traces being brought within a
predefined distance of the LD for electrical coupling purposes via,
for instance, wire bonds.
[0020] The present disclosure therefore provides numerous
advantageous over other TOSA approaches. For example, manufacturing
of a TOSA may be conducted in a modular fashion whereby a
feedthrough device and TOSA housing may be manufactured and
configured separate from each other. For instance, components such
as conductive traces and MPDs may be mounted/coupled to the
feedthrough device in a parallel manufacturing process to allow for
the TOSA housing and associated components to be completed apart
from the feedthrough device, with the net result decreasing
production time, reducing errors, and ultimately increasing yield.
In addition, a TOSA housing with vertically-mounted MPDs consistent
with the present disclosure advantageously reduces overall housing
dimensions while allowing for LDs to be disposed in close proximity
of conductive traces for electrical coupling purposes. RF signal
quality may therefore be enhanced via relatively short wire bonds,
for example, while simultaneously reducing cost, time-per-unit, and
complexity to manufacture each TOSA.
[0021] As used herein, the terms hermetic-sealed and
hermetically-sealed may be used interchangeably and refer to a
housing that releases a maximum of about 5*10-8 cc/sec of filler
gas. The filler gas may comprise an inert gas such as nitrogen,
helium, argon, krypton, xenon, or various mixtures thereof,
including a nitrogen-helium mix, a neon-helium mix, a
krypton-helium mix, or a xenon-helium mix.
[0022] As used herein, "channel wavelengths" refer to the
wavelengths associated with optical channels and may include a
specified wavelength band around a center wavelength. In one
example, the channel wavelengths may be defined by an International
Telecommunication (ITU) standard such as the ITU-T dense wavelength
division multiplexing (DWDM) grid. This disclosure is equally
applicable to coarse wavelength division multiplexing (CWDM). In
one specific example embodiment, the channel wavelengths are
implemented in accordance with local area network (LAN) wavelength
division multiplexing (WDM), which may also be referred to as
LWDM.
[0023] The term "coupled" as used herein refers to any connection,
coupling, link or the like and "optically coupled" refers to
coupling such that light from one element is imparted to another
element. Such "coupled" devices are not necessarily directly
connected to one another and may be separated by intermediate
components or devices that may manipulate or modify such signals.
On the other hand, the term "direct optical coupling" refers to an
optical coupling via an optical path between two elements that does
not include such intermediate components or devices, e.g., a
mirror, waveguide, and so on, or bends/turns along the optical path
between two elements.
[0024] The term substantially, as generally referred to herein,
refers to a degree of precision within acceptable tolerance that
accounts for and reflects minor real-world variation due to
material composition, material defects, and/or
limitations/peculiarities in manufacturing processes. Such
variation may therefore be said to achieve largely, but not
necessarily wholly, the stated characteristic. To provide one
non-limiting numerical example to quantify "substantially," minor
variation may cause a deviation of up to and including .+-.5% from
a particular stated quality/characteristic unless otherwise
provided by the present disclosure.
[0025] Referring to the Figures, FIG. 1, an optical transceiver
100, consistent with embodiments of the present disclosure, is
shown and described. In this embodiment, the optical transceiver
100 includes a multi-channel TOSA arrangement and a multi-channel
ROSA arrangement 106 coupled to a substrate 102, which may also be
referred to as an optical module substrate. The substrate 102 may
comprise, for example, a printed circuit board (PCB) or PCB
assembly (PCBA). The substrate 102 may be configured to be
"pluggable" for insertion into an optional transceiver cage
109.
[0026] In the embodiment shown, the optical transceiver 100
transmits and receives four (4) channels using four different
channel wavelengths (.lamda.1, .lamda.2, .lamda.3, .lamda.4) via
the multi-channel TOSA arrangement 104 and the multi-channel ROSA
arrangement 106, respectively, and may be capable of transmission
rates of at least about 25 Gbps per channel. In one example, the
channel wavelengths .lamda.1, .lamda.2, .lamda.3, .lamda.4 may be
1270 nm, 1290 nm, 1310 nm, and 1330 nm, respectively. Other channel
wavelengths are within the scope of this disclosure including those
associated with local area network (LAN) wavelength division
multiplexing (WDM). The optical transceiver 100 may also be capable
of transmission distances of 2 km to at least about 10 km. The
optical transceiver 100 may be used, for example, in internet data
center applications or fiber to the home (FTTH) applications.
Although the following examples and embodiments show and describe a
4-channel optical transceiver, this disclosure is not limited in
this regard. For example, the present disclosure is equally
applicable to 2, 6, or 8-channel configurations.
[0027] In more detail, the multi-channel TOSA arrangement 104
includes a TOSA housing 114 with a plurality of sidewalls that
define an optical component cavity 220, which may be referred to as
simply a cavity (See FIG. 4). The cavity 220 includes a plurality
of laser arrangements 110 disposed therein, which will be discussed
in more detail below, with each laser arrangement of the plurality
of laser arrangements 110 being configured to transmit optical
signals having different associated channel wavelengths. Each laser
arrangement may include passive and/or active optical components
such as a laser diode (LD), monitor photodiode (MPD), laser diode
driver (LDD), and so on. Additional components comprising each
laser arrangement include filters, focusing lenses, filtering
capacitors, and so on.
[0028] To drive the plurality of laser arrangements 110, the
optical transceiver 100 includes a transmit connecting circuit 112
to provide electrical connections to the plurality of laser
arrangements 110 within the housing 114. The transmit connecting
circuit 112 may be configured to receive driving signals (e.g.,
TX_D1 to TX_D4) from, for example, circuitry within the optical
transceiver cage 109. As shown, the housing 114 may be hermetically
sealed to prevent ingress of foreign material, e.g., dust and
debris. Therefore, a plurality of transit (TX) traces 117 (or
electrically conductive paths) are patterned on at least one
surface of the substrate 102 and are electrically coupled with a
feedthrough device 116 of the TOSA housing 114 to bring the
transmit connecting circuit 112 into electrical communication with
the plurality of laser arrangements 110, and thus, electrically
interconnect the transmit connecting circuit 112 with the
multi-channel TOSA arrangement 104. The feedthrough device 116 may
comprise, for instance, ceramic, metal, or any other suitable
material.
[0029] In operation, the multi-channel TOSA arrangement 104 may
then receive driving signals (e.g., TX_D1 to TX_D4), and in
response thereto, generates and launches multiplexed channel
wavelengths on to an output waveguide 120 such as a transmit
optical fiber. The generated multiplexed channel wavelengths may be
combined based on a multiplexing device 124 such as an arrayed
waveguide grating (AWG) that is configured to receive emitted
channel wavelengths 126 from the plurality of laser assemblies 110
and output a signal carrying the multiplexed channel wavelengths on
to the output waveguide 120 by way of optical fiber receptacle
122.
[0030] Continuing on, the multi-channel ROSA arrangement 106
includes a demultiplexing device 124, e.g., an arrayed waveguide
grating (AWG), a photodiode (PD) array 128, and an amplification
circuitry 130, e.g., a transimpedance amplifier (TIA). An input
port of the demultiplexing device 124 may be optically coupled with
a receive waveguide 134, e.g., an optical fiber, by way of an
optical fiber receptacle 136. An output port of the demultiplexing
device 124 may be configured to output separated channel
wavelengths on to the PD array 128. The PD array 128 may then
output proportional electrical signals to the TIA 130, which then
may be amplified and otherwise conditioned. The PD array 128 and
the transimpedance amplifier 136 detect and convert optical signals
received from the receive waveguide 134, e.g., an optical fiber,
into electrical data signals (RX_D1 to RX_D4) that are output via
the receive connecting circuit 108. In operation, the PD array 128
may then output electrical signals carrying a representation of the
received channel wavelengths to a receive connecting circuit 132 by
way of conductive traces 119 (which may be referred to as
conductive paths).
[0031] Referring now to FIGS. 2-3, an example optical transceiver
module 200 is shown consistent with an embodiment of the present
disclosure. The optical transceiver module 200 may be implemented
as the optical transceiver 100 of FIG. 1, the discussion of which
is equally applicable to FIGS. 2-3 and will not be repeated for
purposes of brevity. As shown, the optical transceiver module 200
includes a substrate 202 that extends from a first end 252 to a
second end 254 along a longitudinal axis 250. The first end 252 may
electrically couple to a transceiver cage to receive driving
signals, e.g., TX_D1 to TX_D4, and therefore, may be referred to as
an electrical coupling end. On the other hand, the second end 254
includes a multi-channel TOSA arrangement 204 and a multi-channel
ROSA arrangement 206 for sending and receiving channel wavelengths,
respectively, and therefore may be referred to as an optical
coupling end.
[0032] In more detail, the substrate includes at least a first
mounting surface 256 for mounting of optical components, patterning
of conductive traces (e.g., conductive traces 117, 119). Disposed
adjacent the first end 252, the substrate 202 includes a plurality
of pads/terminals for electrically communicating with, for
instance, associated circuitry in a transceiver cage. The substrate
202 includes a multi-channel TOSA arrangement 204 and multi-channel
ROSA arrangement 206 disposed adjacent the second end. The
multi-channel ROSA arrangement includes amplification circuitry
230, a PD array 228, and a demultiplexing device 224 disposed
thereon. An input port 235 of the demultiplexing device 224 may be
coupled to an optical coupling receptacle 236 by way of a receive
intermediate fiber 268. Accordingly, the demultiplexing device 224
can receive a multiplexed signal 264 from a receive waveguide,
e.g., the receive waveguide 134 of FIG. 1. An output port of the
demultiplexing device 224 may be optically aligned with the PD
array 228 and output separated channel wavelengths thereon.
Electrical signals representative of the separated channel
wavelengths may then be amplified/filtered by the amplification
circuitry before being passed to the receive connecting circuit
132.
[0033] As shown, the TOSA housing 214 is defined by a plurality of
sidewalls. A first end 258 of the TOSA housing edge mounts to, and
electrically couples with, the second end 258 of the substrate 202.
A second end 259 of the TOSA housing 214 couples to an optical
coupling receptacle 222 by way of a transmit intermediate fiber
269. The first end 258 of the TOSA housing 214 may also be referred
to as an electrical coupling end, and the second end 259 may also
be referred to as an optical coupling end. In an embodiment, the
TOSA housing 214 may be securely attached to the substrate 202 via
one or more electrical interconnect devices as discussed and
described in greater detail in co-pending U.S. patent application
Ser. No. 16/116,087 filed on Aug. 29, 2018 and entitled
"Transmitter Optical Subassembly with Hermetically-Sealed Light
Engine and External Arrayed Waveguide Grating", the teaching of
which are hereby incorporated in their entirety.
[0034] In an embodiment, the TOSA housing 214 of the multi-channel
TOSA arrangement 204 may be hermetically sealed, although in other
embodiments the housing may not necessarily be hermetically sealed.
Accordingly, the multi-channel TOSA arrangement 204 may also be
referred to as a hermetically-sealed light engine that may be
particularly well suited for long-distance transmission, e.g., up
to and beyond 10 km. The TOSA housing 214 can include a feedthrough
device 262 at least partially disposed in a cavity of the TOSA
housing 214 to allow for electrical interconnection between the
substrate 202 and the multi-channel TOSA arrangement 204. The
housing 214 may include a longitudinal axis that extends
substantially parallel relative to the longitudinal axis 250 of the
substrate 202. The housing 214 may comprise, for example, metal,
plastic, ceramic, or any other suitable material. The housing 214
may be formed from multiple pieces, or a single piece, of
material.
[0035] The housing 214 may further define a laser cavity 220 (FIG.
4) which may be filled with an inert gas to form an inert
atmosphere. In one embodiment, the inert atmosphere sealed within
the hermetically-sealed container comprises nitrogen, and
preferably, 1 atmosphere (ATM) of nitrogen. The inert atmosphere
may also be formed from nitrogen, helium, argon, krypton, xenon, or
various mixtures thereof, including a nitrogen-helium mix, a
neon-helium mix, a krypton-helium mix, or a xenon-helium mix. The
inert gas or gas mix included within the hermetically-sealed cavity
220 may be selected for a particular refractive index or other
optical property. Gases may also be selected based on their ability
to promote thermal insulation. For instance, Helium is known to
promote heat transfer may be utilized alone or in addition to
others of the aforementioned gases. In any event, the terms
hermetic-sealed and hermetically-sealed may be used interchangeably
and refers to a housing that releases a maximum of about 5*10-8
cc/sec of filler gas.
[0036] Turning to FIGS. 4-7, an example embodiment of the TOSA
housing 214 of the multi-channel TOSA arrangement 204 is shown in
isolation. As shown, the housing 214 extends from a first end 452
to a second end 454 along a longitudinal axis 450. A plurality of
sidewalls 214-1 to 214-6 define the TOSA housing 214 and a cavity
220 therebetween. Note, the embodiment shown in FIG. 4 omits the
sidewall 214-6 (FIG. 2) that forms a cover portion merely for
purposes of clarity.
[0037] The feedthrough device 262 at least partially defines the
first end 452 of the TOSA housing 214 and includes a plurality of
electrical interconnects 464, e.g., bus bars, external to the
cavity 220 for mounting to and electrically coupling with the
substrate 102. The plurality of electrical interconnects 464 can
provide power and radio frequency (RF) driving signals to the
plurality of laser arrangements 210. The feedthrough device 262
further includes at least one mounting surface such as a vertical
monitor photodiode (MPD) mounting surface, which will be discussed
in greater detail below.
[0038] Following the feedthrough device 262 within the cavity 220,
a plurality of laser arrangements 210 are disposed on and are
supported by a mounting surface provided at least in part by the
sidewall 214-4. A multiplexing device 224 is also disposed on and
supported by the mounting surface provided at least by the sidewall
214-4. The multiplexing device 224 includes a plurality of input
ports 456, with each input port being optically aligned with an
associated laser arrangement of the plurality of laser arrangements
210. The multiplexing device 224 further includes an output port
458 which is shown more clearly in FIG. 6. The output port 458 of
the multiplexing device 224 is optically aligned with an aperture
462 defined by the sidewall 214-3 of the TOSA housing 214. The
aperture 462 may then transition to a fiber coupling receptacle
462, with the fiber coupling receptacle 462 being configured to
receive the intermediate optical fiber 269 (FIG. 2).
[0039] Thus, in operation, the multiplexing device 224 receives
channel wavelengths 466 emitted by the plurality of laser
assemblies along direction D1 at the plurality of inputs and then
outputs a multiplexed signal 468 having each of the emitted channel
wavelengths 466 for transmission via an external transmit optical
fiber, for example.
[0040] FIG. 7 shows an enlarged perspective view of the cavity 220
of the housing 214 in accordance with an embodiment. As shown, the
feedthrough device 262 includes a step/shoulder configuration
defined by a first mounting surfacing 702 that extends in parallel
with the longitudinal axis 450 of the TOSA housing 214, a second
mounting surface 704 that extends parallel with the first mounting
surface, and a third mounting surface 706 that adjoins the first
and second mounting surfaces 702, 704 and extends substantially
transverse to each of the same. Thus, the first, second and third
mounting surfaces 702, 704 and 706 provide a multi-tiered or
multi-step mounting structure for coupling to optical components.
Each of the mounting surfaces of the feedthrough device 262 will
now be discussed in turn.
[0041] The first mounting surface 702 includes a first plurality of
conductive traces/paths 708 patterned thereon. The first plurality
of conductive traces 708 may be configured to provide power from
the substrate 202 and to pass data signals from a plurality of MPDs
712 that are mounted to and supported by the third mounting
surface. To this end, the first mounting surface 702 may also be
referred to as a MPD trace mounting surface/section. The second
mounting surface 704 includes a second plurality of conductive
traces/paths 711 disposed thereon. The second plurality of
conductive traces/paths 711 may be configured to provide power and
data signals from the substrate 202 to each of the plurality of
lasers arrangements 210. To this end, the second mounting surface
704 may be referred to as a LD trace mounting surface/section.
[0042] Continuing on, the third mounting surface 706 extends
substantially transverse relative to the first and second mounting
surfaces 702, 704 and adjoins the same, as discussed above. The
third mounting surface 706 may be configured to mount and support a
plurality of MPDs shown collectively as 712 and individually as
712-1 to 712-4. Each MPD of the plurality of MPDs 712 may be
supported by a MPD submount 714, with the MPD submount 714
providing electrical traces for electrically interconnecting MPDs
to associated conductive traces of the MPD trace mounting section
708. The MPD submount 714 may be a single piece, e.g., a single PCB
or other suitable substrate, or may be multiple pieces. One
advantage of a single piece MPD submount 714 is that attachment and
alignment of MPDs to the feedthrough device 262 can be simplified
as each MPD may be placed on to the MPD submount 714 at predefined
positions prior to insertion of the feedthrough device 262 into the
cavity 202 of the housing 214. Accordingly, coupling the MPD
submount 714 to the feedthrough device 262 optically aligns each of
the MPDs disposed thereon without necessarily performing additional
alignment steps.
[0043] As further shown, each MPD of the plurality of MPDs 712
includes a light receiving region, e.g., light receiving surface
716-4 of MPD 712-4 shown in FIG. 8B, on an upper/top surface of
each chip that is optically aligned with a corresponding laser
arrangement of the plurality of laser arrangements 210. This
vertical mounting of each MPD allows for a smaller overall
footprint for the feedthrough device 262, and by extension,
shortens the overall length of the TOSA housing 214. This vertical
mounting configuration achieves housing size reduction by freeing
the space behind/adjacent each laser arrangement to permit the LD
traces of the second mounting surface 704 to extend below the
plurality of MPDs 712 and be disposed in close proximity of the
plurality of laser assemblies 201. This removal of the MPDs from
being behind/adjacent a corresponding laser arrangement also
advantageously allows for relatively short electrical
interconnection via wire bonding between the LD traces of the
second mounting surface 704 and each laser arrangement, which
reduces issues such as time of flight (TOF) and impedance
mismatching that can ultimately degrade RF signal quality.
[0044] Continuing on, each of the plurality of laser arrangements
210 includes a laser diode supported by a laser submount 213 and
optional thermoelectric cooling (TEC) arrangement. For instance,
the laser arrangement 210-4 associated with channel 4 (CH4)
includes a laser diode 211-4 mounted to and supported by the laser
diode submount 213. As shown in the cross-sectional view of FIG.
8B, the laser diode submount 213 is mounted to and is supported by
TEC devices 720. In turn, TEC devices 720 are mounted to and
supported by a surface provided by sidewall 214-4 of the TOSA
housing 214. The laser diode submount may also support thermistors
such as thermistor 724-4 (FIG. 7). Following the plurality of laser
assemblies 210, each laser arrangement can include a focusing lens
e.g., focusing lens 726-4, mounted to and supported by the laser
diode submount 713. The laser submount 213 may comprise a single
piece, such as shown, or may be formed from multiple pieces.
[0045] Following the plurality of laser arrangements 210, the
multiplexing device 224 is mounted to and is supported by a
multiplexing submount 720. The input ports 456 of the multiplexing
device 224 are optically aligned with the plurality of laser
arrangements 210. To this end, a plurality of optical paths 850
extend longitudinally through the cavity 220, with each optical
path extending from a corresponding laser diode. A portion of
optical power, e.g., 2% or less, gets emitted from a surface
opposite the emission face of each LD (also known as a back-side
emission surface) and is registered by each MPD, e.g., converted to
a proportional electrical current, to form a feedback loop to
ensure optical power. Thus, each of the plurality of optical paths
850 also intersects with the vertically mounted MPDs 712, and more
particularly, a light receiving region of each corresponding
vertically mounted MPDs 712, e.g., light receiving region
716-4.
[0046] During operation, channel wavelengths emitted by each of the
plurality of laser assemblies 210 is launched on to a corresponding
path of the plurality of optical paths 850, with each of the
plurality of optical paths 850 extending substantially parallel
relative to each other. As discussed above, a portion of the
optical power gets emitted from a surface opposite of the emission
surface of each laser diode, which may be referred to as a
back-side emission surface, thus launching a portion of optical
power towards the MPDs 712. Each light receiving region of the
MPDs, e.g., light receiving region 716-4, then registers this
portion of optical power for purposes of providing a feedback loop,
e.g., by converting optical power to a proportional electrical
current. The emitted channel wavelengths then get received via
input ports 456 of the multiplexing device 224. The multiplexing
device 224 then combines the received channel wavelengths into a
multiplexed optical signal 263 (see FIG. 2). At an output 458 of
the multiplexing device 224 the multiplexed signal 263 is output
via the aperture on to the intermediate optical fiber 269 (See FIG.
2), and then ultimately to an external transmit optical fiber (not
shown).
[0047] FIG. 9 shows another example embodiment of a TOSA housing
204' in accordance with aspects of the present disclosure. As
shown, the TOSA housing 204' includes a plurality of sidewalls to
provide a cavity therebetween, which is substantially similar to
that of the TOSA housing 204. However, the TOSA housing 204' does
not include a multiplexing device within the cavity and instead
couples to a first end of a plurality of waveguides (not shown),
e.g., optical fibers, via apertures 480-1 to 480-4. A second end of
the plurality of waveguides may be optically coupled to an external
multiplexing device, such as an AWG. This allows the TOSA 204' to
have a relatively small overall footprint, which can significantly
reduce overall costs and complexity that characterizes
hermetically-sealed housing. Put simply, the lesser the volume and
number of passive/optical components within the cavity of the TOSA
housing 204', the less the complexity, time and cost necessary to
manufacture the TOSA housing 204'. The feedthrough device 262' may
be configured substantially similar to that of the feedthrough
device 262, the description of which is equally applicable to the
embodiment of FIG. 9 but will not be repeated for brevity. For
instance, the vertical MPD mounting surface 490 allows for MPDs to
be mounted thereon to advantageously reduce the overall length of
the TOSA housing 204' relative to other approaches that place MPDs
behind or otherwise adjacent corresponding LDs.
[0048] In accordance with an aspect of the present disclosure a
transmitter optical subassembly (TOSA) module is disclosed. The
TOSA module comprising a laser diode (LD) mounting surface, at
least a first LD disposed on the LD mounting surface, the first LD
having a back-side emission surface for emitting a portion of
optical power along a first optical path, a base portion providing
a vertical MPD mounting surface, and a first MPD disposed on the
vertical MPD mounting surface, the first MPD having a light
receiving region optically aligned with the first LD via the first
optical path based at least in part on the vertical MPD mounting
surface extending substantially transverse relative to the LD
mounting surface such that the first optical path intersects with
the light receiving region of the first MPD.
[0049] In accordance with another aspect of the present disclosure
a method for optically coupling monitor photodiodes (MPDs) to
corresponding laser diodes (LDs) in a multi-channel optical
transceiver (TOSA) housing is disclosed. The method comprising
mounting at least one MPD to a vertical MPD mounting surface
provided by a feedthrough device, patterning a plurality of
conductive traces on to one or more surfaces of the feedthrough
device, and inserting the feedthrough device into a cavity of the
TOSA housing to bring the plurality of conductive traces into close
proximity with the LDs in the TOSA, wherein inserting the
feedthrough device into the cavity causes each of the at least one
MPDs mounted to the vertical MPD mounting surface to optically
couple with a back-side emission surface of each corresponding
LD.
[0050] In accordance with yet another aspect of the present
disclosure a multi-channel optical transceiver module is disclosed.
The multi-channel optical transceiver including a printed circuit
board assembly (PCBA), a transmitter optical subassembly (TOSA)
arrangement coupled to the PCBA, the TOSA arrangement comprising a
laser diode (LD) mounting surface, at least a first LD disposed on
the LD mounting surface, the first LD having a back-side emission
surface for emitting a portion of optical power along a first
optical path, a base portion providing a vertical MPD mounting
surface, a first MPD disposed on the vertical MPD mounting surface,
the first MPD having a light receiving region optically aligned
with the first LD via the first optical path based at least in part
on the vertical MPD mounting surface extending substantially
transverse relative to the LD mounting surface such that the first
optical path intersects with the light receiving region of the
first MPD.
[0051] While the principles of the disclosure have been described
herein, it is to be understood by those skilled in the art that
this description is made only by way of example and not as a
limitation as to the scope of the disclosure. Other embodiments are
contemplated within the scope of the present disclosure in addition
to the exemplary embodiments shown and described herein.
Modifications and substitutions by one of ordinary skill in the art
are considered to be within the scope of the present disclosure,
which is not to be limited except by the following claims.
* * * * *