U.S. patent application number 15/759100 was filed with the patent office on 2018-10-04 for multi-channel transmitter optical subassembly (tosa) with an optical coupling receptacle providing an off-center fiber.
The applicant listed for this patent is Applied Optoelectronics Inc.. Invention is credited to I-Lung HO, Kai-Sheng LIN, Chong WANG, Jun ZHENG.
Application Number | 20180284366 15/759100 |
Document ID | / |
Family ID | 58239849 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180284366 |
Kind Code |
A1 |
LIN; Kai-Sheng ; et
al. |
October 4, 2018 |
MULTI-CHANNEL TRANSMITTER OPTICAL SUBASSEMBLY (TOSA) WITH AN
OPTICAL COUPLING RECEPTACLE PROVIDING AN OFF-CENTER FIBER
Abstract
A multi-channel transmitter optical subassembly (TOSA) with an
off-center fiber in an optical coupling is disclosed, and can
provide passive compensation for beam displacement introduced by
optical isolators. The optical coupling receptacle can include an
optical isolator configured to receive a focused light beam from a
focus lens within the TOSA. The optical coupling receptacle may be
offset such that a center line of the focused light beam entering
the optical isolator is offset from a center line of a fiber within
optical coupling receptacle. Thus the optical isolator receives the
focused light beam from the focus lens and introduces beam
displacement such that an optical signal is launched generally
along a center line of the fiber. Thus the expected beam
displacement introduced by the optical isolator is eliminated or
otherwise mitigated by the offset between a center line of the
fiber and a center position of the focus lens.
Inventors: |
LIN; Kai-Sheng; (Sugar Land,
TX) ; HO; I-Lung; (Sugar Land, TX) ; ZHENG;
Jun; (Missouri City, TX) ; WANG; Chong;
(Stafford, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Optoelectronics Inc. |
Sugar Land |
TX |
US |
|
|
Family ID: |
58239849 |
Appl. No.: |
15/759100 |
Filed: |
September 6, 2016 |
PCT Filed: |
September 6, 2016 |
PCT NO: |
PCT/US16/50401 |
371 Date: |
March 9, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14850367 |
Sep 10, 2015 |
9696503 |
|
|
15759100 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4292 20130101;
G02B 6/4246 20130101; G02B 6/4263 20130101; H04B 10/40 20130101;
H01S 5/0078 20130101; G02B 6/4209 20130101; G02B 6/4228 20130101;
G02B 6/32 20130101; G02B 6/4215 20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42; H04B 10/40 20130101 H04B010/40; H01S 5/00 20060101
H01S005/00; G02B 6/32 20060101 G02B006/32 |
Claims
1. A multi-channel transmitter optical subassembly (TOSA) including
a plurality of lasers, the TOSA comprising: a housing including a
plurality of sidewalls, the plurality of sidewalls forming a
compartment defined by an inner surface therein, the compartment
including a light path, the light path being optically coupled to
each of the plurality of lasers and extending laterally from a
first end to a second end of the housing along a first major axis;
a focus lens disposed at the second end of the housing configured
to receive at least a portion of light emitted by the plurality of
lasers via the light path and to output a focused light beam; and
an optical coupling receptacle fixedly attached to the second end
of the housing and configured to couple the light path to a fiber,
the optical coupling receptacle including an optical isolator
configured to receive the focused light beam and launch the focused
light beam in a forward direction into the fiber while reducing
backreflection, wherein a center line of the fiber is offset from a
center of the focus lens, and wherein the offset passively
compensates for beam displacement introduced by the optical
isolator such that the focused light beam is launched generally
into a center of the fiber.
2. The multi-channel TOSA of claim 1, wherein the offset between
the center line of the fiber and the center of the focus lens is
about 50 microns.
3. The multi-channel TOSA of claim 1, wherein the offset between
the center line of the fiber and the center of the focus lens is at
least 10 microns.
4. The multi-channel TOSA of claim 1, wherein the offset between
the center line of the fiber and the center of the focus lens is
based at least in part on a physical position of the optical
coupling receptacle relative to the position of the focus lens.
5. The multi-channel TOSA of claim 4, wherein the optical isolator
is angled in the optical coupling receptacle at about 8 degrees
relative to a center line of the focused light beam.
6. The multi-channel TOSA of claim 1, wherein the plurality of
lasers comprise TO can laser packages.
7. The multi-channel TOSA of claim 6, further comprising filters
aligned with the TO can laser packages to pass and reflect laser
light at associated channel wavelengths.
8. The multi-channel TOSA of claim 1, wherein the optical coupling
receptacle is configured to optically couple a signal having
multiple different channel wavelengths to a transmit optical
fiber.
9. An optical transceiver module comprising: a transceiver housing;
a multi-channel transmitter optical subassembly (TOSA) having a
plurality of transistor outline (TO) can laser packages fixedly
attached thereto and located in the transceiver housing for
transmitting optical signals at different channel wavelengths, the
TOSA comprising: a housing including a plurality of sidewalls, the
plurality of sidewalls forming a compartment defined by an inner
surface therein, the compartment including a light path, the light
path being optically coupled to each of the plurality of TO can
laser packages and extending laterally from a first end to a second
end of the housing along a first major axis; a focus lens disposed
at the second end of the housing configured to receive at least a
portion of light emitted by the plurality of lasers via the light
path and to output a focused light beam; and an optical coupling
receptacle fixedly attached to the second end of the housing and
configured to couple the light path to a fiber, the optical
coupling receptacle including an optical isolator configured to
receive the focused light beam and launch the focused light beam in
a forward direction into the fiber while reducing backreflection,
wherein a center line of the fiber is offset from a center of the
focus lens, and wherein the offset passively compensates for beam
displacement introduced by the optical isolator such that the
focused light beam is launched generally into a center of the
fiber; a multi-channel receiver optical assembly (ROSA) located in
the transceiver housing for receiving optical signals at different
channel wavelengths.
10. The optical transceiver module of claim 9, wherein the offset
between the center line of the fiber and the center of the focus
lens is about 50 microns.
11. The optical transceiver module of claim 9, wherein the offset
between the center line of the fiber and the center of the focus
lens is at least 10 microns.
12. The optical transceiver module of claim 9, wherein the offset
between the center line of the fiber and the center of the focus
lens of the is based at least in part on a physical position of the
optical coupling receptacle relative to the focus lens.
13. The optical transceiver module of claim 12, wherein the optical
isolator is angled at about 8 degrees relative to a center line of
the focused light beam.
14. The optical transceiver module of claim 9, wherein the
plurality of TO can laser packages comprise at least four TO can
laser packages.
15. The optical transceiver module of claim 9, wherein the
multi-channel TOSA includes integrated multiplexing optics
configured to launch an optical signal into a transmit fiber, the
optical signal having multiple different channel wavelengths.
16. The optical transceiver module of claim 15, wherein the
integrated multiplexing optics provide course wavelength division
multiplexing (CWDM).
17. The optical transceiver module of claim 15, wherein the
integrated multiplexing optics include filters aligned with
respective ones of the TO can laser packages to pass and reflect
laser light at associated channel wavelengths.
18. The optical transceiver module of claim 9, wherein the optical
coupling receptacle is fixedly attached to a sidewall opening at an
end of the housing of the multi-channel TOSA.
19. The optical transceiver module of claim 9, wherein the optical
isolator comprises a plurality of isolator chips in series.
20. The optical transceiver module of claim 9, wherein the optical
transceiver is a Quad Small Form-factor Pluggable (QSFP)
transceiver module and the multi-channel TOSA is configured to
transmit at four different channel wavelengths at transmission
rates of at least about 10 Gbps per channel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to co-pending U.S. application
Ser. No. 14/837,993 titled "Multi-Channel Transmitter Optical
Subassembly (TOSA) With Opposing Placement of Transistor Outline
Can Laser Packages" filed on Aug. 27, 2015, which is herein
incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to optical transceiver
modules, and more particularly, to a multi-channel transmitter
optical subassembly (TOSA) configured to couple to and launch an
optical signal into an off-center fiber in order to passively
compensate for beam displacement introduced by an optical
isolator.
BACKGROUND INFORMATION
[0003] 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 speeds in smaller optical transceiver modules for a lower
cost has presented challenges, for example, with respect to
maintaining optical efficiency (power), thermal management,
insertion loss, and manufacturing yield.
[0004] Optical transceiver modules generally include one or more
transmitter optical subassemblies (TOSAs) for transmitting optical
signals. One consideration in maintaining TOSA performance is
backreflection of laser light. Backreflection can occur when, for
example, laser energy incident to a laser cavity reflects back in
the direction it originated from. To minimize or otherwise mitigate
backreflection, TOSAs can include passive optics such as an optical
isolator. Optical isolators allow the transmission of light in only
one direction, and thus, prevent or otherwise mitigate
backreflection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] These and other features and advantages will be better
understood by reading the following detailed description, taken
together with the drawings wherein:
[0006] FIG. 1 schematically illustrates an embodiment of an optical
transceiver module including a multi-channel transmitter optical
subassembly (TOSA) and a multi-channel receiver optical subassembly
(ROSA).
[0007] FIG. 2 is a perspective view of an example small form-factor
(SFF) pluggable transceiver with a multi-channel TOSA and a
multi-channel ROSA, in accordance with an embodiment of the present
disclosure.
[0008] FIG. 3 is a perspective view of an embodiment of the
multi-channel TOSA for use in the optical transceiver shown in FIG.
2.
[0009] FIG. 4A is a cross-sectional view of the multi-channel TOSA
of FIG. 3 taken along the line A-A, in accordance with an
embodiment of the present disclosure.
[0010] FIG. 4B is a plan view of the multi-channel TOSA of FIG. 3
and illustrates internal optical components along a light path that
extends laterally to an off-center fiber within an optical coupling
receptacle of the multi-channel TOSA, in accordance with an
embodiment of the present disclosure.
[0011] FIG. 4C shows another plan view of the multi-channel TOSA of
FIG. 3, and illustrates a fiber having a center line offset
relative to the center of a focus lens within the multi-channel
TOSA, in accordance with an embodiment of the present
disclosure.
[0012] FIG. 5A shows a perspective view of the multi-channel TOSA
of FIG. 3, in accordance with an embodiment of the present
disclosure.
[0013] FIG. 5B shows a cross-sectional view of the multi-channel
TOSA of FIG. 5A taken along the line B-B.
DETAILED DESCRIPTION
[0014] As previously discussed, multi-channel TOSAs can use optical
isolators to reduce backreflection during optical signal
transmission. However, optical isolators can introduce beam
displacement (offset) such that the line of propagation in the
forward direction of the optical isolator is off-axis from the
light arriving at an input of the optical isolator. Even relatively
small amounts of beam displacement, such as a few microns, can
cause an appreciable reduction in optical power. Some approaches to
TOSAs compensate for this through active compensation procedures
after attachment of an optical coupling receptacle. For example,
one approach includes fixedly attaching an optical coupling
receptacle to the housing of a TOSA, and then compensating for beam
displacement introduced by an optical isolator associated with the
optical coupling receptacle through active post-attachment
alignment of CAN laser packages.
[0015] In some cases, a beam can be titled to counteract the
displacement introduced by the isolator. However, this also
requires a proportional adjustment of associated filters within the
TOSA housing to ensure that the filters maintain a 45 degree angle
of incidence relative to the lasers. Active alignment of CAN laser
packages using, for instance, laser hammering can be time
consuming, error prone, and expensive to perform. The relatively
small dimensions of small form factor (SFF) designs can further
complicate such alignment and compensation. This can cause a
reduction in yield during manufacturing of TOSAs.
[0016] Thus, in accordance with an embodiment, a multi-channel TOSA
having an off-center fiber position in an optical coupling
receptacle is disclosed, and can provide passive compensation for
beam displacement introduced by optical isolators. In more detail,
the optical coupling receptacle can include an optical isolator
configured to receive a focused light beam from a focus lens within
the multi-channel TOSA. The fiber may be positioned within the
optical coupling receptacle at an offset such that a center line of
the focused light beam entering the optical isolator is offset from
a center line of a fiber. The center line of the focus light beam
may be a function of the physical center of the lens. Thus it may
also be accurate to describe the center line of the fiber as being
offset from a physical center of the focus lens. However, it should
be appreciated that some lenses have an optical center not
necessarily in the physical center of the lines. In any event, this
disclosure is equally applicable in either scenario, with minor
modification, and should not be construed as limited in this
regard.
[0017] In use, the optical isolator receives the focused light beam
from the focus lens and introduces beam displacement such that an
optical signal is launched generally along a center line of the
fiber. In a general sense, the expected beam displacement
introduced by the optical isolator is eliminated or otherwise
mitigated by the offset of the center of the fiber relative to the
center of the focus lens.
[0018] The offset between the center line of the fiber and the
center of the focus lens may be provided by, for example, attaching
the optical coupling receptacle to the multi-channel TOSA housing
at a position offset from the center of the focus lens. In this
example, a first sidewall opening may be formed on an end of the
multi-channel TOSA housing, and configured to mount the focus lens.
Next, a second sidewall opening may be formed on the end of the
multi-channel housing and configured to mount an optical coupling
receptacle. The second sidewall opening may be formed off-center
from the first sidewall opening such that a center point of the
second sidewall opening is offset along a Y axis from a center
point of the first sidewall opening. The offset of the off-center
optical coupling receptacle may be 10 to 100 microns relative to
the center of the focus lens. Other offsets will be apparent in
light of this disclosure and may be based on, for example, isolator
type, a particular number of isolators employed, isolator
thickness, and other isolator-specific factors.
[0019] In more detail, the multi-channel TOSA can include a
plurality of TO can laser packages fixedly attached to one or more
side walls of the multi-channel TOSA housing, and may also include
an optical coupling receptacle fixedly attached or otherwise
integrated into an end of the multi-channel TOSA housing. The
multi-channel TOSA housing may include a compartment defined by an
inner surface of the sidewalls, with the compartment providing a
light path to optically couple each of the TO can laser packages
thereto. The light path may extend laterally from a first end to a
second end of the multi-channel TOSA housing along a first major
axis. A focus lens disposed at the second end of the multi-channel
TOSA housing may receive at least a portion of laser light via the
light path, and output a focused light beam to an optical coupling
receptacle which couples an optical signal to an associated
transmit fiber. The optical coupling receptacle may include an
optical isolator configured to receive the focused light beam and
propagate the same in a forward direction to a fiber while reducing
backreflection. The optical isolator may introduce beam
displacement, with that displacement causing the optical isolator
to propagate the focused beam generally along a center line of the
fiber. Thus the optical coupling receptacle may include a center
line which is generally offset from a center line of the focused
light beam launched into the optical coupling receptacle.
[0020] The multi-channel TOSA with off-center fiber disclosed
herein may provide numerous benefits and advantages over other
multi-channel TOSA approaches that also include an optical
isolator. For example, the multi-channel TOSA disclosed herein
allows the attachment of an optical coupling receptacle to an end
of the multi-channel TOSA without necessarily requiring a full
active alignment process, or beam compensation through filter
tilting, which characterizes other multi-channel TOSA approaches.
In addition, the off-center fiber provides, in a sense, a built-in
degree of coupling optimization such that a predetermined optical
power may be achieved even prior to fine-grain and course active
alignment procedures such as laser hammering of TO can laser
packages.
[0021] 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 or course wavelength division
multiplexing (CWDM). 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.
[0022] As used herein, "optical center" refers to the point on a
principal axis of a lens for which the incident direction of a
light ray passing through is parallel to the emergent direction.
The optical center is not necessarily the physical center of a
lens, and is instead a function of the composition and geometries
of the particular lens.
[0023] Now turning to FIG. 1, there is an optical transceiver 100
consistent with embodiments of the present disclosure. In more
detail, the optical transceiver 100 transmits and receives four (4)
channels using four different channel wavelengths (.lamda..sub.1,
.lamda..sub.2, .lamda..sub.3, .lamda..sub.4) and may be capable of
transmission rates of at least about 10 Gbps per channel. In one
example, the channel wavelengths .lamda..sub.1, .lamda..sub.2,
.lamda..sub.3, .lamda..sub.4 may be 1270 nm, 1290 nm, 1080 nm, and
1330 nm, respectively. 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.
In an embodiment, the optical transceiver 100 implements the
specification SFF-8436 titled "QSFP+10 Gbs 4.times. PLUGGABLE
TRANSCEIVER Rev 4.8" (hereinafter QSFP+), published on Oct. 31,
2013 by the Electronic Industries Alliance (EIA).
[0024] This embodiment of the optical transceiver 100 includes a
multi-channel TOSA 110 for transmitting optical signals on
different channel wavelengths, and a multi-channel ROSA 112 for
receiving optical signals on different channel wavelengths. As
shown, a transceiver housing 102 includes the multi-channel TOSA
110 and the multi-channel ROSA 112. A transmit connecting circuit
104 and a receive connecting circuit 108 provide electrical
connections to the multi-channel TOSA 110 and the multi-channel
ROSA 112, respectively, within the transceiver housing 102. The
transmit connecting circuit 104 and the receive connecting circuit
108 may communicate with external systems via data bus 103. In some
cases, data bus 103 is a 38-pin connector that comports with
physical connector QSFP standards and data communication
protocols.
[0025] In any event, the transmit connecting circuit 104
electrically couples to the electronic components in the
multi-channel TOSA 110 (e.g., TO can laser packages), and the
receive connecting circuit 108 electrically couples to the
electronic components (e.g., the photodiode packages) in the
multi-channel ROSA 112. The transmit connecting circuit 104 and the
receive connecting circuit 108 include at least conductive paths to
provide electrical connections, and may also include additional
circuitry. The multi-channel TOSA 110 transmits and multiplexes
multiple different channel wavelengths, and is coupled to an
optical interface port 114. The optical interface port 114 may
include an LC connector port, although other connector types are
also within the scope of this disclosure. For example, the optical
interface port 114 may comprise a multi-fiber push on (MPO)
connector receptacle.
[0026] In cases where the optical interface port 114 comprises a
duplex, or bi-directional, LC receptacle, the LC connector
receptacle provides optical connections to the multi-channel TOSA
110, and provides optical connections to the multi-channel ROSA
112. The LC connector receptacle may be configured to receive and
be coupled to a mating LC connector 116 such that transmit optical
fiber 122 of the external fibers 124 optically couples to the
multi-channel TOSA 110, and the receive optical fiber 117 of the
external fibers 124 optically couples to the multi-channel ROSA
112.
[0027] The multi-channel TOSA 110 includes multiple TO can laser
packages and optics for producing associated channel wavelengths,
and couples the same into the transmit optical fiber 122. In
particular, the lasers in the multi-channel TOSA 110 convert
electrical data signals (TX_D1 to TX_D4) received via the transmit
connecting circuit 104 into modulated optical signals transmitted
over transmit optical fiber 122. The lasers may include, for
example, distributed feedback (DFB) lasers with diffraction
gratings. The multi-channel TOSA 110 may also include monitor
photodiodes for monitoring the light emitted by the lasers. The
multi-channel TOSA 110 may further include one or more temperature
control devices, such as a resistive heater and/or a thermoelectric
cooler (TEC), for controlling a temperature of the lasers, for
example, to control or stabilize the laser wavelengths.
[0028] The multi-channel ROSA 112 includes multiple photodiode
packages, and optics such as mirrors and filters for receiving a
multiplexed optical signal and de-multiplexing the same into
associated channel wavelengths. The multi-channel ROSA 112 can
detect, amplify, and convert such optical signals received via the
receive optical fiber 117, and can provide the converted optical
signals as electrical data signals (RX_D1 to RX_D4) that are output
via the receive connecting circuit 108. In some cases, the
photodiode packages can include integrated transimpedance
amplifiers (TIAs).
[0029] This embodiment of the optical transceiver 100 includes 4
channels and may be configured for coarse wavelength division
multiplexing (CWDM), although other numbers of channels are
possible.
[0030] Referring to FIG. 2, an example small form-factor (SFF)
pluggable optical transceiver 200 with a multi-channel TOSA and a
multi-channel ROSA is shown. The embodiment shown in FIG. 2 is one
example of the optical transceiver 100 of FIG. 1 implemented in a
small form-factor. For example, the optical transceiver 200 may
implement the QSFP+ specification. As shown, the optical
transceiver 200 includes a transceiver housing 102, a multi-channel
TOSA 110 in one region of the transceiver housing 102, and a
multi-channel ROSA 112 located in another region of the transceiver
housing 102. The multi-channel TOSA 110 electrically couples to
transmit flexible printed circuits (FPCs) 204 and couples to the
optical interface port 114 at an end of the transceiver housing
102. The multi-channel ROSA 112 electrically couples to a receive
FPC 208, and couples to the optical interface port 114 at the end
of the transceiver housing 102.
[0031] The multi-channel TOSA 110 includes TO can laser packages
214-1 to 214-4, with each containing optical components such as a
laser diode. The TO can laser packages 214-1 to 214-4 may provide,
for example, output power from 1.85 mW to 2 W, although other
output power is within the scope of this disclosure. The TO can
laser packages 214-1 to 214-4 may provide a broad spectrum of
channel wavelengths, or may be configured to provide a relatively
narrow spectrum of channel wavelengths such as a single channel
wavelength. In some cases, the TO can laser packages 214-1 to 214-4
provide center wavelengths 375 nm to 1650 nm, for example. In an
embodiment, the TO can laser packages 214-1 to 214-4 are O3.8 mm,
O5.6 mm, or O9 mm TO cans, although other configurations are also
within the scope of this disclosure. For instance, the TO can laser
packages can include O9.5 mm and TO-46 cans.
[0032] One particular example of a multi-channel TOSA particularly
well suited for use in the optical transceiver 200 is discussed in
greater detail in the co-pending U.S. application Ser. No.
14/837,993 titled "Multi-Channel Transmitter Optical Subassembly
(TOSA) With Opposing Placement of Transistor Outline Can Laser
Packages" filed on Aug. 27, 2015. Such a multi-channel TOSA departs
from other TOSA approaches by providing staggered TO can laser
packages positioned on opposite sidewalls. The multi-channel TOSA
110 of FIG. 2 illustrates one such example of a staggered and
opposing TO can laser package configuration. The staggered and
opposing arrangement can increase space between adjacent TO can
laser packages, which can simplify laser welding processes, reduce
error, and increase yield.
[0033] The multi-channel ROSA 112 includes photodiode packages
222-1 to 222-4, with each containing optical components such as a
photodiode and TIA, for example. In some cases, the photodiodes can
provide about -13 dBm sensitivity, or less, for each associated
channel wavelength. In an embodiment, the photodiode packages are
TO-46 packages, although other package types are also within the
scope of this disclosure.
[0034] Referring to FIG. 3, one embodiment of a multi-channel TOSA
110 for use in the optical transceiver module shown in FIG. 2 is
shown in greater detail. As shown, the multi-channel TOSA 110
includes a housing 202 with first and second sidewalls 308 and 310,
respectively, positioned on opposite sides of the housing 202 and
extending generally in parallel along a first major axis 303 from a
first end 326 to a second end 327, and forming a compartment
defined by an inner surface within the housing 202. The housing 202
can further include an optical coupling receptacle 324 configured
to optically couple an associated transmit fiber such as transmit
optical fiber 122 to the multi-channel TOSA 110.
[0035] As shown, the multi-channel TOSA 302 includes first and
second TO can laser packages 304-1 and 304-2 fixedly attached to
the first and second sidewall openings 306-1 and 306-2 of the first
sidewall 308, respectively, and a third TO can laser package 304-3
fixedly attached to the third sidewall opening 306-3 opposing the
first and second TO can laser packages 304-1 and 304-2. The housing
202 further includes a third sidewall 312 at the first end 326 and
adjoining the first and second sidewalls 308 and 310, the third
sidewall 312 including a fourth sidewall opening 306-4 and a fourth
TO can laser package 304-4 fixedly attached thereto.
[0036] Referring now to FIG. 4A, with additional reference to FIG.
4B, a cross-sectional view of the multi-channel TOSA 110 of FIG. 3
taken along line A-A is shown. As shown, the housing 202 also forms
a compartment 316, or internal cavity that defines a light path 330
(FIG. 4B) that extends laterally generally along a center line 322.
Light may travel along the light path 330 which extends through
filters 318-1 to 318-3 before encountering focus lens 320. After
encountering focus lens 320, light is output as a focused beam into
the optical coupling receptacle 324. Within the optical coupling
receptacle 324, an optical isolator 328 receives the focused beam
and can optically couple the same into fiber 325. As previously
discussed, the optical isolator 328 can eliminate or otherwise
mitigate backreflection. The optical isolator 328 may be angled
relative to the center line 322 by a predetermined amount to
further assist in preventing backreflection. For example, the
optical isolator 328 may be angled 6 to 8 degrees relative to the
center line 322. As shown, the optical isolator 328 includes 3
isolator chips stacked in series. Other numbers and configurations
of isolator chips will be apparent in light of this disclosure.
[0037] As shown, the fiber 325 extends generally coaxial with the
compartment 316 of the multi-channel TOSA housing 202. To receive
the fiber 325, the multi-channel TOSA housing 202 includes a cavity
342 having a diameter suitable for receiving a portion of fiber
325. For example, the cavity may comprise a rounded bore having a
diameter between 8 and 70 microns, depending on a desired fiber
type. Likewise, a ferrule receiving region 340 may define a bore
having a diameter suitable to receive and hold a ferrule associated
with the length of fiber.
[0038] Although a center line of the fiber 325 appears to generally
align with the center line 322 of the compartment 316, this is not
necessarily the case as the center line of the fiber 325 is offset
relative to the center line 322 by a number of microns, as
discussed in greater detail below. The offset between the center
line of fiber 325 and the center line 322 may be a range between 10
to 100 microns, which is better illustrated in FIG. 4C. In any
event, distance X from an outer surface of the housing 202 to the
center line 322 is different from that of distance Y, with distance
Y being measured from a line extending from the outer surface of
the housing 202 to the center line of the fiber 325. This
arrangement allows a physical position of the optical coupling
receptacle 324 to compensate for the beam displacement that may be
introduced by the optical isolator 328.
[0039] As shown, the filters 318-1 to 318-3 are positioned on
filter holders 319-1 to 319-3, respectively. An optical coupling
receptacle 324 extends from the second end 327 for optically
coupling the associated channel wavelengths of TO can laser
packages 304-1 to 304-4 to the transmit optical fiber 122. Thus the
filters 318-1 to 318-3, the focus lens 320, and the optical
coupling receptacle 324 are generally aligned or otherwise
positioned along a longitudinal axis provided by the light path
330. This combination of optics may be accurately described as
multiplexing optics and can provide coarse wavelength division
multiplexing (CWDM) in an optical signal, for example.
[0040] Referring now to FIG. 4B, with additional reference to FIG.
4A, a schematic view of the multi-channel TOSA 110 provides further
detail regarding the off-center position of fiber 325 relative to
the light path 330, with light path 330 generally following the
center line 322. The long axis J of the housing 202 may include a
length of approximately 7 mm. The multi-channel TOSA 110 may
further include a length K along its long axis of approximately
2.16 mm between an output side of the focus lens 230 and the output
side of the optical isolator 328. In addition, the multi-channel
TOSA 110 may further include a length L along its long axis of
approximately 3 mm between the output side of the optical isolator
328 and a ferrule receiving region 340 of the optical coupling
receptacle. The ferrule receiving region 340 may include a length
of M being approximately 4 mm. The provided measurements are not
intended to be limiting and other lengths of the multi-channel TOSA
are within the scope of this disclosure.
[0041] As shown, a center line 322 of the light path 330 extending
from the filter 318-1 plots the center line of the light path 330
which a light beam generally follows prior to encountering the
focus lens 320. From there, the light beam also includes a center
line defined by center line 322, but becomes a focused light beam
by virtue of passing through focus lens 320. The focused light beam
then encounters optical isolator 328. As previously discussed, the
optical isolator introduces beam displacement thus causing the
focused light beam to have a center line that generally follows the
center line 329 of the optical coupling receptacle 324, and more
importantly, a center line of the fiber 325. Thus the offset
distance 331 representing the offset of the center line 329 of the
optical coupling receptacle relative to the center line. The offset
distance 331 may be chosen based on the known amount of beam
displacement introduced by the optical isolator 328, for example.
In addition, the offset distance may also be based on the angle at
which the optical isolator 328 is disposed within the optical
coupling receptacle 324. In any event, the offset can be calculated
based in part on the pre-determined amount of beam displacement
introduced by the optical isolator 328 and by its particular
orientation/angle relative to the center line 322.
[0042] Referring now to FIG. 4C, with additional reference to FIG.
4A-B, another schematic view of the multi-channel TOSA 110 provides
further detail regarding the off-center position of the fiber 325
relative to center line 322. The introduction of beam displacement
by the optical illustrator may be better understood by way of
illustration. Consider that without the optical isolator 328, the
focal point 344 extending from the focus lens 320 has a length M.
This means that the fiber 325 could be positioned adjacent thereto
and receive a focused light beam to launch the same into the
associated transmit fiber 122.
[0043] However, the presence of the optical isolator causes the
focal length of a light beam following light path 330 to extend
laterally to the offset focal point generally shown at 346. The
offset distance between focal point 344 and offset focal point 346
is shown as length N, which may be accurately described as a
lateral or X-axis offset. In one particular example, the length N
is about 0.33 mm. In addition, the displacement introduced by the
optical isolator causes the offset focal point 346 to offset a
distance generally equal to the offset 331, which may be accurately
described as a vertical or Y-axis offset. In one particular
example, the offset 331 is about 50 microns. Thus to ensure optimal
or otherwise suitable optical power provided by multi-channel TOSA,
the optical signal propagated along the center line 329 is aligned
with the offset focal point 46 such that a light beam propagated
therefrom is launched substantially into the center of the fiber
325.
[0044] Now referring to FIG. 5A, a perspective view of the
multi-channel TOSA 110 is shown, in accordance with an embodiment.
As shown, the multi-channel TOSA housing 102 includes an end with a
first sidewall opening 50 configured to fixedly attach an optical
coupling receptacle, and a second sidewall opening 52 configured to
mount a focus lens. As discussed below with regard to FIG. 4B, the
offset between a center line of the fiber 325 (FIG. 4B) and the
center of the focus lens may be provided by, for example, attaching
the optical coupling receptacle to the multi-channel TOSA housing
at a position offset from the center of the focus lens. To this
end, the second sidewall opening 52 may be formed off-center from
the first sidewall opening 50 such that a center point of the
second sidewall opening 52 is offset along a Y axis from a center
point of the first sidewall opening, as shown in greater detail in
FIG. 5B, and discussed below. When mounted to the first sidewall
opening 50, the offset of the off-center optical coupling
receptacle may be 10 to 100 microns relative to the center of the
focus lens. Other offsets will be apparent in light of this
disclosure and may be based on, for example, isolator type, a
particular number of isolators employed, isolator thickness, and
other isolator-specific factors.
[0045] Referring now to FIG. 5B, a cross-sectional view taken along
the line B-B of FIG. 5A is shown, in accordance with an embodiment
of the present disclosure. As shown, the center point 54 of the
second sidewall opening 52 is offset from the center point 56 of
the first sidewall opening 50. The offset is shown as offset
distance 331. Thus, when the optical coupling receptacle 324 is
fixedly attached to the first sidewall opening 50, the fiber 325
includes a center line generally extending from point 56, which is
offset by offset distance 331 from the center point 56, or more
precisely, from the center of the focus lens 320.
[0046] Returning to FIGS. 4A and 4B, one example methodology of
multiplexing multiple different channel wavelengths using the
multi-channel TOSA 110 will now be discussed. In use, the filters
318-1 to 318-3, and other optics associated with the TO can laser
packages 304-1 to 304-4 such as collimating lenses, mirrors can
provide wavelength-dependent transmission and reflectivity such
that each respective channel wavelength associated with TO can
laser packages 304-1 to 304-4 is optically coupled to light path
330, and more precisely, multiplexed and launched into the transmit
optical fiber 122 via fiber 325. For example, the filter 318-3 may
be configured to pass channel wavelengths less than 1290 nm, namely
channel wavelength .lamda..sub.1 associated with CAN laser package
304-4, and reflect channel wavelengths greater than or equal to
1290 nm, namely channel wavelength .lamda..sub.2 associated with TO
can laser package 304-2.
[0047] In a similar manner, the filter 318-2 may be configured to
pass channel wavelengths of less than 1310 nm (e.g., channel
wavelengths .lamda..sub.1 and .lamda..sub.2) and reflect channel
wavelengths equal to or greater than 1310 nm, namely channel
wavelength .lamda..sub.3 associated with TO can laser package
304-3. Filter 318-1 may be configured to pass channel wavelengths
of less than 1330 nm (e.g., channel wavelengths .lamda..sub.1,
.lamda..sub.2 and .lamda..sub.3) and reflect channel wavelengths
equal to or greater than 1330 nm, namely channel wavelength
.lamda..sub.4 associated with TO can laser package 304-1. Thus an
optical signal launched into transmit optical fiber 122 can include
multiple different channel wavelengths .lamda..sub.1,
.lamda..sub.2, .lamda..sub.3 and .lamda..sub.4. This arrangement
may be accurately described as an integrated optical multiplexer,
or an integrated multi-stage optical multiplexer with each stage
being provided, in part, by a respective one of the filters 318-1
to 318-3.
[0048] It should be appreciated in light of this disclosure that
the use of the TOSA 110 is not necessarily limited to a 4 channel
configuration.
Further Example Embodiments
[0049] In one aspect, a multi-channel transmitter optical
subassembly (TOSA) including a plurality of lasers is disclosed.
The TOSA may comprise a housing including a plurality of sidewalls,
the plurality of sidewalls forming a compartment defined by an
inner surface therein, the compartment including a light path, the
light path being optically coupled to each of the plurality of
lasers and extending laterally from a first end to a second end of
the housing along a first major axis, a focus lens disposed at the
second end of the housing configured to receive at least a portion
of light emitted by the plurality of lasers via the light path and
to output a focused light beam, and an optical coupling receptacle
fixedly attached to the second end of the housing and configured to
couple the light path to a fiber, the optical coupling receptacle
including an optical isolator configured to receive the focused
light beam and launch the focused light beam in a forward direction
into the fiber while reducing backreflection, wherein a center line
of the fiber is offset from a center of the focus lens, and wherein
the offset passively compensates for beam displacement introduced
by the optical isolator such that the focused light beam is
launched generally into a center of the fiber.
[0050] In one aspect, the offset between the center line of the
fiber and the center of the focus lens may be about 50 microns.
[0051] In one aspect, the offset between the center line of the
fiber and the center of the focus lens may be at least 10
microns.
[0052] In one aspect, the offset between the center line of the
fiber and the center of the focus lens may be based at least in
part on a physical position of the optical coupling receptacle
relative to the position of the focus lens.
[0053] In one aspect, the optical isolator may be angled in the
optical coupling receptacle at about 8 degrees relative to a center
line of the focused light beam.
[0054] In one aspect, the plurality of lasers comprise TO can laser
packages.
[0055] In one aspect, the multi-channel TOSA may further include
filters aligned with the TO can laser packages to pass and reflect
laser light at associated channel wavelengths.
[0056] In one aspect, the optical coupling receptacle is configured
to optically couple a signal having multiple different channel
wavelengths to a transmit optical fiber.
[0057] In accordance with another aspect, an optical transceiver
module is disclosed. The optical transceiver module may include a
transceiver housing, a multi-channel transmitter optical
subassembly (TOSA) having a plurality of transistor outline (TO)
can laser packages fixedly attached thereto and located in the
transceiver housing for transmitting optical signals at different
channel wavelengths, the TOSA comprising, a housing including a
plurality of sidewalls, the plurality of sidewalls forming a
compartment defined by an inner surface therein, the compartment
including a light path, the light path being optically coupled to
each of the plurality of TO can laser packages and extending
laterally from a first end to a second end of the housing along a
first major axis, a focus lens disposed at the second end of the
housing configured to receive at least a portion of light emitted
by the plurality of lasers via the light path and to output a
focused light beam, and an optical coupling receptacle fixedly
attached to the second end of the housing and configured to couple
the light path to a fiber, the optical coupling receptacle
including an optical isolator configured to receive the focused
light beam and launch the focused light beam in a forward direction
into the fiber while reducing backreflection, wherein a center line
of the fiber is offset from a center of the focus lens, and wherein
the offset passively compensates for beam displacement introduced
by the optical isolator such that the focused light beam is
launched generally into a center of the fiber, and a multi-channel
receiver optical assembly (ROSA) located in the transceiver housing
for receiving optical signals at different channel wavelengths.
[0058] In one aspect, the offset between the center line of the
fiber and the center of the focus lens may be about 50 microns.
[0059] In one aspect, the offset between the center line of the
fiber and the center of the focus lens may be at least 10
microns.
[0060] In one aspect, the offset between the center line of the
fiber and the center of the focus lens of the may be based at least
in part on a physical position of the optical coupling receptacle
relative to the focus lens.
[0061] In one aspect, the optical isolator may be angled at about 8
degrees relative to a center line of the focused light beam.
[0062] In one aspect, the plurality of TO can laser packages may
comprise at least four TO can laser packages.
[0063] In one aspect, the multi-channel TOSA may include integrated
multiplexing optics configured to launch an optical signal into a
transmit fiber, the optical signal having multiple different
channel wavelengths. In this aspect, the integrated multiplexing
optics may provide course wavelength division multiplexing (CWDM).
Further in this aspect, the integrated multiplexing optics may
include filters aligned with respective ones of the TO can laser
packages to pass and reflect laser light at associated channel
wavelengths.
[0064] In one aspect, the optical coupling receptacle may be
fixedly attached to a sidewall opening at an end of the housing of
the multi-channel TOSA.
[0065] In one aspect, the optical isolator may comprise a plurality
of isolator chips in series.
[0066] In one aspect, the optical transceiver may be a Quad Small
Form-factor Pluggable (QSFP) transceiver module and the
multi-channel TOSA is configured to transmit at four different
channel wavelengths at transmission rates of at least about 10 Gbps
per channel.
[0067] 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.
* * * * *