U.S. patent application number 15/150254 was filed with the patent office on 2016-11-17 for space active optical cable.
The applicant listed for this patent is LOCKHEED MARTIN CORPORATION. Invention is credited to Harsha Krishna KOPURU, Rebekah Jean MITCHELL, Lance A. WOOD.
Application Number | 20160334591 15/150254 |
Document ID | / |
Family ID | 57249512 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160334591 |
Kind Code |
A1 |
WOOD; Lance A. ; et
al. |
November 17, 2016 |
SPACE ACTIVE OPTICAL CABLE
Abstract
A space active optical cable (SAOC) includes a cable including
one or more optical fibers, and two or more electrical transceivers
on opposing ends of the cable and interconnected by the cable. Each
of the electrical transceivers includes an enclosure that encloses
one or more light sources, one or more light detectors, and control
electronics. Also included in the enclosure are a coupling medium
to couple light into and out of the one or more optical fibers. The
coupling medium can be reflecting surface or an on-axis mount. The
enclosure provides a suitable heat propagation and electromagnetic
interference (EMI) shielding, and the cable and the two or more
electrical transceivers are radiation resistant. SAOC features
optionally support a health check algorithm that allows trending
optical performance in the absence of an optical connector and a
potential surface treatment to increase nominally low emissivity of
an EMI conductive surface.
Inventors: |
WOOD; Lance A.; (Winter
Park, CO) ; KOPURU; Harsha Krishna; (Parker, CO)
; MITCHELL; Rebekah Jean; (Littleton, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LOCKHEED MARTIN CORPORATION |
Bethesda |
MD |
US |
|
|
Family ID: |
57249512 |
Appl. No.: |
15/150254 |
Filed: |
May 9, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62161767 |
May 14, 2015 |
|
|
|
62206806 |
Aug 18, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/4284 20130101;
G02B 6/4415 20130101; G02B 6/4277 20130101; G02B 6/4206 20130101;
G02B 6/4246 20130101; G02B 6/428 20130101; G02B 6/4286 20130101;
G02B 6/4267 20130101; H04B 10/40 20130101; G02B 6/4214
20130101 |
International
Class: |
G02B 6/42 20060101
G02B006/42; G02B 6/44 20060101 G02B006/44; H04B 10/40 20060101
H04B010/40 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under
contract number FA8620-11-C-3142 awarded by the United States
Government. The government has certain rights in this invention.
Claims
1. A space active optical cable (SAOC) comprising: a cable
comprising one or more optical fibers; and two or more electrical
transceivers on opposing ends of the cable and interconnected by
the cable, each of the electrical transceivers of the two or more
electrical transceivers comprising: an enclosure enclosing: one or
more light sources, one or more light detectors, and control
electronics enclosed in the enclosure; and a coupling medium
configured to couple light into and out of the one or more optical
fibers, wherein: the enclosure provides a suitable heat propagation
and electromagnetic interference (EMI) shielding, and the cable and
the two or more electrical transceivers are radiation
resistant.
2. The SAOC of claim 1, wherein each of the electrical transceivers
comprise space rated electrical interface configured to receive
power and communicate signals including data, command, control, and
telemetry signals.
3. The SAOC of claim 1, wherein each light source of the one or
more light sources is configured to convert a received (RX)
electrical signal into light, and wherein each light detector of
the one or more light detectors is configured to convert received
light into an electrical signal simultaneously with conversion of
the RX electrical signal.
4. The SAOC of claim 1, wherein the coupling medium comprises a
reflecting surface, wherein each of the electrical transceiver is
configured to utilize a shaped reflecting surface to focus light
from each light source of the one or more light sources into an
optical fiber and simultaneously focus received light from an
optical fiber of the one or more optical fibers into a light
detector of the one or more light detectors.
5. The SAOC of claim 1, wherein the cable, the one or more
electrical transceivers are built using space-rated parts,
materials, and processes, wherein the space-rated parts, materials,
and processes are quality controlled for vacuum compatibility and
reliability.
6. The SAOC of claim 1, wherein the coupling medium comprises an
on-axis alignment mount, wherein each light source of the one or
more light sources comprises a space-qualified vertical cavity
surface-emitting laser (VCSEL), and wherein space-qualified VCSEL
is quality controlled for radiation resistance and reliability.
7. The SAOC of claim 1, wherein the enclosure is processed to have
a laser-charred finish using short laser pulses to increase
absorption and emissivity, wherein the short laser pulses are
configured to produce a charred surface that is thermally
conductive.
8. The SAOC of claim 1, wherein the coupling medium comprises a
reflecting surface, and wherein the reflecting surface is enhanced
by shaping and/or coating with a reflective material to improve
optical coupling efficiency and to protect the reflecting
surface.
9. The SAOC of claim 1, wherein each of the electrical transceivers
provides autonomous management of configuration of electrical and
optical components for sustained performance in space environments,
mitigating temperature and radiation affects.
10. The SAOC of claim 1, wherein each of the electrical
transceivers enables optical performance trending without optical
connectors, wherein the optical performance trending is achieved
using bit error rate (BER) and receiver signal strength indicator
(RSSI) in a sensitive low VCSEL drive regime.
11. The SAOC of claim 10, wherein the optical performance trending
during a lifetime of the SAOC is accomplished using electrical
interfaces only, in a health check (HC) configuration perceptive to
optical losses, wherein the HC configuration is established with a
per part optical drive level with acceptable characteristics
including output signal strength and bandwidth for nominally
repeatable BER and RSSI.
12. A method for providing a space active optical cable (SAOC), the
method comprising: providing a cable comprising one or more optical
fibers; providing a first electrical transceiver for coupling to a
first end of the cable; enclosing the first electrical transceiver
in a first enclosure enclosing a light detector and a first
reflecting surface configured to reflect a first incident light;
processing the first enclosure to provide a predetermined heat
propagation and electromagnetic interference (EMI) specification
and to include radiation hard components; and providing the cable
and the first electrical transceiver to be radiation resistant.
13. The method of claim 12, further comprising: configuring the
light detector to convert a reflected light into a transmit (TX)
electrical signal, and configuring the first reflecting surface to
generate the reflected light by reflecting the first incident light
from the one or more optical fibers.
14. The method of claim 12, further comprising: providing a second
electrical transceiver coupled to a second end of the cable; and
enclosing the second electrical transceiver in a second enclosure
enclosing a light source and a second reflecting surface configured
to reflect a second incident light.
15. The method of claim 14, further comprising configuring the
first electrical transceiver and the second electrical transceiver
to receive power and communicate signals including data, command,
control, and telemetry signals.
16. The method of claim 14, further comprising configuring the
second electrical transceiver to receive a receive (RX) electrical
signal and to use the light source to generate the second incident
light based on the RX electrical signal, wherein a reflecting
surface of the second electrical transceiver is configured to
reflect the second incident light onto the one or more optical
fibers.
17. The method of claim 14, wherein processing the first enclosure
comprises providing a laser-charred finish using femtosecond laser
pulses, and wherein the second enclosure is processed similar to
the first enclosure.
18. The method of claim 14, further comprising shaping the first
reflecting surface and the second reflecting surface and coating
with a reflective material including gold or silver to improve
optical coupling efficiency.
19. The method of claim 14, wherein providing the first electrical
transceiver and the second electrical transceiver including
automatic configuration algorithms including a health-check (HC)
process for assessing optical performance by using electrical
interfaces, by using bit error rate (BER) and a receiver signal
strength indicator (RSSI) in a sensitive low drive regime.
20. The method of claim 19, wherein the HC process comprises
determining an HC configuration over a planned operational thermal
environment that results in an optical signal quality below a
planned operational level, wherein the optical signal quality is
strong enough to avoid adverse threshold effects with an acceptable
input impedance (R.sub.IN) and bandwidth (BW) behavior, while
maintaining electrical interface signal integrity margins.
21. The method of claim 20, wherein the HC process further
comprises performing repeated measurements of bit error rate (BER)
and receiver signal strength indicator (RSSI) to establish
performance statistics for the SAOC, the performance statistics
comprising an HC-BER and an HC-RSSI statistics.
22. The method of claim 20, wherein the HC process further
comprises, in context of an integrated system, repeating HC-BER and
HC-RSSI measurements to establish system performance statistics
including a system HC-BER and a system HC-RSSI.
23. The method of claim 22, wherein the HC process further
comprises, through an operating life of the integrated system,
measuring the BER and the RSSI and detecting optical link
malfunction or degradation by comparing the measured BER and the
RSSI with the system HC-BER and the system HC-RSSI.
24. The method of claim 20, wherein the HC process is applied to
generically implemented active optical cables in addition to the
SAOC.
25. A method of providing an active optical cable (AOC), the method
comprising: processing an enclosure to create a charred finish
using laser pulses by: forming a nickel layer over surfaces of the
enclosure; and charring the surfaces of the enclosure using
femto-second laser pulses, while a power level of the femto-second
laser pulses are increased sharply to a predetermined-level and
reduced steeply to avoid ablating the nickel layer; and using the
enclosure to enclose a first electrical transceiver for coupling to
a transmit (TX) end of the AOC, wherein: a second electrical
transceiver for coupling to a receive (RX) end of the AOC is
enclosed similarly, the first electrical transceiver comprises a
first optical coupler formed by a first reflector surface and a
light detector, and the second electrical transceiver comprises a
second optical coupler formed by a second reflector surface and a
light source.
26. The method of claim 25, wherein the first and the second
electrical transceiver enable optical performance trending without
optical connectors, wherein the optical performance trending is
achieved using bit error rate (BER) and receiver signal strength
indicator (RSSI) in a sensitive low VCSEL drive regime.
27. The method of claim 26, wherein the optical performance
trending during a lifetime of the AOC is accomplished using
electrical interfaces only, in a health check (HC) configuration
perceptive to optical losses, wherein the HC configuration is
established with a per part optical drive level with acceptable
characteristics including output signal strength and bandwidth for
nominally repeatable BER and RSSI.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119 from U.S. Provisional Patent Applications
62/161,767 filed May 14, 2015 and 62/206,806 filed Aug. 18, 2015,
which are incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0003] The present invention generally relates to electro-optics,
and more particularly, to a space active optical cable, optionally
with a high emissivity conductive surface, high coupling
efficiency, and a custom health check algorithm for trending
optical performance.
BACKGROUND
[0004] Space applications such as spacecraft communication
applications require high-speed data links to communicate digital
information. At high data rates, fiber optic links are more
attractive than copper links, due to bandwidth performance
limitations of copper links over long lengths. Optical fiber is
light weight and is inherently immune to electromagnetic
interference (EMI). Traditional space based fiber optic links are
printed circuit board (PCB) mounted transceivers, requiring board
space and optical connectors at the box wall. Multiple programs
have experienced significant issues with fiber optic connectors,
such as, a space program had impacts totaling millions of dollars
from optical connector non-conformances, and an aircraft program
experienced significantly delayed delivery based on optical
connector issues. Even without issues, optical connectors may need
extra effort in the form of inspection, cleaning, and special
testing not needed for electrical connectors.
[0005] An active optical cable (AOC) eliminates optical connectors,
having electrical only interfaces, while maintaining the advantages
of fiber optic data links and reducing internal PCB impacts by
mounting the optical transceiver in a connector backshell. An
existing AOC has low optical coupling efficiency, when using flat
reflective surface. The optical source divergence, geometry to the
fiber, and surface roughness allow significant light to not be
coupled into the fiber. The space active optical cable is designed
and processed for space environments, radiation and vacuum, as well
as for high reliability and extreme temperatures.
SUMMARY
[0006] In some aspects, a space active optical cable (SAOC)
includes a cable including one or more optical fibers, and two or
more electrical transceivers on opposing ends of the cable and
interconnected by the cable. Each of the electrical transceivers
includes an enclosure that encloses one or more light sources, one
or more light detectors, and control electronics. Also included in
the enclosure are a reflecting surface or on-axis alignment mount
to couple light into optical fibers. The enclosure provides
suitable means of heat propagation and electromagnetic interference
(EMI) shielding. The cable and the two or more electrical
transceivers are radiation resistant and vacuum compatible.
[0007] In other aspects, a method for providing an SAOC includes
providing a cable comprising one or more optical fibers and a first
electrical transceiver for coupling to a first end of the cable.
The first electrical transceiver is enclosed in a first enclosure
enclosing a light detector and a reflecting surface or on-axis
alignment mount configured to couple light out of one or more fiber
onto one or more detectors. The first enclosure is designed and/or
processed to provide a predetermined path for heat
propagation/conduction, EMI specification compliance and to be made
of radiation resistant components. The cable and the first
electrical transceiver are built to be radiation resistant and
vacuum compatible.
[0008] In yet other aspects, a method of providing an SAOC may
include processing enclosure with a nickel layer over surfaces of
the enclosure and charring the surfaces of the enclosure. The
charring is performed by using short duration, even femto-second,
laser pulses, while the power level of the laser pulse is increased
sharply to a predetermined-level and reduced steeply to avoid
ablating the nickel layer. This leaves the surface conductive,
providing an EMI Faraday cage, while increasing the
absorption/emissivity of the surface. The enclosure is used to
enclose a first electrical transceiver end of the SAOC. The first
electrical transceiver includes a first optical coupler formed by a
first curved reflector surface and a light source and detector. A
second electrical transceiver for coupling to the opposite end of
the SAOC is enclosed in the enclosure similarly. Thus, the SAOC is
bidirectional, both transmitting and receiving at each end,
simultaneously.
[0009] The health check algorithm aspect of the SAOC is a unique
way to trend optical performance in the absence of an optical
connector. The operating drive current is adjusted to an
established value where performance is very sensitive to optical
attenuation. By repeating test in this configuration, Bit Error
Rate (BER) and Receiver Signal Strength Indicator (RSSI) can be
trended indicating a change in optical performance. Health check
may readily apply to most any AOC, not just the SAOC. The foregoing
has outlined rather broadly the features of the present disclosure
in order that the detailed description that follows can be better
understood. Additional features and advantages of the disclosure
will be described hereinafter, which form the subject of the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a more complete understanding of the present disclosure,
and the advantages thereof, reference is now made to the following
descriptions to be taken in conjunction with the accompanying
drawings describing specific aspects of the disclosure,
wherein:
[0011] FIGS. 1A and 1B are a structural diagram and a corresponding
functional diagram of an example of an active optical cable (AOC),
according to certain aspects.
[0012] FIGS. 2A through 2C are diagrams illustrating an example of
a space AOC (SAOC), according to certain aspects.
[0013] FIGS. 3A and 3B are diagrams illustrating examples of system
applications of a SAOC, according to certain aspects.
[0014] FIG. 4 is a diagram illustrating an example of a laser pulse
profile used in charring an enclosure of a SAOC stopping as early
as the peak (dotted line), according to certain aspects.
[0015] FIG. 5 is a diagram illustrating plots of laser modulation
current and corresponding eye diagrams used in performing a health
check, according to certain aspects.
[0016] FIG. 6 is a flow diagram illustrating an example of an
algorithm for health check (HC) of a SAOC, according to certain
aspects.
[0017] FIG. 7 is a flow diagram illustrating an example of a method
for providing a SAOC, according to certain aspects.
[0018] FIG. 8 is a flow diagram illustrating an example of a method
for providing an AOC, according to certain aspects, prior to
cabling the two transceivers together.
DETAILED DESCRIPTION
[0019] The detailed description set forth below is intended as a
description of various configurations of the subject technology and
is not intended to represent the only configurations in which the
subject technology can be practiced. The appended drawings are
incorporated herein and constitute a part of the detailed
description. The detailed description includes specific details for
the purpose of providing a thorough understanding of the subject
technology. However, it will be clear and apparent to those skilled
in the art that the subject technology is not limited to the
specific details set forth herein and can be practiced using one or
more implementations. In one or more instances, well-known
structures and components are shown in block diagram form in order
to avoid obscuring the concepts of the subject technology.
[0020] The present disclosure is directed to an active optical
cable, in part, to methods and configuration for providing a space
active optical cable (SAOC) that satisfies space ratings as
discussed in more details herein. The subject technology
significantly improves optical couplings and provides enclosures
with a permanent finish that satisfy multiple requirements such as
emissivity and EMI performance. The improvement is achieved without
applying tape or paint for emissivity enhancement. The subject
technology allows laser charred finishing that stops at the initial
charred stage (e.g., change in absorption), which increases surface
emissivity, while maintaining properties such as conductivity of
the base material (e.g., nickel).
[0021] FIGS. 1A and 1B are a structural diagram 100A and a
corresponding functional diagram 100B of an example of an active
optical cable (AOC) 110, according to certain aspects of the
subject technology. The AOC 110 includes a cable (e.g., an optical
cable) 102 interconnecting electrical transceivers 104 coupled to
two ends of the cable 102. The optical cable 102 includes one or
multiple optical fibers, each of which can be used for transmission
of data to or reception of data from an electrical transceiver
(e.g., 104). Each of the electrical transceivers 104 can receive an
electrical signal from an electrical interface, generate an optical
signal based on the electrical signal, and provide the generated
optical signal to the cable 102. Each of the electrical
transceivers 104 can simultaneously receive an optical signal from
the cable 102 and generate an electrical signal to be received by
the same electrical interface or another electrical interface.
[0022] In one or more aspects, photonics and support electronics
used in electrical transceivers 104 are small and low-power
semiconductor devices, such that they can be located in an
electrical connector back-shell. As explained above, in the
electrical transceivers 104, electrical data is first converted to
an optical signal in the back-shell, transmitted over optical
fiber, and then converted back to electrical data at a destination
back-shell. In some embodiments, box-to-box, point-to-point,
optical links are accomplished with electrical only connectors to
the outside of the box. Bidirectional links may use a dedicated
fiber for each direction, or may be on a single fiber using an
optical circulator approach for achieving bidirectionality.
[0023] In the functional diagram 100B, the AOC 110 is shown to be
operable to receive power from any of the electrical interfaces
(e.g., 120 and 130) that may be connected to electrical
transceivers 104 through one or both of the power line 112. In some
aspects, at least a portion of the received electrical power over
the power lines 112 is consumed by the internal circuitry of the
electrical transceivers 104. The control lines 114 may be used by
the AOC 100 to communicate control signals with the electrical
interfaces 120 and 130 connected to electrical transceivers 104.
The control signals are electrical signals that, for example, can
be utilized for controlling automatic algorithms that are
responsible for performance management of the AOC 100. The data
communication between the electrical transceivers 104 and other
devices and/or systems connected to the AOC 110 through the
electrical interfaces 120 and 130 is carried over the data line(s)
116 (e.g., lines 1-n, for n bits of data). Mechanical interfaces
are also used to mechanically couple the AOC 110 to the other
systems and/or devices. The mechanical interfaces are controlled
for their thermal conductivity, emissivity and electromagnetic
interference (EMI) qualities to make sure that a reliable thermal
path and an EMI shielding are provided.
[0024] FIGS. 2A through 2C are diagrams illustrating an example of
a space AOC (SAOC) transceiver 200, according to certain aspects of
the subject technology. The SAOC transceiver 200 is a portion of a
SAOC cable, which has a similar general structure as the AOC 110 of
FIG. 1A, except that all components, materials, and processes
involved in the production and maintenance of the components and
materials are space rated, as described herein. Each SAOC cable has
two or more of the SAOC transceiver 200. The SAOC transceiver 200
can receive power, control signals, and data through the power line
112, control line 114, and the data line(s) 116, respectively. In
one or more aspects, the electrical power received through the
power line 112 is used for internal consumption by the electrical
circuitry of the SAOC transceiver 200. The control signals are
electrical signals received over the control line 114 and may be
used to control the functionality and performance of the SAOC
transceiver 200. The data received via the data line(s) 116 are
electrical signals which are converted to optical signals by the
SAOC transceiver 200, as further discussed below.
[0025] In one or more aspect, the SAOC transceiver 200 as shown in
FIG. 2B, includes an optical portion 210 and an electrical portion
220. The SAOC transceiver 200 is enclosed in an enclosure 230 and
is coupled to an electrical interface through an electrical
connector 232 (e.g., a D-sub connector). The electrical interface
may be an interface of a system and/or device connected to the SAOC
transceiver 200 through the electrical connector 232. The
electrical portion 220 includes a laser diode driver (LDD) 222, a
trans-impedance amplifier (TIA) 224, a control circuit 226, and an
electronic circuit 228. One or more lasers 204 and one or more
light detectors 206 may be considered as converters between the
electrical portion 220 and the optical portion 210 and are
electrically coupled to the portion 220, while being optically
coupled to the optical portion 210. The optical portion 210
includes optical components including optical couplers and/or
lenses (e.g., a reflector 218) that optically couple the lasers 204
and light detectors 206 to the optical fibers (e.g., 216) of a
cable (e.g., 102 of FIG. 1A) connected to the SAOC transceiver 200.
The optical components for the optical coupling of a laser 204 to
an optical fiber 214 are shown in a blown-up view 206.
[0026] In some implementations, the optical coupling of the laser
204 to the optical fiber 214 can be performed using an on-axis
mount, as shown in a blown-up view 201. The components of the
on-axis mount include a base submount 203, a vertical submount 205,
the laser 204 (e.g., a VCSEL), the optical fiber 214, and,
optionally, a transparent mounting block 209. The base submount 203
may be made, for example, of a semiconductor material such as
silicon or a radiation hard and vacuum compatible printed circuit
board (PCB) material. The vertical submount 205 may be made, for
example, of alumina (Al2O3) that can support electrical traces from
the laser 204 to the base submount 203. The transparent mounting
block 209 is made, for example, of sapphire or a semiconductor
material. The optical fiber 214 is a multi-mode fiber, although or
a single-mode optical fiber can also be used instead.
[0027] In some implementations, as shown in FIG. 2B, the laser 204
is mounted on the vertical submount, and the transparent mounting
block 209 is not needed. In some aspects, the laser 204 may be
mounted on the base submount 203, in which case the vertical mount
is not used and the optical fiber 214 is mounted on a V groove
created on the base submount 203 to facilitate alignment of the
laser 204 with the optical fiber 207. In some other aspects, the
vertical mount is not used and the laser 204 is mounted on the
transparent mounting block 209, which is between the laser 204 and
the optical fiber 214.
[0028] In one or more aspects, the optical coupler 218 used in the
optical portion 210 is improved for achieving high optical coupling
efficiency, for example, by using a first surface reflection curved
instead of flat, which is critical angle dependent. In addition,
the optical adhesive surface of the reflector 218 could be coated
with a reflective material such as Au or Ag, deposition of which
may further provide protection for the exposed surface. In some
aspects, the surface of the reflector 218, as shown, can be further
shaped or lensed and made smoother to improve coupling efficiency.
The reflector 218 focuses the light from laser 204 into the fiber
214. In some implementations, an actively aligned separate mirror
could be introduced and be held with the optical adhesive currently
used. The disclosed optical coupling can result in significantly
higher coupling efficiency. For example, using a direct alignment
mount on axis with the fiber improvement in coupling efficiency of
up to 70% can be achieved.
[0029] In some aspects, the light detectors 206 are photodiodes
properly biased to be able to detect light photons received from
respective optical fibers 216 coupled to the light detectors 206.
The light detectors 206 can generate current signals in response to
the detection of light photons. The current signal generated by the
light detectors 206 are amplified by the TIA 224, which generates
corresponding voltage signals. The voltage signals generated by the
TIA 224 are processed by the electronic circuit 228 and provided to
the electrical connector 232 for transmission through the
electrical interface of the system and/or device connected to the
SAOC transceiver 200. The light detectors are coupled to fibers 216
with high efficiency couplers of the subject technology similar to
the reflector 218. In one or more aspects, the light detectors 206
are implemented using photo-diodes, such as semiconductor
photodiodes.
[0030] In some aspects, the lasers 204 are vertical cavity
surface-emitting laser (VCSEL) type lasers which are space rated. A
major advantage of VCSELs over edge-emitter lasers is ease of
coupling. VCSELs have a circular surface output that can be coupled
without the need of an additional lens to circularize to output
light. The edge-emitting lasers may utilize a lens to help
circularize the beam, have higher flux density that often requires
angled coupling to avoid back reflection. Edge-emitting lasers have
much higher drive current requiring more power than VCSELs. VCSELs
may also be easily addressed as an array by an array of lenses or
fibers. The VCSELs do not have mm cavity lengths and high flux
density, as the edge-emitting lasers have.
[0031] The lasers 204 may include an array of VCSELs that are
coupled to and driven by the LDD 222, which is a known circuit. The
LDD 222 is driven by signals from the electronic circuit 218 and/or
the control circuit 216. In some aspects, the electronic circuit
228 receives data from data lines 116 of FIG. 2A and performs
suitable processing on the received data before providing the data
in the form of processed electrical signals to the LDD 222. The
lasers 204 generate optical light (signals) for transmission over
the optical fibers 214 of a cable (e.g., 102 of FIG. 1A) connected
to the SAOC transceiver 200. In one or more aspects, the control
circuit 226 receives control signals from control lines 114 of FIG.
2A and based on the received control signals exerts control over
the electronic circuit 228.
[0032] The SAOC 200 is enclosed in the enclosure 230 with good
heat-sink and EMI protection using gaskets and communicates
command, control, and telemetry signals via a serial interface such
as the electrical connector 232. Space qualification challenges may
be met by leveraging space rated components such as qualified
impedance-controlled electrical connectors, radiation resistant
fibers and cables, radiation hard custom electronics, high
reliability and high temperature VCSELs, and the like. For example,
the SAOC 200 may be prepared for use in radiation and vacuum
environment for high-reliability space applications and may include
radiation resistant fibers (e.g., resistant to gamma rays) and
radiation resistant electronics (e.g., resistant to ionizing
radiation, protons, and heavy ions), and space rated parts,
material, and processes. The space rating may include making sure
that the parts and material are qualified for space application
with repeatable and reliable test results such having as low
outgassing. Further, the SAOC 200 may include automatic algorithms
(e.g., routines) for autonomous device maintenance and performance
management in space environments. The routines may be implemented
in firmware and be performed by hardware, for example, one or more
processors (e.g., microcontrollers such as control circuit 226 of
FIG. 2B). In one or more implementations, the firmware and the
processors is part of the electronic circuit 228 and/or the control
circuit 226.
[0033] In some implementations, as part of the space rating
qualifications ruggedization may be performed to survive launch
vibration and/or shock and temperature cycling, using a space
qualified electrical connector (e.g., 232). In one or more aspects,
a corresponding mechanical interface is designed for vacuum
pressure compatible thermal management and EMI performance. For
example, a Faraday cage may be used with conductive heat transfer.
As part of the space rating, the material and components used in
the SAOC 200 are selected to be operable in extended operating
temperature (e.g., .about.100.degree. C. at SAOC interface) and
satisfy high reliability requirements of a multi-year mission
use.
[0034] In one or more implementations, the SAOC 200 may also serve
as a platform 250 for RF-over-fiber, as shown FIG. 2C, or other
connector back-shell based applications. In some aspects, the
platform 250 of the subject technology eliminates the need for
optical connectors for space applications. This is especially
attractive because space applications do not have multiple
bulkheads as, for example, a ship might have. The platform 250
provides a readily usable solution for high-speed point-to-point
data links. In one or more aspects, the platform 250 is coupled
through the interface 240 (e.g., a serial interface) to an
electrical interface of another devices or system connected to the
platform 250. The interface 240, similar to the electrical
connector 232 of FIG. 2B can receive power and communicate control
and data signals. The platform 250 includes a light source 252,
local oscillator (LO) modulator 254, a radio-frequency (RF)
modulator 256, and a light processor 258. The light source 252
includes, for example, a distributed feedback (DFB) laser, which is
a type of laser diode, quantum cascade laser, or optical fiber
laser with an active region that is periodically structured as a
diffraction grating. The light source 252 generates an optical
carrier signal which can be modulated with LO and RF signals, as
desired. The LO modulator 254 receives an LO electrical signal as
an input and modulates the optical carrier signal with the LO
signal. The RF modulator 256 receives an RF electrical signal as an
input and modulates the optical carrier signal with the RF
signal.
[0035] The light processor 258 includes a filter and lock-diode
unit 260 and mirrors 255. The light processor 258 receives laser
light from the DFB laser 252 and LO and RF modulated lights from
the LO modulator 254 and RF modulator 256 and provides a heterodyne
output light signal to an optical fiber 270 (e.g., a single-mode
optical fiber). The filter and lock diode unit 260 includes a
filter component that can filter the RF signal as desired and a
wave locking laser diode that can lock the modulated laser light to
the filter. In one or more aspects, the filter component is a
multi-layer optical filter such as a
wave-length-division-multiplexing (WAD) filter. The platform 250
may further include other RF photonics circuits including a
low-noise amplifier (LNA) and one or more optical switches for
routing and redundancy purposes.
[0036] FIGS. 3A and 3B are diagrams illustrating examples of system
applications 300A and 300B of SAOC 320, according to certain
aspects of the subject technology. As shown in FIG. 3A, one or more
SAOC 320 similar to SAOC 200 of FIG. 2B, may be used in digital
data transfer at high date rates with strict mass and power
limitations that demand an optical solution, for example, a
fiber-based sensor application. In some aspects, the SAOC 320
facilitates communication between payload instruments 310 and a
control and communication system 330. Examples of the payload
instruments include GPS communication devices, earth sensor and
imaging devices, and space sensor and imaging devices. Other
applications of the SAOC include analog RF over fiber applications.
In an analog RF over fiber application, as shown in FIG. 3B, one or
more RF antennas can be coupled to an on board system processing
360 using a modified SAOC 350 such as the SAOC 250 of FIG. 2C. The
on board system processing 360 may, for example, include RF
demodulator and base-band circuitry to further process a heterodyne
signal generated by the modified SAOC 350.
[0037] FIG. 4 is a diagram illustrating an example of a laser pulse
profile 400 used in charring the enclosure of a SAOC stopping as
early as the peak (dotted line), according to certain aspects of
the subject technology. Space hardware including SAOC (e.g., 200 of
FIG. 2B), as explained above, have to satisfy EMI requirements and
emissivity requirements simultaneously. This can become challenging
as the material properties often conflict. For example, nickel is
one of the most desired materials for EMI performance, but has a
smooth reflective surface, while high emissivity requires the use
of a material with a dark or opaque finish. Space-rated thermal
paints are often used to paint nickel black to achieve both
requirements. Paints, however, do not adhere well to nickel and
have proven to flake off frequently during handling of other
managed service provider (MSP) hardware, creating foreign object
damage (FOD). The paint option is not suitable for the SAOC because
paint flakes off and as a result exposes the surface underneath.
This counters the original intent of providing a uniform thermally
conductive surface that enhances heat radiation.
[0038] Another available option is to use Kapton tape applied to
the external surface of the hardware during vehicle assembly. The
Kapton tape can raise other concerns, for example, lengthening the
assembly process and changing the mass and dimensions of the
hardware. It also impedes remove and replace (RandR) and raises
concerns of adverse residues and appearance of the hardware.
[0039] The subject technology improves surface emissivity, for
example, of the SAOC enclosure (e.g., 230 of FIG. 2B) by using
laser charring using laser pulse profiles with controlled results.
In some aspects, laser charring can be performed by applying high
optical power laser profile 400 of FIG. 4 to the subject surface
(e.g., nickel surface) to greatly increase absorption, and then a
steep reduction in power to avoid ablating the material. Focused or
diffused laser beam, laser wavelength and angle of incidence, and
other factors, such as roughness of the surface, may affect the
suitable laser profile for the charring process. The process stops
at the initial charred stage, which increases the surface
absorption and emissivity, assuming absorption relationship given
by Kirchhoff's law of thermal radiation, while maintaining the base
material properties, e.g. conductivity of nickel. Charring in the
context of the subject disclosure is performed to change absorption
properties of the surface and is not continued to result in a burnt
product. It is understood that emissivity concerns radiative (e.g.,
with a wavelength of several microns) heat transfer, in the
wavelengths beyond the visible range (unless at very high
temperatures) and the results may not be evaluated based on visual
appearance. The ease of implementing a laser charred finish, raster
over most any shape surface is especially attractive, along with
the permanent nature of the finish.
[0040] While the SAOC of the subject technology has many advantages
over the existing optical connectors, it needs additional measures
to replace the unavailable direct measurement opportunities to
verify optical link performance as discussed herein with respect to
health check (HC) of the optical links.
[0041] FIG. 5 is a diagram illustrating plots of laser modulation
currents 500 and corresponding eye diagrams 510 used in performing
a health check, according to certain aspects of the subject
technology. Existing PCB mounted optical transceivers use optical
connectors to exit/enter the housing. This allows direct evaluation
of optical link margin at the optical connector, but results in
other challenges. An algorithm referred to as SAOC health check
(HC) described herein allows optical link performance verification
by trending bit error rate (BER) performance of the entire
electrical-optical-electrical link in a configuration (e.g., an
operating state) designed to yield sensitive (e.g., low margin)
optical link performance with strong electrical link performance.
It is understood that any test-to-test variation in BER performance
in this operating state is directly attributable to a change in
optical link performance, which may be used to evaluate the health
of optical drive and optical transmission components over the
system lifetime. The data shown in plots 500 and 510 are HC proof
of concept regarding BER sensitivity. The plots 500 show that laser
modulation currents of the VCSELS (e.g., 204 of FIG. 2B) can be
adjusted to perform health check, for example, by reducing the
laser modulation currents with fixed pre-bias current (e.g., about
0.8 mA) until bit error occurs. The laser modulation current (Imod)
values are reduced from about 2.6 mA to about 1 mA. The occurrence
of the bit error is indicated by the eye diagrams 510. For example
at Imod=1.0 mA, the eye is almost closed, which is an indication of
a higher bit error rate.
[0042] In some aspects, SAOC telemetry such as receiver signal
strength indicator (RSSI) and other performance management
algorithms may play roles in implementing the SAOC HC algorithm.
Precise and repeatable control of optical performance management
parameters enables trending of optical link health and performance
throughout integration, test, and product life, even when the SAOC
is used in a space vehicle which is on orbit.
[0043] The SAOC optical link performance helps to detect hardware
defects or issues during integration and testing stage and to
understand device failure modes, preserve remaining life, and
switch to redundant systems when available. The SAOC HC provides a
measure to trend SAOC optical link performance margin using data
accessible via electrical interfaces only. An established low
consistent drive per end, in a loss sensitive regime, allows
performance to be trended through BER and RSSI parameters. The BER
is commonly measured in most systems, even on orbit, or can be
measured using an external BER tester. The RSSI is related to
detector photocurrent at the end of the optical link indicating a
measure of optical transmission performance. Precise control of
optical configuration is an aspect of the SAOC HC algorithm. It is
known and understood that optical component performance will vary
with environmental parameters (e.g., temperature). Precision
sensing of the environmental parameters along with other factors
such as precise and repeatable tuning of the SAOC optical drive and
receiving configuration parameters for the current environment can
be useful in calibrating the BER performance changes that would
otherwise be attributed to these factors.
[0044] Knowledge of optical link performance and stability ensures
that performance degradation may be detected during integration and
testing so that any defective or nonconforming hardware may be
screened out. This knowledge is also useful in operational phases
of a space program to aid in anomaly analysis and to support system
operation and maintenance decisions. The subject SAOC HC defines a
repeatable measure of optical link performance in the SAOC
configuration using data accessible via electrical interfaces.
[0045] FIG. 6 is a flow diagram illustrating an example of an
algorithm for health check (HC) of a SAOC, according to certain
aspects of the subject technology. In some aspects, the HC
algorithm can be implemented in firmware and be executed by
hardware such one or more processors or controllers, for example,
the control circuit 226 of FIG. 2B. The SAOC HC algorithm may be
executed at multiple levels of assembly, anywhere that a
pseudorandom binary sequence (PRBS) suitable for BER measurements
may be generated and checked. In one or more aspects, at operation
block 610 a HC configuration is determined. The HC configuration is
determined over a planned operational environment (e.g., thermal
environment) that results in an optical signal quality below a
planned operational level (e.g., VCSEL drive current). The optical
signal (e.g., detector photo-current) quality, measured at the
receiver, is normally strong enough to avoid adverse threshold
effects with an acceptable input impedance (R.sub.IN) and bandwidth
(BW) behavior, while maintaining electrical interface signal
integrity margins. The acceptable R.sub.IN and BW depends on the
system, for example, an acceptable values of R.sub.IN can be about
50-100.OMEGA. and acceptable values of BW may in the GHz range. In
other words, the HC configuration intentionally generates a high
optical link BER and low photocurrent at the optical receiver.
[0046] At operation block 620, the SAOC electrical interfaces are
configured using control signals to perform with full operational
margin. For each unit assembled, at operation block 630, BER and
photocurrent measurements are taken in the HC configuration to
establish baseline performance statistics for the assembly (630).
The measurements of BER are performed repeatedly to establish
performance statistics for the assembly including the SAOC. Test
equipment and/or the flight assembly provide self-synchronizing
PRBS patterns to conduct BER testing in the HC configurations. This
enables HCs during integration and testing and in flight, as
warranted. In one or more aspects, RSSI is also measured and the
performance statistics includes an HC-BER and an HC-RSSI statistics
for the assembly. At operation block 640, during the operation
lifetime of the assembly, BER is evaluated regularly. It is
understood that physical degradation or damage to the optical link
in an assembly results in a change in BER compared to HC-BER
configuration. At control operation block 650, the measured BER is
compared to the HC-BER. If the measured BER is not higher than that
HC-BER, the assembly is in a stable condition with healthy optical
links and the control is passed to the operation block 640.
Otherwise, if the measured BER is higher than that HC-BER, an
optical link failure is detected.
[0047] In one or more aspects, there are a number of approaches to
HC configuration definition. For example, a common laser drive
condition may be used to yield in family optical BER and
photocurrent. Each assembly may be characterized for a particular
BER and photocurrent performance. In some aspects, custom laser
drive condition is developed for each assembly that yields a common
response and each assembly configuration is evaluated to spot
outliers. In one or more aspects, the HC configurations are
characterized over temperature to account for known optical thermal
compensation effects. The HC configuration may be characterized
coarsely over temperature, for example, using low, ambient, and
high temperatures for expected effects. The HC configuration may be
characterized finely with temperature if necessary to allow
trending within family. Statistical analysis of assembly level
testing and trending yields pass/fail criteria for determining
in-family versus degraded assembly performance.
[0048] In some aspects, the SAOC optical link signal integrity is
purposely compromised in the HC configuration, but in a consistent
and predictable manner necessary to obtain meaningful BER
measurements and statistics. The SAOC HC algorithm is perceptive to
drive, source, coupling, transmission, detector degradation. The
SAOC HC is implemented for each assembled serial number to
establish baseline performance statistics, and performance is
trended over the life of the assembly. The HC configuration may be
commanded throughout the life of the unit to check for changes
(e.g., degradation) in optical link performance. BER and receiver
photocurrent measurements provide perceptivity to optical source
changes, fiber/coupling changes or detector degradation, even
signal integrity across the electrical interface, for example, when
the BER is high but photocurrent has an expected value. The HC
approach can increase the confidence that all units are in
known-good and stable states throughout and at the completion of
system environmental testing and through the operational use of
each optical link. The HC algorithm can similarly be beneficial to
terrestrial AOCs that also lack an optical connector to interrogate
the optical path/performance.
[0049] FIG. 7 is a flow diagram illustrating an example of a method
700 for providing a SAOC, according to certain aspects of the
subject technology. According to the method 700 a cable (e.g., 102
of FIG. 1A) including one or more optical fibers is provided (710).
A first electrical transceiver (e.g., 104 of FIG. 1A, or 200 of
FIGS. 2A and 2B) for coupling to a first end of the cable is
provided (720). The first electrical transceiver is enclosed in a
first enclosure (e.g., 230 of FIG. 2B) enclosing a light detector
(e.g., 206 of FIG. 2B) and a first reflecting surface (e.g., 218 of
FIG. 2B) configured to reflect a first incident light (730). The
first enclosure is processed to provide a predetermined heat
propagation and electromagnetic interference (EMI) specification
and to become radiation hard (740). The cable and the first
electrical transceiver are built to be radiation hard (750).
[0050] FIG. 8 is a flow diagram illustrating an example of a method
800 for providing an AOC (e.g., 110 of FIG. 1A), according to
certain aspects of the subject technology. According to the method
800, an enclosure (e.g., 230 of FIG. 2B) is processed to create a
charred finish using laser pulses (810), by forming a nickel layer
over surfaces of the enclosure (812) and charring the surfaces of
the enclosure (814). The charring is performed by using
femto-second laser pulses, while a power level of the femto-second
laser pulses are increased sharply to a predetermined-level and
reduced steeply (e.g., with profile 400 of FIG. 4) to avoid
ablating the nickel layer. The enclosure is used to enclose a first
electrical transceiver (e.g., 200 of FIG. 2B) for coupling to an
end of the AOC. The first electrical transceiver includes a first
optical coupler formed by a first reflector surface (e.g., similar
to 218 of FIG. 2B) and a light detector (e.g., 206 of FIG. 2B). A
second electrical transceiver for coupling to a opposite end of the
AOC is enclosed in the enclosure similarly. The second electrical
transceiver includes a second optical coupler formed by a second
reflector surface (e.g., 218 of FIG. 2B) and a light source (e.g.,
204 of FIG. 2B).
[0051] The description of the subject technology is provided to
enable any person skilled in the art to practice the various
aspects described herein. While the subject technology has been
particularly described with reference to the various figures and
aspects, it should be understood that these are for illustration
purposes only and should not be taken as limiting the scope of the
subject technology.
[0052] A reference to an element in the singular is not intended to
mean "one and only one" unless specifically stated, but rather "one
or more." The term "some" refers to one or more. Underlined and/or
italicized headings and subheadings are used for convenience only,
do not limit the subject technology, and are not referred to in
connection with the interpretation of the description of the
subject technology. All structural and functional equivalents to
the elements of the various aspects described throughout this
disclosure that are known or later come to be known to those of
ordinary skill in the art are expressly incorporated herein by
reference and intended to be encompassed by the subject technology.
Moreover, nothing disclosed herein is intended to be dedicated to
the public regardless of whether such disclosure is explicitly
recited in the above description.
[0053] Although the invention has been described with reference to
the disclosed aspects, one having ordinary skill in the art will
readily appreciate that these aspects are only illustrative of the
invention. It should be understood that various modifications can
be made without departing from the spirit of the invention. The
particular aspects disclosed above are illustrative only, as the
present invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are
intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular illustrative aspects disclosed above
may be altered, combined, or modified and all such variations are
considered within the scope and spirit of the present invention.
While compositions and methods are described in terms of
"comprising," "containing," or "including" various components or
steps, the compositions and methods can also "consist essentially
of" or "consist of" the various components and operations. All
numbers and ranges disclosed above can vary by some amount.
Whenever a numerical range with a lower limit and an upper limit is
disclosed, any number and any subrange falling within the broader
range are specifically disclosed. Also, the terms in the claims
have their plain, ordinary meaning unless otherwise explicitly and
clearly defined by the patentee. If there is any conflict in the
usages of a word or term in this specification and one or more
patent or other documents that may be incorporated herein by
reference, the definitions that are consistent with this
specification should be adopted.
* * * * *