U.S. patent application number 17/083922 was filed with the patent office on 2022-05-05 for system and method for testing optical receivers.
The applicant listed for this patent is Mellanox Technologies, Ltd.. Invention is credited to Tatyana ANTONENKO, Yaakov GRIDISH, Itshak KALIFA, Elad MENTOVICH, Tamir SHARKAZ.
Application Number | 20220137120 17/083922 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220137120 |
Kind Code |
A1 |
ANTONENKO; Tatyana ; et
al. |
May 5, 2022 |
SYSTEM AND METHOD FOR TESTING OPTICAL RECEIVERS
Abstract
Disclosed are a testing unit, system, and method for testing and
predicting failure of optical receivers. The testing unit and
system are configured to apply different values of current,
voltage, heat stress, and illumination load on the optical
receivers during testing. The test methods are designed to check
dark current, photo current, forward voltage, and drift over time
of these parameters.
Inventors: |
ANTONENKO; Tatyana; (Rishon
LeTsiyon, IL) ; GRIDISH; Yaakov; (Yoqneam Ilit,
IL) ; SHARKAZ; Tamir; (Kfar Tavor, IL) ;
KALIFA; Itshak; (Bat Yam, IL) ; MENTOVICH; Elad;
(Tel Aviv, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mellanox Technologies, Ltd. |
Yokneam |
|
IL |
|
|
Appl. No.: |
17/083922 |
Filed: |
October 29, 2020 |
International
Class: |
G01R 31/26 20060101
G01R031/26; H01S 5/00 20060101 H01S005/00; G01R 1/04 20060101
G01R001/04 |
Claims
1. A testing unit for use in a system for testing and predicting
failure of optical receivers, the testing unit comprising: a) a
testing board configured to support at least one socket, wherein
the at least one socket is configured to be coupled to a substrate
configured to support at least one optical receiver; and b) an
emitter board configured to support at least one optical emitter;
wherein, the emitter board is supported adjacent to the testing
board such that the emitter board is substantially parallel to the
testing board and each of the one or more optical emitters on the
emitter board is substantially aligned with a corresponding socket
of the testing board.
2. The testing unit of claim 1 comprising at least one support rail
configured to support and to attach the emitter board onto the
testing board.
3. The testing unit of claim 1 comprising an edge connector on the
emitter board, the edge connector configured to allow electrical
communication between components on the emitter board and other
components of the system.
4. The testing unit of claim 1 comprising a first connector located
on the emitter board configured to allow electrical communication
between the at least one optical emitter and the first
connector.
5. The testing unit of claim 1 comprising a second connector
configured to mate with the first connector located on the emitter
board and to electrically connect the at least one optical emitter
on the emitter board to the testing board.
6. The testing unit of claim 1 comprising electrical traces on the
testing board configured to allow electrical communication between
edge connector and the optical receivers on the substrates in the
sockets on the testing board and to allow electrical communication
between the emitters on the emitter board and the edge connector
via the second connector.
7. The testing unit of claim 1, wherein the optical receivers are
photodiodes.
8. The testing unit of claim 1, wherein the one or more optical
emitters on the emitter board are configured to provide an
illumination load on the at least one optical receiver on the
testing board.
9. The testing unit of claim 1, wherein the at least one socket is
arranged on a top surface of the testing board.
10. The testing unit of claim 1, wherein the at least one optical
emitter is arranged on a bottom surface of the emitter board
11. The testing unit of claim 1, wherein the electrical traces on
the testing board are configured to allow electrical signals
related to one or more testing methods to be sent from the edge
connector to each of the optical receivers on the testing board and
allow various parameters or outputs to be transmitted as electrical
signals from each of the optical receivers to the edge
connector.
12. The testing unit of claim 11, wherein the parameters or outputs
of the optical receivers are at least one of: an output voltage, an
output current, and an operating temperature.
13. The testing unit of claim 1, wherein the optical emitters are
one of: vertical-cavity surface-emitting lasers (VCSELs), light
emitting diodes (LEDs), and arrays of LEDs.
14. The testing unit of claim 1, wherein when in an operational
configuration, in which the bottom surface of the emitter board is
substantially aligned with the testing board, the emitter board
supports the same number of optical emitters as the number of
sockets supported by the corresponding testing board and the
configuration or orientation of these optical emitters matches that
of the orientation of sockets of the testing board so as allow for
optical communication between each optical emitter and the optical
receivers in the socket beneath it.
15. A system for testing and predicting failure of optical
receivers, the system comprising: a) at least one testing unit
according to claim 1; b) at least one driver in electrical
communication with a plurality of optical receivers in one or more
sockets on the testing board of the at least one testing unit and
in electrical communication with the one or more optical emitters
on the emitter board of the at least one testing unit via the end
connector and electrical traces on the testing board; the driver
configured to apply a voltage input to at least one optical
receiver, to activate at least one optical emitter that is in
optical communication with the at least one optical receiver, and
to monitor a corresponding output parameter from the at least one
optical receiver; c) at least one control unit configured to
execute or otherwise control the operation of the testing methods
and procedures applied to the optoelectronic components supported
by the testing unit via the at least one driver; d) at least one
power supply configured to supply electrical power to the at least
one driver and to the control unit; and e) electrical connections
configured to allow electrical communication between the components
of the system.
16. A system according to claim 15 additionally comprising at least
one backplane element configured to support and be in electrical
communication with the at least one testing unit; wherein, any
number of testing units are supported by a backplane element and/or
the system includes any number of additional backplane
elements.
17. A system according to claim 15, wherein the system does not
include a backplane element and the testing unit is directly
connected to a driver or to a control unit.
18. A system according to claim 15, wherein the drivers include
circuitry and/or optoelectronic elements configured to multiplex
outputs signals received by the driver from testing units into a
combined signal for transmission over a shared transmission medium
to a control unit or other device in electrical communication with
the driver.
19. A system according to claim 15, wherein the at least one driver
is further configured to determine a pass state or a fail state of
any number of a plurality of optical receivers based on a
comparison of various output parameters to corresponding output
parameter thresholds.
20. A system according to claim 15, wherein the control unit is in
electrical communication with at least one sensor to monitor or
control input, output, and/or ambient conditions of the system,
wherein the at least one sensor is selected from the following:
thermometers, pressure sensors, humidity sensors, accelerometers,
photo resistors, and barometers.
21. A system according to claim 15, wherein the control unit
operates as a computer or computer program product.
22. A system according to claim 15, wherein the processor includes
or is associated with an apparatus comprising: a) a memory device
configured to store various testing procedures, testing parameters,
and/or threshold values configured to evaluate the reliability of a
photodiode; b) a processor configured to execute instructions
stored in the memory device or otherwise accessible to the
processor; c) a communication interface configured as a device or
circuitry embodied in either hardware or a combination of hardware
and software that is configured to receive and/or transmit data
either using wired or wireless techniques between at least one of:
computing devices, servers, drivers, and testing units; and d) a
user interface in communication with the processor and configured
to receive an indication of a user input and/or to provide an
audible, visual, mechanical, or other output to a user.
23. A system according to claim 15, wherein the driver includes
some or all of the circuitry or operation of the control unit.
24. A system according to claim 21, wherein the driver includes
some or all of the circuitry or operation of the control unit.
25. A system according to claim 15 comprising sixteen optical
receivers in eight sockets on sixteen testing boards, wherein the
system is configured to be controlled by a single control unit;
thereby enabling testing, with and without illumination, up to 2048
optical receivers without taking the optical receivers out of the
system.
26. A method of testing and predicting failure of optical
receivers, the method comprising: A. placing the following
components of a system for testing and predicting failure of
optical receivers within a temperature controlled oven: a) a
testing board configured to support at least one socket, wherein
each socket is configured to receive a substrate configured to
support at least one optical receiver; and b) an emitter board
configured to support at least one optical emitter; wherein, the
emitter board is supported above the testing board such that the
emitter board is substantially parallel to the testing board and
each of the one or more optical emitters on the emitter board is
substantially aligned with a corresponding socket of the testing
board; and B. carrying out all tests without removing the testing
board or the emitter board from the oven.
27. The method of claim 26, wherein the optical receivers are
photodiodes.
28. The method of claim 26, wherein the method is carried out using
a system that can be manually controlled or programmed to
automatically carry out the reliability tests on individual optical
receivers in any socket on any testing board.
29. The method of claim 26, comprising a pre-test comprised of the
following steps: a) check substrate temperature to determine if it
is inside a designed operating range of an optical receiver; b)
check that an optical receiver to be tested is present; c) apply
current on the optical receiver and check that a measured voltage
is inside a designed operating range of the optical receiver; d)
check for an open or a short circuit and leakage on the optical
receiver; e) in case of fail of any of steps a to d, the test
stops.
30. The method of claim 26, comprising a first test procedure
comprised of the following steps: a) apply reverse voltage on the
optical receiver and check that the dark current is inside the
designed operating range of the optical receiver; b) apply reverse
voltage on the optical receive, turn on illumination, and check
that the photo current is inside the designed operating range of
the optical receiver; c) apply forward current on the optical
receiver and check that the forward voltage is inside the designed
operating range of optical receiver; d) in case of fail of any of
the steps a to c, the optical receiver is marked as FAIL; and e) in
case no failure in steps a to c, document the dark current, photo
current, forward voltage, and temperature at Time=0; wherein in
steps a and b the reverse voltage can be applied using different
voltage values and in step c the forward current can be applied
using different current values.
31. The method of claim 26, comprising a second test procedure,
which comprises the following two options: A) first option is
without illumination: a) raise the temperature of a substrate above
ambient; b) apply a constant reverse voltage on an optical
receiver. c) measure the substrate temperature periodically and
check if the temperature is above or below a preset value; and d)
if the temperature is above or below a preset value the test stops;
e) measure dark current periodically and check if inside a designed
operating range of the optical receiver; and f) in case of fail of
step d the optical receiver is marked as FAIL. wherein the test is
carried out at a constant temperature. B) second option with
illumination: a) raise the temperature of a substrate; b) apply a
constant reverse voltage on an optical receiver and turn on
illumination; c) measure substrate temperature periodically and
check if the temperature is above or below a preset value; d) in
case of fail the test stops; e) measure photo current periodically
and check if inside the designed operating range of the optical
receiver; and f) in case of fail of step e the optical receiver is
marked as FAIL.
32. The method of claim 26, comprising a third test procedure
comprised of the following steps: a) apply reverse voltage on an
optical receiver and check that the dark current is inside the
designed operating range of the optical receiver; b) apply reverse
voltage on optical receiver, turn on illumination, and check that
the photo current is inside a designed operating range of the
optical receiver; c) apply forward current on the optical receiver
and check that the forward voltage is inside the designed operating
range of the optical receiver; d) in case of fail of any of the
steps a to c, the optical receiver is marked as FAIL; e) in case no
failure in steps a to c, document the dark current, photo current,
forward voltage, and temperature at Time=X. f) determine drift of
dark current, photo current, and forward voltage between Time=0 and
Time=X and check if inside a designed limit for the optical
receiver; and g) in case the drift of one or more of the parameters
is outside the designed limit the optical receiver is marked as
FAIL; wherein: i) in steps a and b the reverse voltage can be
applied using different voltage values and in step c the forward
current can be applied using different current values; and ii) when
computing the drift in step d the temperature and illumination
conditions should be same at time=0 and time=X.
33. The method of claim 26, wherein the first test procedure, the
second test procedure, and the third test procedure are run
consecutively and the data in the database from the first procedure
is used for Time=0 in step f of the third procedure.
34. The method of claim 26, wherein the second test procedure and
the third test procedure are repeated cyclically and any
measurement can be used as Time=0 allowing drift to be determined
in step f of the third procedure.
Description
FIELD OF THE INVENTION
[0001] The invention is from the field of testing optoelectronic
devices. Specifically the invention relates to a system and method
for testing optical receivers, for example photodiodes, in order to
predict failure of the optical receiver.
BACKGROUND OF THE INVENTION
[0002] Optical communication systems, such as those used in data
centers, include optical transmitters, e.g. vertical-cavity
surface-emitting lasers (VCSELs) and optical receivers, e.g.
photodiodes, which transmit and receive optical signals via optical
cables. One of the causes of failures in optical system is random
failure of photodiodes.
[0003] Prior art photodiode testing systems are designed to perform
different modes of burn-in testing. These testing modes typically
involve applying various regimens of stress, e.g. elevated
voltages, to photodiodes under different environmental conditions
for extended periods of time to evaluate their performance.
Examples of commercially available systems for testing photodiodes
using these methods are manufactured by Electron Test Equipment
Limited of Dublin Ireland and MKS Instruments, Inc. of Andover,
Mass., U.S.A.
[0004] The function of a photodiode in an optical communication
system is to convert incoming light, for example from a VCSEL, to
electronic signals. Adding light during the test will cause
additional stress to the component and will better simulate the
working conditions of PD dies inside modules. To the best of the
inventor's knowledge currently commercially available testing
systems do not take into account the influence of incident light on
the performance and reliability of photodiodes.
[0005] It is a purpose of the present invention to provide a system
and method of testing photodiodes in order to predict failures.
[0006] It is another purpose of the present invention to include
incident light on photodiodes during the test in order to cause
additional stress to the component and better simulate the working
conditions of the photdiode inside modules.
[0007] Further purposes and advantages of this invention will
appear as the description proceeds.
SUMMARY OF THE INVENTION
[0008] In a first aspect the invention is a testing unit for use in
a system for testing and predicting failure of optical receivers.
The testing unit comprises: [0009] a) a testing board configured to
support at least one socket, wherein the at least one socket is
configured to be coupled to a substrate configured to support at
least one optical receiver; and [0010] b) an emitter board
configured to support at least one optical emitter.
[0011] The emitter board is supported adjacent to the testing board
such that the emitter board is substantially parallel to the
testing board and each of the one or more optical emitters on the
emitter board is substantially aligned with a corresponding socket
of the testing board.
[0012] Embodiments of the testing unit comprise at least one
support rail configured to support and attach the emitter board
onto the testing board.
[0013] Embodiments of the testing unit comprise an edge connector
on the emitter board, the edge connector configured to allow
electrical communication between components on the emitter board
and other components of the system.
[0014] Embodiments of the testing unit comprise a first connector
located on the emitter board configured to allow electrical
communication between the at least one optical emitter and the
first connector.
[0015] Embodiments of the testing unit comprise a second connector
configured to mate with the first connector located on the emitter
board and to electrically connect the at least one optical emitter
on the emitter board to the testing board.
[0016] Embodiments of the testing unit comprise electrical traces
on the testing board configured to allow electrical communication
between edge connector and the optical receivers on the substrates
in the sockets on the testing board and to allow electrical
communication between the emitters on the emitter board and the
edge connector via the second connector.
[0017] In embodiments of the testing unit the optical receivers are
photodiodes.
[0018] In embodiments of the testing unit the one or more optical
emitters on the emitter board are configured to provide an
illumination load on the at least one optical receiver on the
testing board.
[0019] In embodiments of the testing unit the at least one socket
is arranged on a top surface of the testing board.
[0020] In embodiments of the testing unit the at least one optical
emitter is arranged on a bottom surface of the emitter board
[0021] In embodiments of the testing unit the electrical traces on
the testing board are configured to allow electrical signals
related to one or more testing methods to be sent from the edge
connector to each of the optical receivers on the testing board and
allow various parameters or outputs to be transmitted as electrical
signals from each of the optical receivers to the edge connector.
In these embodiments the parameters or outputs of the optical
receivers are at least one of: an output voltage, an output
current, and an operating temperature.
[0022] In embodiments of the testing unit the optical emitters are
one of: vertical-cavity surface-emitting lasers (VCSELs), light
emitting diodes (LEDs), and arrays of LEDs.
[0023] In embodiments of the testing unit, when the testing unit is
in an operational configuration, in which the bottom surface of the
emitter board is substantially aligned with the testing board, the
emitter board supports the same number of optical emitters as the
number of sockets supported by the corresponding testing board and
the configuration or orientation of these optical emitters matches
that of the orientation of sockets of the testing board so as allow
for optical communication between each optical emitter and the
optical receivers in the socket beneath it.
[0024] In a second aspect the invention is a system for testing and
predicting failure of optical receivers. The system comprises:
[0025] a) at least one testing unit according to the first aspect;
[0026] b) at least one driver in electrical communication with a
plurality of optical receivers in one or more sockets on the
testing board of the at least one testing unit and in electrical
communication with the one or more optical emitters on the emitter
board of the at least one testing unit via the end connector and
electrical traces on the testing board; the driver configured to
apply a voltage input to at least one optical receiver, to activate
at least one optical emitter that is in optical communication with
the at least one optical receiver, and to monitor a corresponding
output parameter from the at least one optical receiver; [0027] c)
at least one control unit configured to execute or otherwise
control the operation of the testing methods and procedures applied
to the optoelectronic components supported by the testing unit via
the at least one driver; [0028] d) at least one power supply
configured to supply electrical power to the at least one driver
and to the control unit; and [0029] e) electrical connections
configured to allow electrical communication between the components
of the system.
[0030] Embodiments of the system comprise at least one backplane
element configured to support and be in electrical communication
with the at least one testing unit; wherein, any number of testing
units are supported by a backplane element and/or the system
includes any number of additional backplane elements.
[0031] Embodiments of the system do not include a backplane element
and the testing unit is directly connected to a driver or to a
control unit.
[0032] In embodiments of the system the drivers include circuitry
and/or optoelectronic elements configured to multiplex outputs
signals received by the driver from testing units into a combined
signal for transmission over a shared transmission medium to a
control unit or other device in electrical communication with the
driver.
[0033] In embodiments of the system the at least one driver is
further configured to determine a pass state or a fail state of any
number of a plurality of optical receivers based on a comparison of
various output parameters to corresponding output parameter
thresholds.
[0034] In embodiments of the system the control unit is in
electrical communication with at least one sensor to monitor or
control input, output, and/or ambient conditions of the system,
wherein the at least one sensor is selected from the following:
thermometers, pressure sensors, humidity sensors, accelerometers,
photo resistors, and barometers.
[0035] In embodiments of the system the control unit operates as a
computer or computer program product. In these embodiments of the
system the driver can include some or all of the circuitry or
operation of the control unit.
[0036] In embodiments of the system the processor includes or is
associated with an apparatus comprising: [0037] a) a memory device
configured to store various testing procedures, testing parameters,
and/or threshold values configured to evaluate the reliability of a
photodiode; [0038] b) a processor configured to execute
instructions stored in the memory device or otherwise accessible to
the processor; [0039] c) a communication interface configured as a
device or circuitry embodied in either hardware or a combination of
hardware and software that is configured to receive and/or transmit
data either using wired or wireless techniques between at least one
of: computing devices, servers, drivers, and testing units; and
[0040] d) a user interface in communication with the processor and
configured to receive an indication of a user input and/or to
provide an audible, visual, mechanical, or other output to a
user.
[0041] In these embodiments of the system the driver can include
some or all of the circuitry or operation of the control unit.
[0042] Embodiments of the system comprise sixteen optical receivers
in eight sockets on sixteen testing boards. In these embodiments
the system is configured to be controlled by a single control unit;
thereby enabling testing, with and without illumination, up to 2048
optical receivers without taking the optical receivers out of the
system.
[0043] In a third aspect the invention is a method of testing and
predicting failure of optical receivers. The method comprises:
[0044] A. placing the following components of a system for testing
and predicting failure of optical receivers within a temperature
controlled oven: [0045] a) a testing board configured to support at
least one socket, wherein each socket is configured to receive a
substrate configured to support at least one optical receiver; and
[0046] b) an emitter board configured to support at least one
optical emitter; [0047] wherein, the emitter board is supported
above the testing board such that the emitter board is
substantially parallel to the testing board and each of the one or
more optical emitters on the emitter board is substantially aligned
with a corresponding socket of the testing board; and [0048] B.
carrying out all tests without removing the testing board or the
emitter board from the oven.
[0049] In embodiments of the method the optical receivers are
photodiodes.
[0050] Embodiments of the method are carried out by a system, which
can be manually controlled or programmed to automatically carry out
the reliability tests on individual optical receivers in any socket
on any testing board.
[0051] Embodiments of the method comprise a pre-test comprised of
the following steps: [0052] a) check substrate temperature to
determine if it is inside a designed operating range of an optical
receiver; [0053] b) check that an optical receiver to be tested is
present; [0054] c) apply current on the optical receiver and check
that a measured voltage is inside a designed operating range of the
optical receiver; [0055] d) check for an open or a short circuit
and leakage on the optical receiver; [0056] e) in case of fail of
any of steps a to d, the test stops.
[0057] Embodiments of the method comprise a first test procedure
comprised of the following steps: [0058] a) apply reverse voltage
on the optical receiver and check that the dark current is inside
the designed operating range of the optical receiver; [0059] b)
apply reverse voltage on the optical receive, turn on illumination,
and check that the photo current is inside the designed operating
range of the optical receiver; [0060] c) apply forward current on
the optical receiver and check that the forward voltage is inside
the designed operating range of optical receiver; [0061] d) in case
of fail of any of the steps a to c, the optical receiver is marked
as FAIL; and [0062] e) in case no failure in steps a to c, document
the dark current, photo current, forward voltage, and temperature
at Time=0; [0063] wherein in steps a and b the reverse voltage can
be applied using different voltage values and in step c the forward
current can be applied using different current values.
[0064] Embodiments of the method comprise a second test procedure,
which comprises the following two options: [0065] A) first option
is without illumination: [0066] a) raise the temperature of a
substrate above ambient; [0067] b) apply a constant reverse voltage
on an optical receiver. [0068] c) measure the substrate temperature
periodically and check if the temperature is above or below a
preset value; and [0069] d) if the temperature is above or below a
preset value the test stops; [0070] e) measure dark current
periodically and check if inside a designed operating range of the
optical receiver; and [0071] f) in case of fail of step d the
optical receiver is marked as FAIL. [0072] wherein the test is
carried out at a constant temperature. [0073] B) second option with
illumination: [0074] a) raise the temperature of a substrate;
[0075] b) apply a constant reverse voltage on an optical receiver
and turn on illumination; [0076] c) measure substrate temperature
periodically and check if the temperature is above or below a
preset value; [0077] d) in case of fail the test stops; [0078] e)
measure photo current periodically and check if inside the designed
operating range of the optical receiver; and [0079] f) in case of
fail of step e the optical receiver is marked as FAIL.
[0080] Embodiments of the method comprise a third test procedure
comprised of the following steps: [0081] a) apply reverse voltage
on an optical receiver and check that the dark current is inside
the designed operating range of the optical receiver; [0082] b)
apply reverse voltage on optical receiver, turn on illumination,
and check that the photo current is inside a designed operating
range of the optical receiver; [0083] c) apply forward current on
the optical receiver and check that the forward voltage is inside
the designed operating range of the optical receiver; [0084] d) in
case of fail of any of the steps a to c, the optical receiver is
marked as FAIL; [0085] e) in case no failure in steps a to c,
document the dark current, photo current, forward voltage, and
temperature at Time=X. [0086] f) determine drift of dark current,
photo current, and forward voltage between Time=0 and Time=X and
check if inside a designed limit for the optical receiver; and
[0087] g) in case the drift of one or more of the parameters is
outside the designed limit the optical receiver is marked as FAIL;
[0088] wherein: [0089] i) in steps a and b the reverse voltage can
be applied using different voltage values and in step c the forward
current can be applied using different current values; and [0090]
ii) when computing the drift in step d the temperature and
illumination conditions should be same at time=0 and time=X.
[0091] In embodiments of method the first test procedure, the
second test procedure, and the third test procedure are run
consecutively. In these embodiments the data in the database from
the first procedure can be used for Time=0 in step f of the third
procedure.
[0092] In embodiments of method the second test procedure and the
third test procedure are repeated cyclically. In these embodiments
any measurement can be used as Time=0 allowing drift to be
determined in step f of the third procedure.
[0093] All the above and other characteristics and advantages of
the invention will be further understood through the following
illustrative and non-limitative description of embodiments thereof,
with reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0094] FIG. 1 schematically shows a diagram of a system for testing
optical receivers in accordance with the present invention;
[0095] FIG. 2 schematically shows a block diagram of an example
apparatus that may be configured in accordance with some
embodiments discussed herein;
[0096] FIG. 3 schematically shows a side view of a testing unit in
accordance with some embodiments discussed herein;
[0097] FIG. 4 symbolically shows a top view of a testing board of
FIG. 1 in accordance with some embodiments discussed herein;
[0098] FIG. 5 symbolically shows a perspective view of a socket,
substrate, and plurality of optical receivers in accordance with
some embodiments discussed herein;
[0099] FIG. 6 symbolically shows a top view of a substrate of FIG.
4 in accordance with some embodiments discussed herein;
[0100] FIG. 7 symbolically shows a top view of a particular
configuration of the substrate of FIG. 4 in accordance with some
embodiments discussed herein; and
[0101] FIG. 8 symbolically shows a bottom view of the emitters
board of FIG. 3 in accordance with some embodiments discussed
herein;
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0102] FIG. 1 schematically shows a system 100 for testing and
predicting failure of optical receivers. System 100 includes
testing units 102, backplane elements 104, drivers 108, a control
unit 112, and a power supply 114. The testing units 102 include or
otherwise support various optoelectronic components, such as
optical emitters and optical receivers, so that one or more testing
procedures may be performed on the optoelectronic components
supported thereon. As shown, in some embodiments, a testing unit
102 may be supported by a backplane element 104 such that the
backplane element 104 is in electrical communication with the
testing unit 102. To establish and maintain electrical
communication, in some embodiments, the testing unit may include an
edge connector 106 configured to be received by a corresponding
connector of the backplane element 104. The connection between the
backplane element 104 and the testing unit 102 is such that
electrical signals may flow between them. Additionally, and as
shown in FIG. 1, the backplane element 104 may also be configured
to support one or more testing units 102 where each testing unit
may define a corresponding edge connector 106 in order to
electrically connect with the backplane element 104. While
reference hereinafter may be made to one testing unit 102 and/or
one corresponding backplane element 104, the present disclosure
contemplates that any number of testing units 102 may be supported
by a backplane element 104 and/or that the system 100 may include
any number of additional backplane elements 104. Furthermore, in
some embodiments, the system 100 may not include a backplane
element 104 such that the testing unit may be directly connected to
a driver 108 or a control unit 112. Said another way, the present
disclosure contemplates that any number of structural support
elements (e.g., datacenter racks, cabinets, testing chambers,
ovens, or the like) may function to support the testing unit 102
and/or may facilitate electrical connection between the testing
unit 102 and an electrical or current input device (e.g., the
driver 108) and/or may function to control values of parameters of
environmental conditions surrounding testing unit 102 (e.g. the
temperature).
[0103] Driver 108 is configured to generate inputs (e.g., a voltage
input) that are applied to optoelectronic components (e.g.,
photodiodes) supported by the testing unit 102. For example, the
driver 108 may be configured to generate and apply a stress current
or voltage to the testing unit 102 supported by the backplane 104.
The driver 108 is in electrical communication with a plurality of
optical receivers (e.g., a plurality of optical receivers 502 in
FIG. 5) in one or more sockets (e.g., one or more sockets 302 in
FIG. 3) and in electrical communication with the one or more
optical emitters (e.g., one or more optical emitters 314 in FIG. 3)
on the emitters board (e.g., a emitter board 304 in FIG. 3). The
driver 108 is configured to apply a voltage input to at least one
optical receiver and to monitor a corresponding output parameter
(e.g., output voltage, operating temperature, etc.). Further, the
driver 108 is configured to receive electrical signals output by
the testing unit 102 that may be directed to a control unit 112
described herein below. Furthermore, the driver 108 may include
circuitry and/or optoelectronic elements (e.g., a multiplexer)
configured to multiplex outputs signals received by the driver 108
from the testing unit 102 into a combined signal for transmission
over a shared transmission medium (e.g. an optical fiber or the
like) to a control unit 112 or other device in electrical
communication with the driver 108. In some embodiments, the driver
108 may be further configured to determine a pass state or a fail
state of any number of a plurality of optical receivers based on a
comparison of various output parameters to corresponding output
parameter thresholds.
[0104] In some embodiments, the driver 108 may be in electrical
communication with the backplane element 104 via a rigid-flex
printed circuit board (PCB) 110. Additionally, in some embodiments,
the system 100 may include one or more drivers 108 configured to
provide inputs to one or more testing units 102. By way of example,
in some embodiments, the number of drivers 102 used by the system
100 may correspond to the number of testing units 102 used by the
system such that each driver 108 provides an input to a
corresponding testing unit 102. By way of a more particular example
as shown in FIG. 1, in some embodiments, the system 100 may include
four (4) drivers 108 each in electrical communication with a
backplane element 104 and a corresponding testing unit 102. While
illustrated with the driver 108 providing inputs to only one
corresponding testing unit 102, the present disclosure contemplates
that any number of drivers may provide inputs to any number of
testing units 102. Said another way, one driver 108 may provide
inputs to multiple testing units 102 and/or multiple drivers 108
may provide inputs to a single corresponding testing unit 102.
[0105] In some embodiments, the system 100 may also include a
control unit 112 configured to execute or otherwise control the
operation of the testing methods and procedures applied to the
optoelectronic components supported by the testing unit 102. In
some embodiments, the control unit 112 may be in electrical
communication with the driver 108 such that electrical signals may
be provided to the driver 108 (e.g., voltage inputs) and electrical
signals may be provided from the driver 108 to the control unit 112
(e.g., output parameters, multiplex signals, or the like). As would
be understood by one or ordinary skill in the art in light of the
present disclosure, with reference in particular to the description
of below FIG. 3, the control unit 112 may operate as a computer or
computer program product. In particular, the control unit 112 may
be configured to execute one or more testing methods (e.g.,
measurements, algorithms, protocols, or the like) by directing or
otherwise controlling operation of the driver 108. Thus, the
control unit 112 may provide commands to the driver 108 to apply
various inputs (e.g., voltages) to the testing unit 102 and may
receive output data (e.g., electrical signals) from the testing
unit 102 via the driver 108. Furthermore, the control unit 112 may
be configured to monitor or control various other variables or
parameters of the system 100. For example, the control unit 112 may
be in electrical communication with one or more sensors (e.g.,
thermometers, pressure sensors, humidity sensors, accelerometers,
photo resistors, barometers, and the like) so as to monitor input,
output, and/or ambient conditions of the system 100. For example,
the control unit 112 may monitor the ambient temperature of the
system 100 and/or the output temperature of one or more
optoelectronic components (e.g., when subjected to a voltage input)
via electrical communication with one or more thermometers.
Although described herein with respect to the control unit 112
executing testing methods or procedures via input commands to the
driver 108, the present disclosure contemplates that the driver 108
may also include some or all of the circuitry or operation of the
control unit 112. Said another way, the driver 108 may be integral
to the control unit 112 in physical structure and/or operation.
Similar to the backplane element 104 and the driver 108 above, in
some embodiments, the system 100 may comprise one or more control
units 112 configured to direct the operation of one or more drivers
108. In any embodiment described herein, the system 100 may include
one or more power supplies 114 configured to provide power to one
or more of the control unit 112 and/or the driver 108.
[0106] Regardless of the type of device that embodies the control
unit 112 or the driver 108, the control unit 112 and/or driver 108
may include or be associated with an apparatus 200 as shown in FIG.
2. In this regard, the apparatus 200 may include or otherwise be in
communication with a processor 202, a memory device 204, a
communication interface 206, and/or a user interface 208. As such,
in some embodiments, although devices or elements are shown as
being in communication with each other, hereinafter such devices or
elements should be considered to be capable of being embodied
within the same device or element and thus, devices or elements
shown in communication should be understood to alternatively be
portions of the same device or element.
[0107] In some embodiments, the processor 202 (and/or co-processors
or any other processing circuitry assisting or otherwise associated
with the processor) may be in communication with the memory device
204 via a bus for passing information among components of the
apparatus 200. The memory device 204 may include, for example, one
or more volatile and/or non-volatile memories. In other words, for
example, the memory device 204 may be an electronic storage device
(e.g., a computer readable storage medium) comprising gates
configured to store data (e.g., bits) that may be retrievable by a
machine (e.g., a computing device like the processor). The memory
device 204 may be configured to store information, data, content,
applications, instructions, or the like for enabling the apparatus
200 to carry out various functions in accordance with an example
embodiment of the present invention. In this regard, the memory
device 204 may store various testing procedures, testing
parameters, and/or threshold values configured to evaluate the
reliability of a photodiode as discussed below. For example, the
memory device 204 could be configured to buffer input data for
processing by the processor 202. Additionally or alternatively, the
memory device 204 could be configured to store instructions for
execution by the processor 202.
[0108] As noted above, the apparatus 200 may be embodied by the
driver 108 or the control unit 112 configured to be utilized in an
example embodiment of the present invention. However, in some
embodiments, the apparatus 200 may be embodied as a chip or chip
set. In other words, the apparatus 200 may comprise one or more
physical packages (e.g., chips) including materials, components
and/or wires on a structural assembly (e.g., a baseboard). The
structural assembly may provide physical strength, conservation of
size, and/or limitation of electrical interaction for component
circuitry included thereon.
[0109] The processor 202 may be embodied in a number of different
ways. For example, the processor 202 may be embodied as one or more
of various hardware processing means such as a coprocessor, a
microprocessor, a controller, a digital signal processor (DSP), a
processing element with or without an accompanying DSP, or various
other processing circuitry including integrated circuits such as,
for example, an ASIC (application specific integrated circuit), an
FPGA (field programmable gate array), a microcontroller unit (MCU),
a hardware accelerator, a special-purpose computer chip, or the
like.
[0110] In an example embodiment, the processor 202 may be
configured to execute instructions stored in the memory device 204
or otherwise accessible to the processor 202. Alternatively or
additionally, the processor 202 may be configured to execute hard
coded functionality. As such, whether configured by hardware or
software methods, or by a combination thereof, the processor 202
may represent an entity (e.g., physically embodied in circuitry)
capable of performing operations according to an embodiment of the
present invention while configured accordingly. Thus, for example,
when the processor 202 is embodied as an ASIC, FPGA or the like,
the processor 202 may be specifically configured hardware for
conducting the operations described herein. Alternatively, as
another example, when the processor 202 is embodied as an executor
of software instructions, the instructions may specifically
configure the processor 202 to perform the algorithms and/or
methods described herein when the instructions are executed.
However, in some cases, the processor 202 may be a processor 202 of
a specific device (e.g., a control unit 112 or driver 108 as shown
in FIG. 1) configured to be employed by an embodiment of the
present invention by further configuration of the processor 202 by
instructions for performing the algorithms and/or operations
described herein.
[0111] Meanwhile, the communication interface 206 may be any means
such as a device or circuitry embodied in either hardware or a
combination of hardware and software that is configured to receive
and/or transmit data between computing devices and/or servers. For
example, the communication interface 206 may be configured to
communicate wirelessly with the one or more drivers 108 and/or
testing units 102, such as via Wi-Fi, Bluetooth, or other wireless
communications techniques. In some instances, the communication
interface may alternatively or also support wired communication.
For example, the communication interface 206 may be configured to
communicate via wired communication with other components of the
driver 108 and/or testing unit 102.
[0112] In some embodiments, the apparatus 200 may optionally
include a user interface 208 in communication with the processor
202, such as by user interface circuitry, to receive an indication
of a user input and/or to provide an audible, visual, mechanical,
or other output to a user. As such, the user interface 208 may
include, for example, a keyboard, a mouse, a display, a touch
screen display, a microphone, a speaker, and/or other input/output
mechanisms. The user interface may also be in communication with
the memory 204 and/or the communication interface 206, such as via
a bus.
[0113] With reference to FIG. 3, a testing unit 102 of the system
100 is schematically illustrated. As shown, the testing unit 102
may include a testing board 300, an emitter board 304, one or more
support rails 306, and an edge connector 106. As shown, in some
embodiments, the testing board 300 may be configured to support one
or more sockets 302 via a top surface of the testing board 300. As
described hereinafter with reference to FIGS. 4-7, each of the one
or more sockets 302 may receive a substrate supporting one or more
optical receivers for receiving optical signals (e.g., a substrate
500 and an optical receiver 502 in FIG. 5). The testing board 300
of the testing unit 102 may include a substrate, circuit board, or
any other support structure which allows electrical signals to be
directed to the socket 302, and subsequently to the optical
receivers supported thereon, from the driver 108 via the backplane
104 (in FIG. 1). In particular, the testing board may define one or
more electrical traces, connections, or the like configured to
allow electrical communication between the plurality of optical
receivers (e.g., optical receivers 502 in FIG. 5) and the driver
108 (see FIG. 1). As described above with reference to FIG. 1, the
testing board 300 (e.g., of the testing unit 102) may define an
edge connector 106 configured to be received by a corresponding
connector of the backplane element 104. The connection between the
backplane element 104 and the testing unit 102 may be such that
electrical signals may flow therebetween.
[0114] The testing unit 102 may also include a emitter board 304
supporting one or more optical emitters 314 (e.g., LEDs) via a
bottom surface of the emitter board 304. As described more fully
hereinafter, the one or more optical emitters may be configured to
transmit optical signals to be received by a plurality of optical
receivers, which are configured to convert the optical signals to
corresponding electrical signals. As shown in FIG. 3, the one or
more optical emitters 314 may be in optical communication via
alignment of the testing board 300 with the emitter board 304. For
example, the testing unit 102 may be configured such that the top
surface of the testing board 300 supporting the one or more sockets
302 is disposed opposite the bottom surface of the testing board
300 supporting the one or more optical emitters 314.
[0115] The testing unit 102 may further include one or more support
rails 306 attached to one of the testing board 300 or the emitter
board 304, and the one or more support rails 306 may be configured
to attach the testing board 300 to the emitter board 304. While
illustrated with three (3) support rails 306 in FIG. 3, the present
disclosure contemplates that any number of support rails may be
used in any configuration. Additionally, the support rails 306 may
be attached to either one of the emitter board 304 or testing board
300 so long as the one or more support rails 306 may be configured
to substantially align each of the one or more optical emitters 314
of the emitter board with a corresponding socket 302 of the testing
board 300 such that optical signals transmitted by an optical
emitter (e.g., an optical emitter 314 in FIG. 3) of the emitter
board 304 may be received by the corresponding optical receiver 502
of the socket 302 when the testing unit 102 is in an operational
configuration. Still further, the emitter board 304 may also be
disposed substantially parallel with respect to the testing board
300 via the support rails 306 and located such that the distance
between the emitter board 304 and the socket 302 of the testing
board 300 is, for example, less than 9.33 mm; but in general will
depend on the type of optical emitter 314 being used.
[0116] In an embodiment, the emitter board 304 will comprise a LED
array e.g. 4.times.4 or 6.times.6, positioned above each socket 302
on testing board 300. This source will assure that each point
inside the socket area containing the photodiodes 502 will receive
the same light intensity during a test. In some embodiments, and as
shown in FIG. 3, the testing board 300 may include a first
connector 310 (e.g. a female connector) configured to receive a
corresponding second connector 308 (e.g. a male connector) defined
by the emitter board 304. The connection between first connector
310 and the corresponding second connector 308 may facilitate
securing and aligning the sensor emitter 304 with respect to the
testing board 300 such that optical communication between the one
or more optical emitters 314 and the plurality of optical receivers
502 (e.g., shown in FIG. 5) received by the socket 302 are
maintained. As would be understood by one of ordinary skill in the
art in light of the present disclosure, each of the testing board
300 or the emitter board 304 may define any attachment mechanism
(e.g., snaps, grooves, or the like) in order to secure the emitter
board 304 to the testing board 300.
[0117] With reference to FIG. 4, a top view of a testing board 300
configured to support eight (8) optical receivers (not shown) via
eight (8) sockets 302 is illustrated. In some embodiments, the
testing board 300 may be configured (e.g., sized and shaped) so as
to form a connecting portion 400 and a testing portion 402. In such
an embodiment, the connecting portion 400, including the edge
connector 106 described above with reference to FIGS. 1-2, may
define a first width W.sub.1, and the testing portion 402 may
define a second width W.sub.2. As shown in FIG. 4, the first width
W.sub.1 of the connection portion 400 may be less than the second
width W.sub.2 of the testing portion 402 so as to form a T-shaped
testing board 300. While described with reference to a T-shaped
testing board 300 with eight (8) sockets 302, the present
disclosure contemplates that any number of sockets 302 may be
supported by the testing board 300 in any configuration.
Furthermore, the present disclosure contemplates that the testing
board 300 may be any shape or size so as to be received by a
corresponding backplane element (e.g., backplane element 104 in
FIG. 1).
[0118] With reference to FIGS. 5-7, a socket 302 configured to
receive a substrate 500 supporting a plurality of optical receivers
502 (e.g., photodiodes) is illustrated. As shown, the substrate 500
may be configured to be received by a socket 302 such that
electrical signals received by the socket 302 (e.g., via electrical
communication with the testing board 300) may be transmitted from
the socket 302 to the substrate 500, and further transmitted to a
plurality of optical receivers 502 supported thereon. The plurality
of optical receivers 502 are configured to convert the optical
signals received from the optical emitters 314 to corresponding
electrical signals. As shown in FIG. 7, the plurality of optical
receivers 502 may be connected with a contact point 602 of the
substrate 500 via one or more wire bonds 600. As described
hereinafter with regard to one or more testing methods applied to
the plurality of optical receivers 502, the connection of at least
one optical receivers 502 with a corresponding contact point 602
via the wire bond 600 may allow various parameters or outputs
(e.g., an output voltage, an output current, an operating
temperature, etc.) to be transmitted as electrical signals from the
respective optical receiver 502 to a control unit (e.g., the
control unit 112 in FIG. 1) for analysis. In some embodiments, the
substrate 500 received by the socket 302 may support sixteen (16)
optical receivers (e.g., photodiodes). While described in reference
to sixteen (16) optical receivers 502 supported by a single
substrate 500, the present disclosure contemplates that any number
of optical receivers 502 may be supported by a corresponding
substrate 500 in any configuration. Furthermore, with reference to
FIGS. 6-7, the present disclosure contemplates that any orientation
or configuration of wire bonds 600 and contact points 602 may be
unitized by embodiments of the present invention such that one or
more of the plurality of optical receivers 502 is in electrical
communication with a driver (e.g., driver 108).
[0119] With reference to FIG. 8, a bottom view of the emitter board
304 is schematically illustrated. As shown, the bottom surface of
the emitter board 304 may be configured to support one or more
optical emitters 314 (e.g., VCSELs, LEDs, LED arrays). When in an
operational configuration, in which the bottom surface of the
emitter board 304 is substantially aligned with the testing board
300, each optical emitter 314 may be configured to transmit optical
signals to the plurality of optical receivers 502, which are
configured to convert the optical signals to corresponding
electrical signals. In some embodiments, the emitter board 304 may
support eight (8) optical emitters 314. However, the present
disclosure contemplates that any number of optical emitters 314 may
be supported by the emitter board 304 so as to transmit optical
signals to the plurality of optical receivers 502 provided in the
corresponding sockets 302 of the testing board 300. As would be
evident to one of ordinary skill in the art in light of the present
disclosure, the emitter board 304, in some embodiments, may support
the same number of optical emitters 314 as the number of sockets
302 supported by the corresponding testing board 300. Furthermore
the configuration or orientation of these optical emitters 314 may
match that of the orientation of sockets 302 of the testing board
300 so as allow for optical communication between the
optoelectronic elements supported thereon. In an example embodiment
described herein, the emitter board 304 may define eight (8)
optical emitters 314 positioned to substantially align with eight
(8) corresponding sockets 302 of the testing board 300 such that a
set of sixteen (16) optical receivers 502 of each socket 302 is in
optical communication with a single corresponding optical emitter
314. Accordingly, in such an embodiment, the emitter board 304
supports eight (8) optical emitters 314 in optical communication
with a maximum of one hundred twenty-eight (128) optical receivers
502.
[0120] As described below in detail with reference to particular
testing methods, the testing system 100 may serve to provide
electrical inputs to a plurality of optical receivers 502 and
monitor corresponding output parameters. By way of example, with
reference to FIGS. 1, 3, and 5, the control unit 112 may execute a
testing method by directing the driver 108 to provide a voltage
input to at least one of the plurality of optical receivers 502.
The control unit 112 may provide this command via electrical
signals transmitted to the driver 108. The driver 108 may then
provide a corresponding voltage input to the testing unit 102 via
electrical signals transmitted by the driver 108 to the testing
unit via the rigid-flex PCB 110, the backplane 104, and the edge
connector 106 (FIG. 1). The electrical signals may then be provided
to at least one optical receiver 502 via electrical traces 312 of
the testing board 300, socket 302, and substrate 500. Similarly,
the control unit 112 and driver 108 may activate the optical
emitters 314 on emitter board 304 to provide light when desired.
The optical receiver 502 converts the optical signals to electrical
signals that are transferred to control unit 112. The control unit
112 analyses and/or determines various parameters or outputs of the
optical receiver 502 based upon these electrical signals to
determine passage or failure of the optical receiver. Although
described as providing a voltage input to a single optical
receiver, the present disclosure contemplates that the control unit
112 and/or driver 108 may selectively apply inputs to any number or
combination of the plurality of optical transmitters 502.
[0121] A system built according to the above comprises sixteen
optical receivers 502 in eight sockets 302 on sixteen testing
boards 300 and will be controlled by a single control unit 112 to
enable testing, with and without illumination, up to 2048 optical
receivers 502 without taking the optical receivers out of the
system. This reduces time and optical receiver failure due to
handling issues.
[0122] Different types of reliability tests will now be outlined
that can be carried out using the system described above. As
described, the system can be manually controlled or programmed to
automatically carry out the different tests on individual optical
receiver 502 on any testing board 300 or in any socket 302 in which
it is located. Specifically the tests described below are for
photodiodes and the PASS/FAIL state that is determined by the test
is specific to each photodiode.
[0123] Three testing procedures and a pre-test will now be
described. Each of the testing procedures is a separate program in
memory device 204 of apparatus 200 and may be run separately.
However the normal flow for photodiode reliability testing will
consist of running the pre-test and then the three test procedures
consecutively with procedures two and three repeated cyclically,
wherein the overall test time and number of stress intervals can be
chosen by the operator. An example of a typical test time is two
thousand (2000) hours and number of stress cycles is eight (8).
[0124] Pre-Test
[0125] This test is carried out before each test procedure if they
are carried out separately and only before the first test if the
test procedures are carried out sequentially. [0126] a. Check the
substrate temperature to determine if it is inside the designed
operating range of the optical receiver. [0127] b. Check that the
optical receiver to be tested is present. [0128] c. Apply current
on the optical receiver and check that the voltage is the designed
operating range of the optical receiver. [0129] d. Check for an
open or short circuit and leakage on optical receiver. [0130]
.fwdarw.In case of fail of any of steps a to d the test stops.
[0131] A. First Test Procedure
[0132] The purpose of this test is to determine the current-voltage
(I-V) characteristics of the optical receiver prior to applying
stress. This test can be carried out without illumination (steps a
and c) and with illumination (step b). [0133] a. Apply reverse
voltage on optical receiver (can be applied using different voltage
values). Check that the dark current is inside the designed
operating range of the optical receiver. [0134] b. Apply reverse
voltage on optical receiver (can be applied using different voltage
values). Turn on the illumination and check that the photo current
is inside the designed operating range of the optical receiver.
[0135] c. Apply forward current on optical receiver (can be applied
using different current values). Check that the forward voltage is
inside the designed operating range of optical receiver. [0136]
.fwdarw.In case of fail of any of the steps a to c, the optical
receiver is marked as FAIL. [0137] .fwdarw.Document the dark
current, photo current, forward voltage, and temperature at
Time=0.
[0138] B. Second Test Procedure
[0139] The purpose of this test is to check the effect of thermal
stress on the optical receiver. The procedure can be carried out in
two options--either without or with illumination. The overall
concept of this test is to keep photodiodes in a constant
temperature environment and under constant reverse voltage for a
period of time (e.g. 24 hours). Constant illumination can also be
added and, in both options, values of parameters are periodically
checked, (e.g. every 10 minutes).
[0140] 1st Option: Without Illumination [0141] a. Raise temperature
of the substrate above ambient (in an embodiment this is carried
out by locating the testing units 102 in an oven and raising the
temperature in the oven) [0142] b. Apply constant reverse voltage
on optical receiver. [0143] c. Measure the substrate temperature
periodically and check if the temperature is above or below a
preset value (note that this test should be carried out at a
constant temperature, e.g. 85.degree. C.). [0144] .fwdarw.In case
of fail the test stops. [0145] d. Measure dark current periodically
and check if inside the designed operating range of the optical
receiver. [0146] .fwdarw.In case of fail of step d the optical
receiver is marked as FAIL.
[0147] 2nd Option: With Illumination [0148] a. Raise temperature of
substrate. [0149] b. Apply constant reverse voltage on optical
receiver and turn on illumination. [0150] c. Measure substrate
temperature periodically and check if the temperature is above or
below a preset value. [0151] .fwdarw.In case of fail the test
stops. [0152] d. Measure photo current periodically and check if
inside the designed operating range of the optical receiver. [0153]
.fwdarw.n case of fail of step d optical receiver is marked as
FAIL.
[0154] C. Third Test Procedure
[0155] The purpose of this test is to check the drift of the I-V
characteristics of the optical receiver, with and without
illumination, over time. Also if carried out cyclically with the
second test procedure the effect of thermal stress on the drift of
the I-V characteristics of the optical receiver over time is
checked. In this test the parameters are recorded at least at two
different times. [0156] a. Apply reverse voltage on optical
receiver (can be applied using different voltage values). Check
that the dark current is inside the designed operating range of the
optical receiver. [0157] b. Apply reverse voltage on optical
receiver (can be applied using different voltage values). Turn on
the illumination and check that the photo current is inside the
designed operating range of the optical receiver. [0158] c. Apply
forward current on optical receiver (can be applied using different
current values). Check that the forward voltage is inside the
designed operating range of the optical receiver. [0159] .fwdarw.In
case of fail of any of the steps a to c, the optical receiver is
marked as FAIL. [0160] .fwdarw.Document the dark current, photo
current, forward voltage, and temperature at Time=X. [0161] d.
Compute the drift of dark current, photo current, and forward
voltage between Time=0 and Time=X and check if inside the designed
limit for the optical receiver. [0162] .fwdarw.In case the drift of
one or more of the parameters is outside the designed limit the
optical receiver is marked as FAIL.
[0163] Note that: [0164] i) When computing the drift in step d the
temperature and illumination conditions should be same at time=0
and time=X. [0165] ii) The values of the parameters in step d may
be used to check the drift relative to measurements at time=0,
before any stress is applied. The data in the database from the
first procedure can be used for time=0 allowing drift to be
computed; but there is an option in program to set any measurement
as "time=0", the point relative to which the drift will be
computed.
[0166] Although embodiments of the invention have been described by
way of illustration, it will be understood that the invention may
be carried out with many variations, modifications, and
adaptations, without exceeding the scope of the claims.
* * * * *