U.S. patent application number 15/854712 was filed with the patent office on 2019-01-24 for method and system for optical vector analysis.
The applicant listed for this patent is Nanjing University of Aeronautics and Astronautics. Invention is credited to Yuqing Heng, Shupeng Li, Shilong Pan, Ting Qing, Min Xue.
Application Number | 20190028191 15/854712 |
Document ID | / |
Family ID | 60335776 |
Filed Date | 2019-01-24 |
![](/patent/app/20190028191/US20190028191A1-20190124-D00000.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00001.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00002.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00003.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00004.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00005.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00006.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00007.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00008.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00009.png)
![](/patent/app/20190028191/US20190028191A1-20190124-D00010.png)
View All Diagrams
United States Patent
Application |
20190028191 |
Kind Code |
A1 |
Xue; Min ; et al. |
January 24, 2019 |
Method and System for Optical Vector Analysis
Abstract
An apparatus comprises an optical detecting signal generator
configured to provide an optical spectrum comprising two frequency
carriers, the two frequency carriers having two different nominal
carrier frequencies, and the output port of the optical detecting
signal generator being further configured to be coupled to a device
under test (DUT); an optical to electrical converter configured to
generate a first electrical current based on the optical spectrum
without the optical spectrum passing through the DUT; and generate
a second electrical current based on the optical spectrum after the
optical spectrum passes through the DUT; and a data processor
coupled to the optical to electrical converter, the data processor
being configured to determine a transfer function of the DUT at an
average of the two different nominal carrier frequencies based on
the first electrical current and the second electrical current.
Inventors: |
Xue; Min; (Nanjing, CN)
; Pan; Shilong; (Nanjing, CN) ; Qing; Ting;
(Nanjing, CN) ; Li; Shupeng; (Nanjing, CN)
; Heng; Yuqing; (Nanjing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanjing University of Aeronautics and Astronautics |
Nanjing |
|
CN |
|
|
Family ID: |
60335776 |
Appl. No.: |
15/854712 |
Filed: |
December 26, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 10/077 20130101;
H04B 10/07 20130101; H04B 10/60 20130101; H04B 10/0775 20130101;
H04B 10/50 20130101; H04B 10/40 20130101; H04B 10/0779
20130101 |
International
Class: |
H04B 10/077 20060101
H04B010/077 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2017 |
CN |
201710591672.8 |
Claims
1. An apparatus comprising: an optical detecting signal generator
configured to provide, through an output port of the optical
detecting signal generator, an optical spectrum comprising two
frequency carriers, the two frequency carriers having two different
nominal carrier frequencies, and the output port of the optical
detecting signal generator being further configured to be coupled
to a device under test (DUT); an optical to electrical converter
configured to: generate a first electrical current based on the
optical spectrum without the optical spectrum passing through the
DUT; and generate a second electrical current based on the optical
spectrum after the optical spectrum passes through the DUT; and a
data processor coupled to the optical to electrical converter, the
data processor being configured to determine a transfer function of
the DUT at an average of the two different nominal carrier
frequencies based on the first electrical current and the second
electrical current.
2. The apparatus of claim 1, wherein the optical spectrum comprises
one or more additional frequency carriers in addition to the two
frequency carriers, and any pair of frequency carriers, except the
two frequency carriers, selected from a group consisting of the one
or more additional frequency carriers and the two frequency
carriers has a spacing in frequency greater than a difference
between the two different nominal carrier frequencies.
3. The apparatus of claim 1, wherein both the first electrical
current and the second electrical current have a single nominal
carrier frequency equal to a difference between the two different
nominal carrier frequencies.
4. The apparatus of claim 3, further comprising a signal extractor
coupled to the optical to electrical converter and the data
processor, the signal extractor being configured to: receive,
through an input port of the signal extractor, an electrical
current from the optical to electrical converter; extract an
amplitude and a phase of the electrical current; and provide,
through an output port of the signal extractor, the amplitude and
the phase of the electrical current to the data processor, wherein
the electrical current is either the first electrical current or
the second electrical current.
5. The apparatus of claim 4, wherein the transfer function of the
DUT at the average of the two different nominal carrier frequencies
is determined by: | H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2
) | = | i ( .omega. ( o , 2 ) - .omega. ( o , 1 ) ) | | i SYS (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) | ; and ##EQU00015## D DUT
( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) = e j { .phi. [ i (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) ] - .phi. [ i SYS ( .omega.
( o , 2 ) - .omega. ( o , 1 ) ) ] } ( .omega. ( o , 2 ) - .omega. (
o , 1 ) ) ##EQU00015.2## wherein | H DUT ( .omega. ( o , 1 ) +
.omega. ( o , 2 ) 2 ) | ##EQU00016## is an amplitude of the
transfer function of the DUT at the average of the two different
nominal carrier frequencies, denoted by .omega.(o,1) and
.omega.(o,2), respectively, wherein
i.sub.SYS(.omega.(o,2)-.omega.(o,1)) is the first electrical
current, and i(.omega.(o,2)-.omega.(o,1)) is the second electrical
current, wherein |i.sub.SYS(.omega.(o,2)-.omega.(o,1))| is an
amplitude of the first electrical current, and
|i(.omega.(o,2)-(.omega.(o,1))| is an amplitude of the second
electrical current, and wherein
.PHI.[i.sub.SYS(.omega.(o,2)-.omega.(o,1))] is a phase of the first
electrical current, and .PHI.[i(.omega.(o,2)-.omega.(o,1))] is a
phase of the second electrical current.
6. The apparatus of claim 5, wherein the optical detecting signal
generator comprises: a radiation generator configured to emit,
through an output port of the radiation generator, a radiation
having a nominal wavelength; and an optical modulator coupled to
the radiation generator, the optical modulator being configured to:
receive, through a first input port of the optical modulator, the
radiation from the radiation generator; receive, through a second
input port of the optical modulator, a first radio-frequency (RF)
signal having a first RF frequency, and a second RF signal having a
second RF frequency, the first RF frequency being different than
the second RF frequency; generate the optical spectrum by
modulating the radiation based on the first RF signal and the
second RF signal; and output, through an output port of the optical
modulator, the optical spectrum.
7. The apparatus of claim 6, wherein the radiation generator
comprises: a comb source configured to provide an optical frequency
comb having a plurality of equally spaced optical frequency
carriers; and a tunable optical filter coupled to the comb source,
the tunable optical filter being configured to output one frequency
carrier, controllable by the data processor, of the optical
frequency comb.
8. The apparatus of claim 5, wherein the optical detecting signal
generator comprises: a mode-locked laser; and a tunable optical
filter coupled to the mode-locked laser, wherein the tunable
optical filter is configured to output two optical frequency
carriers, controllable by the data processor, of a radiation
provided by the mode-locked laser.
9. A method comprising: providing an optical spectrum comprising
two frequency carriers, the two frequency carriers having two
different nominal carrier frequencies; generating a first
electrical current based on the optical spectrum without the
optical spectrum passing through a device under test (DUT);
generating a second electrical current based on the optical
spectrum after the optical spectrum passes through the DUT; and
determining, by a data processor, a transfer function of the DUT at
an average of the two different nominal carrier frequencies based
on the first electrical current and the second electrical
current.
10. The method of claim 9, wherein the optical spectrum comprises
one or more additional frequency carriers in addition to the two
frequency carriers, and any pair of frequency carriers, except the
two frequency carriers, selected from a group consisting of the one
or more additional frequency carriers and the two frequency
carriers has a spacing in frequency greater than a difference
between the two different nominal carrier frequencies.
11. The method of claim 9, wherein both the first electrical
current and the second electrical current have a single nominal
carrier frequency equal to a difference between the two different
nominal carrier frequencies.
12. The method of claim 11, further comprising: receiving an
electrical current; extracting an amplitude and a phase of the
electrical current; and providing the amplitude and the phase of
the electrical current to the data processor, wherein the
electrical current is either the first electrical current or the
second electrical current.
13. The method of claim 12, wherein the transfer function of the
DUT at the average of the two different nominal carrier frequencies
is determined by: | H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2
) | = | i ( .omega. ( o , 2 ) - .omega. ( o , 1 ) ) | | i SYS (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) | ; and ##EQU00017## D DUT
( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) = e j { .phi. [ i (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) ] - .phi. [ i SYS ( .omega.
( o , 2 ) - .omega. ( o , 1 ) ) ] } ( .omega. ( o , 2 ) - .omega. (
o , 1 ) ) ##EQU00017.2## wherein | H DUT ( .omega. ( o , 1 ) +
.omega. ( o , 2 ) 2 ) | ##EQU00018## is an amplitude of the
transfer function of the DUT at the average of the two different
nominal carrier frequencies, denoted by .omega.(o,1) and
.omega.(o,2), respectively, wherein
i.sub.SYS(.omega.(o,2)-.omega.(o,1)) is the first electrical
current, and i(.omega.(o,2)-.omega.(o,1)) is the second electrical
current, wherein |i.sub.SYS(.omega.(o,2)-.omega.(o,1))| is an
amplitude of the first electrical current, and
|i(.omega.(o,2)-(.omega.(o,1))| is an amplitude of the second
electrical current, and wherein
.PHI.[i.sub.SYS(.omega.(o,2)-.omega.(o,1))] is a phase of the first
electrical current, and .PHI.[i(.omega.(o,2)-.omega.(o,1))] is a
phase of the second electrical current.
14. The method of claim 13, wherein the optical spectrum is
provided by: receiving a first radio-frequency (RF) signal having a
first RF frequency, and a second RF signal having a second RF
frequency, the first RF frequency being different than the second
RF frequency; generating the optical spectrum by modulating a
radiation having a nominal wavelength based on the first RF signal
and the second RF signal; and outputting the optical spectrum.
15. The method of claim 14, further comprising generating the
radiation, wherein the radiation is generated by: providing an
optical frequency comb having a plurality of equally spaced optical
frequency carriers; and outputting one frequency carrier of the
optical frequency comb.
16. An apparatus comprising: an optical multiple-carrier generator
configured to provide, through an output port of the optical
multiple-carrier generator, an optical spectrum having a plurality
of optical frequency carriers, wherein the output port of the
optical multiple-carrier generator is further configured to be
coupled to a device under test (DUT); a splitter configured to:
receive, through an input port of the splitter, the optical
spectrum; and provide each of a plurality of portions of the
optical spectrum to a respective one of a plurality of channels;
the plurality of channels coupled to the splitter, wherein each of
the plurality of channels comprises an optical to electrical
converter, the optical to electrical converter being configured to:
receive a respective portion of the optical spectrum, the
respective portion of the optical spectrum comprising two frequency
carriers, and the two frequency carriers having two different
nominal carrier frequencies; generate a first electrical current
based on the respective portion of the optical spectrum without the
optical spectrum passing through the DUT; and generate a second
electrical current based on the respective portion of the optical
spectrum after the optical spectrum passes through the DUT; and a
data processor coupled to the plurality of channels, wherein the
data processor is configured to determine, with respect to each of
the plurality of channels, a transfer function of the DUT at an
average of the two different nominal carrier frequencies based on
the first electrical current and the second electrical current.
17. The apparatus of claim 16, wherein both the first electrical
current and the second electrical current have a single nominal
carrier frequency equal to a difference between the two different
nominal carrier frequencies.
18. The apparatus of claim 17, wherein each of the plurality of
channels further comprises a signal extractor coupled to the
optical to electrical converter, the signal extractor being
configured to: receive, through an input port of the signal
extractor, an electrical current from the optical to electrical
converter; extract an amplitude and a phase of the electrical
current; and provide, through an output port of the signal
extractor, the amplitude and the phase of the electrical current to
the data processor, wherein the electrical current is either the
first electrical current or the second electrical current.
19. The apparatus of claim 18, wherein the transfer function of the
DUT at the average of the two different nominal carrier frequencies
is determined by: | H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2
) | = | i ( .omega. ( o , 2 ) - .omega. ( o , 1 ) ) | | i SYS (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) | ; and ##EQU00019## D DUT
( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) = e j { .phi. [ i (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) ] - .phi. [ i SYS ( .omega.
( o , 2 ) - .omega. ( o , 1 ) ) ] } ( .omega. ( o , 2 ) - .omega. (
o , 1 ) ) ##EQU00019.2## wherein | H DUT ( .omega. ( o , 1 ) +
.omega. ( o , 2 ) 2 ) | ##EQU00020## is an amplitude of the
transfer function of the DUT at the average of the two different
nominal carrier frequencies, denoted by (.omega.(o,1) and
.omega.(o,2), respectively, wherein
i.sub.SYS(.omega.(o,2)-.omega.(o,1)) is the first electrical
current, and i(.omega.(o,2)-(.omega.(o,1)) is the second electrical
current, wherein |i.sub.SYS(.omega.(o,2)-.omega.(o,1))| is an
amplitude of the first electrical current, and
|i(.omega.(o,2)-(.omega.(o,1))| is an amplitude of the second
electrical current, and wherein
.PHI.[i.sub.SYS(.omega.(o,2)-.omega.(o,1))] is a phase of the first
electrical current, and .PHI.[i(.omega.(o,2)-.omega.(o,1))] is a
phase of the second electrical current.
20. The apparatus of claim 19, wherein the optical multiple-carrier
generator comprises: a plurality of laser sources configured to
emit a plurality of radiations, each of the plurality of radiations
having a different nominal wavelength; and a multiplexer coupled to
the plurality of laser sources, wherein the multiplexer is
configured to provide a combined radiation by combining the
plurality of radiations.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Chinese Patent
Application No. 201710591672.8, filed on Jul. 19, 2017. The
disclosure of the aforementioned application is hereby incorporated
by reference in their entireties.
BACKGROUND
1. Technical Field
[0002] The present disclosure relates generally to a method and a
system related to performing optical vector analysis. In
particular, the present disclosure relates to a method and a system
suitable for determining a transfer function of an optical device
at various operating frequencies.
2. Discussion of Technical Background
[0003] Optical vector analysis may be performed to determine a
transfer function of an optical device at various operating
frequencies of the optical device. The transfer function of the
optical device may also be referred to as a transmission response
of the optical device, indicating a relationship, caused by the
optical device, between an input signal received by the optical
device and an output signal outputted by the optical device. The
transfer function of the optical device may be further used to
determine a plurality of characteristics of the optical device at
the various operating frequencies. Examples of the characteristics
may include, but not limited to, insertion loss, dispersion, group
delay, polarization dependent loss, and polarization mode
dispersion.
SUMMARY
[0004] In an exemplary embodiment, there is provided an apparatus
comprising: an optical detecting signal generator configured to
provide, through an output port of the optical detecting signal
generator, an optical spectrum comprising two frequency carriers,
the two frequency carriers having two different nominal carrier
frequencies, and the output port of the optical detecting signal
generator being further configured to be coupled to a device under
test (DUT); an optical to electrical converter configured to:
generate a first electrical current based on the optical spectrum
without the optical spectrum passing through the DUT; and generate
a second electrical current based on the optical spectrum after the
optical spectrum passes through the DUT; and a data processor
coupled to the optical to electrical converter, the data processor
being configured to determine a transfer function of the DUT at an
average of the two different nominal carrier frequencies based on
the first electrical current and the second electrical current.
[0005] In another exemplary embodiment, there is provided a method
comprising: providing an optical spectrum comprising two frequency
carriers, the two frequency carriers having two different nominal
carrier frequencies; generating a first electrical current based on
the optical spectrum without the optical spectrum passing through a
DUT; generating a second electrical current based on the optical
spectrum after the optical spectrum passes through the DUT; and
determining, by a data processor, a transfer function of the DUT at
an average of the two different nominal carrier frequencies based
on the first electrical current and the second electrical
current.
[0006] In yet another exemplary embodiment, there is provided an
apparatus comprising: an optical multiple-carrier generator
configured to provide, through an output port of the optical
multiple-carrier generator, an optical spectrum having a plurality
of optical frequency carriers, wherein the output port of the
optical multiple-carrier generator is further configured to be
coupled to a DUT; a splitter configured to: receive, through an
input port of the splitter, the optical spectrum; and provide each
of a plurality of portions of the optical spectrum to a respective
one of a plurality of channels; the plurality of channels coupled
to the splitter, wherein each of the plurality of channels
comprises an optical to electrical converter, the optical to
electrical converter being configured to: receive a respective
portion of the optical spectrum, the respective portion of the
optical spectrum comprising two frequency carriers, and the two
frequency carriers having two different nominal carrier
frequencies; generate a first electrical current based on the
respective portion of the optical spectrum without the optical
spectrum passing through the DUT; and generate a second electrical
current based on the respective portion of the optical spectrum
after the optical spectrum passes through the DUT; and a data
processor coupled to the plurality of channels, wherein the data
processor is configured to determine, with respect to each of the
plurality of channels, a transfer function of the DUT at an average
of the two different nominal carrier frequencies based on the first
electrical current and the second electrical current.
[0007] Other concepts relate to software for performing the optical
vector analysis as described herein. A software product, in accord
with this concept, includes at least one machine-readable
non-transitory medium and information carried by the medium.
[0008] In an exemplary embodiment, there is provided a
machine-readable tangible and non-transitory medium having
information, wherein the information, when read by a hardware
processor system, causes the hardware processor system to perform
following: providing an optical spectrum comprising two frequency
carriers, the two frequency carriers having two different nominal
carrier frequencies; generating a first electrical current based on
the optical spectrum without the optical spectrum passing through a
DUT; generating a second electrical current based on the optical
spectrum after the optical spectrum passes through the DUT; and
determining, by a data processor, a transfer function of the DUT at
an average of the two different nominal carrier frequencies based
on the first electrical current and the second electrical
current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The embodiments will be more readily understood in view of
the following description when accompanied by the below figures and
wherein like reference numerals represent like elements,
wherein:
[0010] FIG. 1 is a schematic diagram of an optical vector analyzer
suitable for performing optical vector analysis on a device under
test (DUT) according to an embodiment of the present
disclosure;
[0011] FIG. 2 is a schematic diagram of an embodiment of an optical
detecting signal generator;
[0012] FIG. 3 is a schematic diagram of another embodiment of the
optical detecting signal generator;
[0013] FIG. 4 is a schematic diagram of yet another embodiment of
the optical detecting signal generator;
[0014] FIG. 5 is a schematic diagram of a radiation generator
according to an embodiment of the present disclosure;
[0015] FIG. 6 is a schematic diagram of a comb source according to
an embodiment of the present disclosure;
[0016] FIG. 7 is a schematic diagram of yet another embodiment of
the optical detecting signal generator;
[0017] FIG. 8 is a schematic diagram of yet another embodiment of
the optical detecting signal generator;
[0018] FIG. 9 is a schematic diagram of another optical vector
analyzer suitable for performing optical vector analysis on a DUT
according to an embodiment of the present disclosure;
[0019] FIG. 10 is a flowchart of an exemplary process for
performing an optical vector analysis on a DUT by an optical vector
analyzer according to an embodiment of the disclosure; and
[0020] FIG. 11 depicts a general computer architecture on which the
present disclosure can be implemented.
DETAILED DESCRIPTION
[0021] Reference will now be made in detail to the embodiments of
the present disclosure, examples of which are illustrated in the
accompanying drawings. While the present disclosure will be
described in conjunction with the embodiments, it will be
understood that they are not intended to limit the present
disclosure to these embodiments. On the contrary, the present
disclosure is intended to cover alternatives, modifications, and
equivalents, which may be included within the spirit and scope of
the present disclosure as defined by the appended claims.
[0022] In addition, in the following detailed description of
embodiments of the present disclosure, numerous specific details
are set forth in order to provide a thorough understanding of the
present disclosure. However, it will be recognized by one of
ordinary skill in the art that the present disclosure may be
practiced without these specific details. In other instances,
well-known methods, procedures, components, and circuits have not
been described in detail as not to unnecessarily obscure aspects of
the embodiments of the present disclosure.
[0023] Referring to FIG. 1, a schematic diagram of an optical
vector analyzer 100 is shown according to an embodiment of the
disclosure. The optical vector analyzer 100 may be used to perform
an optical vector analysis on a device under test (DUT) 120. In
particular, the optical vector analyzer 100 may be used to
determine a transfer function of the DUT 120 at various operating
frequencies. As shown, the optical vector analyzer 100 may comprise
an optical detecting signal generator 110, an optical to electrical
converter 130, a signal extractor 150, a data processor 170, and a
display 190. The various components may be arranged as shown or in
any other suitable manner.
[0024] The optical detecting signal generator 110 may be configured
to provide an optical spectrum comprising at least two frequency
carriers. In an embodiment, the at least two frequency carriers are
at least two optical frequency carriers. Each frequency carrier is
an electromagnetic radiation having a single nominal carrier
frequency or a narrow frequency range around a nominal carrier
frequency. The nominal carrier frequency of a frequency carrier may
be a frequency corresponding to a peak power of the frequency
carrier.
[0025] An exemplary optical spectrum provided by the optical
detecting signal generator 110 is shown in FIG. 1 as directed by
arrow 115. In an embodiment, the optical spectrum, as in a dashed
circle 185 in FIG. 1, includes a first frequency carrier having a
first nominal carrier frequency, denoted by .omega..sub.(o, 1), and
a second optical frequency carrier having a second nominal carrier
frequency, denoted by .omega..sub.(o, 2). The spacing between the
first optical frequency carrier and the second optical frequency
carrier may be denoted by .DELTA..omega.. In an embodiment, the
optical spectrum includes, in addition to the first optical
frequency carrier and the second optical frequency carrier, one or
more additional optical frequency carriers, each of which has a
different nominal carrier frequency, denoted by .omega..sub.(o,
-M), . . . .omega..sub.(o, 0), .omega..sub.(o,3), . . . , and
.omega..sub.(o,N), where M and N are integers. Particularly, the
spacing between adjacent optical frequency carriers in the whole
optical spectrum, as directed by arrow 115 in FIG. 1, except the
spacing between the first optical frequency carrier and the second
optical frequency carrier in the dashed circle 185, is greater than
.DELTA..omega.. This also means, any pair of optical frequency
carriers in the whole optical spectrum as directed by arrow 115 in
FIG. 1, except the first optical frequency carrier and the second
optical frequency carrier in the dashed circle 185, has a
difference in frequency which is greater than .DELTA..omega..
[0026] The first carrier frequency, .omega..sub.(o,1), and/or the
second carrier frequency, .omega..sub.(o, 2) may be tunable. In
addition or alternatively, the spacing between the first frequency
carrier and the second frequency carrier, i.e., .DELTA.w is
tunable. In an embodiment, the optical detecting signal generator
110 has an input port coupled to the data processor 170, which may
be used to adjust the first carrier frequency, .omega..sub.(o, 1),
the second carrier frequency, .omega..sub.(o, 2), and/or the
difference between the first carrier frequency and the second
carrier frequency, .DELTA..omega.. In some embodiments, one or more
nominal carrier frequencies, e.g., .omega..sub.(o, -M), . . .
.omega..sub.(o, 0), .omega..sub.(o,3), . . . , and
.omega..sub.(o,N), corresponding to the one or more additional
frequency carriers in the optical spectrum may be, individually or
collectively, tuned by the data processor 170. Further, the optical
detecting signal generator 110 has an output port, denoted by port
A as shown in FIG. 1, configured to output the optical spectrum. In
operation, the output port of the optical detecting signal
generator 110, i.e., port A, may be coupled to the DUT 120.
Alternatively, the output port of the optical detecting signal
generator 110, i.e., port A, may be coupled to the optical to
electrical converter 130 through an input port of the optical to
electrical converter 130, denoted by port B. More details will be
discussed further below.
[0027] The optical to electrical converter 130 may be configured to
convert the optical spectrum to an electrical current. The input
port of the optical to electrical converter 130, i.e., port B, may
be configured to receive the optical spectrum, as an output port of
the optical to electrical converter 130 may be configured to output
the electrical current. The optical to electrical converter 130 may
be configured so that each of the frequency carriers in the optical
spectrum, i.e., .omega..sub.(o, -M), . . . .omega..sub.(o, 0),
.omega..sub.(o, 1), .omega..sub.(o, 2), .omega..sub.(o,3), . . . ,
and .omega..sub.(o,N), in addition to any difference in frequency
between any pair of frequency carriers from the optical spectrum
except the first frequency carrier and the second frequency
carrier, falls out of the operating frequency range of the optical
to electrical converter 130. As a result, the electrical current
includes a single frequency carrier having a nominal carrier
frequency at .DELTA..omega., as shown in FIG. 1 and directed by
arrow 135. In an embodiment, the optical to electrical converter
130 operates only at frequency .DELTA..omega.. In an embodiment,
the optical to electrical converter 130 operates at a narrow
frequency range around .DELTA..omega.. In an embodiment, the
optical to electrical converter 130 operates at a frequency range
between zero and .DELTA..omega.. In an embodiment, the input port
of the optical to electrical converter 130, i.e., port B, may be
coupled to the output port of the optical detecting signal
generator 110, i.e., port A, directly. Accordingly, the electrical
current is converted, by the optical to electrical converter 130,
from the optical spectrum provided by the optical detecting signal
generator 110 directly, i.e., without the optical spectrum passing
through the DUT 120. In an embodiment, the input port of the
optical to electrical converter 130, i.e., port B, may be coupled
to the output port of the DUT 120, as the output port of the
optical detecting signal generator 110, i.e., port A, may be
coupled to the input port of the DUT 120. Accordingly, the
electrical current is converted, by the optical to electrical
converter 130, from the optical spectrum provided by the optical
detecting signal generator 110 after the optical spectrum passes
through the DUT 120.
[0028] The signal extractor 150 may have an input port coupled to
the output port of the optical to electrical converter 130 and
configured to receive the electrical current. The signal extractor
150 may be configured to measure the electrical current. In
particular, the signal extractor 150 may be configured to measure
the electrical current by determining amplitude and phase of the
electrical current, respectively, at one or more frequencies
including .DELTA..omega.. The signal extractor 150 may further have
an output port coupled to an input port of the data processor 170
and configured to output the measurement results (i.e., the
amplitude and the phase of the electrical current) to the data
processor 170.
[0029] The data processor 170 may have the input port coupled to
the output port of the signal extractor 150 and configured to
receive the measurement results from the signal extractor 150. The
data processor 170 may be configured to determine the transfer
function of the DUT 120 at various operating frequencies based on
the measurement results received from the signal extractor 150. The
transfer function of the DUT 120 may also be referred to as a
transmission response of the DUT 120. In an embodiment, the
transfer function of the DUT 120 may be indicative of a
relationship, caused by the DUT 120, between an input signal
received by the DUT 120 and a corresponding output signal outputted
by the DUT 120. The transfer function of the DUT 120 may further be
used to determine a plurality of characteristics of the DUT 120 at
the various operating frequencies. Examples of the characteristics
may include, but not limited to, insertion loss, dispersion, group
delay, polarization dependent loss, and polarization mode
dispersion.
[0030] Further, the data processor 170, as described above, may be
coupled to the optical detecting signal generator 110. The data
processor 170 may be configured to adjust the first carrier
frequency, .omega..sub.(o,1), the second carrier frequency,
.omega..sub.(o, 2), and/or the difference between the first carrier
frequency and the second carrier frequency, .DELTA..omega..
Optionally, the data processor 170 may be further configured to
tune, individually or collectively, one or more nominal carrier
frequencies, e.g., .omega..sub.(o, -M), . . . .omega..sub.(o, 0),
.omega..sub.(o,3), . . . , and .omega..sub.(o,N), corresponding to
the one or more additional frequency carriers in the optical
spectrum as described above.
[0031] The display 190 may have an input port coupled to the output
port of the data processor 170 and configured to display the
transfer function of the DUT 120, e.g., in forms of showing both
amplitude and phase of the transfer function of the DUT 120 and/or
the plurality of characteristics of the DUT 120 at various
operating frequencies received from and determined by the data
processor 170.
[0032] In an embodiment, a device characterization process and a
system calibration process may be implemented respectively in order
to perform the optical vector analysis on the DUT 120. The order of
performing the device characterization process and the system
calibration process may be interchangeable.
[0033] When the optical spectrum provided by the optical detecting
signal generator 110 includes only the first frequency carrier and
the second frequency carrier, the electrical field of the optical
spectrum may be expressed by:
E.sub.c(t)=A.sub.1exp(j.omega..sub.(o,1)t)+A.sub.2exp(j.omega..sub.(o,2)-
t) (1)
where E.sub.c(t) represents the electrical field of the optical
spectrum provided by the optical detecting signal generator 110,
A.sub.1 represents an amplitude of the electrical field of the
first frequency carrier, and A.sub.2 represents an amplitude of the
electrical field of the second frequency carrier.
[0034] Alternatively, when the optical spectrum provided by the
optical detecting signal generator 110 includes one or more
additional frequency carriers in addition to the first frequency
carrier and the second frequency carrier, the electrical field of
the optical spectrum may be expressed by:
E.sub.c(t)=A.sub.-Mexp(j.omega..sub.(o,-M)t)+A.sub.-M+1exp(j.omega..sub.-
(o,-M+1)t)+ . . . +A.sub.Nexp(j.omega..sub.(o,N)t) (2)
where E.sub.c(t) represents the electrical field of the optical
spectrum provided by the optical detecting signal generator 110,
A.sub.-M, . . . , A.sub.N represent amplitudes of the electrical
fields of the corresponding frequency carriers in the optical
spectrum, respectively. However, it should be noted that any pair
of the nominal carrier frequencies, except .omega..sub.(o,1) and
.omega..sub.(o, 2), selected from .omega..sub.(o, -M),
.omega..sub.(o, -M+1), . . . , .omega..sub.(o, N), has a difference
greater than |.omega..sub.(o, 1)-.omega..sub.(o, 2)| or
.DELTA..omega.. This is done so that the electrical current
converted by the optical to electrical converter 130 from the
optical spectrum includes a single nominal carrier frequency at
.DELTA..omega..
[0035] When performing the system calibration process, the output
port of the optical detecting signal generator, i.e., port A, is
coupled to the input port of the optical to electrical converter
130, i.e., port B, directly. As a result, the optical to electrical
converter 130 may convert the optical spectrum, whose electrical
field is expressed by either equation (1) or equation (2), to a
first electrical current, which may be subsequently measured by the
signal extractor 150 through determining the amplitude and the
phase of the first electrical current, and finally obtained by the
data processor 170. Accordingly, the first electrical current may
be expressed by:
i.sub.SYS(.DELTA..omega.)=A.sub.2A.sub.1*H.sub.SYS(.omega..sub.(o,2))H.s-
ub.SYS*(.omega..sub.(o,1)) (3)
where i.sub.SYS(.DELTA..omega.) is the first electrical current
including the single nominal carrier frequency of .DELTA..omega.,
A.sub.1* is complex conjugate of the amplitude of the electrical
field of the first frequency carrier, H.sub.SYS(.omega..sub.(o,2))
is the transfer function of the system (i.e., the optical vector
analyzer 100) at the frequency of .omega.(o,2), and
H*.sub.SYS(.omega..sub.(o,1)) is complex conjugate of the transfer
function of the system at the frequency of .omega.(o,1).
[0036] When performing the device characterization process, the
output port of the optical detecting signal generator 110, i.e.,
port A, is coupled to the input port of the DUT 120, as the input
port of the optical to electrical converter 130, i.e., port B, is
coupled to the output port of the DUT 120. As a result, the optical
to electrical converter 130 may convert the optical spectrum, after
the optical spectrum passing through the DUT 120, to a second
electrical current, which may be subsequently measured by the
signal extractor 150 through determining the amplitude and the
phase of the second electrical current, and finally obtained by the
data processor 170.
[0037] Accordingly, when the optical spectrum provided by the
optical detecting signal generator 110 includes only the first
frequency carrier and the second frequency carrier, the electrical
field of the optical spectrum after passing through the DUT 120 may
be expressed by:
E.sub.DUT(t)=A.sub.1H(.omega..sub.(o,1))exp(j.omega..sub.(o,1)t)+A.sub.2-
H(.omega..sub.(o,2))exp(j.omega..sub.(o,2)t) (4)
where E.sub.DUT(t) represents the electrical field of the optical
spectrum after passing through the DUT 120, H(.omega..sub.(o, 1))
is the transfer function resulting from both the DUT 120 and the
system at the frequency of .omega..sub.(o, 1), and
H(.omega..sub.(o, 2)) is the transfer function resulting from both
the DUT 120 and the system at the frequency of
.omega..sub.(o,2).
[0038] Alternatively, when the optical spectrum provided by the
optical detecting signal generator 110 includes the one or more
additional frequency carriers in addition to the first frequency
carrier and the second frequency carrier, the electrical field of
the optical spectrum after passing through the DUT 120 may be
expressed by:
E.sub.DUT(t)=A.sub.-MH(.omega..sub.(o,-M))exp(j.omega..sub.(o,-M)t)+
. . . +A.sub.NH(.omega..sub.(o,N))exp(j.omega..sub.(o,N)t) (5)
where H(.omega..sub.(o, -M)), . . . , H(.omega..sub.(o, N))
represent the transfer function resulting from both the DUT 120 and
the system at the frequencies of .omega..sub.(o, -M), . . . ,
.omega..sub.(o, N), respectively.
[0039] Further, the second electrical current may be expressed
by:
i(.DELTA..omega.)=A.sub.2A.sub.1*H(.omega..sub.(o,2))H*(.omega..sub.(o,1-
)) (6)
where i(.DELTA..omega.) is the second electrical current including
the single nominal carrier frequency of A.omega.,
H(.omega..sub.(o,2)) is the transfer function resulting from both
the DUT 120 and the system at the frequency of .omega.(o,2), and
H*(.omega..sub.(o,1)) is complex conjugate of the transfer function
resulting from both the DUT 120 and the system at the frequency of
.omega.(o,1).
[0040] The relationship between H(.omega..sub.(o,2)) and
H.sub.SYS(.omega..sub.(o,2)) may be expressed by:
H(.omega..sub.(o,2))=H.sub.SYS(.omega..sub.(o,2))H.sub.DUT(.omega..sub.(-
o,2)) (7)
where H.sub.DUT(.omega..sub.(o,2)) represents the transfer function
of the DUT 120 at the frequency of .omega..sub.(o,2).
[0041] In addition, the relationship between H*(.omega..sub.(o,1))
and H*.sub.SYS(.omega..sub.(o,1)) may be expressed by:
H*(.omega..sub.(o,1))=H.sub.SYS*(.omega..sub.(o,1))H.sub.DUT*(.omega..su-
b.(o,1)) (8)
where H*.sub.DUT(.omega..sub.(o,1)) represents the complex
conjugate of the transfer function of the DUT 120 at the frequency
.omega..sub.(o,1).
[0042] Upon completion of the system calibration process and the
device characterization process, the data processor may be further
configured to make the following determination based on equations
(3), (6), (7), and (8):
i ( .DELTA. .omega. ) i SYS ( .DELTA. .omega. ) ) = H DUT ( .omega.
( o , 2 ) ) H DUT * ( .omega. ( o , 1 ) ) ( 9 ) ##EQU00001##
[0043] Assuming .DELTA.w is very small, H(.omega..sub.(o,2)) and
H*.sub.DUT(.omega..sub.(o,1)) can be approximated by
H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) and H DUT * (
.omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) ##EQU00002##
respectively. Accordingly, the data processor 170 may be further
configured to make the following determination based on equations
(9):
H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) = i ( .DELTA.
.omega. ) i SYS ( .DELTA. .omega. ) ( 10 ) D ( .omega. ( o , 1 ) +
.omega. ( o , 2 ) 2 ) = exp [ j .phi. ( i ( .DELTA. .omega. ) ) - j
.phi. ( i SYS ( .DELTA. .omega. ) ) ] .DELTA. .omega. ( 11 )
##EQU00003##
where
H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) ##EQU00004##
is the transfer function of the DUT 120 at the average of the first
nominal carrier frequency and the second nominal carrier
frequency,
H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) ##EQU00005##
is amplitude of the transfer function of the DUT 120 at the average
of the first nominal carrier frequency and the second nominal
carrier frequency, |i.sub.SYS(.DELTA..omega.)| is the amplitude of
the first current, which can be measured by the signal extractor
150 and obtained by the data processor 170, |i(.DELTA..omega.)| is
the amplitude of the second current, which can be measured by the
signal extractor 150 and obtained by the data processor 170,
D ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) ##EQU00006##
is the group delay of the DUT 120 at the average of the first
nominal carrier frequency and the second nominal carrier frequency,
.PHI.[i.sub.SYS(.DELTA..omega.)] is the phase of the first current,
which can be measured by the signal extractor 150 and obtained by
the data processor 170, and .PHI.[i(.DELTA..omega.)] is the phase
of the second current, which can be measured by the signal
extractor 150 and obtained by the data processor 170. The phase of
the transfer function of the DUT 120 at the average of the first
nominal carrier frequency and the second nominal carrier frequency
may be further determined by integrating
D ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) ##EQU00007##
with respect to frequency.
[0044] In an embodiment, the first nominal carrier frequency
.omega..sub.(o,1), the second nominal carrier frequency,
.omega..sub.(o,2), and/or the difference between the first nominal
carrier frequency and the second nominal carrier frequency, i.e.,
.DELTA..omega., may be adjusted, for example, by the data processor
170. This is done so that the transfer function of the DUT 120 at
various other operating frequencies may be determined accordingly
by performing one or more additional sets of the device
characterization process and the system calibration process as
described above. In an embodiment, the first nominal carrier
frequency, .omega..sub.(o,1), the second nominal carrier frequency,
.omega..sub.(o,2) may be adjusted by an equal amount while keeping
the difference of the first nominal carrier frequency and the
second nominal carrier frequency, i.e., .DELTA..omega., the same.
In an embodiment, the equal amount may be greater than or equal to
.DELTA..omega.. As a result, the nominal carrier frequency of both
the first electrical current and the second electrical current
converted by the optical to electrical converter 130 would never be
changed, which reduces the frequency-dependent measurement errors
for the optical to electrical converter 130 and the signal
extractor 150 and thereby improves the accuracy and stability of
performance of the optical vector analyzer 100.
[0045] Referring to FIG. 2, a schematic diagram of an embodiment of
the optical detecting signal generator 110 is depicted. As shown,
the optical detecting signal generator 110 includes a radiation
generator 210, an optical modulator 220, a first tunable
radio-frequency (RF) signal generator 240, a second tunable RF
signal generator 250, and an RF combiner 260. In an embodiment, the
optical detecting signal generator 110 may, optionally, further
include an optical filter 230.
[0046] The radiation generator 210 may be configured to provide an
electromagnetic radiation having a nominal carrier frequency,
.omega..sub.c. An exemplary spectral profile of the electromagnetic
radiation provided by the radiation generator 210 is shown in FIG.
2 as directed by arrow 215. The nominal carrier frequency of the
electromagnetic radiation, i.e., .omega..sub.c, may be tunable. As
shown, the radiation generator 210 has an input port coupled to the
data processor 170 and configured to receive a control signal from
the data processor 170, which may be used to tune the nominal
carrier frequency of the electromagnetic radiation, i.e.,
.omega..sub.c. The radiation generator 210 further includes an
output port coupled to the optical modulator 220 and configured to
output the electromagnetic radiation to the optical modulator
220.
[0047] The optical modulator 220 may include a first input port
coupled to the radiation generator 210 and configured to receive
the electromagnetic radiation from the radiation generator 210. The
optical modulator 220 may include a second input port configured to
receive a first RF signal having a first RF frequency,
.omega..sub.1, and a second RF signal having a second RF frequency,
.omega..sub.2. The optical modulator 220 may be configured to
generate a modulated optical spectrum by modulating the first RF
frequency and the second RF frequency on the electromagnetic
radiation received from the radiation generator. An example
spectral profile of the modulated optical spectrum is shown in FIG.
2 as directed by arrow 225.
[0048] In an embodiment, the optical modulator 220 is a single
sideband modulator, which generates a sideband on one side of the
nominal carrier frequency, .omega..sub.c, with respect to each of
the first RF frequency, .omega..sub.1, and a second RF frequency,
.omega..sub.2. As a result, the modulated optical spectrum is shown
in solid lines in the spectral profile directed by arrow 225, which
includes the nominal carrier frequency of .omega..sub.c, a first
sideband frequency of .omega..sub.c+.omega..sub.1, and a second
sideband frequency of .omega..sub.c+.omega..sub.2. The difference
between the first sideband frequency and the second sideband
frequency, i.e., .DELTA..omega.=.omega..sub.2-.omega..sub.1 is
smaller than both the first RF frequency, .omega..sub.1 and the
second RF frequency, .omega..sub.2. Subsequently, the modulated
optical spectrum, e.g., in solid line, may be outputted directly
through the output port of the optical detecting signal generator
110, i.e., port A in FIG. 1. Alternatively, the modulated optical
spectrum, e.g., in solid line, may subsequently pass through the
optical filter 230 before outputted through the output port of the
optical detecting signal generator 110, i.e., port A in FIG. 1. In
an embodiment, the output port of the optical modulator 220, when
the optical filter 230 is not included in the optical vector
analyzer 100, is the output port of the optical vector analyzer
100, i.e., port A.
[0049] In an embodiment, the optical modulator 220 is a double
sideband modulator, which generates a sideband on each side of the
nominal carrier frequency, .omega..sub.c, with respect to each of
the first RF frequency, .omega..sub.1, and a second RF frequency,
.omega..sub.2. As a result, the modulated optical spectrum is shown
in both solid lines and dashed lines in the spectral profile
directed by arrow 225, which includes the nominal carrier frequency
of .omega..sub.c, the first sideband frequency of
.omega..sub.c+.omega..sub.1, the second sideband frequency of
.omega..sub.c+.omega..sub.2, a third sideband frequency of
.omega..sub.c-.omega..sub.1, and a fourth sideband frequency of
.omega..sub.c-.omega..sub.2. The difference between the first
sideband frequency and the second sideband frequency, or between
the third sideband frequency and the fourth sideband frequency,
i.e., .DELTA..omega.=.omega..sub.2-.omega..sub.1 is smaller than
both the first RF frequency, .omega..sub.1, and the second RF
frequency, .omega..sub.2. Subsequently, the modulated optical
spectrum, e.g., in both the solid line and the dashed line, may be
pass through the optical filter 230 before outputted through the
output port of the optical detecting signal generator 110, i.e.,
port A in FIG. 1.
[0050] As shown in FIG. 2, the first RF signal having the first RF
frequency, .omega..sub.1, and the second RF signal having the
second RF frequency, .omega..sub.2 may be provided to the second
input port of the optical modulator 220 through the use of the
first tunable RF signal generator 240, the second tunable RF signal
generator 250, and the RF combiner 260. The first tunable RF signal
generator 240 may be configured to provide a first sinusoidal
signal at the first RF frequency of .omega..sub.1. The second
tunable RF signal generator 250 may be configured to provide a
second sinusoidal signal at the second RF frequency of
.omega..sub.2. The RF combiner 260 may be configured to receive
both the first sinusoidal signal from the first tunable RF signal
generator 240 and the second sinusoidal signal from the second
tunable RF signal generator 250. The RF combiner 260 may be further
configured to provide both the first sinusoidal signal having the
first RF frequency of .omega..sub.1 and the second sinusoidal
signal having the second RF frequency of .omega..sub.2 to the
optical modulator 220. In an embodiment, the first RF signal is the
first sinusoidal signal, as the second RF signal is the second
sinusoidal signal. The first tunable RF signal generator 240 and
the second tunable RF signal generator 250 may be coupled to the
data processor 170, which may be used to tune the first RF
frequency of .omega..sub.1, the second RF frequency of
.omega..sub.2, or both.
[0051] The optical filter 230 may include an input port configured
to receive the modulated optical spectrum. The optical filter 230
may be configured to provide a filtered optical spectrum based on
the modulated optical spectrum. The optical filter 230 may be a
bandpass filter or a band-stop filter. In an embodiment, the
filtered optical spectrum may include the first sideband frequency
of .omega..sub.c+.omega..sub.1 and the second sideband frequency of
.omega..sub.c+.omega..sub.2, as shown in an example spectral
profile as directly by arrow 235. Optionally, the filtered optical
spectrum may further include the nominal carrier frequency of co,
and/or only one of the third sideband frequency of
.omega..sub.c-.omega..sub.1 and the fourth sideband frequency of
.omega..sub.c-.omega..sub.2. In an embodiment, the filtered optical
spectrum may include the third sideband frequency of
.omega..sub.c-.omega..sub.1 and the fourth sideband frequency of
.omega..sub.c-.omega..sub.2. Optionally, the filtered optical
spectrum may further include the nominal carrier frequency of co,
and/or only one of the first sideband frequency of
.omega..sub.c+.omega..sub.1 and the second sideband frequency of
.omega..sub.c+.omega..sub.2. The optical filter 230 may further
include an output port configured to output the filtered optical
spectrum. In an embodiment, the optical port of the optical filter
230 may be the output port of the optical vector analyzer 100,
i.e., port A, in FIG. 1.
[0052] Referring to FIG. 3, a schematic diagram of another
embodiment of the optical detecting signal generator 110 is
depicted. Different than that in FIG. 2, the first RF signal having
the first RF frequency, .omega..sub.1, and the second RF signal
having the second RF frequency, .omega..sub.2 may be provided to
the second input port of the optical modulator 220 through the use
of the first tunable RF signal generator 240, an RF splitter 345,
an RF frequency shifter 350, and the RF combiner 260. As described
above, the first tunable RF signal generator 240 may be configured
to provide the first sinusoidal signal at the first RF frequency of
.omega..sub.1. The RF splitter 345 may be configured to split the
first sinusoidal signal in half. The RF splitter 345 may be further
configured to provide a half of the first sinusoidal signal to a
first input port of the RF combiner 260. In addition, the RF
splitter 345 may be configured to provide the other half of the
first sinusoidal signal to an input port of the RF frequency
shifter 350. The RF frequency shifter 350 may be configured to
shift the RF frequency of the first sinusoidal signal by an amount
equal to .DELTA..omega.=.omega..sub.2-.omega..sub.1, producing the
second sinusoidal signal having the second RF frequency of
.omega..sub.2. The RF frequency shifter 350 may be finally
configured to output the second sinusoidal signal to a second input
port of the RF combiner 260. The RF combiner 260 may be configured
to receive the first sinusoidal signal having the first RF
frequency of .omega..sub.1 and the second sinusoidal signal having
the second RF frequency of .omega..sub.2. The RF combiner 260 may
be further configured to output both the first sinusoidal signal
and the second sinusoidal signal to the optical modulator 220.
[0053] In an embodiment, as shown in FIG. 3, the first tunable RF
signal generator 240 and the RF frequency shifter 350 may be
coupled to the data processor 170, which may be used to tune the
first RF frequency of .omega..sub.1, the frequency shift
(.DELTA..omega.=.omega..sub.2-.omega..sub.1), or both.
[0054] Referring to FIG. 4, a schematic diagram of yet another
embodiment of the optical detecting signal generator 110 is
depicted. Different than those in FIG. 2 and FIG. 3, the first RF
signal having the first RF frequency, .omega..sub.1, and the second
RF signal having the second RF frequency, .omega..sub.2 may be
provided to the second input port of the optical modulator 220
through the use of a third tunable RF signal generator 440, a
fourth tunable RF signal generator 450, and a frequency mixer 460.
The third tunable RF signal generator 440 may be configured to
provide a third sinusoidal signal at a third RF frequency of
.omega. 1 + .omega. 2 2 . ##EQU00008##
The fourth tunable RF signal generator 450 may be configured to
provide a fourth sinusoidal signal at a fourth RF frequency of
.omega. 1 - .omega. 2 2 , ##EQU00009##
assuming .omega..sub.2>.omega..sub.1. The frequency mixer 460
may be configured to receive both the third sinusoidal signal from
the third tunable RF signal generator 440 and the fourth sinusoidal
signal from the fourth tunable RF signal generator 450. The
frequency mixer 460 may be further configured to generate the first
RF signal having the first RF frequency of .omega..sub.1 by
combining the third sinusoidal signal and the fourth sinusoidal
signal. The frequency mixer 460 may be further configured to
generate the second RF signal by subtracting the fourth sinusoidal
signal from the third sinusoidal signal. The frequency mixer 460
may be finally configured to provide the first RF signal having the
first RF frequency of .omega..sub.1 and the second RF signal having
the second RF frequency of .omega..sub.2 to the second input port
of the optical modulator 220. The third tunable RF signal generator
440 and the fourth tunable RF signal generator 450 may be coupled
to the data processor 170, which may be used to tune the third RF
frequency of
.omega. 1 + .omega. 2 2 , ##EQU00010##
the fourth RF frequency of
.omega. 1 - .omega. 2 2 , ##EQU00011##
or both, resulting in adjustment in the first RF frequency of
.omega..sub.1 and the second RF frequency of .omega..sub.2.
[0055] Referring to FIG. 5, a schematic diagram of the radiation
generator 210 is shown according to an embodiment of the present
disclosure. The radiation generator 210 may include a comb source
510 and a tunable optical filter 520 coupled to the comb source
510.
[0056] The comb source 510 may be configured to provide an optical
frequency comb comprising a plurality of equally spaced optical
frequency carriers. In some examples, the plurality of equally
spaced optical frequency carriers may have a same amplitude or
similar amplitude, resulting in a flat spectral profile. In some
other examples, the plurality of equally spaced optical frequency
carriers may have different amplitudes. An example of the optical
frequency comb is shown in FIG. 5 as directed by arrow 515. As
shown, the spectral spacing between the adjacent optical frequency
carriers, denoted by .DELTA..OMEGA., is the same. In an embodiment,
.DELTA..OMEGA. may be below 10 GHz, 10 GHz, between 10 GHz and 20
GHz, 20 GHz, between 20 GHz and 30 GHz, 30 GHz, between 30 GHz and
40 GHz, 40 GHz, between 40 GHz and 50 GHz, 50 GHz, and so on. In an
embodiment, the comb source 510 may be coupled to the data
processor 170, which may be used to adjust the nominal carrier
frequencies of the plurality of equally spaced optical frequency
carriers and/or the spacing between the adjacent optical frequency
carriers of the comb source 510, i.e., .DELTA..OMEGA..
[0057] The tunable optical filter 520 may be configured to select
one optical frequency carrier from the plurality of equally spaced
optical frequency carriers provided by the comb source 510. The
tunable optical filter 520 may be further configured to provide the
selected optical frequency carrier to the optical modulator 220. In
an embodiment, the tunable optical filter 520 may be a tunable
optical bandpass filter. For example, the tunable optical filter
520, whose spectral profile is denoted as a dashed box 545 in the
optical spectral profile as directed by arrow 525, may have an
operating frequency at around .omega..sub.(c,2) with a
predetermined bandwidth. As such, the tunable optical filter 520
may be used to select an optical frequency carrier centered at the
nominal carrier frequency of .omega..sub.(c,2), while filtering out
the other optical frequency carriers. As a result, the tunable
optical filter 520 may provide an electromagnetic radiation (i.e.,
the selected optical frequency carrier) at the nominal carrier
frequency of .omega..sub.(c,2), as directed by arrow 535, to the
optical modulator 220. In an embodiment, the tunable optical filter
520 may be a tunable optical band-stop filter.
[0058] In an embodiment, the tunable optical filter 520 may be
coupled to the data processor 170, which may be used to control and
adjust the operating frequency of the tunable optical filter 520.
For example, the operating frequency of the tunable optical filter
520 may be red shifted (e.g., as shown in the leftward arrow) or
blue shifted (e.g., as shown in the rightward arrow). This is done
so that an optical frequency carrier at another carrier frequency
may be selected and provided by the radiation generator 210 to the
optical modulator 220 after adjustment.
[0059] Referring to FIG. 6, a schematic diagram of the comb source
510 is shown according to an embodiment of the present disclosure.
As shown, the comb source 510 includes a laser diode 630, a first
polarization controller 640, an RF source 610, a power adjuster
620, a polarization modulator 650, a second polarization controller
660, and a polarizer 670. The first polarization controller 640 may
be similar to the second polarization controller 660. As shown, the
laser diode 630, the RF source 610, and/or the power adjuster 620
may be coupled to the data processor 170.
[0060] The laser diode 630 may be configured to provide an
electromagnetic radiation having a single optical frequency carrier
at a nominal carrier frequency of .omega..sub.c (for example, as
shown in FIG. 6 and directed by arrow 635). In an embodiment, the
laser diode 630 may be a continuous wave laser configured to
provide the single optical frequency carrier at the nominal carrier
frequency of .omega..sub.c with a narrow bandwidth (or a narrow
linewidth). In an embodiment, the nominal carrier frequency of
.omega..sub.c may be adjusted by the data processor 170. In an
embodiment, the tuning range of the laser diode 630 may be smaller
than the tuning range of the tunable optical filter 520 in FIG.
5.
[0061] The first polarization controller 640 may be coupled to the
laser diode 630 and configured to tune the polarization state of
the electromagnetic radiation received from the laser diode 630.
The first polarization controller 640 may be further configured to
output the electromagnetic radiation to the polarization modulator
650 after the polarization state is adjusted.
[0062] The polarization modulator 650 may be coupled to the first
polarization controller 640 and the power adjuster 620. The
polarization modulator 650 may be configured to modulate the
polarization of the electromagnetic radiation received from the
first polarization controller 640 according to the RF signal
received from the power adjuster 620. The polarization modulator
650 may be further configured to provide the electromagnetic
radiation after polarization modulation to the second polarization
controller 660.
[0063] The RF source 610 may be configured to provide an RF signal
to the power adjuster 620 at a frequency of .DELTA..OMEGA.. In an
embodiment, the RF source 610 may be coupled to the data processor
170, which may be used to adjust the power and/or the frequency of
.DELTA..OMEGA..
[0064] The power adjuster 620 may be coupled to the RF source 610
and configured to adjust the power of the RF signal provided to the
polarization modulator 650. In an embodiment, the power adjuster
620 may comprise a tunable RF amplifier with an adjustable power
amplification. In an embodiment, the power adjuster 620 may
comprise a tunable RF attenuator with an adjustable power
attenuation. In an embodiment, the amount of power amplification
and/or power attenuation may be adjusted by the data processor
170.
[0065] The second polarization controller 660 may be coupled to the
polarization modulator 650 and configured to adjust the
polarization state of the electromagnetic radiation received from
the polarization modulator 650. The second polarization controller
660 may be further configured to provide the electromagnetic
radiation after the polarization state is adjusted to the polarizer
670.
[0066] The polarizer 670 may be configured to receive the
electromagnetic radiation from the second polarization controller
660 and output a portion of the electromagnetic radiation matching
to a predefined polarization. By carefully adjusted the first
polarization controller 640, the power adjuster 620, the
polarization modulator 650, and the second polarization controller
660, the outputted portion of the electromagnetic radiation may be
an optical frequency comb with an equal spacing of .DELTA..OMEGA.
and a flat spectral profile, for example, as shown in FIG. 6 as
directed by arrow 675. In some examples, the comb source 510 may
comprise more than one polarization modulator 650 to provide a
larger number of optical frequency carriers. More details about the
comb source 510 may be found in Chao He, et. al, "Ultrafast optical
frequency comb generated based on cascaded polarization
modulators," Optics Letters Vol. 37, No. 18, pages 3834-3836,
published on Sep. 15, 2012, which is incorporated by reference in
its entirety.
[0067] Referring to FIG. 7, a schematic diagram of another
embodiment of the optical detecting signal generator 110 is
depicted. In this embodiment, the optical detecting signal
generator 110 may include a mode-locked laser 710 and a tunable
optical filter 720 coupled to the mode-locked laser 710.
[0068] The mode-locked laser 710 may be configured to provide an
optical frequency comb comprising a plurality of equally spaced
optical frequency carriers. In some examples, the plurality of
equally spaced optical frequency carriers may have the same
amplitude or similar amplitudes, resulting in a flat spectral
profile. In some other examples, the plurality of equally spaced
optical frequency carriers may have different amplitudes. An
example of the optical frequency comb is shown in FIG. 7 as
directed by arrow 715. As shown, the plurality of equally spaced
optical frequency carriers has a plurality of nominal carrier
frequencies, some of which are denoted by .omega..sub.(M,1),
.omega..sub.(M,2), .omega..sub.(M,3), and .omega..sub.(M,4) as
shown in FIG. 7. The spectral spacing between the adjacent optical
frequency carriers, denoted by .DELTA..omega., is the same. In an
embodiment, .DELTA.w may be below 1 MHz, 1 MHz, between 1 MHz and
10 MHz, 10 MHz, between 10 MHz and 100 MHz, 100 MHz, between 100
MHz and 1 GHz, 1 GHz, and so on. In an embodiment, the mode-locked
laser 710 is a mode-locked fiber laser. In an embodiment, the
mode-locked laser 710 may be coupled to the data processor 170,
which may be used to adjust the frequencies of the plurality of
equally spaced optical frequency carriers and/or the spacing, i.e.,
.DELTA..omega., between the adjacent optical frequency carriers of
the mode-locked laser 710.
[0069] The tunable optical filter 720 may be configured to select
two of the plurality of equally spaced optical frequency carriers
provided by the mode-locked laser 710. In an embodiment, the
tunable optical filter 720 may be configured to select two adjacent
optical frequency carriers from the plurality of equally spaced
optical frequency carriers provided by the mode-locked laser 710.
The tunable optical filter 720 may be further configured to output
the selected carriers. In an embodiment, the tunable optical filter
720 is a tunable optical bandpass filter. For example, the tunable
optical filter 720, whose spectral profile is denoted by a dashed
box 745 in FIG. 7 as directed by arrow 725, may have an operating
bandwidth and/or operating frequency range including the
frequencies of the selected optical frequency carriers, for
example, .omega..sub.(M,1) and .omega..sub.(M,2) (and excluding the
nominal carrier frequencies of the other unselected optical
frequency carriers). As a result, the tunable optical filter 720
may provide the filtered radiation or the filtered optical spectrum
including the selected optical frequency carrier, for example,
having the nominal carrier frequencies of .omega..sub.(M,1) and
.omega..sub.(M,2), as shown and directed by arrow 735. In an
embodiment, the tunable optical filter 720 is a tunable optical
band-stop filter.
[0070] In an embodiment, the tunable optical filter 720 may be
coupled to the data processor 170, which may be used to control and
adjust the operating bandwidth and/or operating frequency range of
the tunable optical filter 720. For example, when the tunable
optical filter 720 is a tunable optical bandpass filter, the
operating frequency range (indicated by the spectral profile 745)
of the tunable optical filter 720 may be red shifted (e.g., as
shown in the leftward arrow) or blue shifted (e.g., as shown in the
rightward arrow), for example, controlled by the data processor
170. This is done so that another pair of optical frequency
carriers may be selected and provided by the optical detecting
signal generator 110 after adjustment.
[0071] Referring to FIG. 8, a schematic diagram of another
embodiment of the optical detecting signal generator 110 is
depicted. In this embodiment, the optical detecting signal
generator 110 includes a plurality of laser sources 810.sub.1, 2, .
. . , P, where the number of laser sources 810.sub.1, 2, . . . , P
is denoted by a positive integer, P. The optical detecting signal
generator 110 further includes a multiplexer 815 coupled to the
plurality of laser sources 810.sub.1, 2, . . . , P. In some
examples, the optical detecting signal generator 110 may further
include a tunable optical filter 820. In some other examples, the
optical detecting signal generator 110 may not include the tunable
optical filter 820.
[0072] Each of the plurality of laser sources 810.sub.1, 2, . . . ,
P may be configured to emit a radiation including one or more
optical frequency carriers. In an embodiment, each of the plurality
of laser sources 810.sub.1, 2, . . . , P may be a continuous wave
laser configured to emit a radiation having a different single
nominal carrier frequency. For example, as shown, the first laser
source 810.sub.1 may emit a first radiation having a first nominal
carrier frequency, .omega..sub.(o,1), the second laser source
810.sub.2 may emit a second radiation having a second nominal
carrier frequency, .omega..sub.(o,2), . . . , and the P.sub.th
laser source 810.sub.P may emit a P.sub.th radiation having a
P.sub.th nominal carrier frequency, .omega..sub.(o,P). In an
embodiment, the plurality of laser sources 810.sub.1, 2, . . . , P
may be coupled to the data processor 170, which may be used to
adjust one or more nominal carrier frequencies selected from
.omega..sub.(o,1), .omega..sub.(o,2), . . . , and
.omega..sub.(o,P).
[0073] The multiplexer 815 may include a plurality of input ports
coupled to the plurality of laser sources 810.sub.1, 2, . . . , P
and configured to receive the plurality of radiations, including a
plurality of carrier frequencies denoted by .omega..sub.(o,1),
.omega..sub.(o,2), . . . , .omega..sub.(o,P), provided by the
plurality of laser sources 810.sub.1, 2, . . . , P. The multiplexer
815 may be further configured to combine the plurality of
radiations and output, through an output port of the multiplexer
815, the combined radiation. An example combined radiation is shown
in FIG. 8 as directed by arrow 825. As shown, the difference
between the first carrier frequency, .omega..sub.(o,1) and the
second carrier frequency, .omega..sub.(o,1) is denoted by
.DELTA..omega..sub.1, the difference between the second carrier
frequency, .omega..sub.(o,2) and the third carrier frequency,
.omega..sub.(o,3) is denoted by .DELTA..omega..sub.2, and so on. In
an embodiment, the spacing between adjacent optical frequency
carriers in the combined radiation may be equal. In an embodiment,
the spacing between adjacent optical frequency carriers in the
combined radiation may not be the same. In an embodiment, the
multiplexer 815 may be configured by employing a plurality of
2.times.1 optical fiber combiners.
[0074] In an embodiment, the optical detecting signal generator 110
may not include the tunable optical filter 820. Accordingly, the
combined radiation may be outputted directly through the output
port of the multiplexer 815. This can be done when a specific pair
of optical frequency carriers included in the combined radiation
has a spacing smaller than any other pair of optical frequency
carriers included in the combined radiation, and none of the
plurality of carrier frequencies, e.g., .omega..sub.(o,1),
.omega..sub.(o,2), . . . , .omega..sub.(o,P) and any difference in
frequency between any pair of optical frequency carriers, except
the specific pair of optical frequency carriers included in the
combined radiation, falls within the operating bandwidth or
operating frequency range of the optical to electrical converter
130 in the optical vector analyzer 100 as shown in FIG. 1. The
output port of the multiplexer 815 is the output port of the
optical detecting signal generator 110, i.e., port A.
[0075] In an embodiment, the optical detecting signal generator 110
may further include the tunable optical filter 820 configured to
provide a filtered radiation upon receipt of the combined
radiation. In an embodiment, the tunable optical filter 820 may be
a tunable bandpass filter. Accordingly, the tunable optical filter
820 may be configured to select a pair of optical frequency
carriers from the combined radiation as the spectral difference
between the pair of optical frequency carriers is within the
operating frequency range or operating bandwidth of the optical to
electrical converter 130. Optionally, the tunable optical filter
820 may be further configured to select one or more additional
optical frequency carriers when the spectral spacing of the pair of
optical frequency carriers is smaller than any other pair of
optical frequency carriers selected from the combined radiation.
For example, the operating frequency range of the tunable optical
filter 820 may be indicated by a corresponding spectral profile and
illustrated by a dashed box 830. In this example, only the second
carrier frequency, .omega..sub.(o,2), and the third carrier
frequency, .omega..sub.(o,3) are within the optical frequency range
of the tunable optical filter 820. As a result, the filtered
radiation, as shown in an example spectral profile as directed by
arrow 840, includes only the second carrier frequency,
.omega..sub.(o,2), and the third carrier frequency,
.omega..sub.(o,3). In an embodiment, the tunable optical filter 820
may be a tunable band-stop filter.
[0076] In an embodiment, the tunable optical filter 820 may be
coupled to the data processor 170, which may be used to tune the
operating frequency range of the tunable optical filter 820. For
example, when the tunable optical filter 820 is a tunable optical
bandpass filter, the operating frequency range (indicated by the
spectral profile 830) of the tunable optical filter 820 may be red
shifted (e.g., as shown in the leftward arrow) or blue shifted
(e.g., as shown in the rightward arrow), for example, controlled by
the data processor 170. This is done so that other suitable one or
more optical frequency carriers may be selected and provided by the
optical detecting signal generator 110 after adjustment.
[0077] Referring to FIG. 9, a schematic diagram of another optical
vector analyzer 900 is shown according to an embodiment of the
disclosure. The optical vector analyzer 900 may be suitable to
perform the optical vector analysis of the DUT 120. As shown, the
optical vector analyzer 900 comprises an optical multiple-carrier
generator 910, a splitter 920, a plurality of optical to electrical
converters 930.sub.1, 2, . . . , n, a plurality of signal
extractors 940.sub.1, 2, . . . , n, the data processor 170, and the
display 190.
[0078] The optical multiple-carrier generator 910 may be configured
to provide an electromagnetic radiation having a plurality of
optical frequency carriers, each of which corresponding to a
different nominal carrier frequency. An example spectral profile of
the electromagnetic radiation provided by the optical
multiple-carrier generator 910 is shown in FIG. 9 as directed by
arrow 915. As shown, the electromagnetic radiation provided by the
optical multiple-carrier generator 910 includes a plurality of
carrier frequencies denoted by .omega..sub.(o,1),
.omega..sub.(o,2), . . . , and .omega..sub.(o,S+1). In addition,
the difference between the first carrier frequency
.omega..sub.(o,1), and the second carrier frequency,
.omega..sub.(o,2), is denoted by .DELTA..omega..sub.1, the
difference between the second carrier frequency .omega..sub.(o,2),
and the third carrier frequency, .omega..sub.(o,3), is denoted by
.DELTA..omega..sub.2, . . . , and the difference between the
S.sub.th carrier frequency .omega..sub.(o,S), and the (S+1).sub.th
carrier frequency, .omega..sub.(o,S+1), is denoted by
.DELTA..omega..sub.s. In an embodiment, the optical
multiple-carrier generator 910 may be configured similarly to the
comb source 510. Accordingly,
.DELTA..omega..sub.1=.DELTA..omega..sub.2= . . .
=.DELTA..omega..sub.S. In an embodiment, the optical
multiple-carrier generator 910 may be configured similarly to the
optical detecting signal generator 110 as shown in FIG. 8,
excluding the tunable optical filter 820. In this embodiment, the
differences between adjacent nominal carrier frequencies are equal,
i.e., .DELTA..omega..sub.1=.DELTA..omega..sub.2= . . .
=.DELTA..omega..sub.S. Alternatively, at least two of the
differences between the adjacent carrier frequencies are not the
same.
[0079] In an embodiment, the optical multiple-carrier generator 910
may be coupled to the data processor 170, which may adjust the
nominal carrier frequencies and/or the differences between adjacent
carrier frequencies of the electromagnetic radiation provided by
the optical multiple-carrier generator 910. The optical
multiple-carrier generator 910 further includes an output port,
denoted by port A, configured to output the electromagnetic
radiation.
[0080] The splitter 920 may have an input port, denoted as the port
B. In an embodiment, the input port of the splitter 920, i.e., the
port B, may be coupled to the output port of the optical
multiple-carrier generator, i.e., the port A (for example, during
the system calibration process). As a result, the splitter 920 may
be configured to receive the electromagnetic radiation provided by
the optical multiple-carrier generator 910 directly without the
electromagnetic radiation passing through the DUT 120. In an
embodiment, the input port of the splitter 920, i.e., the port B,
may be coupled to the output port of the DUT 120 as the output port
of the optical multiple-carrier generator 910, i.e., port A is
coupled to the input port of the DUT 120. As a result, the splitter
920 may be configured to receive the electromagnetic radiation
provided by the optical multiple-carrier generator 910 after the
electromagnetic radiation passing through the DUT 120.
[0081] In either situation, the splitter 920 may be further
configured to provide a plurality of portions of the
electromagnetic radiation, and direct each portion to a respective
one of a plurality of frequency channels. Specifically, each
portion of the electromagnetic radiation may include a specific
pair of carrier frequencies. When a portion of the electromagnetic
radiation includes more than two carrier frequencies, the specific
pair of carrier frequencies can be determined such that a
difference between the specific pair of carrier frequencies is
smaller than any other pair of carrier frequencies selected from
the more than two carrier frequencies. Further, each of the
plurality of frequency channels includes one optical to electrical
converter 930.sub.1, 2, . . . n followed by one signal extractor
940.sub.1, 2, . . . n. The optical to electrical converters
930.sub.1, 2, . . . , n are similar to the optical to electrical
converter 130 in FIG. 1. Each of the optical to electrical
converters may be configured to convert the corresponding portion
of the electromagnetic radiation to an electrical current including
a single nominal carrier frequency equal to the spectral difference
of the corresponding specific pair of the nominal carrier
frequencies. Example portions of the electromagnetic radiation
provided to the optical to frequency converters 930.sub.1, 2, . . .
, n is shown in FIG. 9 as directed by arrows 925 and 945, as
example spectral profiles of the electrical currents provided by
the optical to electrical converters 930.sub.1, 2, . . . , n are
shown as directed by arrows 935 and 955. Further, the signal
extractors 940.sub.1, 2, . . . n are similar to the signal
extractor 150 in FIG. 1. The signal extractors 940.sub.1, 2, . . .
n are configured to extract the amplitude and the phase of the
corresponding electrical currents provided by the corresponding
optical to electrical converters 930.sub.1, 2, . . . n, which are
subsequently provided to the data processor 170 followed by the
display 190. With respect to each frequency channel, the data
processor 170 may determine the transfer function of the DUT 120 at
an average of carrier frequencies in relation to the corresponding
specific pair of carrier frequencies.
[0082] In an embodiment, the splitter 920 may be coupled to the
data processor 170, which may be used to determine each of the
plurality of portions of the electromagnetic radiation to be
selected by the splitter 920 to the corresponding channel.
[0083] Similar to the description above associated with the optical
vector analyzer 100, the device characterization process and the
system calibration process as described associated with FIG. 1 may
be implemented respectively in order to perform the optical vector
analysis on the DUT 120 using the optical vector analyzer 900.
However, by including a plurality of frequency channels in parallel
each comprising an optical to electrical converter 930.sub.1, 2, .
. . , n and a signal extractor 940.sub.1, 2, . . . , n, the data
processor 170 in FIG. 9 may determine the transfer function of the
DUT 120 at a greater number of operating frequencies upon
completion of one device characterization process and one system
calibration process. Further, one or more additional device
characterization processes and system calibration processes, as
described above, may be performed to determine, by, e.g., the data
processor 170 in the optical vector analyzer 900 as shown in FIG.
9, the transfer functions of the DUT 120 at other operating
frequencies after adjusting the nominal carrier frequencies
associated with the electromagnetic radiation provided by the
optical multiple-carrier generator 910.
[0084] Referring to FIG. 10, a flowchart 1000 of an exemplary
process for performing the optical vector analysis on a DUT is
shown according to an embodiment of the disclosure. In an
embodiment, the exemplary process as shown in the flowchart 1000
may be performed by the optical vector analyzers 100, 900.
[0085] At step 1010, an optical spectrum comprising two frequency
carriers is provided. Specifically, the two frequency carriers have
two different nominal carrier frequencies. In an embodiment, the
optical spectrum has, in addition to the two frequency carriers,
one or more additional frequency carriers. Any pair of spectrum
carriers, except the two frequency carriers, selected from a group
consisting of the two frequency carriers and the one or more
additional frequency carriers has a difference in frequency greater
than the spacing between the two frequency carriers. In an
embodiment, the optical spectrum may be provided by the optical
detecting signal generator 110 or the optical multiple-carrier
generator 910.
[0086] At step 1020, a first electrical current is generated based
on the optical spectrum without the optical spectrum passing
through the DUT, e.g., the DUT 120. In an embodiment, the first
electrical current may be generated by the optical to electrical
converter 130, or 930.sub.1, 2, . . . , n. The step 1020 may be
performed in a system calibration process, when, as shown in FIG.
1, the output port, i.e., port A, of the optical detecting signal
generator 110 is coupled directly to the input port, i.e., port B,
of the optical to electrical converter 130, or when, as shown in
FIG. 9, the output port, i.e., port A, of the optical
multiple-carrier generator 910 is coupled directly to the input
port, i.e., port B, of the splitter 920.
[0087] At step 1030, a second electrical current is generated based
on the optical spectrum after the optical spectrum passes through
the DUT, e.g., the DUT 120. In an embodiment, the second electrical
current may be generated by the optical to electrical converter
130, or 930.sub.1, 2, . . . , n. The step 1030 may be performed in
a device characterization process, when, as shown in FIG. 1, the
output port, i.e., port A, of the optical detecting signal
generator 110 is coupled to the input port of the DUT 120 as the
input port, i.e., port B, of the optical to electrical converter
130 is coupled to the output port of the DUT 120, or when, as shown
in FIG. 9, the output port, i.e., port A, of the optical
multiple-carrier generator 910 is coupled to the input port of the
DUT 120 as the input port, i.e., port B, of the splitter 920 is
coupled to the output port of the DUT 120.
[0088] At step 1040, a transfer function of the DUT, e.g., the DUT
120, is determined at an average of the two different nominal
carrier frequencies based on the first electrical current and the
second electrical current. In an embodiment, the transfer function
of the DUT, e.g., the DUT 120, may be determined by the data
processor 170 in FIG. 1 and FIG. 9.
[0089] In an embodiment, there is provided an apparatus comprising:
an optical detecting signal generator configured to provide,
through an output port of the optical detecting signal generator,
an optical spectrum comprising two frequency carriers, the two
frequency carriers having two different nominal carrier
frequencies, and the output port of the optical detecting signal
generator being further configured to be coupled to a DUT; an
optical to electrical converter configured to: generate a first
electrical current based on the optical spectrum without the
optical spectrum passing through the DUT; and generate a second
electrical current based on the optical spectrum after the optical
spectrum passes through the DUT; and a data processor coupled to
the optical to electrical converter, the data processor being
configured to determine a transfer function of the DUT at an
average of the two different nominal carrier frequencies based on
the first electrical current and the second electrical current.
[0090] In an embodiment, the optical spectrum comprises one or more
additional frequency carriers in addition to the two frequency
carriers, and any pair of frequency carriers, except the two
frequency carriers, selected from a group consisting of the one or
more additional frequency carriers and the two frequency carriers
has a spacing in frequency greater than a difference between the
two different nominal carrier frequencies.
[0091] In an embodiment, both the first electrical current and the
second electrical current have a single nominal carrier frequency
equal to a difference between the two different nominal carrier
frequencies.
[0092] In an embodiment, the apparatus further comprises a signal
extractor coupled to the optical to electrical converter and the
data processor, the signal extractor being configured to: receive,
through an input port of the signal extractor, an electrical
current from the optical to electrical converter; extract an
amplitude and a phase of the electrical current; and provide,
through an output port of the signal extractor, the amplitude and
the phase of the electrical current to the data processor, wherein
the electrical current is either the first electrical current or
the second electrical current.
[0093] In an embodiment, the transfer function of the DUT at the
average of the two different nominal carrier frequencies is
determined by:
| H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) | = | i (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) | | i SYS ( .omega. ( o , 2
) - .omega. ( o , 1 ) ) | ; and ##EQU00012## D DUT ( .omega. ( o ,
1 ) + .omega. ( o , 2 ) 2 ) = e j { .phi. [ i ( .omega. ( o , 2 ) -
.omega. ( o , 1 ) ) ] - .phi. [ i SYS ( .omega. ( o , 2 ) - .omega.
( o , 1 ) ) ] } ( .omega. ( o , 2 ) - .omega. ( o , 1 ) ) , wherein
| H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) |
##EQU00012.2##
is an amplitude of the transfer function of the DUT at the average
of the two different nominal carrier frequencies, denoted by
.omega.(o,1) and .omega.(o,2), respectively, wherein
i.sub.SYS(.omega.(o,2)-.omega.(o,1)) is the first electrical
current, and i(.omega.(o,2)-.omega.(o,1)) is the second electrical
current, wherein |i.sub.SYS(.omega.(o,2)-(.omega.(o,1))| is an
amplitude of the first electrical current, and
|i(.omega.(o,2)-(.omega.(o,1))| is an amplitude of the second
electrical current, and wherein
.PHI.[i.sub.SYS(.omega.(o,2)-(.omega.(o,1))] is a phase of the
first electrical current, and .PHI.[i(.omega.(o,2)-(.omega.(o,1))]
is a phase of the second electrical current.
[0094] In an embodiment, the optical detecting signal generator
comprises: a radiation generator configured to emit, through an
output port of the radiation generator, a radiation having a
nominal wavelength; and an optical modulator coupled to the
radiation generator, the optical modulator being configured to:
receive, through a first input port of the optical modulator, the
radiation from the radiation generator; receive, through a second
input port of the optical modulator, a first RF signal having a
first RF frequency, and a second RF signal having a second RF
frequency, the first RF frequency being different than the second
RF frequency; generate the optical spectrum by modulating the
radiation based on the first RF signal and the second RF signal;
and output, through an output port of the optical modulator, the
optical spectrum.
[0095] In an embodiment, the radiation generator comprises: a comb
source configured to provide an optical frequency comb having a
plurality of equally spaced optical frequency carriers; and a
tunable optical filter coupled to the comb source, the tunable
optical filter being configured to output one frequency carrier,
controllable by the data processor, of the optical frequency
comb.
[0096] In an embodiment, the optical detecting signal generator
comprises: a mode-locked laser; and a tunable optical filter
coupled to the mode-locked laser, wherein the tunable optical
filter is configured to output two optical frequency carriers,
controllable by the data processor, of a radiation provided by the
mode-locked laser.
[0097] In an embodiment, there is provided a method comprising:
providing an optical spectrum comprising two frequency carriers,
the two frequency carriers having two different nominal carrier
frequencies; generating a first electrical current based on the
optical spectrum without the optical spectrum passing through a
DUT; generating a second electrical current based on the optical
spectrum after the optical spectrum passes through the DUT; and
determining, by a data processor, a transfer function of the DUT at
an average of the two different nominal carrier frequencies based
on the first electrical current and the second electrical
current.
[0098] In an embodiment, the optical spectrum comprises one or more
additional frequency carriers in addition to the two frequency
carriers, and any pair of frequency carriers, except the two
frequency carriers, selected from a group consisting of the one or
more additional frequency carriers and the two frequency carriers
has a spacing in frequency greater than a difference between the
two different nominal carrier frequencies.
[0099] In an embodiment, both the first electrical current and the
second electrical current have a single nominal carrier frequency
equal to a difference between the two different nominal carrier
frequencies.
[0100] In an embodiment, the method further comprises: receiving an
electrical current; extracting an amplitude and a phase of the
electrical current; and providing the amplitude and the phase of
the electrical current to the data processor, wherein the
electrical current is either the first electrical current or the
second electrical current.
[0101] In an embodiment, the transfer function of the DUT at the
average of the two different nominal carrier frequencies is
determined by:
| H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) | = | i (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) | | i SYS ( .omega. ( o , 2
) - .omega. ( o , 1 ) ) | ; and ##EQU00013## D DUT ( .omega. ( o ,
1 ) + .omega. ( o , 2 ) 2 ) = e j { .phi. [ i ( .omega. ( o , 2 ) -
.omega. ( o , 1 ) ) ] - .phi. [ i SYS ( .omega. ( o , 2 ) - .omega.
( o , 1 ) ) ] } ( .omega. ( o , 2 ) - .omega. ( o , 1 ) ) , wherein
| H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) |
##EQU00013.2##
is an amplitude of the transfer function of the DUT at the average
of the two different nominal carrier frequencies, denoted by
.omega.(o,1) and .omega.(o,2), respectively, wherein
i.sub.SYS(.omega.(o,2)-.omega.(o,1)) is the first electrical
current, and i(.omega.(o,2)-.omega.(o,1)) is the second electrical
current, wherein |i.sub.SYS(.omega.(o,2)-.omega.(o,1))| is an
amplitude of the first electrical current, and
|i(.omega.(o,2)-.omega.(o,1))| is an amplitude of the second
electrical current, and wherein
.PHI.[i.sub.SYS(.omega.(o,2)-.omega.(o,1))] is a phase of the first
electrical current, and .PHI.[i(.omega.(o,2)-.omega.(o,1))] is a
phase of the second electrical current.
[0102] In an embodiment, the optical spectrum is provided by:
receiving a first RF signal having a first RF frequency, and a
second RF signal having a second RF frequency, the first RF
frequency being different than the second RF frequency; generating
the optical spectrum by modulating a radiation having a nominal
wavelength based on the first RF signal and the second RF signal;
and outputting the optical spectrum.
[0103] In an embodiment, the method further comprises generating
the radiation, wherein the radiation is generated by: providing an
optical frequency comb having a plurality of equally spaced optical
frequency carriers; and outputting one frequency carrier of the
optical frequency comb.
[0104] In an embodiment, there is provided an apparatus comprising:
an optical multiple-carrier generator configured to provide,
through an output port of the optical multiple-carrier generator,
an optical spectrum having a plurality of optical frequency
carriers, wherein the output port of the optical multiple-carrier
generator is further configured to be coupled to a DUT; a splitter
configured to: receive, through an input port of the splitter, the
optical spectrum; and provide each of a plurality of portions of
the optical spectrum to a respective one of a plurality of
channels; the plurality of channels coupled to the splitter,
wherein each of the plurality of channels comprises an optical to
electrical converter, the optical to electrical converter being
configured to: receive a respective portion of the optical
spectrum, the respective portion of the optical spectrum comprising
two frequency carriers, and the two frequency carriers having two
different nominal carrier frequencies; generate a first electrical
current based on the respective portion of the optical spectrum
without the optical spectrum passing through the DUT; and generate
a second electrical current based on the respective portion of the
optical spectrum after the optical spectrum passes through the DUT;
and a data processor coupled to the plurality of channels, wherein
the data processor is configured to determine, with respect to each
of the plurality of channels, a transfer function of the DUT at an
average of the two different nominal carrier frequencies based on
the first electrical current and the second electrical current.
[0105] In an embodiment, both the first electrical current and the
second electrical current have a single nominal carrier frequency
equal to a difference between the two different nominal carrier
frequencies.
[0106] In an embodiment, each of the plurality of channels further
comprises a signal extractor coupled to the optical to electrical
converter, the signal extractor being configured to: receive,
through an input port of the signal extractor, an electrical
current from the optical to electrical converter; extract an
amplitude and a phase of the electrical current; and provide,
through an output port of the signal extractor, the amplitude and
the phase of the electrical current to the data processor, wherein
the electrical current is either the first electrical current or
the second electrical current.
[0107] In an embodiment, the transfer function of the DUT at the
average of the two different nominal carrier frequencies is
determined by:
| H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) | = | i (
.omega. ( o , 2 ) - .omega. ( o , 1 ) ) | | i SYS ( .omega. ( o , 2
) - .omega. ( o , 1 ) ) | ; and ##EQU00014## D DUT ( .omega. ( o ,
1 ) + .omega. ( o , 2 ) 2 ) = e j { .phi. [ i ( .omega. ( o , 2 ) -
.omega. ( o , 1 ) ) ] - .phi. [ i SYS ( .omega. ( o , 2 ) - .omega.
( o , 1 ) ) ] } ( .omega. ( o , 2 ) - .omega. ( o , 1 ) ) , wherein
| H DUT ( .omega. ( o , 1 ) + .omega. ( o , 2 ) 2 ) |
##EQU00014.2##
is an amplitude of the transfer function of the DUT at the average
of the two different nominal carrier frequencies, denoted by
.omega.(o,1) and .omega.(o,2), respectively, wherein
i.sub.SYS.omega.(o,2)-.omega.(o,1)) is the first electrical
current, and i(.omega.(o,2)-.omega.(o,1)) is the second electrical
current, wherein |i.sub.SYS(.omega.(o,2)-.omega.(o,1))| is an
amplitude of the first electrical current, and
|i(.omega.(o,2)-(.omega.(o,1))| is an amplitude of the second
electrical current, and wherein
.PHI.[i.sub.SYS(.omega.(o,2)-.omega.(o,1))] is a phase of the first
electrical current, and .PHI.[i.omega.(o,2)-(.omega.(o,1))] is a
phase of the second electrical current.
[0108] In an embodiment, the optical multiple-carrier generator
comprises: a plurality of laser sources configured to emit a
plurality of radiations, each of the plurality of radiations having
a different nominal wavelength; and a multiplexer coupled to the
plurality of laser sources, wherein the multiplexer is configured
to provide a combined radiation by combining the plurality of
radiations.
[0109] Referring to FIG. 11, a computer system 1100 is shown. The
computer system 1100 includes a bus 1102 or other communication
mechanism to communicate information, and a processor 1104 (or
multiple processors 1104 and 1105) coupled with the bus 1102 to
process information. In an embodiment, the computer system 1100
includes a main memory 1106, such as a random access memory (RAM)
or other dynamic storage device, coupled to the bus 1102 to store
information and instructions to be executed by the processor 1104.
The main memory 1106 may be used to store temporary variables or
other intermediate information during execution of instructions to
be executed by the processor 1104. In an embodiment, the computer
system 1100 includes a read only memory (ROM) 1108 or other static
storage device coupled to the bus 1102 to store essentially static
information and instructions for the processor 1104. In an
embodiment, a storage device 1110, such as a solid state drive,
magnetic disk or optical disk, is provided and coupled to the bus
1102 to store information and instructions.
[0110] The computer system 1100 may be coupled via the bus 1102 to
a display 1112, such as a cathode ray tube (CRT) or flat panel or
touch panel display, to display information to a computer user. In
an embodiment, an input device 1114, including or providing
alphanumeric and other keys, is coupled to the bus 1102 to
communicate information and command selections to the processor
1104. Another type of user input device is a cursor controller
1116, such as a mouse, a trackball, or cursor direction keys, to
communicate direction information and command selections to the
processor 1104 and to control cursor movement on the display 1112.
A touch panel (screen) display may also be used as an input
device.
[0111] The computer system 1100 may be suitable to implement
methods as described herein in response to the processor 1104
executing one or more sequences of one or more instructions
contained in, e.g., the main memory 1106. Such instructions may be
read into the main memory 1106 from another computer-readable
medium, such as the storage device 1110. In an embodiment,
execution of sequences of instructions contained in the main memory
1106 causes the processor 1104 to perform process steps described
herein. One or more processors in a multi-processing arrangement
may be employed to execute the sequences of instructions contained
in the main memory 1106. In an embodiment, a hard-wired circuitry
may be used in place of or in combination with software
instructions. Thus, embodiments are not limited to any specific
combination of hardware circuitry and software.
[0112] The term "computer-readable medium" as used herein refers to
any medium that participates in providing instructions to the
processor 1104 for execution. Such a medium may take many forms,
including but not limited to, non-volatile media, volatile media,
and transmission media. Non-volatile media include, for example,
solid state, optical or magnetic disks, such as the storage device
1110. Volatile media include dynamic memory, such as the main
memory 1106. Non-volatile and volatile media are considered
non-transitory. Non-transitory transmission media include coaxial
cables, copper wire and fiber optics, including the wires that
comprise the bus 1102. Transmission media can also take the form of
acoustic or light waves, such as those generated during RF and
infrared (IR) data communications. Common forms of
computer-readable media include, for example, a floppy disk, hard
disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any
other optical medium, punch cards, paper tapes, any other physical
medium with patterns of holes, an RAM, a PROM, and EPROM, a
FLASH-EPROM, a solid state disk or any other memory chip or
cartridge, a carrier wave as described herein, or any other medium
from which a computer can read.
[0113] Various forms of computer readable media may be involved in
carrying one or more sequences of one or more instructions to the
processor 1104 for execution. For example, the instructions may
initially be borne on a magnetic disk of a remote computer. The
remote computer can load the instructions into its dynamic memory
and send the instructions over communications medium (e.g., by line
or wireless). The computer system 1100 can receive the transmitted
data and place the data on the bus 1102. The bus 1102 carries the
data to the main memory 1106, from which the processor 1104
retrieves and executes the instructions. The instructions received
by the main memory 1106 may optionally be stored on the storage
device 1110 either before or after execution by the processor
1104.
[0114] The computer system 1100 may also include a communication
interface 1118 coupled to the bus 1102. The communication interface
1118 provides a two-way data communication coupling to a network
link 1120 that is connected to a local network 1122. For example,
the communication interface 1118 may be an integrated services
digital network (ISDN) card or a modem to provide a data
communication connection to a corresponding type of line. As
another example, the communication interface 1118 may be a local
area network (LAN) card to provide a data communication connection
to a compatible LAN. Wireless links may also be implemented. In any
such implementation, the communication interface 1118 sends and
receives electrical, electromagnetic or optical signals that carry
digital data streams representing various types of information.
[0115] The network link 1120 typically provides data communication
through one or more networks to other data devices. For example,
the network link 1120 may provide a connection through the local
network 1122 to a host computer 1124 or to data equipment operated
by an Internet Service Provider (ISP) 1126. The ISP 1126 in turn
provides data communication services through the worldwide packet
data communication network, commonly referred to as the internet
1128. The local network 1122 and the internet 1128 both use
electrical, electromagnetic or optical signals that carry digital
data streams. The signals through the various networks and the
signals on the network link 1120 and through the communication
interface 1118, which carry the digital data to and from the
computer system 1100, are exemplary forms of carrier waves
transporting the information.
[0116] The computer system 1100 can send messages and receive data,
including program code, through the network(s), the network link
1120, and the communication interface 1118. In the internet
example, a server 1130 might transmit a requested code for an
application program through the internet 1128, the ISP 1126, the
local network 1122 and the communication interface 1118. In
accordance with one or more embodiments, one such downloaded
application implements a method as described herein. The received
code may be executed by the processor 1104 as it is received,
and/or stored in the storage device 1110, or other non-volatile
storage for later execution. In this manner, the computer system
1100 may obtain application code.
[0117] An embodiment may take the form of a computer program
containing one or more sequences of machine-readable instructions
describing a method as disclosed herein, or a data storage medium
(e.g. semiconductor memory, magnetic or optical disk) having such a
computer program stored therein. Further, the machine readable
instruction may be embodied in two or more computer programs. The
two or more computer programs may be stored on one or more
different memories and/or data storage media.
[0118] Any controllers described herein may each or in combination
be operable when the one or more computer programs are read by one
or more computer processors located within at least one component
of the optical vector analyzer. The controllers may each or in
combination have any suitable configuration for receiving,
processing, and sending signals. One or more processors are
configured to communicate with the at least one of the controllers.
For example, each controller may include one or more processors for
executing the computer programs that include machine-readable
instructions for the methods described above. The controllers may
include data storage medium for storing such computer programs,
and/or hardware to receive such medium. So the controller(s) may
operate according the machine readable instructions of one or more
computer programs.
[0119] Those skilled in the art will recognize that the present
disclosure is amenable to a variety of modifications and/or
enhancements. For example, although the implementation of various
components described above may be embodied in a hardware device, it
can also be implemented as a firmware, firmware/software
combination, firmware/hardware combination, or a
hardware/firmware/software combination.
[0120] While the foregoing description and drawings represent
embodiments of the present disclosure, it will be understood that
various additions, modifications, and substitutions may be made
therein without departing from the spirit and scope of the
principles of the present disclosure as defined in the accompanying
claims. One skilled in the art will appreciate that the present
disclosure may be used with many modifications of form, structure,
arrangement, proportions, materials, elements, and components and
otherwise, used in the practice of the disclosure, which are
particularly adapted to specific environments and operative
requirements without departing from the principles of the present
disclosure. The presently disclosed embodiments are therefore to be
considered in all respects as illustrative and not restrictive, the
scope of the present disclosure being indicated by the appended
claims and their legal equivalents, and not limited to the
foregoing description.
* * * * *