DETAILED ACTION
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Specification
The lengthy specification has not been checked to the extent necessary to determine the presence of all possible minor errors. Applicant’s cooperation is requested in correcting any errors of which applicant may become aware in the specification.
Claim Rejections - 35 USC § 112 – Scope of Enablement
The following is a quotation of 35 U.S.C. 112(a):
(a) IN GENERAL.—The specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and shall set forth the best mode contemplated by the inventor or joint inventor of carrying out the invention.
The following is a quotation of 35 U.S.C. 112 (pre-AIA ), first paragraph:
The specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same and shall set forth the best mode contemplated by the inventor of carrying out his invention.
Claims 1-18 are rejected under 35 U.S.C. 112(a) or 35 U.S.C. 112 (pre-AIA ), first paragraph, because the specification, while being enabling for a limited scope based on the teachings in the application, does not reasonably provide enablement for the full scope recited in the claims. The specification does not enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the invention commensurate in scope with these claims.
MPEP 2164.08 states: “The Federal Circuit has repeatedly held that ‘the specification must teach those skilled in the art how to make and use the full scope of the claimed invention without ‘undue experimentation’.” In re Wright, 999 F.2d 1557, 1561, 27 USPQ2d 1510, 1513 (Fed. Cir. 1993).
Scope Claim 1 - Chromatic Dispersion Compensation Processing.
Claim 1, third paragraph, recites performing chromatic dispersion compensation processing:
perform chromatic dispersion compensation processing on an electrical signal based on a received optical signal, the processing being based on a carrier frequency and frequency band of a relevant channel among a plurality of channels included in the optical signal;
In general, the claimed optical repeater takes a carrier frequency and frequency band of a relevant channel in the optical signal and turns it into chromatic dispersion compensation processing.
This has a broad scope that broadly recites performing the chromatic dispersion compensating processing “based on” the received the carrier frequency and frequency band. In other words, the chromatic dispersion compensating processing is not limited to using the carrier frequency and frequency band in any particular way.
Also, the carrier frequency and frequency band are qualified with “a relevant channel”. However, this appears to include any channel that is used (i.e., if a channel to used, then it is “relevant”). In other words, this includes any configuration that uses any channel to achieve the desired results.
Scope of Claim 1 - Phase Conjugation Processing.
Claim 1, last paragraph, recites:
perform phase conjugation processing on the electrical signal based on the received optical signal.
This has a broad scope that includes performing phase conjugation processing “based on” the received optical signal. In other words, it has a scope that includes performing phase conjugation processing using the received optical signal in any way.
Other Claims.
Independent claims 7 and 13 are a method and a non-transitory storage media performing the functionality of claim 1 and have a similarly broad scope.
Dependent claims 2-6, 8-12, and 14-18 depend from the independent claims and recite additional functionality.
In summary, the claims recite broad functional language.
Teachings of the Application - General.
FIG. 8 illustrates an embodiment of an optical repeater including a DSP for performing chromatic dispersion compensation processing 231 and phase conjugation processing 232.
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This is a high level illustration of the DSP receiving an electrical signal based on a received optical signal (e.g., received at coherent receiver 210). The configuration/functionality of the DSP is discussed:
[0092] The digital signal processing portion 230 performs specific signal processing without performing processing that involves significant delays, such as code error correction (data regeneration). This allows the required signal quality to be compensated while minimizing signal delay. In the present example embodiment, the digital signal processing portion 230 has a chromatic dispersion compensation portion 231 (equivalent to the chromatic dispersion compensation portion 23 in FIG. 6) that performs chromatic dispersion processing and a phase conjugation processing portion 232 (equivalent to the phase conjugation portion 22 in FIG. 6) that performs phase conjugation processing.
In other words, FIG. 8 illustrates that the phase conjugation processing and the chromatic dispersion compensation processing are performed by software/structure in a DSP 230.
Teachings of the Application - Chromatic Dispersion Compensation Processing.
The chromatic dispersion compensation portion 231 is discussed:
[0093] The chromatic dispersion compensation through digital signal processing can be realized by convolution of the impulse response of the inverse transfer function of an optical transmission line with the received signal. Thus, for example, the chromatic dispersion compensation portion 231 may be configured with a transversal filter (FIR filter). Since the characteristics of optical transmission lines can be modeled by an FIR filter, chromatic dispersion can be compensated by an FIR filter with inverse characteristics. The FIR filter performs TDE (Time Domain Equalizing), which equalizes the received signal in the time-delay domain, while FDE (Frequency Domain Equalization), which equalizes the received signal in the frequency domain, may achieve the same characteristics. By configuring the chromatic dispersion compensation portion with FDE, the circuit scale can be reduced compared to that of an FIR filter.
FIG. 11 illustrates a high level processing flow for chromatic dispersion compensation configured by FDE processing including an overlap addition portion 411, a FFT portion 412, a frequency response multiplication portion 413, an IFFT portion 414, and an overlap removal portion 415.
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See also:
[0096] FIG. 11 is a configuration example in a case where the chromatic dispersion compensation portion 231 is configured by FDE processing. The chromatic dispersion compensation portion 231 in FIG. 11 is an example of an overlap FDE configuration and includes an overlap addition portion 411, a fast Fourier transform portion 412, a frequency response multiplication portion 413, an inverse fast Fourier transform portion 414, and an overlap removal portion 415.
[0098] The overlap addition portion 411 causes a portion of the front and rear signals to overlap the input signal (digital signal). The fast Fourier transform portion 412 then performs a fast Fourier transform (FFT) of the overlapped signal to convert the signal into a frequency domain signal.
[0099] The frequency response multiplication portion 413 multiplies and equalizes the frequency response of the chromatic dispersion of the transmission line according to the chromatic dispersion compensation amount notified by the control device 100 and the carrier frequency and signal band of each channel.
FIG. 12A illustrates determining the frequency response coefficient used in the frequency response multiplication portion 413.
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This describes the processing used to perform chromatic dispersion compensation “based on” inputs such as the received optical signal the carrier frequency, and the frequency band. See also:
[0100] FIG. 12A is a first diagram showing an overview of determining the frequency response coefficient of the transmission line chromatic dispersion used in the frequency response multiplication portion 413, which is equalized according to the notified chromatic dispersion compensation amount and the carrier frequency and signal bandwidth of each channel. Suppose that the optical repeater 200 receives optical signals of the first channel 1ch, the second channel 2ch, and the third channel 3ch. The carrier frequencies for each channel are f1, f2, and f3, and the respective frequency bands are Δf1, Δf2, and Δf3. Curve L at the bottom of FIG. 12A shows the phase of the chromatic dispersion frequency response. The frequency response multiplication portion 413 multiplies the frequency response coefficient converted from the phase component to the complex component by the signal input from the fast Fourier transform portion 412. A complex number coefficient such as that used for the frequency application coefficient can be obtained by computing exp(iθ) from the phase component θ as indicated by the curve L at the bottom of FIG. 12A. Phase conjugation processing is performed first in the digital signal processing portion 230, followed by chromatic dispersion compensation processing. Based on the frequency inversion due to phase conjugation and the chromatic dispersion frequency response of the entire received signal bandwidth (Δf1+Δf2+Δf3), the frequency response multiplication portion 413 of each channel of the optical repeater 200 multiplies the signal of each channel input from the fast Fourier transform portion 412 by the chromatic dispersion frequency response of each frequency band of each corresponding channel.
[0101] More specifically, the frequency response multiplication portion 413 specifies the coefficient in the region of Δf3 out of the chromatic dispersion frequency response of the entire bandwidth (Δf1+Δf2+Δf3) of the received signal as the frequency application coefficient for chromatic dispersion compensation to channel 1ch, and multiplies that coefficient by the signal input from the fast Fourier transform portion 412 corresponding to channel 1ch. The frequency response multiplication portion 413 specifies the coefficient in the region of Δf2 out of the chromatic dispersion frequency response of the entire bandwidth (Δf1+Δf2+Δf3) of the received signal as the frequency application coefficient for chromatic dispersion compensation to channel 2ch, and multiplies that coefficient by the signal input from the fast Fourier transform portion 412 corresponding to channel 2ch. The frequency response multiplier 413 specifies the coefficient in the region of Δf1 out of the chromatic dispersion frequency response of the entire bandwidth (Δf1+Δf2+Δf3) of the received signal as the frequency application coefficient for chromatic dispersion compensation to channel 3ch, and multiplies that coefficient by the signal input from the fast Fourier transform portion 412 corresponding to channel 3ch. This takes into account frequency component inversion due to the phase conjugation process.
FIG. 12B also illustrates determining the frequency response coefficient used in the frequency response multiplication portion 413.
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This describes the processing used to perform chromatic dispersion compensation “based on” inputs such as the received optical signal the carrier frequency, and the frequency band. See also:
[0102] FIG. 12B is a second diagram showing an overview of determining the frequency response coefficient of the transmission line chromatic dispersion used in the frequency response multiplication portion 413, which is equalized according to the notified chromatic dispersion compensation amount and the carrier frequency and signal bandwidth of each channel. Suppose that the optical repeater 200 receives optical signals of the first channel 1ch, the second channel 2ch, and the third channel 3ch. The carrier frequencies for each channel are f1, f2, and f3, and the respective frequency bands are Δf1, Δf2, and Δf3. The curve L at the bottom of FIG. 12b shows the phase of the chromatic dispersion frequency response, and the frequency response multiplication portion 413 multiplies the frequency response coefficient converted from the phase component to the complex component by the signal input from the fast Fourier transform portion 412. Chromatic dispersion compensation processing is performed first in the digital signal processing portion 230, followed by phase conjugation processing.
[0103] Based on the chromatic dispersion frequency response of the entire received signal bandwidth (Δf1+Δf2+Δf3), the frequency response multiplication portion 413 of each channel of the optical repeater 200 multiplies the signal of each channel input from the fast Fourier transform portion 412 by the chromatic dispersion frequency response of each frequency band of each corresponding channel. More specifically, the frequency response multiplication portion 413 specifies the coefficient in the region of Δf1 out of the chromatic dispersion frequency response of the entire bandwidth (Δf1+Δf2+Δf3) of the received signal as the frequency application coefficient for chromatic dispersion compensation to channel 1ch, and multiplies that coefficient by the signal input from the fast Fourier transform portion 412 corresponding to channel 1ch. The frequency response multiplication portion 413 specifies the coefficient in the region of Δf2 out of the chromatic dispersion frequency response of the entire bandwidth (Δf1+Δf2+Δf3) of the received signal as the frequency application coefficient for chromatic dispersion compensation to channel 2ch, and multiplies that coefficient by the signal input from the fast Fourier transform portion 412 corresponding to channel 2ch. The frequency response multiplier 413 specifies the coefficient in the region of Δf3 out of the chromatic dispersion frequency response of the entire bandwidth (Δf1+Δf2+Δf3) of the received signal as the frequency application coefficient for chromatic dispersion compensation to channel 3ch, and multiplies that coefficient by the signal input from the fast Fourier transform portion 412 corresponding to channel 3ch.
These teachings appear to be at the heart of the enablement of the chromatic dispersion compensation processing. See:
[0104] This enables the optical repeater 200 to also compensate for differences in group delay characteristics between channels in a case where receiving multi-channel signals, and to compensate for inter-channel nonlinear distortion due to phase conjugation.
Finally, the IFFT portion 414 and overlap removal portion 415 are discussed.
[0105] The inverse fast Fourier transform portion 414 then performs the inverse fast Fourier transform (IFFT) to convert the signal into a time-domain signal. The overlap removal portion 415 removes the overlapping portion from the restored signal in the time domain and outputs it. In a case where using FDE, the chromatic dispersion compensation amount can be adjusted by changing the inverse transfer function. The overlap addition portion 411 and overlap removal portion 415 may be omitted.
In other words, the application teaches particular and complex programming/configurations/steps in order to perform chromatic dispersion compensation processing.
Teachings of the Application - Phase Conjugation Processing.
The phase conjugation processing is also tied to the discussion above with reference to FIGS. 11, 12A, and 12B. See:
[0104] This enables the optical repeater 200 to also compensate for differences in group delay characteristics between channels in a case where receiving multi-channel signals, and to compensate for inter-channel nonlinear distortion due to phase conjugation.
The phase conjugation processing is discussed with reference to equation (1). See:
[0106] Phase conjugation processing by digital signal processing determines the complex conjugate of the input digital signal. That is, the sign of the imaginary component Q in the Ix, Qx, Iy, and Qy signals is inverted as in the following Expression (1).
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In other words, the application teaches particular and complex programming/configurations/steps in order to perform phase conjugation processing.
Teachings of the Application - Order of Operations.
The application also teaches that the phase conjugation processing is performed before the chromatic dispersion compensation processing. With reference to FIG. 12A, see:
[0100] FIG. 12A is a first diagram showing an overview of determining the frequency response coefficient of the transmission line chromatic dispersion used in the frequency response multiplication portion 413, which is equalized according to the notified chromatic dispersion compensation amount and the carrier frequency and signal bandwidth of each channel. Suppose that the optical repeater 200 receives optical signals of the first channel 1ch, the second channel 2ch, and the third channel 3ch. The carrier frequencies for each channel are f1, f2, and f3, and the respective frequency bands are Δf1, Δf2, and Δf3. Curve L at the bottom of FIG. 12A shows the phase of the chromatic dispersion frequency response. The frequency response multiplication portion 413 multiplies the frequency response coefficient converted from the phase component to the complex component by the signal input from the fast Fourier transform portion 412. A complex number coefficient such as that used for the frequency application coefficient can be obtained by computing exp(iθ) from the phase component θ as indicated by the curve L at the bottom of FIG. 12A. Phase conjugation processing is performed first in the digital signal processing portion 230, followed by chromatic dispersion compensation processing. Based on the frequency inversion due to phase conjugation and the chromatic dispersion frequency response of the entire received signal bandwidth (Δf1+Δf2+Δf3), the frequency response multiplication portion 413 of each channel of the optical repeater 200 multiplies the signal of each channel input from the fast Fourier transform portion 412 by the chromatic dispersion frequency response of each frequency band of each corresponding channel.
With reference to FIG. 12B, see:
[0102] FIG. 12B is a second diagram showing an overview of determining the frequency response coefficient of the transmission line chromatic dispersion used in the frequency response multiplication portion 413, which is equalized according to the notified chromatic dispersion compensation amount and the carrier frequency and signal bandwidth of each channel. Suppose that the optical repeater 200 receives optical signals of the first channel 1ch, the second channel 2ch, and the third channel 3ch. The carrier frequencies for each channel are f1, f2, and f3, and the respective frequency bands are Δf1, Δf2, and Δf3. The curve L at the bottom of FIG. 12b shows the phase of the chromatic dispersion frequency response, and the frequency response multiplication portion 413 multiplies the frequency response coefficient converted from the phase component to the complex component by the signal input from the fast Fourier transform portion 412. Chromatic dispersion compensation processing is performed first in the digital signal processing portion 230, followed by phase conjugation processing.
In other words, the application teaches a particular order of operations for the chromatic dispersion compensation processing and the phase conjugation processing.
The Claims do not Recite the Particular Structure, Materials, or Steps.
As discussed above, the application teaches how to make and use the invention using particular structure, materials, and steps in a particular order to implement the chromatic dispersion compensation processing and the phase conjugation processing. As also discussed above, the claims recite the desired functionality/results, but do not recite the particular structure, materials, or steps that accomplish the claimed functionality/results. This results in claims having a scope that is much broader than the teachings of the application.
When considering the teachings of the application and the scope of the claims, as discussed above, see MPEP 2173.05(g), 4th paragraph:
… Further, without reciting the particular structure, materials or steps that accomplish the function or achieve the result, all means or methods of resolving the problem may be encompassed by the claim. Ariad Pharmaceuticals., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1353, 94 USPQ2d 1161, 1173 (Fed. Cir. 2010) (en banc). Unlimited functional claim limitations that extend to all means or methods of resolving a problem may not be adequately supported by the written description or may not be commensurate in scope with the enabling disclosure, both of which are required by 35 U.S.C. 112(a) and pre-AIA 35 U.S.C. 112, first paragraph. In re Hyatt, 708 F.2d 712, 714, 218 USPQ 195, 197 (Fed. Cir. 1983); Ariad, 598 F.3d at 1340, 94 USPQ2d at 1167. …
This supports a conclusion that the scope of the claims is not commensurate with the teachings of the application.
No Teaching of a General Case for the Full Scope of the Claims.
The Examiner also notes that there is no teaching of an apparatus, method, or storage medium with the broad scope recited in the claims. On the contrary, as discussed above, the application teaches the use of particular structure or steps to programming to achieve the recited functionality.
If a general case commensurate with the scope of the claims were contemplated or discovered by the inventors, its disclosure and a description of its operation would be expected as part of the application in order to support broad claims, such as claims 1, 7, and 13. This is particularly true because, as discussed above, the embodiments that are disclosed in the application require fairly complex and particular structures and algorithms. These structures and algorithms would be unnecessary if a general case had been known by the inventors, and yet the application does not include a disclosure of a general case.
This supports a conclusion that the scope of the claims is not commensurate with the teachings of the application.
Other Considerations.
The nature of the invention is signal processing related to optical communications systems, devices, and methods. The components used in the various embodiments were known to one of ordinary skill. For example, one or ordinary skill would be familiar with components such as digital signal processors, ADCs, DACs, PDs, and optical sources, in the context of the invention. Therefore, no teachings of how to make these individual components is required.
The application teaches how to arrange these elements with other elements in particular combinations in order to achieve the desired results (e.g., see FIG. 8). These combinations are particular and complex. Nonetheless, one or ordinary skill would know how to make and use the disclosed embodiments of the invention from the teachings of the application.
Furthermore, it would have been obvious that some elements may be modified or replaced with other elements known to have the same or similar functionality, and to make some modifications to the particular structures disclosed.
Similarly, one of ordinary skill would also know how to perform other tasks in the present technological area and related to the invention, such as providing power to components (although power supplies and power specifications are not explicitly taught in the application), and splicing/coupling the electrical and optical components together (although this is not explicitly taught in the application), and managing the temperature of electrical and optical components which are susceptible to performance degradation and undesirable operational variations based on temperature (although this is not explicitly taught in the application), and shielding components from EM interference that can be generated by such devices (although this is not explicitly taught). Although this is not an exhaustive list, the obvious modifications based on the disclosure and the knowledge of one or ordinary skill are nonetheless of a limited scope.
However, these modifications do not address the issues raised above regarding the disparity between the scope of the claims and the teachings of the application.
Experimentation.
As discussed above, the application does not teach the full scope of the claims. As a result, the claims include many possible structures/steps/functions, and not all possibilities within the scope of the claims will produce the desired results or functions.
As a result, if one of ordinary skill were to attempt to make and use the full scope of the claims, it would require making, testing, or otherwise evaluating a large number of possible combination of structures and/or programming to find what works to perform the desired functionality. This results in a practically unlimited number of embodiments that would need to be made, tested, or otherwise evaluated to determine which embodiments are operative and which are inoperative. In other words, this would require almost infinite experimentation.
This supports a finding that undue experimentation would be required to make and use the full scope of the claims.
Conclusion.
After careful consideration the Examiner has concluded that the specification does not enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the invention commensurate in scope with these claims. In other words, the specification fails to teach those skilled in the art how to make and use the full scope of the claimed invention without ‘undue experimentation’.
Conclusion
The prior art made of record and not relied upon is considered pertinent to applicant's disclosure.
US 2004/0213578 (Takahara) at FIG. 4 teaches chromatic dispersion compensation in an optical communication system including a transmitter 100, receiver 150, repeater 120, and a control circuit 160.
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[0041] In the conventional chromatic dispersion compensation controlling system shown in FIG. 4, an optical signal transmitted from a transmitter 100 is transmitted through a transmission line 110, is amplified by an optical amplifier 120 and is inputted to a variable dispersion compensator 130. The chromatic dispersion of the optical signal is compensated by a variable dispersion compensator 130. Then, the optical signal is converted into an electric signal by an optical/electric converter 140, and is received by a receiver 150. In the receiver 150, the error rate or similar information of the received signal is computed, and is transmitted to the control circuit 160 of the variable dispersion compensator 130. The control circuit 160 controls the amount of dispersion compensation of the variable dispersion compensator 130, etc., based on this error rate or similar information. In this case, the error information detecting function of the receiver 150 acts as a chromatic dispersion monitor.
[0042] If chromatic dispersion changes due to a change in some condition, the conventional chromatic dispersion monitor searches for the optimal chromatic dispersion point using an algorithm, such as a dithering method or a down-hill method, since there is no means for determining whether the amount of chromatic dispersion compensation is excessive or insufficient. For the dithering method, see Patent document 4, and for the down-hill method, see Non-patent document 10.
FIG. 5 illustrates one method of adjusting dispersion compensation based to minimize error rate.
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FIG. 7 illustrates a more sophisticated dispersion compensator including a decision threshold setting circuit 12 which sets a threshold for a change the applied dispersion compensation.
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See, for example:
[0135] The monitor system comprises, for example, a demultiplexer 10, a data flip-flop (DFF) 11, a decision threshold setting circuit 12, a delay circuit 13, an integration circuit 14 and a control circuit 15. The demultiplexer 10 extracts a part of an electric signal transmitted from a photo-diode 3 to an equalizing amplifier 4 as a monitor signal and transmits it to a DFF 11. The DFF 11 compares the level of the monitor signal from the demultiplexer 10 with a decision threshold set by the decision threshold setting circuit 12 in timing synchronous with a clock signal received from a clock recovery circuit 7 through the delay circuit 14, and outputs the result of the comparison to the integration circuit 13 as a logical value. The integration circuit 13 averages logical values outputted from the DFF 11 by timewise integrating them and outputs the result to the control circuit 15. The control circuit 15 detects a change in chromatic dispersion, caused in the transmission line 1, based on the level of an output signal from the integration circuit 13 as described later, and feedback controls the amount of dispersion compensation in a variable dispersion compensator 2 so as to bring the chromatic dispersion close to zero, by reducing the change. In this case, the above-mentioned control circuit 15 is provided with the functions of a dispersion detection unit and a control unit.
[0074] The chromatic dispersion compensation controlling system of the present invention is used to compensate for chromatic dispersion caused when transmitting an optical signal through a transmission line. The chromatic dispersion compensation controlling system comprises a peak detection unit detecting the peak value of a received signal and a control unit determining whether chromatic dispersion caused in an optical signal is excessive in a positive or negative direction, by comparing the peak value with a predetermined threshold and supplying a control signal to the variable chromatic dispersion compensator.
FIG. 31 illustrates an embodiment using a demultiplexer 22 and plural parallel variable dispersion compensators 2, PDs 3, and receivers 20.
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FIG. 32 illustrates an embodiment in which the variable dispersion compensator is before the demultiplexer 22.
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US 2012/0263456 (Tanaka) at FIG. 6 teaches a system including a transmitter 3 (see also FIG. 2), a coherent receiver 4 (see also FIG. 3), and chromatic dispersion compensation.
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In particular, FIG. 6 shows a chromatic dispersion adder 41, a skew compensator 32, and a controller 32. The operation is generally described in [0086]:
[0086] The controller 42 controls the chromatic dispersion amount of the chromatic dispersion adder 41 in accordance with the chromatic dispersion amount detected by the chromatic dispersion compensator 33. In addition, the controller 42 controls the skew suppression in the Tx inter-channel delay controller 14 and/or the Rx inter-channel delay controller 32 based on the Q factor obtained by the signal quality detector 34.
See also [0080] regarding additional description of the controller 32:
[0080] The Rx inter-channel delay controller 32 is realized by providing a digital filter for each channel (XI, XQ, YI, YQ). In this case, tap coefficients of each digital filter is determined in accordance with a command from the controller 42. The configuration and the operation of the digital filters realizing the Rx inter-channel delay controller 32 are described in, for example, Japanese Laid-Open Patent Publication No. 2010-193204. The Rx inter-channel delay controller 32 may be disposed on an input side of the digital signal processor 25. The Rx inter-channel delay controller 32 may be realized by a phase shifter that shifts a phase of an analog signal of each channel (XI, XQ, YI, YQ). In this case, a phase shift amount of each phase shifter is determined in accordance with the command from the controller 42. The Rx inter-channel delay controller 32 may control a delay time on a digital signal or may control a delay time on an analog signal.
US 2009/0238578 (Taylor).at FIG. 7 teaches a device implementing chromatic dispersion compensation using plural parallel CD compensators 704.
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See, for example, the CD compensation modules 704. FIG. 8B shows that the sib-bands can be non-overlapping or overlapping.
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Advantages and disadvantages of each approach are discussed in [0047]:
[0047] There are many possible designs of sub-band spectral response. For example the sub-band analysis filters may be chosen to have square non-overlapping spectral responses, as shown in FIG. 8A. Typically it requires a large amount of computations to obtain square edges for such a filter, and realistically the sub-band filter spectral response may have some side lobes. These features will in turn lead to a penalty in the quality of the compensated signal due to aliasing. An alternative set of sub-band analysis filter spectral responses is given in FIG. 8B, where each response has a decaying edge and where the responses overlap. The rounded nature means that the a small amount of computations may provide an actual response close to the design target. There are two approaches to the choice of sub-band sample rate that may be taken with the overlapping sub-band spectral responses. The sample rate may be set to DELTA.f.sub.total/N.sub.sub-bands where N.sub.sub-bands is the number of sub-bands and .DELTA.f.sub.total is the input signal bandwidth as indicated on FIG. 8B. This option, known as maximally decimated sub-bands, will mean that there is some aliasing, and the analysis and synthesis filter functions should be chosen to minimize the amount of aliasing. Alternatively the sub-band sample rate may be set to .DELTA.f.sub.band, which is higher than .DELTA.f.sub.total/N.sub.sub-bands. There will then be no aliasing. It is advantageous to choose .DELTA.f.sub.band to be related to .DELTA.f.sub.total by a ratio of integers. The width of the sub-band should be chosen carefully, since when .DELTA.f.sub.band is large the savings on amount of computations for the CD compensation part is reduced, and when .DELTA.f.sub.band is too small more computations are needed to implement the analysis and synthesis filter banks.
Different forms of CD are discussed:
[0007] The optical signal may be distorted by propagation through the optical fiber. There are several distinct propagation effects that can occur, as described in "Nonlinear fiber optics" by Govind P. Agrawal (Academic Press, 2nd ed., 1995). Chromatic dispersion (CD) is the propagation effect most often encountered. A 10 Gb/s on-off modulated optical signal is substantially distorted by CD after propagation through about 100 km of non-dispersion shifted fiber (NDSF), so it is necessary to compensate for chromatic dispersion in some way in order to transmit over longer distances than 100 km. The usual way to compensate for CD is via dispersion compensation fiber (DCF), an optical component placed in line with the transmission fiber. DCF has the positive feature that it compensates exactly for chromatic dispersion, but it has disadvantages that it is expensive, it is physically large in size, it has substantial optical loss, and the amount of CD being compensated is fixed. There are ways to compensate for chromatic dispersion in the electronics of the receiver after photodetection. For example, "Adaptive Electronic Feed-Forward Equaliser and Decision Feedback Equaliser for the Mitigation of Chromatic Dispersion and PMD in 43 Gbit/s Optical Transmission Systems" by B. Franz et al. (ECOC 2006 conference, Cannes, France, paper We1.5.1, September 2006) describes an electronic domain CD compensator using analog signal processing, and "Performance of a 10.7 Gb/s Receiver with Digital Equaliser using Maximum Likelihood Sequence Estimation" by A. Farbert et al. (ECOC 2004 conference, Stockholm, Sweden, paper Th4.1.5, September 2004) describes one using digital signal processing. Compensation in the electrical domain is expected to cost less than using optical components because of the nature of mass production of electronics. However electrical compensation of CD following direct detection can only compensate for a small amount of chromatic dispersion, equivalent to perhaps 100 km of NDSF at 10 Gb/s, because direct detection discards the phase of the optical signal. For this reason on long fiber optic transmission systems most of the CD compensation has been done via DCF, with electrical domain compensation simply trimming the amount of compensation.
[0008] Recently two new methods of electrical domain CD compensation have been proposed which are able in principle to compensate for unlimited transmission distances. Both methods use digital signal processing and effectively operate on a discrete-time representation of the electric field of the optical signal. The first method precompensates for chromatic dispersion, and is disclosed in U.S. Pat. No. 7,023,601. An optical signal is transmitted which may not resemble the information content, and after propagation through optical fiber the chromatic dispersion of the fiber transforms the optical signal into the desired form, which does resemble the information content. A pair of Mach-Zehnder optical modulators in the transmitter allow the inphase and quadrature parts (the real and imaginary parts) of the electric field to be modulated independently. Each of the two Mach-Zehnder modulators is driven by an electrical signal set by a digital-to-analog (D/A) converter, which in turn, is controlled by a digital signal processor. The DSP calculates the electric field of the precompensated optical signal such that after propagating through the known chromatic dispersion of the fiber optic transmission system the correct optical signal arrives at the receiver. The receiver may be a direct detection receiver, given that the precompensated optical signal is calculated to become an on-off modulated signal after propagation through the optical fiber. Alternatively, the receiver may be of a more advanced design, such as a coherent receiver, and the optical signal arriving at the receiver may then be a phase modulated signal.
[0009] The second method of CD compensation that operates on the electric field of the optical signal is with a phase diverse coherent receiver, as described in U.S. Patent Application Number 2004/0114939. A conventional optical signal is transmitted, such as an on-off modulated signal or a phase modulated signal. The optical signal becomes distorted by the chromatic dispersion of the fiber optic transmission system. The coherent receiver uses DSP to calculate the electric field of the incoming optical signal, and these electric field values can then be acted upon to compensate for the effect of the chromatic dispersion.
US 7,558,479 (Robinson) teaches performing dispersion compensation in an optical communication system. See FIGS. 1a, 1b.
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(45) FIGS. 1a and 1b are block diagrams schematically illustrating principal operations of the proposed system for providing chromatic dispersion compensation. FIG. 1a shows an embodiment in which dispersion compensation is implemented at the transmitting end of the communications system. Conversely, FIG. 1b illustrates an embodiment in which dispersion compensation is implemented at the receiving end of the communications system.
(46) As shown in FIG. 1a, the optical communications system is represented by electrical-to-optical (E/O) and optical-to-electrical (O/E) converters 2 and 6 separated by an optical link 4 represented by a system transfer function H(w). In order to simplify the present description, the E/O and O/E converter blocks 2 and 6 shown in FIG. 2 are considered to be ideal, in the sense that they do not introduce any signal distortions that are not otherwise accounted for by the system transfer function H(w). Signal distortions introduced by the system transfer function are compensated by deriving a compensation function c(t) that optimizes system performance. For chromatic dispersion, for example, the compensation function c(t) will be equivalent to the complex conjugate H*(w) of the system transfer function H(w).
In other words, it teaches to calculate a conjugate of the system transfer function to compensate for distortions.
FIG. 2 illustrates an embodiment of the transmitter with feedback which detects parameters 22 and derives the compensation function c(t) 24, and provides that information to the digital filter DF 14, which is applied to the modulation signal, which then goes to the non-linear compensator 16.
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(49) FIG. 2 is a block diagram schematically illustrating principal elements and operations of a first example of compensation modulator 10. As shown in FIG. 2, the input signal x(t) is filtered by a digital filter 14 which accepts the compensation function c(t) as an input. Various known digital filter types may be used to implement the digital filter 14, such as, for example, Finite Impulse Response (FIR) filters, Infinite Impulse Response (IIR) filters, and Fast Fourier Transform (FFT filters). Alternatively, the digital filter 14 may be implemented using a Random Access Memory Look-up Table (RAM LUT), as will be described in greater detail below. In either case, the digital filter 14 generates the predistorted signal x.sup.1(t) 12, which compensates chromatic dispersion due to the system transfer function H(w).
(50) The predistorted signal x.sup.1(t) 12 can then be converted into the corresponding predistorted optical signal X.sup.1.sub.OPT(W) by means of a conventional electrical to optical converter 2. For example, in the illustrated embodiment, electrical to optical conversion is accomplished using a tuned optical source 18 such as a narrow band laser coupled to a conventional optical modulator 20. In this case, the predistorted signal 12 can be used as an input to control the optical modulator 20 in a manner known in the art.
(51) Various methods may be used to derive the compensation function c(t). In the example of FIG. 2, the optical signal Y.sup.1.sub.OPT(W) at or near the receiver end of the optical link 4 is monitored (at 22) in order to detect signal quality parameters indicative of dispersion in the optical communications system. In preferred embodiments, the signal quality parameters comprise a direct measurement of dispersion as a function of wavelength across the wavelength band of interest. However, other signal quality parameters such as, for example, the bit error rate or eye closure may be used a proxies for the dispersion. Any of the signal quality parameters may be detected based on an optical signal obtained by tapping the optical link 4 as shown in FIG. 2, or alternatively by analysis of the output signal y(t) generated by the E/O converter 6. A compensation function c(t) which optimizes the detected parameters can then be derived (at 24) deterministically and/or adaptively, using known techniques.
(52) The functional step of deriving the compensation function c(t) can be implemented by any suitable combination of hardware and software, which may be co-located with the receiver, the transmitter, or any other location. In embodiments in which the detected parameters comprise direct measurement of dispersion, the compensation function c(t) can be calculated to minimize (and preferably eliminate) the total dispersion. Where bit error rate and/or eye closure are used as proxies, then the compensation function c(t) would be calculated to optimize these respective values.
FIGS. 3 and 4 illustrate other embodiments of the transmitter.
FIG. 5 illustrates an embodiment of the receiver with dispersion compensation.
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(75) FIG. 5 shows the hardware required in the receiver when the compensation is to be carried out using the digital filtering at the receiver. Where components are used corresponding to those in FIG. 2, the same reference numerals are used and a detailed description is not repeated. The compensation module 10 is provided at the receiver but implements the same function as in the embodiment of FIG. 2.
Any inquiry concerning this communication or earlier communications from the examiner should be directed to DARREN WOLF whose telephone number is (571)270-3378. The examiner can normally be reached Monday through Friday, 7:00 AM to 3:00 PM.
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/DARREN E WOLF/Primary Examiner, Art Unit 2634
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