Abstract: A frequency difference compensation unit (510) generates a carrier recovery signal by compensating for a frequency difference between a local light beam and an optical signal in a plurality of digital signals. A first symbol determination unit (521) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with the signal arrangement of multi-value modulation. A second symbol determination unit (522) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with a signal arrangement in which the number of multi-values of the multi-value modulation is reduced.

Abstract: The disclosed coherent optical receiver includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; a skew addition unit; and a FFT operation unit. The 90-degree hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs multiple optical signals separated into a plurality of signal components. The optoelectronic converter detects the optical signal and outputs a detected electrical signal. The analog-to-digital converter digitizes the detected electrical signal and outputs a detected digital signal. The skew addition unit adds to the detected digital signal an additional skew amount whose absolute value is equal to, whose sign is opposite to a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit. The FFT operation unit performs a fast Fourier transform on the output from the skew addition unit.

Abstract: A frequency difference compensation unit (510) generates a carrier recovery signal by compensating for a frequency difference between a local light beam and an optical signal in a plurality of digital signals. A first symbol determination unit (521) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with the signal arrangement of multi-value modulation. A second symbol determination unit (522) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with a signal arrangement in which the number of multi-values of the multi-value modulation is reduced.

Abstract: A transfer function calculation unit (522) calculates a diagonal matrix G(f) on the basis of a band limit condition g(t) used in a transmission device (20). A transfer function calculation unit (524) calculates a diagonal matrix C(f) on the basis of a wavelength dispersion amount c(t) incurred in an optical transmission path. A transfer function combination unit (526) combines the diagonal matrix G(f) with the diagonal matrix C(f) so as to calculate a diagonal matrix H(f)=G(f)×C(f). An equalization coefficient calculation unit (528) calculates an equalization coefficient matrix W(f)=H(f)H(H(f)HH(f)+(1/Es)×??)?1 used in a multiplication unit (506) by using the diagonal matrix H(f). Here, H(f)H is a Hermitian transposed matrix of a matrix H(f), Es is power of an optical signal, and ?? is a diagonal matrix with N rows and N columns.

Abstract: It is difficult to obtain a demodulated signal with high signal quality in a digital optical receiver because it is difficult to compensate for each of different types of waveform distortion by a high-performance equalization process; therefore, a digital signal processor according to an exemplary aspect of the present invention includes a fixed equalization means for performing a distortion compensation process based on a fixed equalization coefficient on an input digital signal; an adaptive equalization means for performing an adaptive distortion compensation process based on an adaptive equalization coefficient on an equalized digital signal output by the fixed equalization means; a low-speed signal generation means for generating a low-speed digital signal by intermittently extracting one of the input digital signal and the equalized digital signal; a low-speed equalization coefficient calculation means for calculating a low-speed equalization coefficient to be used for a distortion compensation process o

Abstract: A transfer function calculation unit (522) calculates a diagonal matrix G(f) on the basis of a band limit condition g(t) used in a transmission device (20). A transfer function calculation unit (524) calculates a diagonal matrix C(f) on the basis of a wavelength dispersion amount c(t) incurred in an optical transmission path. A transfer function combination unit (526) combines the diagonal matrix G(f) with the diagonal matrix C(f) so as to calculate a diagonal matrix H(f)=G(f)×C(f). An equalization coefficient calculation unit (528) calculates an equalization coefficient matrix W(f)=H(f)H(H(f)HH(f)+(1/Es)×??)?1 used in a multiplication unit (506) by using the diagonal matrix H(f). Here, H(f)H is a Hermitian transposed matrix of a matrix H(f), Es is power of an optical signal, and ?? is a diagonal matrix with N rows and N columns.

Abstract: An optical receiver (20) includes an electrical signal generation unit (200), a first phase compensation unit (101), a distortion compensation unit (102), and a first dispersion compensation unit (400). The electrical signal generation unit (200) generates an electrical signal on the basis of received signal light. The first phase compensation unit (101) performs a phase rotation compensation process on the electrical signal generated by the electrical signal generation unit (200). The distortion compensation unit (102) performs a dispersion compensation process and a phase rotation compensation process in this order, at least once, on the electrical signal after having compensation performed thereon by the first phase compensation unit. The electrical signal generation unit (200), the first phase compensation unit (101), and the distortion compensation unit (102) are incorporated into one semiconductor device.

Abstract: An optical reception device 20 includes an electric signal generation unit 200, a linear compensation unit 301, a nonlinear compensation unit 300, and a second coefficient setting unit 400. The electric signal generation unit 200 generates an electric signal based on an optical signal received over a transmission path 30. The linear compensation unit 301 performs processing for compensating for dispersion that occurs on optical signal in the transmission path 30 to the electric signal, using a first filter coefficient. The second coefficient setting unit 400 determines a second filter coefficient for compensating for a nonlinear effect that occurs on the optical signal in the transmission path 30, using an amount of dispersion that occurs in the transmission path 30. The nonlinear compensation unit 300 performs processing for compensating the electric signal for the nonlinear effect, using the second filter coefficient that is determined by the second coefficient setting unit 400.

Abstract: A nonlinear compensation unit (300) includes a first compensation unit (350) and a second compensation unit (360). The first compensation unit (350) compensates for each of two polarization signals Ex and Ey so as to cancel a first amount of phase rotation which is the amount of phase rotation calculated based on the signal strength of the two polarization signals Ex and Ey. The second compensation unit (360) compensates for each of the two polarization signals Ex and Ey so as to cancel a second amount of phase rotation which is the amount of phase rotation calculated based on the perturbative component of the two polarization signals Ex and Ey. The first compensation unit (350) includes a strength calculation unit (302), a first filter unit (304), and a first phase modulation unit (306). The second compensation unit (360) includes a perturbative component calculation unit (316), a second filter unit (318), a second phase modulation unit (322), and a third phase modulation unit (330).

Abstract: It is difficult to obtain a demodulated signal with high signal quality in a digital optical receiver because it is difficult to compensate for each of different types of waveform distortion by a high-performance equalization process; therefore, a digital signal processor according to an exemplary aspect of the present invention includes a fixed equalization means for performing a distortion compensation process based on a fixed equalization coefficient on an input digital signal; an adaptive equalization means for performing an adaptive distortion compensation process based on an adaptive equalization coefficient on an equalized digital signal output by the fixed equalization means; a low-speed signal generation means for generating a low-speed digital signal by intermittently extracting one of the input digital signal and the equalized digital signal; a low-speed equalization coefficient calculation means for calculating a low-speed equalization coefficient to be used for a distortion compensation process o

Abstract: The disclosed coherent optical receiver includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; a skew addition unit; and a FFT operation unit. The 90-degree hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs multiple optical signals separated into a plurality of signal components. The optoelectronic converter detects the optical signal and outputs a detected electrical signal. The analog-to-digital converter digitizes the detected electrical signal and outputs a detected digital signal. The skew addition unit adds to the detected digital signal an additional skew amount whose absolute value is equal to, whose sign is opposite to a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit. The FFT operation unit performs a fast Fourier transform on the output from the skew addition unit.

Abstract: The disclosed coherent optical receiver includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; a skew addition unit; and a FFT operation unit. The 90-degree hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs multiple optical signals separated into a plurality of signal components. The optoelectronic converter detects the optical signal and outputs a detected electrical signal. The analog-to-digital converter digitizes the detected electrical signal and outputs a detected digital signal. The skew addition unit adds to the detected digital signal an additional skew amount whose absolute value is equal to, whose sign is opposite to a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit. The FFT operation unit performs a fast Fourier transform on the output from the skew addition unit.

Abstract: Signal processing means includes carrier compensation means for compensating for a phase difference and a frequency difference between signal light and local light in relation to two polarization signals, so as to generate two carrier compensated signals, symbol determination means for demodulating the two carrier compensated signals on the basis of a signal arrangement of multi-value modulation, symbol rough-determination means for demodulating the two carrier compensated signals on the basis of a signal arrangement in which the number of multi-values of the multi-value modulation is reduced, selection means for selecting either of an output of the symbol determination means and an output of the symbol rough-determination means, and coefficient setting means for updating filter coefficients of polarized wave separation means by using an output selected by the selection means.

Abstract: An optical receiver (20) includes an electrical signal generation unit (200), a first phase compensation unit (101), a distortion compensation unit (102), and a first dispersion compensation unit (400). The electrical signal generation unit (200) generates an electrical signal on the basis of received signal light. The first phase compensation unit (101) performs a phase rotation compensation process on the electrical signal generated by the electrical signal generation unit (200). The distortion compensation unit (102) performs a dispersion compensation process and a phase rotation compensation process in this order, at least once, on the electrical signal after having compensation performed thereon by the first phase compensation unit. The electrical signal generation unit (200), the first phase compensation unit (101), and the distortion compensation unit (102) are incorporated into one semiconductor device.

Abstract: An optical reception device 20 includes an electric signal generation unit 200, a linear compensation unit 301, a nonlinear compensation unit 300, and a second coefficient setting unit 400. The electric signal generation unit 200 generates an electric signal based on an optical signal received over a transmission path 30. The linear compensation unit 301 performs processing for compensating for dispersion that occurs on optical signal in the transmission path 30 to the electric signal, using a first filter coefficient. The second coefficient setting unit 400 determines a second filter coefficient for compensating for a nonlinear effect that occurs on the optical signal in the transmission path 30, using an amount of dispersion that occurs in the transmission path 30. The nonlinear compensation unit 300 performs processing for compensating the electric signal for the nonlinear effect, using the second filter coefficient that is determined by the second coefficient setting unit 400.

Abstract: In a coherent optical receiver, sufficient demodulation becomes impossible and consequently receiving performance deteriorates if an interchannel skew arises, therefore, a coherent optical receiver according to an exemplary aspect of the invention includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; and a digital signal processing unit, wherein the 90-degree hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components; the optoelectronic converter detects the optical signals and outputs detected electrical signals; the analog-to-digital converter quantizes the detected electrical signals and outputs quantized signals; and the digital signal processing unit includes a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and a demodulation unit for dem

Abstract: A nonlinear compensation unit (300) includes a first compensation unit (350) and a second compensation unit (360). The first compensation unit (350) compensates for each of two polarization signals Ex and Ey so as to cancel a first amount of phase rotation which is the amount of phase rotation calculated based on the signal strength of the two polarization signals Ex and Ey. The second compensation unit (360) compensates for each of the two polarization signals Ex and Ey so as to cancel a second amount of phase rotation which is the amount of phase rotation calculated based on the perturbative component of the two polarization signals Ex and Ey. The first compensation unit (350) includes a strength calculation unit (302), a first filter unit (304), and a first phase modulation unit (306). The second compensation unit (360) includes a perturbative component calculation unit (316), a second filter unit (318), a second phase modulation unit (322), and a third phase modulation unit (330).

Abstract: In a coherent optical receiver, sufficient demodulation becomes impossible and consequently receiving performance deteriorates if an inter-channel skew arises, therefore, a coherent optical receiver according to an exemplary aspect of the invention includes a local light source, a 90° hybrid circuit, an optoelectronic converter, an analog to digital converter, and a digital signal processing unit; wherein the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components; the optoelectronic converter detects the optical signals and outputs detected electrical signals; the analog to digital converter quantizes the detected electrical signals and outputs quantized signals; the digital signal processing unit includes a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and an FFT operation unit for performing a fas

Abstract: In a coherent optical receiver, sufficient demodulation becomes impossible and consequently receiving performance deteriorates if an inter-channel skew arises, therefore, a coherent optical receiver according to an exemplary aspect of the invention includes a local light source, a 90° hybrid circuit, an optoelectronic converter, an analog to digital converter, and a digital signal processing unit; wherein the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components; the optoelectronic converter detects the optical signals and outputs detected electrical signals; the analog to digital converter quantizes the detected electrical signals and outputs quantized signals; the digital signal processing unit includes a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and an FFT operation unit for performing a fas

Abstract: In a coherent optical receiver, sufficient demodulation becomes impossible and consequently receiving performance deteriorates if an inter-channel skew arises, therefore, a method for detecting inter-channel skew in a coherent optical receiver according to an exemplary aspect of the invention includes the steps of: outputting a plurality of optical signals separated into a plurality of signal components by making a test light from a test light source interfere with a local light from a local light source; detecting the optical signals and outputting detected electrical signals; quantizing the detected electrical signals and outputting quantized signals; performing a fast Fourier transform process on the quantized signals; and calculating a difference in propagation delay between the plurality of signal components on the basis of a plurality of peak values in the results of performing the fast Fourier transform process.