Optical signal controller, optical signal control method, and optical signal transmission system
According to an aspect of the present invention, an optical signal control apparatus controls a compensation coefficient of an equalizer of an optical transmitter including the equalizer of a symbol period interval and a digital-to-analog converter (DAC) operating at a symbol period interval sampling rate and having a sampling phase adjustment function, and the sampling phase of the DAC. The optical signal control apparatus includes a skew calculation unit configured to calculate a sampling phase amount from a group delay difference between an in-phase component and a quadrature component based on characteristic information of a device and a transmission path and to output the calculated sampling phase amount to the DAC and a compensation coefficient calculation unit configured to calculate the compensation coefficient in which a phase characteristic of a Nyquist frequency of the DAC is 0 or an integer multiple of π and to output the calculated compensation coefficient to the equalizer.
1 . An optical signal control apparatus that controls a compensation coefficient of an equalizer of an optical transmitter including the equalizer of a symbol period interval and a digital-to-analog converter (DAC) operating at a symbol period interval sampling rate and having a sampling phase adjustment function, and a sampling phase of the DAC, the optical signal control apparatus comprising:
a skew calculation unit configured to calculate a sampling phase amount from a group delay difference between an in-phase component and a quadrature component based on characteristic information, which includes a phase characteristic and an amplitude characteristic, of a device and a transmission path and to output the calculated sampling phase amount to the DAC; and
a compensation coefficient calculation unit configured to calculate the compensation coefficient in which a phase amount of a Nyquist frequency of the DAC is 0 or an integer multiple of π and to output the calculated compensation coefficient to the equalizer, wherein:
the equalizer compensates a transfer function of the device and the transmission path using the calculated compensation coefficient; and
the DAC shifts the phase characteristic of the in-phase component and that of the quadrature component by the group delay difference using the calculated sampling phase amount.
2 . The optical signal control apparatus according to claim 1 , wherein the skew calculation unit causes the DAC to shift the phase characteristic of the in-phase component and that of the quadrature component by the group delay difference, and adds a group delay to the transfer function of the in-phase component and the quadrature component to cause the compensation coefficient calculation unit to calculate the phase amount of the Nyquist frequency of the DAC is 0 or an integer multiple of π and supplies the transfer function coefficient added with the group delay to the compensation coefficient calculation unit.
3 . The optical signal control apparatus according to claim 1 , wherein
the skew calculation unit outputs an amplitude characteristic of the transfer function of the in-phase component and the quadrature component and the phase characteristic of the transfer function of the in-phase component and the quadrature component to the compensation coefficient calculation unit, and
the compensation coefficient calculation unit calculates an inverse characteristic of the amplitude characteristic and calculates a coefficient in which the phase characteristic is downsampled so as to supply to the equalizer as the calculated compensation coefficient.
4 . The optical signal control apparatus according to claim 1 , wherein the characteristic information of the device and the transmission path includes a transfer characteristic of the in-phase component of a polarized wave and a transfer characteristic of the quadrature component, skew information which has been calculated based on the transfer characteristic of the in-phase component of the polarized wave and the transfer characteristic of the quadrature component is supplied to a phase shifter of the DAC.
5 . The optical signal control apparatus according to claim 1 , further comprising a transfer function estimation unit configured to acquire a received signal received from an optical receiver that receives an optical signal, calculate a transfer function of the acquired received signal, and output the calculated transfer function to the skew calculation unit,
wherein
the transfer function estimation unit calculates an inverse transfer function of the transfer function, and
the skew calculation unit adds a group delay to the inverse transfer function so that the phase characteristic of the Nyquist frequency in the DAC is 0 or an integer multiple of π so as to supply to the equalizer as the calculated compensation coefficient.
6 . An optical signal control method of an optical signal control apparatus that controls a compensation coefficient of an equalizer of an optical transmitter including the equalizer of a symbol period interval and a digital-to-analog converter (DAC) operating at a symbol period interval sampling rate and having a sampling phase adjustment function, and a sampling phase of the DAC, the optical signal control method comprising:
calculating a sampling phase amount from a group delay difference between an in-phase component and a quadrature component based on characteristic information, which includes a phase characteristic and an amplitude characteristic, of a device and a transmission path and outputting the calculated sampling phase amount to the DAC;
calculating the compensation coefficient in which a phase amount of a Nyquist frequency of the DAC is 0 or an integer multiple of π and outputting the calculated compensation coefficient to the equalizer,
compensating, by the equalizer, a transfer function of the device and the transmission path using the calculated compensation coefficient; and
shifting, by the DAC, the phase characteristic of the in-phase component and that of the quadrature component by the group delay difference using the calculated sampling phase amount.
7 . An optical signal transmission system comprising:
an optical transmitter including an equalizer of a symbol period interval and a digital-to-analog converter (DAC) operating at a symbol period interval sampling rate and having a sampling phase adjustment function; and
an optical signal control apparatus including a skew calculation unit configured to calculate a sampling phase amount from a group delay difference between an in-phase component and a quadrature component based on characteristic information, which includes a phase characteristic and an amplitude characteristic, of a device and a transmission path and to output the calculated sampling phase amount to the DAC and a compensation coefficient calculation unit configured to calculate the compensation coefficient in which a phase amount of a Nyquist frequency of the DAC is 0 or an integer multiple of π and to output the calculated compensation coefficient to the equalizer, wherein: the equalizer compensates a transfer function of the device and the transmission path using the calculated compensation coefficient; and the DAC shifts the phase characteristic of the in-phase component and that of the quadrature component by the group delay difference using the calculated sampling phase amount.
8 . The optical signal transmission system according to claim 7 , further comprising:
an optical receiver configured to receive an optical signal; and
a transfer function estimation unit configured to acquire a received signal received from the optical receiver and estimate a transfer function of the acquired received signal, wherein
the optical signal transmission system configured to supply the estimated transfer function estimated by the transfer function estimation unit to the optical signal control apparatus so as to compensate the transfer function of the device and the transmission path.