Abstract: A pump light generation unit of an optical amplifier pumping device outputs pump light with a single wavelength or a plurality of wavelengths from a plurality of output ports. A pump light multiplexing unit polarization-multiplexes or wavelength-multiplexes the plurality of pieces of pump light which has been output from the pump light generation unit. A polarization scrambler collectively polarization-scrambles the polarization-multiplexed or wavelength-multiplexed pump light which has been output from the pump light multiplexing unit and outputs the polarization-scrambled pump light to an optical waveguide for pump light. The optical waveguide for pump light inputs the pump light which has been polarization-multiplexed or wavelength-multiplexed by the pump light multiplexing unit to the pump light superimposition unit. A pump light superimposition unit multiplexes the polarization-multiplexed or wavelength-multiplexed pump light and signal light.

Abstract: A depolarizer for depolarizing input light having a plurality of linearly polarized waves whose optical frequency interval is f includes: an input optical waveguide configured to propagate the input light while maintaining linear polarization; a first polarization-maintaining coupler configured to bifurcate the linearly polarized waves output from the input optical waveguide to a first arm and a second arm while maintaining a polarization state; a second polarization-maintaining coupler configured to polarization-multiplex and output the linearly polarized waves propagated through the first arm and the second arm; and a polarization-maintaining variable optical delay line arranged on at least one of the first arm or the second arm, in which the variable optical delay line is adjusted such that a difference in delay time between the linearly polarized waves propagated through the first arm and the second arm becomes close to (n+0.5)/f where n is an arbitrary integer.

Abstract: Provided is a first bias power source that generates a first data bias voltage to be applied to an optical modulation unit for the I component, a second bias power source that generates a second data bias voltage to be applied to an optical modulation unit for the Q component, and a third bias power source that generates a quadrature bias voltage to be applied to an optical phase shifter, a data bias voltage adjustment unit that applies a feedback control to each of the first bias power source and the second bias power source, and a quadrature bias voltage adjustment unit that determines whether or not the quadrature bias voltage is optimal on a basis of a second optical QAM signal generated by an IQ optical modulator, and applies a feedback control to the third bias power source, in which a first optical QAM signal and the second optical QAM signal are generated by the IQ optical modulator but the optical phase difference between an optical electric field EI and an optical electric field EQ differs by ?.

Abstract: A synchronization detection device includes: a correction unit configured to correct sampled data of a waveform on which a dither signal is superimposed, for each period of a reference signal in accordance with a period of the dither signal; a multiplication unit configured to multiply the corrected sampled data by a weight coefficient that is different for each level of the reference signal and associated with a timing of the reference signal; and an averaging unit configured to derive, as a detection result, an average of a result of the multiplication of the corrected sampled data by the weight coefficient.

Abstract: An optical transmission system according to an embodiment includes: an optical transmission unit which modulates an optical signal into which a known signal is inserted and transmits the optical signal; and an optical reception unit which receives the optical signal from the optical transmission unit, wherein the optical reception unit includes: an optical receiver which performs coherent detection of a reception signal of the optical signal received from the optical transmission unit; a receiver transfer function estimation section which estimates a nonlinear response transfer function of the optical receiver based on the known signal included in the reception signal after the detection by the optical receiver; and a receiver compensation section which compensates nonlinear distortion of the reception signal after the detection based on the nonlinear response transfer function which the receiver transfer function estimation section estimates.

Abstract: Provided is a first bias power source that generates a first data bias voltage to be applied to an optical modulation unit for the I component, a second bias power source that generates a second data bias voltage to be applied to an optical modulation unit for the Q component, and a third bias power source that generates a quadrature bias voltage to be applied to an optical phase shifter, a data bias voltage adjustment unit that applies a feedback control to each of the first bias power source and the second bias power source, and a quadrature bias voltage adjustment unit that determines whether or not the quadrature bias voltage is optimal on a basis of a second optical QAM signal generated by an IQ optical modulator, and applies a feedback control to the third bias power source, in which a first optical QAM signal and the second optical QAM signal are generated by the IQ optical modulator but the optical phase difference between an optical electric field EI and an optical electric field EQ differs by ?.

Abstract: A synchronization detection device includes: a correction unit configured to correct sampled data of a waveform on which a dither signal is superimposed, for each period of a reference signal in accordance with a period of the dither signal; a multiplication unit configured to multiply the corrected sampled data by a weight coefficient that is different for each level of the reference signal and associated with a timing of the reference signal; and an averaging unit configured to derive, as a detection result, an average of a result of the multiplication of the corrected sampled data by the weight coefficient.

Abstract: A control processor performs, in a startup sequence of an IQ optical modulator using a nested MZI, a first-stage process of controlling, so that a signal quality of an optical QAM signal output from a monitor port of the IQ optical modulator approaches a target quality, a voltage applied by a Bias_I voltage generator to I-component MZ optical modulator, a voltage applied by a Bias_Q voltage generator to a Q-component MZ optical modulator, and a voltage applied by a Bias_Ph voltage generator to a Bias_Ph phase adjusting means for controlling an optical path length of a parent MZI. After a completion of the first-stage process, the control processor changes a voltage output from the Bias_Ph voltage generator by a predetermined amount.

Abstract: An optical transmission system according to an embodiment includes: an optical transmission unit which modulates an optical signal into which a known signal is inserted and transmits the optical signal; and an optical reception unit which receives the optical signal from the optical transmission unit, wherein the optical reception unit includes: an optical receiver which performs coherent detection of a reception signal of the optical signal received from the optical transmission unit; a receiver transfer function estimation section which estimates a nonlinear response transfer function of the optical receiver based on the known signal included in the reception signal after the detection by the optical receiver; and a receiver compensation section which compensates nonlinear distortion of the reception signal after the detection based on the nonlinear response transfer function which the receiver transfer function estimation section estimates.

Abstract: A control processor performs, in a startup sequence of an IQ optical modulator using a nested MZI, a first-stage process of controlling, so that a signal quality of an optical QAM signal output from a monitor port of the IQ optical modulator approaches a target quality, a voltage applied by a Bias_I voltage generator to I-component MZ optical modulator, a voltage applied by a Bias_Q voltage generator to a Q-component MZ optical modulator, and a voltage applied by a Bias_Ph voltage generator to a Bias_Ph phase adjusting means for controlling an optical path length of a parent MZI. After a completion of the first-stage process, the control processor changes a voltage output from the Bias_Ph voltage generator by a predetermined amount.

Abstract: A control unit of a bias control circuit performs a loop process that fixes a second bias voltage and iterates a process of recording a pair of a first candidate bias voltage and a second candidate bias voltage that are a first bias voltage when optical power of a multi-level QAM signal output by an optical modulator is controlled so that the optical power converges to a value in the vicinity of the maximum value or the minimum value before and after a third bias voltage is increased or decreased by a half-wave voltage while changing the second bias voltage within a predetermined range. The control unit calculates the difference between the first candidate bias voltage and the second candidate bias voltage for each of a plurality of recorded pairs and determines a value between first candidate bias voltage and the second candidate bias voltage of a pair selected on the basis of the calculated difference as the value of the first bias voltage.

Abstract: A control unit of a bias control circuit performs a loop process that fixes a second bias voltage and iterates a process of recording a pair of a first candidate bias voltage and a second candidate bias voltage that are a first bias voltage when optical power of a multi-level QAM signal output by an optical modulator is controlled so that the optical power converges to a value in the vicinity of the maximum value or the minimum value before and after a third bias voltage is increased or decreased by a half-wave voltage while changing the second bias voltage within a predetermined range. The control unit calculates the difference between the first candidate bias voltage and the second candidate bias voltage for each of a plurality of recorded pairs and determines a value between first candidate bias voltage and the second candidate bias voltage of a pair selected on the basis of the calculated difference as the value of the first bias voltage.

Abstract: An optical transmitter includes: an optical modulator including an MZ interferometer, a drive signal input electrode, and a phase difference adjustment bias electrode; a drive amplifier; a phase difference adjustment bias voltage generator; a dithering unit that applies dithering of a predetermined frequency to an amplitude of a drive signal or to a half-wave voltage of the MZ interferometer; a controller unit that changes a phase difference adjustment bias voltage based on a modulation component of the frequency that is superimposed onto modulated light that is output from the optical modulator, to thereby bias the MZ interferometer to a null point; and a synchronous detection circuit that synchronously detects the modulation component of the frequency that is superimposed onto the modulated light. The controller unit changes the phase difference adjustment bias voltage such that a result of synchronous detection by the synchronous detection circuit becomes maximized or minimized.

Abstract: An optical transmitter includes: an optical modulator including an MZ interferometer, a drive signal input electrode, and a phase difference adjustment bias electrode; a drive amplifier; a phase difference adjustment bias voltage generator; a dithering unit that applies dithering of a predetermined frequency to an amplitude of a drive signal or to a half-wave voltage of the MZ interferometer; a controller unit that changes a phase difference adjustment bias voltage based on a modulation component of the frequency that is superimposed onto modulated light that is output from the optical modulator, to thereby bias the MZ interferometer to a null point; and a synchronous detection circuit that synchronously detects the modulation component of the frequency that is superimposed onto the modulated light. The controller unit changes the phase difference adjustment bias voltage such that a result of synchronous detection by the synchronous detection circuit becomes maximized or minimized.

Abstract: An optical transmission system is provided in which the optimum operating point of a Mach-Zehnder interferometer, matched to the optical frequency of the light source on the transmitting side, can be set.

Abstract: The present invention relates to an optical receiver, in which the transmittance of a Mach-Zehnder interferometer can be locked at a normal operation point in a simple structure and control. A transmittance detecting circuit and a minute modulation signal detecting circuit are provided in parallel after a balanced optical receiver, and a switch is selectively connectable either a minute modulation signal detecting circuit and a transmittance detecting circuit. In the initial stage of frequency pull-in, the switch is set to connect the transmittance detecting circuit to the synchronous detection circuit. If the transmittance detecting circuit detects that the transmittance of the Mach-Zehnder interferometer at the carrier frequency becomes a desired transmittance, the connection of the switch is switched from the transmittance detecting circuit to the minute modulation signal detecting circuit.

Abstract: An optical transmission system is provided in which the optimum operating point of a Mach-Zehnder interferometer, matched to the optical frequency of the light source on the transmitting side, can be set.

Abstract: An optical transmission system is provided in which the optimum operating point of a Mach-Zehnder interferometer, matched to the optical frequency of the light source on the transmitting side, can be set.

Abstract: The present invention relates to an automatic dispersion compensating optical link system. Carrier suppressed RZ encoded optical signals generated using carrier suppressing means and binary NRZ code or partial response code, or carrier suppressed clock signals generated using carrier suppressing means and clock signals are transmitted on an optical transmission line. Two bands of the carrier suppressed RZ encoded optical signals or carrier suppressed clock signals transmitted on the optical transmission line are each divided into bands and are received. Phase information of the respective basebands is extracted from the binary NRZ code components or partial response code components or clock signals in each band and the relative phase difference thereof is detected. The chromatic dispersion value of the optical transmission line is then calculated from the relative phase difference.

Abstract: The present invention relates to an optical receiver, in which the transmittance of a Mach-Zehnder interferometer can be locked at a normal operation point in a simple structure and control. A transmittance detecting circuit and a minute modulation signal detecting circuit are provided in parallel after a balanced optical receiver, and a switch is selectively connectable either a minute modulation signal detecting circuit and a transmittance detecting circuit. In the initial stage of frequency pull-in, the switch is set to connect the transmittance detecting circuit to the synchronous detection circuit. If the transmittance detecting circuit detects that the transmittance of the Mach-Zehnder interferometer at the carrier frequency becomes a desired transmittance, the connection of the switch is switched from the transmittance detecting circuit to the minute modulation signal detecting circuit.