Abstract: An optical add/drop multiplexer includes a first optical coupler receiving an optical signal including a plurality of multiplexed wavelengths, a wavelength blocker receiving the optical signal from the first optical coupler, and blocking at least one wavelength of the plurality of multiplexed wavelengths, a first wavelength selective switch, having one input port receiving the outputted optical signal from the first optical coupler and a plurality of output ports, demultiplexing a plurality of arbitrarily selected multiplexed wavelengths from the received optical signal, a second wavelength selective switch, having a plurality of input ports, each input port receiving a different optical signal and one output port, multiplexing a plurality of arbitrarily selected wavelength signals on the plurality of input ports, and a second optical coupler receiving the optical signal output from the wavelength blocker and multiplexed wavelength signal from the second wavelength selective switch.

Abstract: The present invention provides a digital phase estimator, a digital phase locked loop and an optical coherent receiver. The optical coherent receiver comprises a local oscillator laser, for supplying a local oscillator optical signal; an optical 90 degree frequency mixer, for mixing a received optical signal with the local oscillator optical signal; first and second balancing photoelectric detectors, for converting the optical signals outputted from the optical 90 degree frequency mixer into baseband electrical signals; first and second A/D converters, for respectively converting output signals from the first and the second balancing photoelectric detectors into digital signals; a digital phase locked loop, for compensating a phase difference between a carrier signal of the received optical signal and the local oscillator optical signal, and outputting the compensated signal; and a data recovering unit, for recovering data from the compensated signal.

Abstract: An apparatus and a method for a I-Q quadrature modulation transmitter monitor a phase bias between an I branch and a Q branch of the I-Q quadrature modulation transmitter. The I-Q quadrature modulation transmitter includes the I-branch, the Q-branch equipped with a phase bias, and a tap. The apparatus is installed between the tap and the phase bias, and monitors the phase between the I branch and the Q branch which phase is introduced by the phase bias. The apparatus includes the following components: a module squarer, receiving signal from the tap and outputting a module square of the received signal; a multiplier, to multiplying data of the I-branch, data of the Q-branch and the module square to output a multiplied signal; and an averager, averaging the multiplied signal output by the multiplier. The phase between the I branch and the Q branch may be corrected according to monitoring results.

Abstract: An optical add/drop multiplexer includes a first optical coupler receiving an optical signal including a plurality of multiplexed wavelengths, a wavelength blocker receiving the optical signal from the first optical coupler, and blocking at least one wavelength of the plurality of multiplexed wavelengths, a first wavelength selective switch, having one input port receiving the outputted optical signal from the first optical coupler and a plurality of output ports, demultiplexing a plurality of arbitrarily selected multiplexed wavelengths from the received optical signal, a second wavelength selective switch, having a plurality of input ports, each input port receiving a different optical signal and one output port, multiplexing a plurality of arbitrarily selected wavelength signals on the plurality of input ports, and a second optical coupler receiving the optical signal output from the wavelength blocker and multiplexed wavelength signal from the second wavelength selective switch.

Abstract: I branch is provided with a first interferometer, a first balanced optical detector, and a first data recovery circuit. Q branch is provided with a second interferometer, a second balanced optical detector and a second data recovery circuit. In I branch, a mixer multiples input signal of the first data recovery circuit with output signal of the second recovery circuit. An averaging circuit averages output signal of the mixer. In Q branch, a mixer multiples input signal of the second data recovery circuit with output signal of the first recovery circuit. An averaging circuit averages output signal of the mixer. A first phase control apparatus controls the phase of a phase shifter comprised in the first interferometer based on the output signal of the averaging circuit. A second phase control apparatus, in the same manner, controls the phase of a phase shifter comprised in the second interferometer.

Abstract: An optical add/drop multiplexer includes a first optical coupler receiving an optical signal including a plurality of multiplexed wavelengths, a wavelength blocker receiving the optical signal from the first optical coupler, and blocking at least one wavelength of the plurality of multiplexed wavelengths, a first wavelength selective switch, having one input port receiving the outputted optical signal from the first optical coupler and a plurality of output ports, demultiplexing a plurality of arbitrarily selected multiplexed wavelengths from the received optical signal, a second wavelength selective switch, having a plurality of input ports, each input port receiving a different optical signal and one output port, multiplexing a plurality of arbitrarily selected wavelength signals on the plurality of input ports, and a second optical coupler receiving the optical signal output from the wavelength blocker and multiplexed wavelength signal from the second wavelength selective switch.

Abstract: A coherent optical receiver includes; a multiplexing section that multiplexes local oscillation light and received signal light, and outputs two pairs of lights with optical phases different to each other, a photoelectric converting section that executes differential photoelectric converting to convert the output lights from the multiplexing section into electric signals, an AD converting section that converts the respective electric signals output from the photoelectric converting section into digital signals, a digital signal processing section that compensates wavelength dispersion by subjecting the digital signals converted by the AD converting section to arithmetic processing using a digital filter, and then executes reception processing of data included in the received signal light, a monitoring section that monitors an intensity component in a predetermined band of the electric signals output from the photoelectric converting section, and a tap coefficient adjusting section that determines a tap coeffi

Abstract: A core unit arranged in a transmission path includes a through path for causing an input signal to an input port to pass through to an output port, a drop-side port 25a that drops the input signal having a predetermined wavelength, and an add-side port 25b that adds channel having a predetermined wavelength to the input light.

Abstract: The optical node connects N networks to each other (where N is an integer larger than one). Each of the N networks respectively includes a first transmission path and a second transmission path. The optical node includes a switching unit that connects the first transmission path of one network of the N networks to other (N?1) networks; a failure detector that detects failure in the first transmission path of the network; and a control unit that causes the switching unit to connect the second transmission path of the network to the other (N?1) networks when the failure is detected.

Abstract: Branches are grouped into a group 1 including first and second branches, and a group 2 including third and fourth branches. The signal after being passed through a dual pin photodiode in one branch included in the group 1 and being at the earlier stage of a CDR circuit is obtained. Also, from the later stage of the CDR circuit in the other branch in the group 1 is obtained. The obtained signals are passed through low pass filters, and an average value over a plurality of symbols is obtained. The signal from the earlier stage of the CDR circuit is multiplied by the signal from the later stage, and they are averaged. The obtained value reflects the phase difference of the two delay interferometers in the group 1. The group 2 is monitored by using the same method.

Abstract: By comprising a unit 2 making the adjustment related to degradation compensation of a plurality of signals with each wavelength made after multiplexing the signals, a unit 3 multiplexing the outputs of a plurality of units 2, a unit 4 compensating for the waveform degradation of the output of the unit 3, a unit 5 selecting a component with one of a plurality of wavelengths from a part of the output of the unit 4 and a unit 6 detecting the degree of signal degradation from the output of the unit 5 and controlling the adjustment by the unit 2 corresponding to the selected frequency so as to reduce the degree, components disposed for each wavelength in an optical transmission system adopting a wavelength-division multiplexing method can be shared, and the size and cost of an compensator can be reduced.

Abstract: An amount of change of a control signal applied to a polarization controller in a polarization mode dispersion compensator is determined for each feedback loop by evaluating degree of polarization response in past feedback loops.

Abstract: The improved quadrature phase shift keying modulator has a structure such that the average light output power of phase-shift keying modulation light output from the combining unit is changed according to the phase difference between the first and the second optical signal after being combined by means of applying driving signals different in eye crossing percentage by the first modulator and the second modulator, respectively, and has a power monitor monitoring the average light output power of quadrature phase-shift keying modulated light and a phase shift controlling unit which performs feedback control of the phase shift amount in the phase shifting unit based on the average light output power monitored by the power monitor.

Abstract: An optical add/drop multiplexer includes a first optical coupler receiving an optical signal including a plurality of multiplexed wavelengths, a wavelength blocker receiving the optical signal from the first optical coupler, and blocking at least one wavelength of the plurality of multiplexed wavelengths, a first wavelength selective switch, having one input port receiving the outputted optical signal from the first optical coupler and a plurality of output ports, demultiplexing a plurality of arbitrarily selected multiplexed wavelengths from the received optical signal, a second wavelength selective switch, having a plurality of input ports, each input port receiving a different optical signal and one output port, multiplexing a plurality of arbitrarily selected wavelength signals on the plurality of input ports, and a second optical coupler receiving the optical signal output from the wavelength blocker and multiplexed wavelength signal from the second wavelength selective switch.

Abstract: The improved quadrature phase shift keying modulator has a structure such that the average light output power of phase-shift keying modulation light output from the combining unit is changed according to the phase difference between the first and the second optical signal after being combined by means of applying driving signals different in eye crossing percentage by the first modulator and the second modulator, respectively, and has a power monitor monitoring the average light output power of quadrature phase-shift keying modulated light and a phase shift controlling unit which performs feedback control of the phase shift amount in the phase shifting unit based on the average light output power monitored by the power monitor.

Abstract: I branch is provided with a first interferometer, a first balanced optical detector, and a first data recovery circuit. Q branch is provided with a second interferometer, a second balanced optical detector and a second data recovery circuit. In I branch, a mixer multiples input signal of the first data recovery circuit with output signal of the second recovery circuit. An averaging circuit averages output signal of the mixer. In Q branch, a mixer multiples input signal of the second data recovery circuit with output signal of the first recovery circuit. An averaging circuit averages output signal of the mixer. A first phase control apparatus controls the phase of a phase shifter comprised in the first interferometer based on the output signal of the averaging circuit. A second phase control apparatus, in the same manner, controls the phase of a phase shifter comprised in the second interferometer.

Abstract: The present invention provides a digital phase estimator, a digital phase locked loop and an optical coherent receiver. The optical coherent receiver comprises a local oscillator laser, for supplying a local oscillator optical signal; an optical 90 degree frequency mixer, for mixing a received optical signal with the local oscillator optical signal; first and second balancing photoelectric detectors, for converting the optical signals outputted from the optical 90 degree frequency mixer into baseband electrical signals; first and second A/D converters, for respectively converting output signals from the first and the second balancing photoelectric detectors into digital signals; a digital phase locked loop, for compensating a phase difference between a carrier signal of the received optical signal and the local oscillator optical signal, and outputting the compensated signal; and a data recovering unit, for recovering data from the compensated signal.

Abstract: Branches are grouped into a group 1 including first and second branches, and a group 2 including third and fourth branches. The signal after being passed through a dual pin photodiode in one branch included in the group 1 and being at the earlier stage of a CDR circuit is obtained. Also, from the later stage of the CDR circuit in the other branch in the group 1 is obtained. The obtained signals are passed through low pass filters, and an average value over a plurality of symbols is obtained. The signal from the earlier stage of the CDR circuit is multiplied by the signal from the later stage, and they are averaged. The obtained value reflects the phase difference of the two delay interferometers in the group 1. The group 2 is monitored by using the same method.

Abstract: A transmitted optical signal is first subjected to polarization mode dispersion compensation by a polarization mode dispersion compensator (PMDC), and then, its chromatic dispersion is compensated by a variable chromatic dispersion compensator (VDC) after the polarization mode dispersion compensation. How much the optical transmission signal suffers from polarization mode dispersion, which is needed to perform the polarization mode dispersion is measured using a Stokes parameter that is not affected by chromatic dispersion.

Abstract: The degree of polarization of an optical signal is measured by a polarimeter and used for providing a feedback signal to adjust adaptive optics of a polarization mode dispersion compensator. The polarization properties of the polarimeter are determined with high accuracy to match the polarimeter through calibration and used to produce the feedback signal.