Fujitsu Corporation

Yokogawa Electric Corporation

Hitachi Cable, Inc.

Jens Rasmussen

Akihiko Isomura

Hiroki Ooi

Akira Miura

Takafumi Terahara

Yuichi Akiyama

Takeshi Hoshida

George Ishikawa

Zhenning Tao

Kentaro Nakamura

Hiroshi Onaka

Tomoo Takahara

Noriaki Mizuguchi

Kenichi Kaburagi

Lei Li

Yasuyuki Suzuki

Yutaka Kai

Nobuhiro Fukushima

Hiroyuki Matsuura

Naoki Kuwata

Masahiro Yuki

Morio Wada

Kazuo Hironishi

Hideaki Arai

Takashi Toyomaki

Eiji Ishikawa

Yoshinori Nishizawa

Yoshikazu Terayama

Satoshi Takasugi

A phase shift unit provides a prescribed phase difference (&#x3c0;/2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit. A low-frequency signal fis superimposed on one of the optical signals. A signal of which phase is shifted by &#x3c0;/2 from the low-frequency signal fis superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode. 2fcomponent contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit is controlled by feedback control so that the 2fcomponent becomes the minimum.

Optical transmitting apparatus, optical receiving apparatus, and optical communication system comprising them

By using low-frequency signals, an optical transmitting unit modulates one of a wavelength, a transmission timing, and an intensity of light as a carrier wave. A polarization multiplexer synthesizes the output light signals, modulated by the optical transmitting unit, in polarization states orthogonal to each other and generates polarization-multiplexing signals. A polarization splitter splits by extracting two orthogonal polarization components from the polarization-multiplexing signals. The polarization states of the polarization-multiplexing signals are controlled by a polarization controller in an optical receiving unit. A band-pass filter extracts components transmitting through passbands from output signals of the optical receiving unit and outputs an intensity of the components. Based on the intensity output from the filter, a controlling circuit generates feedback control signals for maximizing a ratio of the components of the low-frequency signals and by using the feedback control signals, the polarization controller controls the polarization states of the optical multiplexing signals.

Polarization-multiplexing optical transmitter polarization-multiplexing optical receiver, polarization-multiplexing optical transceiving system, and controlling method thereof

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.

Optical add/drop multiplexer

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.

Digital phase estimator, digital phase locked loop and optical coherent receiver

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.

Optical DQPSK transmitter phase monitor and control

Influence of polarization mode dispersion, occurring in an optical fiber is mitigated by means of polarization scrambling, differential group delay which a received optical signal has is optically suppressed; the optical signal in which differential group delay is thus suppressed is converted into an electric signal; and error correcting processing is carried out on the electric signal obtained, a jitter amplitude in the received optical signal is suppressed, influence of which to a jitter tolerance increases due to increase in speed of the polarization scrambling.

Optical signal transmission system and optical signal transmission method

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.

Phase monitor apparatus, phase control apparatus and methods thereof for optical DQPSK receiver

An interferometer for demodulating a differential M-phase shift keying signal includes a PLC type interferometer main body, a heating portion that heats the PLC type interferometer main body, and an intermediate member having a higher stiffness than that of the PLC type interferometer main body, for bonding the PLC type interferometer main body and the heating portion with each other while being sandwiched therebetween. A linear expansion coefficient difference between the PLC type interferometer main body and the intermediate member is equal to or smaller than 4.5&#xd7;10/&#xb0; C., and a thermal conductivity difference between the PLC type interferometer main body and the intermediate member is equal to or larger than 10 W/mK. A phase of an optical signal flowing through the interferometer is adjusted by using the heating portion and a second heating portion.

Interferometer for demodulating differential M-phase shift keying signal

A data modulator unit generates a DQPSK optical signal in accordance with a data signal. A phase shift unit provides a phase difference of &#x3c0;/2 between a pair of arms. A photodetector converts an output signal of the data modulator unit into an electrical signal. A filter is a low-pass filter with a cut-off frequency lower than a symbol frequency, and filters an output signal of the photodetector. A monitor unit detects power of an output signal of the filter. A phase difference control unit adjusts the amount of phase shift in the phase shift unit so as to minimize power of an output signal of the filter.

Optical transmitting apparatus and optical communication system

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 portthat drops the input signal having a predetermined wavelength, and an add-side portthat adds channel having a predetermined wavelength to the input light.

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&#x2212;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&#x2212;1) networks when the failure is detected.

Optical node and optical add/drop multiplexer

In the optical reception apparatus, a DQPSK polarization multiplexed signal light (S) input thereto is split into horizontally/vertically polarized signal lights (S, S) by a polarization beam splitter (), and the signal lights (S, S) each is branched into two by each of optical couplers (). Then, one branched lights (S, S) by each of the optical couplers () are supplied to a delay interferometer () on the I branch via optical circulators () to be propagated in bidirectional, and the other branched lights (S, S) by each of the optical couplers () are supplied to a delay interferometer () on the Q branch side via optical circulators () to be propagated in bidirectional, so that a set of delay interferometers () is commonly used for horizontally polarized waves and vertically polarized waves.

Optical reception apparatus compatible with DQPSK polarization multiplexing format

A calculation processing unit controls temperature of a Peltier device based on a slope of a waveform obtained by subtracting a waveform of a B-arm monitoring signal from a waveform of an A-arm monitoring signal and a value obtained by subtracting a value B of the B-arm monitoring signal from a value A of the A-arm monitoring signal. Similarly, the calculation processing unit controls a phase of the A-arm and a phase of the B-arm. An A-arm side micro-controller controls temperature of an A-arm side heaterbased on the value of the A-arm monitoring signal, and controls the phase of the A-arm. A B-arm side micro-controller controls temperature of a B-arm side heater based on the value B of the B-arm monitoring signal, and controls the phase of the B-arm.

Phase control apparatus and optical DQPSK receiver

Branches are grouped into a groupincluding first and second branches, and a groupincluding third and fourth branches. The signal after being passed through a dual pin photodiode in one branch included in the groupand 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 groupis 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. The groupis monitored by using the same method.

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Kawasaki, Japan

Jens Rasmussen