Nec Corporation

Nec Laboratories America, Inc.

Kabushiki Kaisha Tajima Sangyo

Tsutomu Tajima

Ting Wang

Philip N Ji

Lei Xu

Shuji Murakami

Yutaka Yano

Yoshiaki Aono

Dayou Qian

Tadayuki Chikuma

Yue-Kai Huang

Takashi Kuriyama

Junqiang Nochur Hu

Ezra Ip

Keiichi Yamada

Yoshihiro Matsumoto

Yoshinori Honma

Masashi Tachigori

Daisuke Uehara

Toshibumi Kawano

Masaki Shiraiwa

Tsukasa Takehana

Toru Hamanaka

Naoya Shiota

Kenzou Tan

Hirokazu Kobayashi

Philip Nan Ji

Systems and methods are disclosed for a filter-less coherent receiving system with a filter-less coherent receiver frontend; a signal-signal beat-noise detector coupled to the filter-less coherent receiver frontend; and a real-time processor coupled to the filter-less coherent receiver frontend and the signal-signal beat-noise detector to reject signal-signal interference.

Digital signal-to-signal beat noise reduction for filter-less coherent receiving system

Methods and devices for compensating for chromatic dispersion are shown that include receiving an input data signal, applying a filter to the data signal, and outputting a CD compensated signal. Applying the filter includes convolving known filter coefficients with a plurality of delayed versions of the data signal using addition and at least one inverse sign operation or using lookup tables and combining outputs to produce a CD compensated signal.

Chromatic dispersion compensation using sign operations and lookup tables

An optical signal division transmission system in which an input optical signal is divided into N parts (termed as 'N-part optical signals') and transmitted at a transmission rate of 1/N, wherein an additional optical wave path is provided separately from an optical wave paths for transmitting said N-part optical signals, and even if a malfunction occurs in any one of said optical wave paths for transmitting said N-part optical signals, transmission of said N-part optical signals is continued, using said additional optical wave path.

Optical signal division transmission system, optical transmitter, optical receiver, and optical signal division transmission method

An optical device includes an interferometer for a received optical differential phase shift keying DPSK signal, and an equalizer integrated with the interferometer in a manner for reducing from optical filtering effects an interference by signal bits of the DPSK signal with signal bits of a contiguous DPSK signal. The interferometer is a Michelson delay interferometer type, but can also be a Mach-Zehnder delay interferometer type on fiber, waveguide or other optical structure. The equalizer is a Fabry-Perot type equalizer, but can be a ring resonator type or a fiber based equalizer.

Integrated equalizer and Michelson interferometer structure for inter-symbol interference-suppressed colorless DPSK demodulation

An apparatus includes an interleaver configuration for at least one of combining or separating odd and even channel groups to achieve channel density doubling; and an optical equalizer for suppressing inter symbol interference within the channels to provide intra-channel equalizing in the optical path, the equalizer being integrated into the interleaver. Preferably, optical equalizer and interleaver are integrated together as a single monolithic device, the optical equalizer includes a passband that has a dip in the channel center to achieve a raised-cosine filtering profile in the optical signal path to achieve inter-symbol interference ISI suppression, and the equalizer includes integration into the optical path of the interleaver to realize a monolithic device combining or separating odd and even channel groups to achieve channel density doubling. Preferably, also, the optical equalizer includes a first equalizer with half the depth of required ripple dips at both a first output port and an input port and a second equalizer with half the depth of required ripple dips at a second output port.

Intra-channel equalizing optical interleaver

The transponder includes a 64B/66B code synchronization bit determination circuitfor notifying a PLL selection control circuit of a control signal which instructs on selection of a variable oscillator or a variable oscillator in response to a case where an electric signal sent from an optical signal reception unitincludes a 64B/66B code synchronization bit, an A1A2 byte determination circuitfor notifying the PLL selection control circuit of a control signal which instructs on selection of a variable oscillator or a variable oscillator in response to a case where an electric signal sent from the optical signal reception unitincludes an A1A2 byte, and the PLL selection control circuitfor controlling a PLL selectorand a PLL selectorbased on a control signal.

Transponder, transmission system, transmission method and transmission program

A wavelength control circuit includes a temperature control loop monitoring the ambient temperature of an LD device and driving an electronic heating and cooling device so that the temperature is constant on the basis of a difference signal between a signal value corresponding to the temperature and a reference signal. In a wavelength control loop, the wavelength of a light signal from the light emitting device is monitored by a wavelength monitor and the electronic heating and cooling device is controlled so that the wavelength is uniform. At power on, the temperature is controlled by the temperature control loop to control LD device wavelength. After the temperature control loop is stabilized, a control is performed with both the temperature control loop and the wavelength monitor.

Wavelength control circuit and wavelength control method of light emitting device

The present invention provides an automatic identification level control circuit, an identification level control method, an automatic identification phase control circuit, an identification phase control method, and an optical receiver, capable of stably setting an optimal identification level or identification phase. An automatic identification level control circuit of the present invention includes a coupling capacitor, an identification circuit, a level fluctuation detection circuit, an identification voltage control circuit, and a low-pass filter. The identification circuit includes limiter amplifiers and flip flops. The level fluctuation detection circuit includes exclusive OR circuits.

AUTOMATIC IDENTIFICATION LEVEL CONTROL CIRCUIT, IDENTIFICATION LEVEL CONTROL METHOD, AUTOMATIC IDENTIFICATION PHASE CONTROL CIRCUIT, IDENTIFICATION PHASE CONTROL METHOD, OPTICAL RECEIVER, AND OPTICAL COMMUNICATION SYSTEM

A transmitting apparatus has a plurality of optical signal transmitters, a plurality of transmitting transponders for converting the wavelengths of optical signals transmitted from the optical transmitters into respective wavelengths and transmitting wavelength-converted optical signals, a wavelength-division-multiplexer for wavelength-division-multiplexing the wavelength-converted optical signals, and an auxiliary transmitting transponder for converting a wavelength of an optical signal transmitted from the optical signal transmitters into a wavelength different from the wavelength-converted optical signals, and transmitting an auxiliary wavelength-converted optical signal. The transmitting transponders are monitored by a supervising unit, which outputs a detected failure signal when it detects a failure of one of the transmitting transponders. In response to the detected failure signal, a transmission switch supplies an output signal from the auxiliary transmitting transponder, rather than the output signal from the failing transmitting transponder, to the wavelength-division-multiplexer. A supervising control signal transmitting unit transmits a supervising control signal to an optical transmission path. In response to the supervising control signal, a receiving apparatus switches from a receiving transponder corresponding to the failing transmitting transponder to a receiving auxiliary transponder.

Transmitting apparatus and receiving apparatus for

A wavelength multiplexing optical transmitting apparatus includes a plurality of optical transmitters for transmitting optical signals having mutually different wavelengths, a wavelength multiplexing circuit for wavelength multiplexing optical signals, an optical amplifier for directly amplifying the wavelength multiplexed optical signal and for producing an amplified multiplexed optical signal, an optical signal counting detector for branching the amplified multiplexed optical signal into signals of the respective wavelengths and for detecting the number of optical signals presently being transmitted, and an optical amplifier control circuit for controlling an output from the optical amplifier according to the number of optical signals; the optical amplifier includes a fiber made of a material to which a rare earth element is added and an excitation light to the fiber; the optical amplifier control circuit includes an excitation light control circuit for controlling an intensity of the excitation light according to the number of light signals; wherein to obtain an intensity of amplified optical signal predetermined according to the number of light signals, the excitation light control circuit sets an injection current to the excitation light source.

Optical amplifying apparatus and linear relay optical amplifier

Optical signals transmitted from optical transmission panels are received by photodetectors, which detect the number of actually transmitted optical signals. A control signal depending on the number of optical signals detected is supplied to an optical amplifier. The intensity of a combined optical signal amplified by the control signal is controlled by controlling a current supplied to a pumping light source. Information representative of the number of optical signals detected is superposed onto the amplified optical signal by generating the current supplied to the pumping light source as a sine-wave signal depending on the detected number of optical signals. In a downstream optical repeater, the information representative of the number of optical signals is extracted, and the optical signal is amplified, after which the information representative of the number of optical signals is superposed again onto the amplified optical signal for transmission. Even when some of the optical transmission panels fail to operate and the optical signals transmitted therefrom are interrupted, since the combined optical signal is amplified depending on the number of optical signals detected, the optical signals are maintained at a constant gain and output level.

Wavelength-division-multiplexing optical amplifier device and

An optical fiber amp repeater, provided on an optical transmission channel in an optical system, having an excitation light output section for supplying an excitation light for amplifying a received optical signal, and a main signal light amplifier section for supplying the optical signal which is amplified while going through the rare earth dope fiber after combining the received optical signal with the excitation light supplied from the excitation light output section, the excitation light output section including an excitation light source for transmitting the excitation light and an excitation light source driving circuit for driving the excitation light source, the excitation light source driving circuit controlling the excitation light source according to a given data and modulating the excitation light by high frequency wave, thereby to create an auxiliary signal containing the given data.

Optical fiber amp repeater of amplifying an optical signal and

In a wavelength multiplexing optical transmission device, first and second optical transmission boards output optical signals which have wavelengths different from each other and on which different sine-wave signals are superposed. The optical signals are coupled by an optical coupler, then divided into two lights by an optical divider. One optical signal is amplified by an optical amplifier. the other optical signal is converted into an electrical signal by a photodiode. The sine-wave signal components are extracted by first and second bandpass filters with the existence of the extracted signals being detected by output detectors. An adder output a reference voltage signal with a voltage according to the number of signals detected. A gain control circuit controls the amplification gain based on a voltage value corresponding to the intensity of an optical signal to be output and the reference voltage value, so that the level of output light can be controlled according to the number of optical signals.

Wavelength multiplexing optical transmission device

A DC bias controller for an optical modulator includes an optical modulator, a demultiplexer, and a controller. The optical modulator intensity-modulates input DC light by a digital main signal superposed with a DC voltage to convert the DC light to an optical signal. The demultiplexer demultiplexes the optical signal from the optical modulator into output signal light and monitor signal light. The controller detects a change in modulation characteristics of the optical modulator on the basis of the monitor signal light from the demultiplexer to control a value of the DC voltage superposed on the digital main signal.

DC bias controller for optical modulator

A wavelength-stabilizing method for use with an optical communication system capable of transmitting and receiving information by means of signal light between a pair of stations each having a coherent optical transmitter and a coherent optical receiver. This method is characterized in that each station transmits signal light while controlling its wavelength at the coherent optical transmitter and receives the incoming signal light together with the local light at a wavelength adjusted in accordance with the wavelength of the incoming signal light.

Growing community of inventors

Tokyo, Japan

Tsutomu Tajima