Nippon Telegraph and Telephone Corporation

Koichi Takiguchi

Katsunari Okamoto

Takashi Goh

Takashi Saida

Tomohiro Shibata

Masao Kato

Takayuki Mizuno

Masao Kawachi

Manabu Oguma

Akira Himeno

Kaname Jinguji

Senichi Suzuki

In the disclosed optical signal processing device, the digital-to-analog conversion of the input optical signals is realized in an optical region, without converting the input optical signals into electric signals for the purpose of signal processing, by splitting input optical signals into plural sets, delaying the split optical signals for mutually different delay amounts while adjusting amplitudes of these optical signals, combining these optical signals, and gating these optical signals on a time axis. It is also possible to realize the processing of the optical signals that are multiplexed on a time axis such as interchanges of time-slots similarly.

Optical signal processing device using optical gate

The object of the present invention is to provide a compact dispersion slope equalizer by which it is possible to simultaneously recover distorted waveforms of WDM signals by dispersion slope of DSF or NZ-DSF at 1.55 &#x3bc;m band, and to compensate for the dispersion of various fiber transmission lines having various dispersion values and variation of dispersion value caused by the temperature change or the like. WDM signals distorted by the dispersion slope of the fiber are introduced into an input waveguide, and are demultiplexed by a wavelength demultiplexer into each wavelength component, and pass through lattice-form optical circuits, transversal-form optical circuits, or the combination of these circuits. The dispersion slope of the signals is compensated for by these circuits. The recovered signals are multiplexed by a wavelength multiplexer, and the multiplexed light is outputted at an output waveguide. Arrayed-waveguide gratings can be used as the wavelength demultiplexer and multiplexer. Also, cascaded configuration of Mach-Zehnder interferometers, bulk-type optical filters, or fiber-type (or waveguide-type) gratings in series can also be used as the wavelength demultiplexer and multiplexer.

Dispersion slope equalizer

A multistage Mach-Zehnder interferometer type optical circuit including any number of symmetrical Mach-Zehnder interferometers and any number of asymmetrical Mach-Zehnder interferometers connected in cascade. In the optical circuit, low coherence light is used first to obtain individual phase control conditions of the symmetrical Mach-Zehnder interferometers without being affected by the asymmetrical Mach-Zehnder interferometers. Second, phase control conditions of the individual asymmetrical Mach-Zehnder interferometers are obtained by controlling the symmetrical Mach-Zehnder interferometers based on the first phase control conditions. Finally, the characteristic adjustment of the whole multistage Mach-Zehnder interferometer type optical circuit is carried out by controlling all the interferometers based on the phase control conditions of both the symmetrical Mach-Zehnder interferometers and asymmetrical Mach-Zehnder interferometers and setting the phase shift amounts of the individual interferometers at appropriate values.

Characteristic adjustment method of multistage Mach-Zehnder interferometer type optical circuit and multistage Mach-Zehnder interferometer type optical circuit

An optical pulse pattern generator can generate optical pulse signals with various periods and patterns. It supplies an optical pulse from an optical pulse source to a variable optical delay line circuit including cascade-connected characteristic-variable asymmetrical Mach-Zehnder interferometers via an optical combiner and splitter. The optical pulse is fed back to the optical combiner and splitter from the final stages of the cascade-connected characteristic-variable a symmetrical Mach-Zehnder interferometers via an optical exclusive OR circuit and optical amplifier. Making directional couplers with variable coupling ratio, and directional couplers with variable coupling ratio in operation can cause the final stage of the cascade-connected characteristic-variable asymmetrical Mach-Zehnder interferometer to produce a random pulse train.

Optical pulse pattern generator

It is an object of the present invention to provide an optical filter which allows parameters to be easily adjusted, which allows birefringence and temperature dependence to be easily compensated for, and which is essentially free from dispersion. The optical filter includes an optical coupler that splits light into two beams, optical couplers connected to outputs of the optical coupler, a first group of two optical waveguide delay lines connected to the coupler, a second group of two optical waveguide delay lines connected to the coupler, an optical coupler that combines lights from the first group of the lines, an optical coupler that combines lights from the second group of the lines, and a multimode interference optical coupler that combines lights from the couplers together.

Optical filter

An optical CDMA encoder-decoder is constructed by combining arrayed-waveguide gratings, matrix optical switches, and delay lines, otherwise by combining arrayed-waveguide grating and variable delay lines, thus providing an encoding process that a wavelength change with respect to time in optical pulses. The light includes a wide spectrum band width inserted into a CDMA encoder/decoder and is demultiplexed by arrayed-waveguide gratings. Each wave length according to the demultiplexed spectrum component spreads out in the time region based on delay time differences produced by delay lines having differential optical lengths. Thus, in CDMA, the dependency of wavelengths on delay time can be set arbitrarily.

CDMA encoder-decoder, CDMA communication system, WDM-CDMA communication system

An optical signal processor according to the present invention is an optical circuit of a lattice configuration. Its basic circuit structure comprises 3 dB directional couplers, two optical waveguides with equal optical path lengths, and two optical waveguides with different optical path lengths (an optical path difference of about 1 to 50 mm). Phase controllers for performing phase shift are provided on the optical waveguides. The portions with equal optical path lengths function as variable directional couplers, and variable directional couplers having arbitrary coupling rates can be constructed by changing the phase controllers on the optical waveguides with equal optical path lengths. As for an adaptive filter, there is adopted a construction in which a photodetector for withdrawing part of output is provided at the output port, and a feedback electric wiring for feedback control is laid.

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Mito, Japan

Koichi Takiguchi