Nippon Telegraph and Telephone Corporation

Ando Electric Company

Masafumi Koga

Tetsuo Takahashi

Atsushi Watanabe

Yutaka Miyamoto

Yoshiaki Kisaka

Masahito Tomizawa

Takuya Ohara

Mitsuhiro Teshima

Takao Matsumoto

Tohru Mori

Ken-ichi Sato

Noboru Takachio

Shigeki Aisawa

Shoko Ohteru

Naohide Nagatsu

Hitoshi Obara

Ken'ichi Sato

A multiplexing transmission system for adding a management overhead to a client signal, and transparently accommodating or multiplexing the client signal to transmit it is provided. The multiplexing transmission system: accommodates a plurality of client signals of different bit rates including a client signal of a bit rate that is not an integral multiple or an integral submultiple of a bit rate of other client signal, and performs rate adjustment for a part or the whole of the plurality of client signals such that the bit rate of each client signal becomes an integral multiple or integral submultiple of the bit rate of other client signal.

Multiplexing transmission system and multiplexing transmission method

A wavelength division multiplexing ring network is constructed using a simple architecture and a fewer number of hardwares between the nodes compared with the conventional ring network. Each node is structured so that any number of multiple waves can be processed, and a fault in the network or within a node is resolved by providing a path-based protection so that switching can be performed without disrupting other nodes or even within one node. The network uses two or four lines of optical fibers, and a half of the fibers are used for communicating in a clockwise direction and a other half of the fibers are used for communicating in a counter-clockwise direction to form a logical network by optical paths contained in optical fibers so as to provide an equal number of relay nodes between two adjacent pairs of nodes throughout the network, where each node includes: multiple optical add/drop circuits; an optical path transmit end and an optical path receive end for freely selecting and outputting multiple combinations of wavelengths to be inserted in each node; and transmission lines provided between the optical add/drop circuits and the optical path transmit end, as well as between the optical add/drop circuits and the optical path receive end for transmitting any multiple waves to be processed within the node so as to establish mutual communication by transmitting processed multiple waves to other nodes. This network design enables to reduce the number of connections between the optical path transmit and receive ends, and also to reduce the number of optical signal op termination circuits.

Optical communication network

By using a combination of a plurality of completely unequally spaced channel allocations, the influence of four wave mixing is mitigated even while it is incompletely unequally spaced channel allocation, and it is possible both to decrease the occupied bandwidth and increase the number of channels. A plurality of completely unequally spacing channel allocations are combined, and the number of channels changes depending on the amount of scattering of an optical fiber and the frequency that there exists zero dispersion wavelengths on a transmission path. The completely unequally spaced channel allocations of N -channels in a first wavelength region including the zero dispersion wavelength &lgr; or the mode zero dispersion wavelength &lgr; are partitioned, and then in sequence the completely unequally spaced channel allocation of N -, N -, . . . , channels is partitioned, and the wavelength interval of N channels is set by combining all or a part thereof (where N &gE;N 24  . . . >N &gE;N &gE;N ).

Wavelength allocation method, a transmission equipment and receiving equipment using this method and a wavelength division multiplex transmission system

An optical amplifier evaluating device has a wavelength multiplex signal light generating section, and an O/E converter, and a frequency discriminating and power detecting device, and a computing section. The wavelength multiplex signal light generating section generates an wavelength multiplex signal light which includes signal lights having different wavelengths and having intensity envelopes modulated by different modulation frequencies which are enough higher than an atom life time in a high energy level or a carrier life time in an amplification medium of an optical amplifier to be evaluated, and supplies the wavelength multiplex signal light to the optical amplifier. The O/E converter converts an output light of the optical amplifier to an electric signal. The frequency discriminating and power detecting section detects signal powers of frequency spectrums which are included in the electric signal and respectively correspond to the modulation frequencies of the signal lights, and detects a noise power of the electric signal at a frequency band which is apart from the modulation frequencies. The computing section determines gains and noise figures of the wavelength multiplex amplification by the optical amplifier based on the signal powers and the noise power wavelength by wavelength.

Device and a method for evaluating an optical amplifier

An optical cross-connect system is provided with M fixed wavelength light sources and external modulators corresponding to respective optical paths, serving as light sources for wavelength conversion devices corresponded to M.times.N optical paths. By means of electrical signals for the converted optical signals carried on the M.times.N optical paths, CW lights input to the external modulators from the respective light sources are modulated, wavelength converted and then output. Accompanying this wavelength conversion, wavelength multiplexed light sources which can select lights from a plurality of fixed wavelength light sources and output to predetermined output ports, are used for the light sources of the plurality of wavelength conversion devices of the cross-connect system. In this way, the light sources of a plurality of wavelength conversion sections are commonalized using a fixed wavelength light source. As a result wavelength multiplexed light sources which can respectively output lights of optional wavelengths to a plurality of output ports using a plurality of fixed wavelength light sources are realized. Moreover, by using such wavelength division multiplexed communication light sources, then a highly realizable and economical optical cross-connect system is possible.

Optical cross-connect system

A multiwavelength simultaneous monitoring circuit capable of precise discrimination of wavelengths of a WDM (Wavelength Division Multiplexed) signal including multiplexed wavelength waves, and suitable for optical integrated circuits having large resistance to vibration. It includes a reference optical source, an AWG (Arrayed-waveguide grating) having periodic center transmission wavelength (or crossover wavelengths) corresponding to the wavelength spacing between multiplexed waves of the WDM signal, a first wavelength error detector for generating a wavelength error signal of an RF signal (reference optical signal) with respect to a zero-cross wavelength on the basis of a ratio between the levels of the RF signal outputted from two output waveguides of the AWG, a control circuit for locking the zero-cross wavelength to the wavelength of the RF signal in response to the wavelength error signal, and a second wavelength error detector for generating wavelength error signals of the multiplexed waves of the WDM signal by detecting signal levels of respective wavelength signals of the WDM signal outputted from each pair of output ports of the AWG.

Multiwavelength simultaneous monitoring circuit employing

The optical circulator according to the present invention comprises three birefringent crystal plates 22, 23, and 24; reciprocal and non-reciprocal rotators 25 of the first group inserted between birefringent crystal plates 22 and 23; reciprocal and non-reciprocal rotators 26 of the second group inserted between birefringent crystal plates 23 and 24; and more than two beam incoming and outgoing ports 27, 28, and 29. The rotating directions of the reciprocal and non-reciprocal rotators 25 of the first group are so set that the directions in which ordinary beam and extraordinary beam are separated on the birefringent crystal plates differ among birefringent crystal plate 23 and birefringent crystal plates 22 and 24, and the electric field vibration directions of the beams agree at birefringent crystal plate 23. The rotating directions of the reciprocal and non-reciprocal rotators 26 of the second group are set so that the polarization face of the beams are perpendicular to each other at birefringent crystal plate 24. According to the above optical circulator, there is no need to use angular prisms or polarization beam splitters as have been required till now.

Optical circulator

An optical wavelength demultiplexer including an optical conversion device which converts a difference in wavelengths of a plurality of input signals into a difference in spatial power distribution of the input light signals, and a pattern recognition element for recognizing patterns of the spatial power distribution and taking out output signals. At the output portion of the optical conversion device, spatial power distributions are formed which are different for different wavelengths. After converting the spatial power distributions by the pattern recognition element into electrical signals, pattern recognition of the signals is performed to regenerate the original input signals with their respective wavelengths. The optical conversion device uses a diffractive grating or a combination of an optical multimode circuit, an optical multimode fiber, and a plurality of optical wavelengths. The pattern recognition element is constructed by a combination of a photo-detector array and a neural network, or a combination of a hologram element, a photo-detector array and a neural network.

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Yokosuka, Japan

Masafumi Koga