The present invention teaches a novel technique for properly aligning the various channel positions of an optical signal splitter/combiner device, such as a DWDM, and associated optical transmitter(s), often a laser. In particular, the described technique establishes and utilizes feedback links between the operating temperature of the splitter/combiner and the operating temperature or operating current of the transmitter(s) to accurately manipulate the wavelengths of these devices in a manner that results in accurate alignment of the device wavelengths to the desired grid of channel positions, λ0, λ1, λ2, λ3, . . . , λn. Furthermore, by providing this active alignment or tracking scheme, the techniques of the present invention allows optical systems to more effectively operate at smaller channel spacings, i.e. ≦ about 50 GHz between adjacent channel positions, and with larger number of channels per device, i.e. ≧ about 32 channels.

Method and apparatus for wavelength-channel tracking and alignment within an optical communications system

A digital transmission system includes at least a client device and a transmission device, and rate-adjusts the client signal transmitted from the client device to the transmission device before accommodating/multiplexing the signal in a frame. The transmission device includes a rate adjusting unit and a frame processing unit. The rate adjusting unit encapsulates the client signal by using a predetermined frame structure, inserts an idle pattern if necessary, and performs rate adjustment into the bit rate which can be contained in the frame. The frame processing unit accommodates/multiplexes the signal after the rate adjustment. The digital transmission system inserts a bit string of the client signal directly in a payload area of the digital frame, or accommodates and multiplexes it. Alternatively, a specific pattern is accommodated in the payload area, or accommodated and multiplexed after performing a reversible digital signal processing.

Digital transmission system and digital transmission method

An optical transmission system comprises a light source to output an optical carrier having a predetermined wavelength, a photoelectric converter, an optical transmission line, an optical circulator to apply an output light from the light source to one end of the optical transmission line and to apply a light through the same end of the optical transmission line to the photoelectric converter, and an optical modulator disposed on the other end of the optical transmission line to return a portion of the light from the optical transmission line as a reference light to the optical transmission line without modulation and to modulate another portion of the light from the optical transmission line with a transmission signal to return it to the optical transmission line as a modulated light.

Optical transmission system

A field effect transistor has a gate electrode, gate-insulating layer, a channel and a source and drain electrodes connected electrically to the channel, the channel comprising an oxide semiconductor, the source electrode or the drain electrode comprising an oxynitride.

Field effect transistor and process for production thereof

An optical apparatus is disclosed wherein increase of the number of wavelength selective switches provided for a standby system can be suppressed The optical apparatus includes a plurality of upstream side optical devices (101 to 104) and a plurality of downstream side optical devices (111 to 114) configured such that a plurality of output ports (#21 to #24) to be set as output destinations of light from a plurality of input ports (#11 to #14) can be changed over for each wavelength. An upstream side standby switch (121) is connected at a plurality of inputs thereof individually to the input ports (#11 to #14) and can change over an output of light from the inputs for each wavelength. A downstream side standby switch (122) is connected at an input thereof to the output of the upstream side standby switch (121) and at a plurality of outputs thereof individually to the output ports (#21 to #24) and can output light from the input to the plural outputs thereof.

Optical apparatus and optical cross connect apparatus

The present invention minimizes trouble and loss caused by a failure polarization scrambler. A polarization scrambler unit 201 of the invention is provided with: two polarization scramblers 2 - 1 and 2 - 1 ; a switching unit for coupling either one of the polarization scramblers 2 - 1 and 2 - 1 to a transmission line fiber 4 ; a detection unit for detecting an output signal from the polarization scrambler 2 - 1 (or the polarization scrambler 2 - 2 ) coupled to the transmission line fiber 4 ; and a controlling unit for switching, via the switching unit, between the polarization scramblers 2 - 1 and 2 - 2 whenever a false output signal is detected by the detection unit. Thus, the polarization scrambler unit 201 has a redundant structure.

Polarization scrambler unit and multi-repeater transmission system incorporating the same

It is the object of the invention to provide a wavelength stability circuit used in a WDM optical transmission system, in which the spacing of wavelengths between adjacent optical signals are always so controlled as to keep a prescribed value. The two optical signals with different wavelengths are respectively generated by two laser diodes and multiplexed by an optical coupler. A portion of the multiplexed optical signals is supplied to an optical heterodyne detection circuit, where the spacing of the wavelengths between the two optical signals is detected. The spacing of the wavelengths between the optical signals is converted into an electrical signal by an O/E converter and a frequency counter, and the electrical signal is compared with a standard voltage in a comparator. The spacing of the wavelengths between the two optical signals is always controlled and stabilized by a control circuit and keeps a prescribed value, where the lasing wavelength of one of the two laser diodes is controlled in accordance with the result of comparison of the comparator.

Wavelength stability circuit

PROBLEM TO BE SOLVED: To prevent the waveform distortions different by signal wavelengths which occur by the dispersions (different by signal wavelengths) of a transmission line. SOLUTION: Dispersion compensation fibers 21 to 2n and 81 to 8n are arranged between optical transmitters 11 to 1n of a transmission equipment 10 of the wavelength multiplex transmission system and an optical multiplexing coupler 3 and between an optical demultiplexing coupler 5 of a reception equipment 30 and optical receivers 71 to 7n. Extents of dispersion of dispersion compensation fibers are determined so as to satisfy a formula D1 +d11 +d12 =0 where D1 is the extent of dispersion in the transmission line for signal wavelength λ1 and d11 and d12 are extents of dispersion of dispersion compensation fibers 21 and 81 respectively, thereby compensating the extent of dispersion in the whole of the system.

Wavelength multiplex transmission system

PROBLEM TO BE SOLVED: To suppress time and effort and a damage when a polarized wave scrambler is failed. SOLUTION: A polarized wave scrambler unit 201 comprises two polarized wave scramblers 2-1, 2-2, a switching unit for coupling a transmission line fiber 4 to any one of the scramblers 2-1, 2-2, a detector for detecting an output signal of the scrambler 2-1 (or the scrambler 2-2) coupled to the fiber 4, and a controller for switching the scrambler 2-1 (or the scrambler 2-2) to the other scrambler 2-2 (or the scrambler 2-1) via a switching unit if the output signal detected by the detector is abnormal. That is, the unit 201 has a redundant constitution. COPYRIGHT: (C)2003,JPO

Polarized wave scrambler unit and multiple-relay transmission system using the same

The mechanism has combiner (1) which combines a light signal and a light command and delivers on exit, a combined signal to an absorption saturable device (2). On exit, it delivers a base light signal upon the combined light signal which exited the combiner. The saturable absorption mechanism allows a fast acting commanded switching response.

Shohei Yamaguchi

Papers

Polarization scrambler unit and multi-repeater transmission system incorporating the same

Wavelength stability circuit

Wavelength multiplex transmission system

Polarized wave scrambler unit and multiple-relay transmission system using the same

Optical switch command mechanism