Nippon Telegraph and Telephone Corporation

Mitsubishi Hitachi Power Systems, Ltd.

Kentaro Uchiyama

Hidehiko Takara

Ippei Shake

Etsu Hashimoto

Masatoshi Saruwatari

Toshio Morioka

Makoto Tanaka

Kenji Kawasaki

Shin Nishimoto

Hiroyuki Endo

Satoki Kawanishi

Wataru Imajuku

Yoshiaki Yamabayashi

Eiichi Yamada

Osamu Kamatani

Koji Nonaka

Yoshinobu Koori

An inspection method for a welded joint formed between a pair of base metals () with a groove part () and an abutment face () being formed on a joint surface Wc between the pair of base metals. The method includes the steps of: forming a recessed groove () opening to a surface of the base metals in advance at one end of the abutment face; irradiating the joint surface Wc with an X-ray generator () placed on a groove part formation side (an exterior space O side) toward the joint surface Wc after at least one pass Pof build-up welding is performed on the groove parts (); and determining the presence or absence of incomplete penetration in the welded joint part W based on an image formed on a photosensitive film () by radiation penetrating the joint surface Wc.

Method for manufacturing a turbine rotor

A monitoring system includes first and second evaluation sections for obtaining an averaged Q-factor parameter and a waveform distortion parameter from an optical signal amplitude histogram collected from optical signals under measurement. The monitoring system further includes a third evaluation section for determining both averaged Q-factor parameter and waveform distortion parameter, and for making a decision as to whether the main factor of the optical signal quality degradation is waveform distortion or not by comparing the averaged Q-factor parameter and waveform distortion parameter with their initial values or initial characteristics which are obtained when no optical signal quality degradation is present.

Method and system for determining origin of optical signal quality degradation

In an ultrahigh-speed clock extraction circuit wherein a local pulse generating light sourcefor generating a local optical pulse stream synchronized in bit phase with an input optical signal pulse stream is placed in a phase-locked loop, when repetition frequencies of the input optical signal pulse stream and the local optical pulse stream bear a particular relationship, a frequency demultiplierand multipliersandare set so that the frequency of a modulation signal for an optical modulatorand a frequency which is a natural-number multiple of the modulation signal frequency, and the frequency of a down-converted version of an optical pulse stream output from a photodetectordiffer from each other.

Ultrahigh-speed clock extraction circuit

It is the object of the present invention to provide a transmission system that transmits a control signal corresponding to the overhead accommodating time division multiplexing information at a frequency that is the same (or nearly the same) as that of the main signal. In order to attain this object, an optical transmitter broadens in a time range the optical waveform of the OTDM signal having a wavelength &lgr; and the control light having a wavelength &lgr; (&ap;&lgr; ), and multiplexes the signal light having an optical peak intensity set low compared to the OTDM signal peak intensity and sending this to an optical transmission fiber. An optical receiver provides a light splitting means that splits into two parts the transmitted OTDM signal and the control light and outputs one part thereof to an optical time division multiplexing means, and at the same time restores the control light included in the other part of the light to the original optical pulse train, and extracts the control information by converting this to an electric signal.

Optical transmission system

A phase-lock loop is formed by a voltage-controlled oscillator, a local optical pulse source, an optical branching device for branching the locally generated optical pulse stream from the local optical pulse source, a harmonic component local generation part for locally generating a harmonic component electrical signal from the one of two branched locally generated optical pulse streams, and a phase comparison part for comparing the phases of the locally generated harmonic component electrical signal and an incoming signal component electrical signal generated from an incoming optical signal pulse stream and for supplying the voltage-controlled oscillator with a control voltage corresponding to the phase difference between the two input electrical signals. The other branched output from the optical branching device is output as a locally generated optical pulse stream bit-phase synchronized with the incoming optical signal pulse stream.

Bit-phase synchronized optical pulse stream local generator

An all-optical time-division demultiplexing circuit is designed to output all the channels of time-division multiplexed signal pulses to different output ports simultaneously. A pulse stream of time-division multiplexed signal pulses and linearly chirped control pulses synchronized with the signal channels are input into an optical Kerr medium. The optical Kerr medium provides locally cross-phase modulation to the control pulse, depending on the presence or absence of the signal pulses of each signal channel. And the optical Kerr medium modulates the power of the component frequencies &ugr;,, &ugr;,, . . . , &ugr;,of the control pulses in accordance with each of the signal channel, by inducing the optical frequency shift to compensate the control pulse chirp on the optical frequency axis. The Kerr medium outputs a power modulated control light, which is separated in a wavelength-division demultiplexing circuit into component frequencies &ugr;,, &ugr;,, . . . , &ugr;,of the control pulses which are to output to respective ports of corresponding to individual signal channels.

All-optical time-division demultiplexing circuit and all-optical TDM-WDM conversion circuit

An all-optical polarization independent optical time division multiplexer and demultiplexer which are stable as well as very fast, while being independent of the polarization state of the input optical signal pulses. The demultiplexer has a wavelength-division-multiplexing coupler for wavelength-division-multiplexing time-division-multiplexed optical signal pulses and optical control pulses, and splitting the optical signal pulses at a splitting ratio of 1:1 into two ports, the optical control pulses being in a polarization state in which two orthogonally polarized components have a substantially identical amplitude; an optical Kerr medium with birefringence, for connecting two ports of the wavelength-division-multiplexing coupler, the optical Kerr medium incorporating a birefringence compensation mechanism for compensating a polarization dispersion between two principal axes of the birefringence; and a wavelength division demultiplexer for wavelength-division-demultiplexing time-wise overlapping optical signal pulses and optical control pulses propagated through the optical Kerr medium, to obtain time-division-demultiplexed optical signal pulses. In the multiplexer, the input and output relationship is reversed in the same configuration.

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Yokosuka, Japan

Kentaro Uchiyama