Nippon Telegraph and Telephone Corporation

Toshio Morioka

Masatoshi Saruwatari

Hidehiko Takara

Kunihiko Mori

Kentaro Uchiyama

Etsu Hashimoto

Eiichi Yamada

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

A multiple-channel all-optical TDM-WDM converter and multiple-channel all-optical TDM demultiplexer which is able to simultaneously and spatially separate optical signal pulse trains of each channel from a TDM optical signal pulse train is structured without using a multistage-structure constitution. A control optical source 10 generates a control optical pulse train containing N optical frequencies, which is synchronous with optical signal pulse trains of N channels which are to be divided from a TDM optical signal pulse train wherein optical signal pulse trains of N channels have been multiplexed in time series. An optical wavelength multiplexer 11 combines the time-division-multiplexed optical signal pulse train and the control optical pulse train. The light output from an optical wavelength multiplexer 11 is input to a nonlinear material 12, which induces a four-wave mixing effect between the control optical pulse stream having the N optical frequencies and optical signal pulse trains of N channels, and outputs a frequency-converted optical pulse train which is the combination of N optical pulse trains having different optical frequencies. An optical wavelength demultiplexer 13 spatially divides the N types of optical pulse trains according to each optical frequency from the frequency-converted optical pulse train.

Multiple-channel all-optical TDM-WDM converter and multiple-channel

A coherent white light source generates a uniform and continuous coherent white light spectra over 200 nm at a low pump power. The source is based on a pump light source which produces pump optical pulses at a wavelength .lambda..sub.0 and an optical waveguide to receive a pump optical pulse at .lambda..sub.0 to generate a white pulse having a wavelength spread of .DELTA..lambda.. The optical waveguide is characterized by having dispersion properties such that four-wave mixing light having a wavelength spread of .lambda..sub.0 .+-..DELTA..lambda./2 is produced, and the power gain of the four-wave mixing light is greater than 1. These properties of the waveguide are defined by: the path length of the waveguide device ln G.sub.0 /(2.vertline..gamma..vertline.P) in units of �km!, an absolute value of the dispersion slope to be not more than 16(.vertline..gamma..vertline.E)(.DELTA..lambda..sup. ln G.sub.0) in units of �ps/nm.sup.2 /km! and an absolute value of the dispersion at the wavelength .lambda..sub.0 to be not more than (16/.pi.c) .lambda..sub.0.sup.2 .vertline..gamma..vertline.P/(.DELTA..lambda.).sup.2 in units of �ps/nm/km!. Examples of optical devices utilizing such a super-wideband coherent white light source are demonstrated.

Coherent white light source and optical devices therewith

The present invention provides an optical parametric circuit for separating four-wave-mixing wave(s) (FWM wave(s)) from signal wave(s) and/or pump waves without using a wavelength filtering device, and optical circuits using the same. The optical parametric circuit of the present invention is made by connecting two output ports of a 2.times.2 optical directional coupler to a nonlinear optical medium via dispersive optical media, each of which has a specific length and a specific propagation constant. By inputting signal waves having carrier angular frequencies .omega..sub.Sj (j=1, 2, . . . N) and pump waves having carrier angular frequencies .omega..sub.P1, .omega..sub.P2 into the first input port of the optical directional coupler, the FWM waves, generated in the nonlinear optical medium, having carrier angular frequencies .omega..sub.fj (=.omega..sub.P1 +.omega..sub.P2 -.omega..sub.S) are output from the second input port of the optical directional coupler. By inputting the signal waves and the pump waves from different input ports of the directional coupler, it is possible to separate amplified signal waves and the FWM waves from the pump waves. By adjusting the lengths and the propagation constants of the dispersive optical media, the amplified signal waves are separated from the pump waves and the FWM wave. The optical parametric circuit is used for wavelength conversion of optical signals, parametric amplification of optical signals, optical phase conjugation (spectral inversion) and for all-optical switching and for optical circuits using the same, for example, optical logic circuits, optical time-division multi/demultiplexers and/or optical sampling circuits.

Optical parametric circuit and optical circuit using the same

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

Toshio Morioka