Nippon Telegraph and Telephone Corporation

Japan Science and Technology Agency

Sumitomo Electric Industries, Limited

Hitachi Cable, Inc.

Ando Electric Company

Other

Tohoku University

Dai Nippon Printing Co., Ltd. and Nippon Telegraph and Telephone Corporation

Dai Nippon Printing Co., Ltd.

Masataka Nakazawa

Eiji Yoshida

Toshihiko Hirooka

Tetsuro Komukai

Masashi Onishi

Hiroo Kanamori

Katsuyuki Imoto

Masaaki Kurihara

Akio Ichikawa

Yoshiaki Miyajima

Toshikazu Segawa

Yoshihiro Kumagai

Rikihiro Iida

Takashi Kogo

Yasuo Kimura

Hiroyuki Ishii

Naoki Fujiwara

Kei Watanabe

Seiichi Kashimura

Mikitaka Itoh

Kohichi Robert Tamura

Toshikazu Kamoshida

Yuka Asahina

Keisuke Kasai

Fujio Kikuchi

A configuration of a DFB laser-based wavelength tunable laser is well known, but long resonators have difficulty in forming uniform resonators due to production variations, thereby inducing limitation in narrowing the spectral linewidth in the DFB laser-based wavelength tunable laser as well. In the semiconductor laser device of the present invention, a semiconductor laser that oscillates in a single mode and a low-loss lightwave circuit using SiOglass are arranged on the common substrate. The lightwave circuit is configured such that part of output light from the semiconductor laser propagates through a certain length of an optical path, and then is reflected by a reflector and is fed back to the semiconductor laser. Output light from the semiconductor laser and an input waveguide of the lightwave circuit can also be configured to be optically connected directly to each other. The present invention can provide a compact laser device with a narrowed spectral linewidth and stable wavelength controllability.

Semiconductor laser device

To compensate a waveform distortion by using a nature that a spectral shape is perfectly retained even if all the linear distortions occur on a time-axis. An optical pulse transmitted from an optical pulse transmitter () via an optical fiber transmission line () is transmitted. An optical Fourier transformer () receives an optical pulse, and optically Fourier-transforms an optical pulse on a time-axis onto a frequency-axis to reproduce the frequency spectrum of an optical pulse on a time-axis be effecting switching between frequency and time, thereby compensating a waveform distortion by a linear effect on the optical fiber transmission line (). A photodetector () receives an optical pulse from the optical Fourier transformer () and transforms this into an electrical signal to thereby obtain a pulse waveform before a transmission over the optical fiber transmission line ().

Optical transmission method and optical transmission apparatus

An OTDM transmitting method and transmitter realizing an OTDM distortion-free transmission substantially not relying upon dispersion. A time division multiplexed OTDM signal from an OTDM signal transmitter () enters an optical Fourier transform unit (). Optical Fourier transform can be carried out most accurately so long as the optical pulse is a chirp-free Fourier transform limit pulse. The optical Fourier transform unit () converts the time waveform of the pulse into a signal on the frequency axis, and an optical inverse Fourier transform unit (') converts a spectral shape on the frequency axis into a time waveform (pulse). An optical fiber transmission line () is a transmission line having an arbitrary dispersion and a polarization mode dispersion. These dispersions may involve a time variation. An OTDM signal receiver () demultiplexes a transmission signal into low-speed optical signals, in a light region, receives optical pulses for respective channels and converts them into electric signals.

OTDM transmission method and apparatus

A small-sized, high-functionality optical pulse compressor capable of generating a low-power, high-repetition-frequency ultrashort pulse train used for ultrafast optical communication and photometry, and a simple-structure optical function generator for realizing an arbitrary time waveform. The optical pulse compressor comprises and optical Fourier transform device (F) having an optical phase modulator () driven by the repetition-frequency of an input optical pulse train and a dispersive medium (), for converting the shape of an input optical pulse frequency spectrum into its time waveform, and an optical filter () inserted ahead of the optical Fourier transform device (F), for reducing the spectrum width of an input optical pulse, wherein the optical Fourier transform device (F) converts a small-spectrum-width optical pulse output from the optical function generator generates an optical pulse. The optical function generator generates an optical pulse having an arbitrary time waveform by reproducing, as it is, a spectrum waveform-shaped arbitrarily by an optical filter on a time-axis by the optical Fourier transform device (F).

Optical pulse compressor, optical function generator, optical pulse compression method, and optical function generation method

Optical Fourier transform is executed over a wide time range. A quadratic function type optical pulse generator () generates a control light pulse of a shape expressed by a quadratic function or a parabola according to a clock signal based on a signal light pulse from an optical coupler (). The signal light pulse inputted is multiplexed by a multiplexer () with the control light pulse optically delayed by an optical delay element () so that the timing is matched with the signal light pulse, and introduced into an optical Kerr medium (). In the optical Kerr medium (), the signal light pulse inputted by the mutual phase modulation between the signal light pulse and the control light pulse is subjected to a linear phase modulation (frequency chirp) over the entire pulse or a wide time range. After that, the signal light pulse isolated by an optical filter () is introduced into the dispersion medium () having a group velocity dispersion (secondary dispersion), thereby converting the time waveform of the inputted signal light pulse into the shape of the frequency spectrum.

Optical fourier transform device and method

The present invention relates to a method of producing an optical fiber-processing phase mask having minimized connection errors that may degrade the spectral line shape and group delay characteristics of an optical fiber diffraction grating fabricated by using the phase mask. The present invention provides a method of producing an optical fiber-processing phase mask having a repeating pattern of grating-shaped grooves and strips provided on one surface of a transparent substrate, so that diffracted light produced by the repeating pattern is applied to an optical fiber to fabricate a diffraction grating in the optical fiber by interference fringes of diffracted light of different orders. In making a mask having a plurality of juxtaposed patterns (P to P ) having a linearly or nonlinearly increasing or decreasing pitch and a uniform groove-strip width ratio, multiple exposure is carried out to minimize difference between the pitch at the joint between patterns having different pitch data and the pitch in each individual pattern.

Method of making phase mask for machining optical fiber and optical fiber having bragg diffraction grating produced using the phase mask for machining optical fiber

An arrayed-waveguide grating (AWG) is provided in a tunable mode-locked laser resonator where when a clock signal corresponding to a predetermined wavelength is input, the arrayed-waveguide grating (AWG) generates an output signal having an oscillation wavelength which has an arbitrary wavelength interval independent of the wavelength of said clock signal and a different propagation delay for each wavelength. Furthermore, a transmitter and a wavelength converter is provided that uses a tunable mode-locked laser where the frequency of the clock signal determines the wavelength and where a transmitted data signal at a fixed data rate is generated by setting the clock signal frequency sufficiently higher than the data rate. Furthermore, a wavelength converter and wavelength router is provided that uses said tunable mode-locked laser and in which the output wavelength is determined by extracting said clock signal from the input data signal. Furthermore, a transmission system is provided that uses said transmitter and/or said wavelength converter, and a receiver that recovers the envelope of said transmitted data signal.

Wavelength-tunable mode-locked laser, wavelength converter and transmission system

The invention relates to a method of fabricating an optical fiber-processing phase mask in which a stitching error ascribable to a deterioration in the wavelength selectivity of the optical fiber diffraction grating to be fabricated is reduced. At an exposure step, a writing stage with a phase mask blank placed thereon is continuously fed in one direction while portions of the phase mask blank corresponding to grooves or strips in a direction perpendicular to the direction of feeding are sequentially scanned with writing beams , whereby the entire area of the phase mask blank to be written is continuously written.

Method of producing phase mask for fabricating optical fiber and optical fiber with bragg's diffraction grating produced by using the phase mask

An ultra-stable microwave output with less jitter than a prior art atomic oscillator is obtained and an ultra-short optical pulse train is generated with a repetition frequency stabilized at the same level as a time standard. The repetition frequency of a regeneratively mode-locked laser pulse oscillator with a superior low-jitter characteristic is locked directly to a resonance frequency of various atoms. The oscillator provides the means for detecting the frequency difference between the clock signal frequency and a predetermined atomic resonance frequency and outputting it as an error signal, a cavity length tuning device for varying the length of a laser cavity so that the clock signal frequency and the predetermined resonance frequency coincide, and a device for negatively feeding back the error signal output from the frequency difference detection device to the cavity length tuning device. This allows the generation of an optical pulse train (optical output) and a clock signal (microwave output) of a repetition frequency stabilized to the predetermined atomic resonance frequency.

Atomic frequency standard laser pulse oscillator

The object of the present invention is to provide an optical pulse generator which very stably generates for a long period of time a high cycling frequency optical pulse chain. In order to obtain this object, in a ring type resonator R, the present invention provides an optical path length regulator 14 which performs high precision optical path length adjustment and an optical path length regulator 60 which performs wide range optical path length adjustment, and extracts a clock signal by converting an optical pulse emitted from the ring type resonator R to an electrical signal by a clock extractor 42, detects the frequency difference between a base frequency signal output form a synthesizer 52 by a frequency difference detector 50, and controls said optical path length regulator 14 and said optical path length regulator 60.

Optical pulse generator

According to the present invention, damage to a photo-detector disposed in clock signal extractor by means of an optical pulse having an optical power exceeding a rated value is prevented. A ring resonator generates a repetitive, high-frequency optical pulse. Optical branching circuit branches a portion of the optical pulse circulating through ring resonator, while optical branching circuit further branches a portion thereof to protective device. Pumping source generates an excitation light for exciting a rare-earth doped optical fiber. Optical multiplexer couples the optical pulse branched by optical branching circuit, and the excitation light. Upon excitation by means of the excitation light, rare-earth doped optical fiber amplifies and emits the incoming optical pulse. The optical power of the excitation light is adjusted such that the output of rare-earth doped optical fiber reaches a saturation power. Optical switch blocks the incoming optical pulse during the time period when pumping source is not emitting an excitation light, and during a fixed time period following the emission of the excitation light. In this manner, the entry of an excessively large optical pulse exceeding the saturation power into photo-detector at the time of starting up the power source is prevented. Optical attenuator attenuates the optical power of the optical pulse emitted from optical switch to an optical power which the photo-detector is capable of photo-detecting. Photo-detector converts the optical pulse emitted from protective device into an electronic signal; narrow band filter extracts a clock signal from the output of photo-detector; and electric amplifier amplifies the output of narrow band filter, and outputs a clock signal. Phase shifter adjusts the phase of this clock signal; electric amplifier amplifies the output of phase shifter, and outputs a clock signal to optical modulator. Optical modulator modulates the intensity of the light circulating through the ring resonator based on the clock signal, and generates an optical pulse.

A harmonically and regeneratively mode-locked laser pulse oscillator having a clock extraction circuit for picking up from a fragment of a laser output a clock signal corresponding to a high-order integer multiple of the fundamental frequency determined by the cavity length of the laser, a phase shifter and an electric amplifier for driving an optical modulator disposed in the laser cavity at the frequency of the clock signal. The laser pulse oscillator has a phase-locked loop including a phase comparator for detecting the phase difference between the clock signal and an external signal fed from a synthesizer with its frequency fixed, a fiber stretcher for controlling the cavity length such that the repetition rate frequency of the laser pulse oscillator is locked to the external signal, and an electric filter and electric amplifier for expanding and contracting the fiber length by feeding back the phase difference detected by the phase comparator to the fiber stretcher. This makes it possible to lock the repetition rate frequency of the optical pulse train to the external signal, and to generate the stabilized, fixed frequency optical pulse train with a high repetition rate over a long time period.

Laser pulse oscillator

Lead-containing fluoride glass comprises 50-70 mol % of ZrF.sub.4, 3-5 mol % of LaF.sub.3, 0.1-3 mol % of YF.sub.3, and 2-15 mol % of NaF and/or LiF and/or CsF, where LaF.sub.3 +YF.sub.3 =4.5-6 mol %, and further comprises lead. An optical fiber comprises a core made of the lead-containing fluoride glass and a cladding surrounding the core. A process for producing an optical fiber comprises forming a base material for a core of the lead-containing fluoride glass, forming a base material for a cladding of fluoride glass containing 30-60 mol % of HfF.sub.4, and drawing the base materials into an optical fiber at a drawing temperature of 315-340 .degree. C.

Lead-containing fluoride glass, optical fiber and process for producing

A pulse compression device is disclosed for generating ultra short pulses in the femtosecond range In the device an input soliton is subjected to pulse width compression by propagation in a rare-earth doped optical fiber having a gradually diminishing group velocity dispersion from an input end to an output end. The pulse compression is produced by the diminishing dispersion value of the optical fiber as well as by adiabatic narrowing generated by a pumping light coupled, through an optical coupler, to the optical fiber by increasing the energy of the input soliton propagating in the optical fiber. By adjusting the light power of the pumping light, the pulse width of the soliton can be freely controlled.

Optical pulse compression device

Lead-containing fluoride glass comprises 50-70 mol % of ZrF.sub.4, 3-5 mol % of LaF.sub.3, 0.1-3 mol % of YF.sub.3, and 2-15 mol % of NaF and/or LiF and/or CsF, where LaF.sub.3 +YF.sub.3 =4.5-6 mol %, and further comprises lead. An optical fiber comprises a core made of the lead-containing fluoride glass and a cladding surrounding the core. A process for producing an optical fiber comprises forming a base material for a core of the lead-containing fluoride glass, forming a base material for a cladding of fluoride glass containing 30-60 mol % of HfF.sub.4, and drawing the base materials into an optical fiber at a drawing temperature of 315.degree.-340.degree. C.

Growing community of inventors

Sendai, Japan

Masataka Nakazawa