Nippon Telegraph and Telephone Corporation

Ando Electric Company

Kabushiki Kaisha Toshiba

Other

Kazuo Aida

Kiyoshi Nakagawa

Hiroshi Kobayashi

Takashi Ikeda

Hiroji Masuda

Motomitsu Yano

Yoshiharu Hidaka

Kouichirou Kamura

Seiji Nogiwa

Yoshiaki Sato

Haruyoshi Uchiyama

Shingo Kawai

Tatsuhiko Takatsu

Shigendo Nishi

Tatuhiko Takatu

Hiroshi Abe

Kenichi Suzuki

Junya Kosaka

Shinji Sakano

Takashi Iwasaki

Tohru Mori

Hideaki Haruyama

Masatoshi Saruwatari

Yoshitada Katagiri

Naoto Sato

Ken-Ichi Suzuki

Shoichiro Yamasaki

Kunihiko Sekiya

Yasuko Nakayama

Shigenobu Minami

Michiaki Okano

Hitoshi Obara

Kazuyoshi Ozawa

Zhixien Li

Fumikazu Ohira

Shinji Nagaoka

Yoshiaki Tachikawa

Nobuhiro Sakakibara

Yoshihiro Hidaka

Broadband switching networks are disclosed, which has a plurality of broadband switch nodes and a broadband switch inter-node transmission line for connecting the plurality of broadband switch nodes, information being transmitted by cells, each of which comprises a header and an information field, wherein the broadband switch node comprises a broadband input and output port for inputting and outputting the cells to and from the broadband inter-node transmission line, and a switch for separating the cells being input through the broadband input and output port and for multiplexing the cells so as to output them, wherein data composed of the plurality of cells is transmitted and received through the broadband switch node by constant bit rate transmission, variable bit rate transmission, or a combination of the constant bit rate transmission and the variable bit rate transmission.

Broadband switching networks

In a light amplification apparatus in which a part of a light output from a light amplification medium is transmitted through a branching means to a light detection means so that light power of the light output is detected by the light detection means whereby at least one of an excitation source and a return means is controlled through a control means so that light branch from a branching means is returned as a return light to the light amplification medium through the branching means again in a state in which light power is adjusted by the return means, and, as a result, the light power of the light output from the light amplification medium can be kept in a desired value while the occurrence of a light surge is suppressed, a light amplification medium control method and a light amplification apparatus wherein a signal light input can be amplified while the occurrence of a light surge is suppressed by a simple structure and with good control response, and a system using the same.

Light amplification medium control method, light amplification apparatus and system using the same

An optical amplifier having a two-stage construction using an erbium doped fiber (EDF) as a gain medium. The erbium dopant concentration is 1000 ppm, and the unsaturated absorption coefficient of the signal beam at 1550 nm is 1 dB/m. The length of the EDF,-,is 10 m, and the length of the EDF,-,is 70 m. The excitation light sources,-,and,-,are semiconductor lasers of 1.53 &mgr;m, and the excitation light power is 100 mW. Multiplexers,-,and,-,are inductive multi-layer film filters, and the gain equalizer,-,is a Fourier filter. The peak loss of the Fourier filter is 17 dB. The gain of the EDF,-,is 25 dB, and the gain of the EDF,-,is 15 dB. Two optical isolators are installed on a pre-stage amplifier, and one on a post-stage amplifier in order to prevent laser oscillation.

Optical amplifier and transmission system using the same

A disk shaped tunable optical filter is formed by a transparent substrate in a disk shape, and a filter layer formed on a top surface of the substrate, having such a filter characteristic that a transmission central wavelength varies along a circumferential direction as a monotonic function of a viewing angle. This disk shaped tunable optical filter can be advatageously utilized in realizing a wavelength discrimination apparatus, a reference wavelength light generation apparatus, an optical packet generation apparatus, and a tunable optical filter module, which are also disclosed.

Disk shaped tunable optical filter

The purpose of the invention is to offer an optical-frequency-stabilized light source with high accuracy and stability of the optical frequency. An optical splitter 8 splits output light from a local light source 7 into two beams. An optical detector 2 detects beat signals formed by the superimposition of the optical frequency difference between the local light source 7 and the output light, and a rectifier 3 rectifies the beat signal. A time measuring circuit 4 measures the time at which the beat signal was obtained. A frequency measuring circuit 5 measures the beat frequency. A CPU 6 outputs the deviation between the output light from the local light source 7 and the target optical frequency. A Fabry-Perot etalon transmission detection circuit 11 outputs an electrical signal corresponding to the optical frequency of the output light from an optical splitter 9. A control circuit 12 controls the optical frequency of the local light source 7 such that the electrical signal always matches the electrical signal corresponding to the target optical frequency. A Fabry-Perot etalon control circuit 10 corrects the relationship between the output electrical signal and the optical frequency of the light input to the Fabry-Perot etalon transmission detection circuit 11.

Optical-frequency-stabilized light source

Broadband switching networks are disclosed, which have a plurality of broadband switch nodes and a broadband switch inter-node transmission line for connecting the plurality of broadband switch nodes, information being transmitted by cells, each of which comprises a header and an information field, wherein the broadband switch nodes comprise a broadband input and output port for inputting and outputting the cells to and from the broadband inter-node transmission line, and a switch for separating the cells being input through the broadband input and output port and for multiplexing the cells so as to output the cells, wherein data composed of the plurality of cells is transmitted and received through the broadband switch nodes by constant bit rate transmission, variable bit rate transmission, or a combination of the constant bit rate transmission and the variable bit rate transmission.

An optical frequency sweep signal generator using an optical frequency variable bandpass filter which can be practically used is provided. The optical frequency sweep signal generator comprises: a circulation control circuit for generating a first electric signal which indicates the start and the end of a sweep; an optical loop circuit; an optical frequency variable bandpass filter, provided in the loop circuit, for suppressing circulation of natural emission light output from an optical amplifier; a light receiving element for converting a part of light output from the optical loop circuit into a second electric signal; a sweep signal analyzing circuit for outputting a set value for compensating for a difference between the center frequency of the optical frequency variable bandpass filter and the optical frequency of the pulsed light based on the first and second electric signals; and a driving circuit for supplying a driving signal for determining the center frequency of the optical frequency variable bandpass filter to the optical frequency variable bandpass filter, based on the first electric signal and the set value.

Optical frequency sweep signal generator

An optical pulse signal produced by modulating a continuous laser light by means of a first pulse having a period sufficiently shorter than the atomic lifetime in the upper energy state of a rare earth doped fiber is input to an optical amplifier to be measured, while an output signal from the optical amplifier is modulated by a second pulse synchronized with the first pulse and having a phase difference relative to the first pulse which can be optionally set so that rapid phase adjustment relative to the first pulse is possible based on the phase at the time of minimum optical power. The noise figure of the optical amplifier is then measured based on, the maximum photoelectric power (P.sub.AMP +P.sub.ASE) and the minimum photoelectric power P.sub.ASE of the resultant optical signal.

Method and apparatus for measuring the noise figure of an optical

A method and device for automatically and accurately measuring a noise figure of an optical amplifier are disclosed. In the method, light pulses which have different wavelengths .lambda..sub.1 .about..lambda..sub.n and have a period shorter than a time constant of extinction of the optical amplifier are generated. The light pulses thus generate are supplied to the optical amplifier. Powers P.sub.AMP1 .about.P.sub.AMPn of amplified lights outputted from the optical amplifier which correspond to the light pulses and have the wavelength .lambda..sub.1 .about..lambda..sub.n and powers P.sub.ASE1 .about.P.sub.ASEn of lights which have the wavelength .lambda..sub.1 .about..lambda..sub.n and are outputted from the optical amplifier when the amplified lights are not outputted from the optical amplifier are measured. Noise figures NF.sub.1 .about.NF.sub.n at the wavelengths .lambda..sub.1 .about..lambda..sub.n the optical amplifier are calculated according to the following equation.

Method and device for measuring a noise figure in optical amplifiers

The invention offers an optical fiber amplifier with good frequency characteristics which allows the gain to be held constant even without an input signal beam and allows gain control with respect to input optical signals with high-speed power fluctuations. An excitation beam source 8 supplies an excitation beam for light amplification and a control beam source 15 supplies a control beam for controlling the gain to an EDF 4 which amplifies a signal beam by means of optical excitation. An excitation beam monitor 9 measures the power of the excitation beam when inputted to the EDF 4 and an excitation beam monitor 12 measures the power of the excitation beam when outputted from the EDF 4. A comparator 11 calculates the ratio between the power measured by the excitation beam monitor 9 and the power measured by the excitation beam monitor 12. A drive circuit 14 controls the power of the control beam supplied by the control beam source 15 based on the results obtained by the comparator 11.

Optical fiber amplifier

An optical polarization controller comprises a polarization control element, a polarizer, a light divider and a photo-detector. The polarization control element rotates a plane of polarization of an Input signal light by a rotation angle in a predetermined rotational direction and outputs the result as a rotated signal light. The polarizer extracts a component of the rotated signal light having a predetermined plane of polarization and outputs the component as a polarized signal light. The light divider divides the polarized signal light into a plurality of polarized signal lights which have the same planes of polarization as the plane of the polarized light outputted by the polarizer. The photo-detector detects a level of one of the plurality of polarized signal lights and supplies a control signal indicating the level to the polarization control element. Under this control, the plane of polarization of the signal light outputted by the polarization control element is controlled so as to correspond to the plane of polarization of the light divider.

Optical polarization controller

A noise determination apparatus for simple and precise determination of a noise factor of an optical fiber amplifier is presented. An optical pulse Pin is inputted via an optical coupler 2 into an optical looping circuit 14, and for every loop around the circuit 14, the spontaneous emission light generated in a rare-earth doped optic fiber amplifier 4 is integrated. The amplitude of the light intensity of the optical pulse train outputted from the optical splitter 3 decreases as the looping cycles are increased, and ultimately, the light intensity of the accumulated spontaneous emission light becomes equal to that of the optical pulse train. The pulse train outputted from the photodetector 7 diminishes. The number of pulses in the looping process from the initial pulse train to the expiration event are counted by means of a pulse counting device 8. Based on the count, the noise factor NF of the optical amplifier 4 is calculated using the gain of the optical amplifier 4, the bandwidth of the bandpass filter 5, oscillation frequency of light and the pulse intensity.

Apparatus for determining noise factor of optical amplifier

A simple, quick and precise method for determining a noise factor of an optical amplifier system is presented and demonstrated with an apparatus based on rare-earth doped optical fibers. The method is based on rapid adjustments of the phase differentials between the input optical signals into and the output optical signals from the optical amplifier to compensate for system variables including the optical fiber lengths within the apparatus as well as in the ancillary devices. A cw laser source is modulated with a first pulse having a significantly shorter cycle than a lifetime of excited atoms within the doped fiber, and the modulated pulses are continually applied to the noise determining apparatus. The optical output signal from the apparatus is synchronized with the first pulse and the optical output signal is further modulated with a series of second pulses having increasing phase differentials in relation to the first pulse. The electrical output power from the noise determining apparatus undergoes a maximum and a minimum values, and the noise factor of the apparatus is calculated by using the values of the respective maximum and the minimum electrical output power.

Method and apparatus for determining noise factor of optical amplifier

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Yokohama, Japan

Kazuo Aida