Nippon Telegraph and Telephone Corporation

Ntt Electronics Corporation

Kazushige Yonenaga

Yutaka Miyamoto

Akira Hirano

Masahito Tomizawa

Hidehiko Takara

Tomoyoshi Kataoka

Mikio Yoneyama

Masahiko Jinno

Shoichiro Kuwahara

Akihiko Matsuura

Koichi Ishihara

Yoshiaki Kisaka

Etsushi Yamazaki

Seiji Okamoto

Takayuki Kobayashi

Takashi Goh

Mitsuteru Yoshida

Akihide Sano

Gentaro Funatsu

Kohki Shibahara

Kenji Sato

Naoki Fujiwara

Masanori Nakamura

Koichi Murata

Hiroyuki Uzawa

Eiji Yoshida

Yosuke Takeuchi

Kengo Horikoshi

Hiroto Kawakami

Yoshiaki Sone

Shigeru Kuwano

Yukio Tsukishima

Masaki Asobe

Toshihide Yoshimatsu

Shigeru Ono

Seiji Norimatsu

Hiromu Toba

Nori Shibata

Kozicki Bartlomiej

Shoichirou Kuwahara

Fumiaki Saitou

An optical signal transmission apparatus includes a modulation unit which modulates a transmission signal, a training signal sequence generation unit which generates a plurality of signal sequences having power concentrated in a plurality of different frequency bands, at least one of an amplitude and a phase of the plurality of signal sequences being modulated, as a training signal sequence, a signal multiplexing unit which appends the training signal sequence to the transmission signal, and an electro-optical conversion unit which converts a signal sequence obtained by appending the training signal sequence to the transmission signal into an optical signal and transmits the optical signal.

Optical signal transmission apparatus and optical signal transmission method

An increase in circuit scale is suppressed and a phase variation caused in a transmission path or the like is compensated for. An optical transmission system includes: a pilot symbol detection unit which detects a plurality of pilot symbols intermittently inserted into a received complex electric field signal that is obtained through coherent detection for a received optical signal; an error signal computation unit which calculates a complex electric field error signal indicating a phase variation at each pilot symbol based on the pilot symbols detected by the pilot symbol detection unit and a predetermined reference symbol; a compensation electric field signal generation unit which estimates a phase variation between the pilot symbols in the received complex electric field signal using filter processing based on the complex electric field error signal calculated by the error signal computation unit; and a phase noise compensation unit which performs phase compensation for the received complex electric field signal based on the phase variation between the pilot symbols estimated by the compensation electric field signal generation unit.

Optical transmission system, phase compensation method, and optical reception apparatus

There is provided a multi-flow optical transceiver that includes (a) a plurality of wavelength-tunable light sources, (b) a plurality of optical modulation units which modulates light with an input signal, (c) an optical multiplexing/demultiplexing switch which couples light from at least one of the wavelength-tunable light sources to at least one of the optical modulation units with any power, (d) an optical coupling unit which couples a plurality of lights, modulated by a plurality of the optical modulation units, to at least one waveguide, (e) at least one multiple carrier generating unit which generates multiple carries, arranged at equal frequency intervals, from light of the wavelength-tunable light source, and (f) a wavelength separation unit which branches the multiple carriers from the multiple carrier generating unit for each wavelength.

Multi-flow optical transceiver, multi-flow optical transponder and multi-flow optical node

An optical communication apparatus, in the sending side, distributes client signals according to destinations and a communication capacity of each destination, electrical-to-optical converts the distributed signals to optical signals having different center frequencies, and multiplexes the optical signals to output, and in the receiving side, the optical communication apparatus divides the wavelength division multiplexed signal to each wavelength (for each sending source), optical-to-electrical converts the divided optical signals to electrical signals, and multiplexes the electrical signals to output. An add/drop port of an optical route switching apparatus includes an input/output port to the optical communication apparatus, and an optical frequency bandwidth is variable according to an optical spectrum width of the optical signal. A network is constructed by using the optical communication apparatus and the optical route switching apparatus.

Optical communication apparatus, optical route switching apparatus and network

A multi-flow optical transceiver provided with a plurality of wavelength-tunable light sources, a plurality of optical modulation units which modulates light with an input signal, an optical multiplexing/demultiplexing switch which couples light from at least one of the wavelength-tunable light sources to at least one of the optical modulation units with any power, and an optical coupling unit which couples a plurality of lights, modulated by a plurality of the optical modulation units, to at least one waveguide.

A bandwidth variable communication apparatus includes: a route exchange unit including a route exchange function for switching an output port of a stream signal of one or more wavelengths input from an input port based on both or a part of wavelength and time, and including a bandwidth change function for changing passable frequency bandwidth in a section from the input port to the output port through which the stream signal passes; and a control unit including a control information transmit-receive function for transmitting and receiving control information for both or a part of the route exchange function and the bandwidth change function of the route exchange unit, and including a control function for controlling the route exchange unit based on the control information. All or a part of the input ports and the output ports are connected to other communication apparatuses via transmission routes.

Bandwidth variable communication apparatus and bandwidth variable communication method

An optical transmission system is provided in which the optimum operating point of a Mach-Zehnder interferometer, matched to the optical frequency of the light source on the transmitting side, can be set. The optical receiver () has an infinitesimal-modulated signal component detection circuit (), which uses the signal train output from a balanced detection circuit () to detect the infinitesimal-modulated signal component applied to the phase adjustment terminal () of an MZI () by an infinitesimal-modulated signal oscillation circuit (); a synchronous detection circuit (), which synchronously detects the infinitesimal-modulated signals output from the infinitesimal-modulated signal component detection circuit () and infinitesimal-modulated signal oscillation circuit () and detects the error signal component arising from the shift between the optical signal carrier frequency and the optical frequency characteristic of the MZI (); and a controller (), which outputs a control signal to adjust the phase difference between two split optical signals output from the MZI () so as to correct the shift amount.

Optical transmission system, optical transmitter for optical transmission system, and optical receiver for optical transmission system

The present invention relates to an optical receiver, in which the transmittance of a Mach-Zehnder interferometer can be locked at a normal operation point in a simple structure and control. A transmittance detecting circuit and a minute modulation signal detecting circuit are provided in parallel after a balanced optical receiver, and a switch is selectively connectable either a minute modulation signal detecting circuit and a transmittance detecting circuit. In the initial stage of frequency pull-in, the switch is set to connect the transmittance detecting circuit to the synchronous detection circuit. If the transmittance detecting circuit detects that the transmittance of the Mach-Zehnder interferometer at the carrier frequency becomes a desired transmittance, the connection of the switch is switched from the transmittance detecting circuit to the minute modulation signal detecting circuit.

Optical receiver using Mach-Zehnder interferometer

An optical transmission system which provides bandwidth restricted optical signal comprises an input terminal () for accepting an electrical binary signal, an amplifier () for amplifying said electrical binary signal to the level requested for operating an electrical-optical converter () such as a Mach Zehnder light modulator, a bandwidth restriction means () which is for instance a low pass filter for restricting bandwidth of said electrical binary signal, and an electrical-optical conversion means () such as a Mach Zehnder light modulator for converting electrical signal to optical signal. Because of the location of the low pass filter () between an output of the amplifier () and the Mach Zehnder light modulator (), the amplifier () may operate in saturation region to provide high level output signal enough for operating the Mach Zehnder light modulator, and a signal shaped by the low pass filter () is applied to the Mach Zehnder light modulator () with excellent waveform. The invention is useful for long distance, large capacity and low cost optical transmission system.

Optical transmission system

A precoding-multiplexing circuit is formed by a precoding circuit for carrying out a precoding with respect to n sets of parallel input binary data signals having a bit rate equal to R/n, to obtain n sets of parallel precoded signals, and a time division multiplexer for time division multiplexing the parallel precoded signals obtained by the precoding circuit, in units of one bit, and outputting time division multiplexed output signal having a bit rate equal to R. In this configuration, the encoding is realized by processing electric signals before the time division multiplexing, so that it becomes possible for the preceding circuit to handle signals which are slower than the transmission rate, and therefore it becomes easier to realize the higher transmission rate.

Precoding circuit and precoding-mulitplexing circuit for realizing very high transmission rate in optical fiber communication

A system which improves wavelength tolerance, compensates dispersion in a simple way, reduces limitation of the fiber input power is disclosed. The operation includes receiving a clock signal from a system clock source; modulating a single mode optical signal based on the clock signal and generating an optical pulse signal having two longitudinal modes, the frequency interval thereof being n&#xd7;B, n being a natural number and B being a transmission speed; generating a partial response signal by converting a binary NRZ signal from a digital signal source in synchronism with the system clock source; and modulating the optical pulse signal based on the partial response signal, and outputting a binary RZ modulated signal. The binary RZ modulated signal is input into a receiver, where two partial response components in the optical spectra of the input signal are divided, and one or both of the components are received.

Optical transmission method, optical transmitter, optical receiver, and optical transmission system

An optical transmitter for realizing a high tolerance with respect to the group velocity dispersion of the optical fibers, a small receiver sensitivity degradation, and an improved stability that is hardly affected by the group velocity dispersion even in the case of network scale expansion, is constructed by a light source section for generating optical clock pulses synchronized with a signal bit rate while maintaining a duty ratio of the optical clock pulses constant, which is capable of variably setting the duty ratio, and an encoding section for encoding the optical clock pulses by using electric signals synchronized with the optical clock pulses while setting a relative optical phase difference between the optical clock pulses in adjacent time-slots to be an odd integer multiple of &pgr;.

Optical transmitter and optical transmitter control method using variable duty ratio setting and alternate phase inversion for optical clock pulses

The present invention relates to an optical transmission system which reduces optical signal bandwidth with return-to-zero (RZ) signal.

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Yokosuka, Japan

Kazushige Yonenaga