Nippon Telegraph and Telephone Corporation

Ntt Electronics Corporation

Mikio Yoneyama

Kazushige Yonenaga

Tomoyoshi Kataoka

Hiroto Kawakami

Shoichiro Kuwahara

Yutaka Miyamoto

Koichi Murata

Masahito Tomizawa

Akira Hirano

Akihide Sano

Gentaro Funatsu

Shigeru Ono

Naoki Fujiwara

Hiroshi Yamazaki

Masahiro Suzuki

Hiroshi Koizumi

Hideyuki Nosaka

Katsuya Tanaka

Hiroyuki Uzawa

Munehiko Nagatani

Eiji Yoshida

Hiroyuki Fukuyama

Takashi Saida

Yosuke Takeuchi

Shin Kamei

Kengo Horikoshi

Jun Endo

Nobuhiro Kikuchi

Hiroaki Katsurai

Toshihiro Itoh

Shigeki Aisawa

Masafumi Nogawa

Masahiro Tachibana

Akihiko Matsuura

Kouichi Ogihara

Fumiaki Saitou

Yves Bouvier

Yuya Oyama

An optical modulator driver circuit () includes an amplifier (, Q, Q, R-R), and a current amount adjustment circuit () capable of adjusting a current amount of the amplifier () in accordance with a desired operation mode. The current amount adjustment circuit () includes at least two current sources (IS) that are individually ON/OFF-controllable in accordance with a binary control signal representing the desired operation mode.

Optical modulator driver circuit and optical transmitter

A light modulation device detects a power of the modulated optical signal modulated by each of an I-component optical modulator and a Q-component optical modulator, synchronously-detects a component of a frequency fd from the power of the modulated optical signal, outputs a dither signal of a frequency fd/n (where n is a positive integer equal to or larger than 1) applied to a first bias voltage or a second bias voltage when adjusting the first bias voltage or the second bias voltage, outputs two dither signals having a frequency fd/m (where m is a positive integer equal to or larger than 1, where n&#x3c;m), which are mutually orthogonal to each other, applied to the first and second bias voltages when adjusting a third bias voltage, and adjusting bias voltages by increasing or decreasing bias voltages based on a synchronous detection result.

Light modulation device and light modulation method

A phase modulation apparatus has a light source outputting continuous light, two phase modulators, and an intensity modulator. The phase modulation apparatus is provided with an RZ phase modulation circuit, in which the phase modulators phase-modulate the continuous light from the light source with data signals input to the phase modulators and generate two phase modulation optical signals, a phase shifter shifts the phase of one phase modulation optical signal by &#x3c0;/2, and an intensity modulator intensity-modulates a multiplexed signal, combined with the other phase modulation optical signal, with an input clock signal CLK to convert the signal into an RZ signal, and, thus, to output the RZ signal, and a phase control circuit which adjusts the phases of the phase modulation optical signals generated by the phase modulator of the RZ phase modulation circuit so that the output of the RZ phase modulation circuit is maximum.

Phase modulation apparatus

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

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

Growing community of inventors

Tokyo, Japan

Mikio Yoneyama