Nippon Telegraph and Telephone Corporation

Ntt Electronics Corporation

Akihiko Matsuura

Yutaka Miyamoto

Kazushige Yonenaga

Akira Hirano

Tomoyoshi Kataoka

Katsuya Tanaka

Masahiro Suzuki

Hiroto Kawakami

Mikio Yoneyama

Masahiro Tachibana

Kenji Sato

Hiromu Toba

Yuya Oyama

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

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

The optical transmission circuit of the present invention has an optical modulatorwhich modulates continuous light at wavelength &#x3bb;o with a signal at repetition frequency fo Hz and outputs alternating phase-inverted pulse light; a bias voltage applying unitwhich applies a bias voltage to the optical modulator; an optical power spectrum measuring unithaving frequency resolution of less than fo Hz which measures the optical power spectrum of light output from the optical modulator; and a control circuit which controls the bias voltage via the bias voltage applying unitbased on measurements of the power spectrum of the output light of the optical modulator, so as to minimize the power intensity of the carrier spectrum component of wavelength &#x3bb;o, or to maximize the power intensity of the spectrum component in both side bands.

Optical transmission circuit

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

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Yokosuka, Japan

Akihiko Matsuura