Nec Corporation

Japan Science and Technology Agency

Yoshihiro Nanbu

Akihiro Tanaka

Akio Tajima

Kazuo Nakamura

Takeshi Takeuchi

Seigo Takahashi

Wakako Maeda

Akihisa Tomita

Kenichi Nishi

Shuuji Suzuki

A communication system capable of employing polarization-dependent phase modulators with a reversing configuration that preserves security against disturbance of a polarization state at a transmission path but without using Faraday mirrors and a communication method using the same are provided. A quantum cryptography system of the present invention includes a first stationa transmission pathand a second station. The first stationhas means for emitting time-divided optical pulses into the transmission pathand measuring a phase difference between the optical pulses returning from the transmission path. The transmission pathis a medium of light. The second stationhas means for reversing traveling directions of the optical pulses, means for producing a phase difference, corresponding to a random number bit value to be transmitted, between the time-divided optical pulses, means for splitting the entering optical pulse into orthogonally polarized components and producing a 180-degree phase difference therebetween, means for rotating each polarization direction by 90 degrees, means for eliminating a component resulting from a deviation from the polarization rotation angle of 90 degrees, and means for attenuating optical pulse intensity to include no more than 1 photon per bit.

Communication system and communication method using the same

The object of the present invention is to provide a variable wavelength semiconductor laser which is large in ontinuous variable wavelength width, simple and convenient in structure, easy to produce, monolithic and small in size, and easy to handle. The variable wavelength semiconductor laser includes an optical gain region formed from two-dimensional or three-dimensional carrier confinement structures having sizes approximately of a thermal de Broglie wavelength whose size dispersion is controlled so that a gain spectrum covers a required variable wavelength region for generating and amplifying light when current is injected, a light absorption control region having a light absorption coefficient which varies depending upon a current injection amount, an optical resonator including the optical gain region and the light absorption control region, and control means for controlling current amounts or voltage values to be injected to the optical gain region and the light absorption control region.

Variable wavelength semiconductor laser

Growing community of inventors

Tokyo, Japan

Yoshihiro Nanbu