Nippon Electric Co., Ltd.

Nec Corporation

Michikazu Kondo

Yoshinori Ohta

Mitsuhito Sakaguchi

Kunio Nagashima

An optical switch with switched optical directional couplers, switched by the application of either 0 volt or a voltage V.sub.1, different from 0 volt. Coupling of almost 100% is achieved when the V.sub.1 voltage is applied to a selected directional coupler, while coupling of 0% to 20% occurs when 0 volt is applied to the selected directional coupler. The optical directional coupler is formed by locating adjacent optical waveguides in close proximity and applying electric field producing electrodes to the waveguides where they are in close proximity such that the substrate below opposing waveguide sections receive electric fields of opposite directions.

Optical switch of switched directional coupler type

In an optical time-division switching system, time-division multiplexed calling and called station signals are arranged in incoming time slots and applied through an incoming common optical medium to a first optical switching circuit that switches the signals to optical bistable devices in which the signals are stored as binary 1's or 0's. A second optical switching circuit is coupled to the bistable devices for reading the stored calling station signal in the time slot of the called station and reading the stored called station signal in the time slot of the calling station to rearrange the signals in outgoing time slots. The signals in the outgoing time slots are applied through an outgoing common optical medium to a time-division demultiplexer which sequentially distributes the signals to the calling and called stations.

Optical time-division switching system employing optical bistable devices

In a light modulator wherein a modulator medium, such as an a-cut lithium tantalate plate, has a Pockels coefficient for converting one of orthogonally polarized components of a light beam to the other thereof in cooperation with an electric field produced in the medium in a direction predetermined relative to the thickness of the medium while the light beam is transmitted between a pair of end surfaces of the medium and wherein a voltage is supplied between that interdigital electrode pair to produce the electric field, digit electrodes of which are distributed along one of a pair of principal surfaces of the medium at a predetermined pitch between the end surfaces, weights are attached to at least those of the digit electrodes which are distributed adjacent to each end surface. Each weight-attached digit electrode contributes to conversion of the polarization to an extent determined by the weight attached thereto. The weights are gradually varied or reduced as the digit electrodes are distributed nearer to each end surface. It is possible to vary the weights by varying those parts of the electric field which are produced in the medium adjacent to the respective digit electrodes, as by varying the voltage supplied between each successive digit electrode pair or by varying the thickness. Alternatively, the weights are varied by varying the ratio of the width of each digit electrode to the gap by which that digit electrode is spaced from a next following digit electrode.

Electrooptic light modulator including weighted interdigital electrodes

First, second and third double refractive elements are aligned along a Y axis. A polarization converter is disposed between the first and second elements for polarizing two light component, produced by the first element and a reflection mirror is disposed between the second and third element for deflecting a first output light of the second element. The second birefringence element operates to separate two light components converted by the polarization converter into converted light and not converted light and to synthesize one of the separated light component to produce a first output light and to convert remaining light component into second and third output light. The third birefringence element operates to synthesize the second and third lights supplied from the second element to form a single output light thereby controlling quantity of light produced by the third element by the polarization converter.

Light quantity control apparatus

In a light wavelength separating modulator there is provided a crystal manifesting an electro-optical effect which rotates the principal axes of the refractive index ellipsoid of the crystal, a plurality of juxtaposed electrodes formed on the crystal in the direction of transmission of light and having different periods, and means for applying modulation signals to respective electrodes. When light generated by a light source, having a light spectrum where half value bandwidth exceeds 100A, is transmitted through the modulator, a light wavelength multiplex signal transmitting apparatus is obtained; whereas when a birefringence body is located on the output side of the modulator, a light wavelength separating switch is obtained.

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Tokyo, Japan

Michikazu Kondo