Nec Corporation

Nippon Electric Co., Ltd.

Kunio Nagashima

Michikazu Kondo

Hirokazu Goto

In an optical memory device comprising a bistable semiconductor laser having two coplanar electrodes (26, 27) injection current sources (31, 32) for the respective electrodes are individually adjusted to make the laser selectively latch first and second optical input signals (P1, P2). It is possible to provide an optical master-slave flip-flop device by optically directly coupling two optical memory devices of the type described to each other in tandem. Furthermore, an optical signal shifting device can be provided by arranging, optically in tandem, a plurality of optical master-slave flip-flop devices of the type described.

Optical memory device comprising a semiconductor laser having

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

A subscriber line circuit comprises a controllable DC to DC converter (41) for producing a converter output signal which becomes a loop signal comprising a DC signal and/or a communication signal of a communication frequency band. First and second voltage signals are dependent (51, 69) on the current and the voltage of the loop signal, respectively. One of the voltage signals is amplified (71) with different transfer functions at DC and in the communication frequency band. The converter is controlled (85-86) by an error between a first sum (81) of the amplified signal and the other voltage signal and a second sum (82) of a reference voltage (E.sub.O) and a signal supplied from an output (27) of an exchange. A subtractor (92) supplies a difference between the exchange output signal and the second voltage signal to an input (25) of the exchange. Preferably, terminals (16, 17) for connection to a subscriber substation are isolated at DC from terminals (18, 19) for connection to the exchange input and output.

Subscriber line circuit comprising a controllable DC/DC converter as a

A switching network with crosstalk elimination capability comprises a group of incoming lines connected to subscribers, a group of outgoing lines intersecting the incoming line group, and a plurality of switching elements provided at preselected crosspoints formed between the incoming lines and the outgoing lines. Crosstalk elimination is provided by means for grounding idle and unused incoming lines and/or idle and unused outgoing lines through impedance elements having a sufficiently low impedance value at a desired frequency band of signals to be exchanged.

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Tokyo, Japan

Kunio Nagashima