International Telephone and Telegraph Corporation

International Standard Electric Corporation

Philip R Couch

Stephen Wright

David L Baldwin

James H Bowen

David A Philpott

A coherent optical receiver for an input optical signal including a local oscillator source of coherent optical signal a single beam splitter/combiner to which both the input and local oscillator signals are applied to produce two substantially identical combined optical signals, a pair of substantially identical photodetectors electrically connected in series, each photodetector receiving one of the combined optical signals, and an output amplifier the input of which is connected to the series connection between the photodetectors.

Coherent optical receiver

A fiber optic direct current coupled data transmission link having a response extending to dc by using a dc coupled receiver and a modified frequency response to avoid data width distortion which allows the dc coupled receiver to work over a wide range of input signal levels.

Direct current coupled data transmission

The data eye monitor includes a pair of comparators which compare the data input signal with a fixed reference voltage and a variable reference voltage with the resultant output of these two comparators being clocked into a digital comparator providing negative pulses representing the difference between the outputs of the two comparators. The negative pulses are coupled to an integrator to which a positive current source is coupled with the integrator providing the variable reference voltage for one of the comparators and also the output voltage of the monitor since the variable reference voltage is proportional to the opening of the data eye.

Data eye monitor

A fiber optic data transmission system is protected against external physical intrusion by obscuring the data in the natural quantum noise and then limiting access to the intruder by means of an optical power alarm. This is accomplished by modulating the data on a very large predetermined average optical power with a very small modulation index and then providing an alarm arrangement which is responsive to the received optical energy to activate an alarm means and to deactivate its associated transmitting arrangement when the received optical energy has an amplitude outside of a given amplitude region.

Secure fiber optic data transmission system

An improved high speed optical receiver provides an output that accurately corresponds to the optical input signal without the distorted signals caused by ac or dc coupled receivers when exposed to signals having varying amplitudes. Delaying and dividing circuits permit the creation of threshold signals which eliminate the drawbacks previously encountered.

Optical data bus receiver with signal waveform restoring means

The position of a pulse, relative to a reference time, defines a digital data state. The position alternates about the reference time such that by monitoring the mean pulse position the reference time may be regenerated in the receiver. The reference time is then used to decode the transmitted signal.

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Roanoke, VA, United States of America

Philip R Couch