International Telephone and Telegraph Corporation

David L Baldwin

Philip R Couch

Gary W Bickel

James H Bowen

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

A multiport optical cable or bus, composed of bundles of parallel fibers interconnected by an optical star structure, has a higher packing fraction and greater efficiency in the mixing and redistribution functions because the star's radiating arms have their individual cladding layers omitted or removed and because they are fused together to form the mixer section or a part of it. Where the numbers of input and output ports and arms are unequal, the unclad arms have their fused portions optically spliced or connected to form a composite mixer section. Several sections may be cascaded, using the same structural principles, to provide additional lower-level optical outputs for control or other purposes. The cladding function for the star structure is provided by separately encasing the radiating arms and mixer section or sections in a light-reflecting material. Preferably, this is a plastic potting compound having an optical index of refraction lower than those of the star arms or mixer portions. Alternatively, a metallic reflective coating may be applied. The invention has particular utility as applied to optical buses comprised of fibers of the plastic clad silica type.

Multiport optical communication system and optical star structure

There is disclosed an optical transmission system which employs a plurality of receiver-transmitter pairs. One of the plurality of pairs is selected to propagate optical signals under control of switching means. The optical signal as propagated is monitored and if a fault is detected in the signal, another redundant receiver-transmitter pair is automatically switched in. This pair is also monitored to determine whether or not the optical signal is valid and if not, the sequence continues until a valid signal is being propagated.

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Roanoke, VA, United States of America

David L Baldwin