British Telecommunications Public Limited Company

British Telecommunications Corporation

Keith J Blow

Nicholas J Doran

Alistair James Poustie

Robert John Manning

Brian P Nelson

David Charles Wood

David Cotter

Kevin Smith

Paul David Townsend

Bimal K Nayar

The present invention relates to an apparatus for determining the sum of first and second optical binary words. The apparatus uses a first optical logic gate and a second optical logic gate to generate respective first and second combination words which represent a logical combination of the binary words applied to the respective logic gates. The first and second combination words are then offset by one bit slot with respect to each other by an offsetting device to generate first and second offset combination words. These offset combination words are repeatedly fed back to the first and second logic gates. The binary sum of the original two words is given by the first combination word when each bit slot of the second combination words has the same logical state.

Binary adder

The present invention relates to a method and apparatus for generating an optical bit slot window in which N bit slots having the same logical state are generated. A switching device is used which is coupled to an optical pulse source which generates optical pulses in successive bit slots, each optical pulse representing a logical state. Switching signals are then applied to a switching input of the switching device so as to selectively switch a connection between the input and an output. Consequently the logical state of the output is controlled to generate the required N bit slot window.

Method of obtaining an optical signal stream

A parity determining circuit is used to determine the parity of a binary word. The binary word is represented by a sequence of optical bit slots. Each bit slot defines a respective one of two complementary logical states. The circuit includes: an input pulse stream generator that generates copies of the binary word; a combining device that receives two binary words, offsets one word with respect to the other, and then combines them to form a combination word; and a circuit that applies a copy of the original binary word together with the combination word to the combining device a number of times in succession. This results in a combination word that has a number of bits in the same logical state and that indicates the parity of the binary word.

Parity determining apparatus and method

A regenerative optical memory comprising a number of concatenated non-linear switching elements coupled by an optical storage element has a transfer function arranged so that only optical data having a pulse amplitude above a predetermined threshold is stored and the amplitude of optical data stored is substantially equalised to at least one predetermined level after a number of circulations within the optical memory. In a preferred embodiment, the optical memory is provided with an optical switching element within the optical loop for selectively switching at least a portion of the data pattern out of the optical loop in response to the application of an optical signal to an input of the optical switching element to alter the contents of the memory.

Optical memory

System and method for key distribution using quantum cryptography

System and method for quantum cryptography

Optical system

An optical switch includes a dual-core optical fibre coupler having waveguides which are erbium doped, silica-based fibre amplifiers. The waveguides are pumped by pump lasers which are used to control the mean differential gain of the waveguides to be zero or a first value at which two values the linear coupler is a cross-coupler or a through-coupler at an operating wavelength.

Optical switch

Optically controlled optical switch

Quantum non-demolition optical tapping

Optical domain digital pulse switching

Square optical pulse generator

An optical fibre, loop interferometer (31) is formed from germania doped silica which exhibits Raman scattering at a threshold intensity to provide a transmitted optical signal from port (49) of coupler (35) whose intensity is a sigmoid function of the intensity of an optical signal input at port (39). It finds application in optical switching and logic operations on optical pulses.

Non-linear inferferometer

Optical nonlinear cross-coupled interferometer and method utilizing same

Optical device

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Woodbridge, United Kingdom

Keith J Blow