Abstract: An optical pulse regeneration unit comprising means for broadening the temporal width and flattening the center portion of an optical pulse and slicing means for slicing the pulse at a point in time so that in use, the pulse immediately after the slicing means contains only the portions of the pulse which at the slicing means were within a specific temporal width/interval about the point in time.

Abstract: In the present invention an optical pulse regenerating transmission line element includes a section of disbursement managed optical fibre transmission line in optical communication with an unbalanced optical interferometer. The transmission line element may be particularly suitable for use with RZ optical pulses, and in particular optical solitons. The dispersion managed optical fibre transmission line includes a first section of optical fibre having a negative dispersion coefficient, connected to a second section of optical fibre having a positive dispersion coefficient. This first section of fibre may be dispersion compensating fibre and the second section of fibre may be standard monomode fibre. It is preferred that the first and second sections of optical fibre are arranged to form a section of dispersion managed optical fibre transmission line having a symmetric dispersion map.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: A method of communication based on quantum cryptography is modified to include an initial step of outputting from, e.g., a transmitter, a single-photon signal, which may be unmodulated. A receiver then randomly selects one of a plurality of encryption alphabets corresponding to different, non-commuting quantum mechanical operators. The receiver modulates the single-photon signal with the selected operator and returns the signal to the transmitter. The transmitter in turn randomly selects a quantum mechanical operator and uses that operator in detecting the returned signal modulated by the receiver. Alternatively, the transmitter may randomly select one of a plurality of encryption alphabets and use that encryption alphabet in modulating the signal. The signal is then further modulated at the receiver using a predetermined encryption alphabet. When the signal is received back at the transmitter, it is detected using the same quantum mechanical operator as was initially used to modulate it.

Abstract: In a method of communication using quantum cryptography an encryption alphabet is used for coding signals for transmission on a quantum channel. The encryption alphabet comprises pairs of operators applied successively to single-photon signals transmitted onto the quantum channel with a predetermined delay between them. When the signals are detected the different signals of each pair are split according to their encoded state and directed to different detectors via paths giving a differential delay. The delay is substantially complementary to the original pre-determined delay. Coincidence detection is employed at the detectors to eliminate spurious detection counts.