Abstract: The invention relates to the control of soliton-soliton interaction through the application of a positive phase shift. For each soliton width there is a critical phase modulation level above which soliton-soliton interaction can be virtually eliminated. This enables the spacing between adjacent solitons to be reduced, increasing the system bandwidth even for long transmission distances. The invention finds application in submarine and other long haul systems.

Abstract: 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.

Abstract: An optical switch comprises an optical fibre Sagnac loop interferometer having an input port and an output port. A source of optical signals at 1.53 .mu.m is coupled to the input port and a source of control optical signals of wavelengths 1.30 .mu.m and 1.31 .mu.m are coupled to the interferometer by a dichroic coupler. The coupler splits the 1.53 .mu.m input optical signal into two signal portions which counterpropagate round the loop and couples the control signal to propagate in one direction only round the loop. The phase difference between the signal portions at the output port is dependent on the intensity of the control optical signal when they recombine at the coupler. The optical control signals are formed by combining at least two optical pulse streams, the pulses of distinct optical pulse streams being non-interferometric, to provide a logical AND gate.

Abstract: A single silica optical fiber (4) is formed in a Sagnac interferometer (2) by forming a fused, dichroic optical fiber coupler (8) having four ports (10, 12, 14 and 16). A 1.3 .mu.m optical data signal is coupled to the port (10) via a dichroic optical fiber coupler (18) which combines it with a 1.53 .mu.m c-w probe signal from laser (16). The coupler (8) splits the 1.53 .mu.m probe signal into two equal intensity, counter-propagating portions and couples the 1.3 .mu.m data signal so it propagates in one direction round the loop (6). The loop (6) exhibits a non-linearity such that the data signal provides a relative phase shift of the counter-propagating c-w probe portions causing a portion of the 1.53 .mu.m signal is switched to port (12). This 1.53 .mu.m switched output provides tapping of the data signal without affecting its intensity.

Abstract: An optical apparatus including a first optical coupling having a first and a second pair of optical communication ports in which substantially equal portions of an optical signal received at a port of one pair of ports are coupled to each port of the other pair of ports; an optical waveguide optically coupling the second pair of ports such that an optical signal leaving either one of the second pair of ports in a first polarization state; a second optical coupling for coupling an optical signal at a second wavelength to the optical waveguide so as to propagate along at least a portion of it in one direction only; and first and second polarizing beam splitters optically coupled to a respective one of the first pair of ports.

Abstract: An all-optical fibre Sagnac antiresonant interferometer (2) is formed from an optical fibre having a non-linear refractive index. The coupler (8) is a dichroic coupler coupling equal portions of a cw optical signal at 1.53 .mu.m from laser (16) to ports (14 and 16) and all of a pulsed optical signal from laser (20 ) to port (14). The intensity of the pulsed optical signal is sufficient to provide a relative phase shift in the counter propagating 1.53 .mu.m signals. The loop (6) is longer than the inverse of the absolute difference in group delays of the cw and pulsed optical so causing a square optical pulse at 1.53 .mu.m to be switched to port (12) of the coupler.

Abstract: 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.

Abstract: An optical device includes a 50-50 cross-coupler having a pair of ports optically coupled by a waveguide which includes a portion of material having a non-linear refractive index with a relaxation time such that the effect on the non-linear portion of a first pulse passing through the portion last long enough to affect the phase of a second pulse relative to the first. It finds application as a logic element, optical amplifier modulator and the like.

Abstract: An optical device for use as an optical switch, optical amplifier or optical logic circuit comprises an optical waveguide such as a W profile optical fiber formed from an assembly of optically conductive media having different refractive indices, at least one of which is non-linear, whereby an optical signal with a single mode is guided or not guided along the waveguide in accordance with the intensity of the signal; and coupling means for coupling at least two optical signals into an input end of the waveguide. A Y-coupler is coupled with the optical waveguide to couple at least two optical signals into an input end of the waveguide. One of the optical signals may comprise a bias signal.

Abstract: A radiation generator in which substantially all the radiation modes are locked with respect to one another comprises a radiation generating cavity defined by mirrors and a crystal for generating a continuous train of non-transform limited pulses of coherent radiation. An external cavity is positioned in association with the radiation generating cavity whereby radiation may pass in use in both directions between the two cavities. The external cavity is defined by a medium having a non-linear transmission characteristic which may be substantially non-dispersive for radiation from the generating cavity, and/or which has a negative group delay dispersion. The radiation path length is such that pulses fed into the external cavity are fed back to the radiation generating cavity in synchronism with a later pulse from the generating cavity.