Abstract: A dispersion management system for soliton or soliton-like transmission systems comprises a length of optical fibre (L) in which a plurality of sections (I) made up of components (N,A) of opposite sign dispersions are concatenated together. The duration of the dispersion compensation phase is short in comparison with the propagation interval in the remainder of the system and that the path average dispersion is anomalous.

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 comprises an optical waveguide (2) formed from at least a first material having a non-linear refractive index n.sub.2 coupled to a first pair of ports (4,5) of an optical coupler (3). An optical signal input at one of the second pair of ports (6,7) of the coupler (3) is split to provide two signals counter propagating around the waveguide loop (2). By selecting the coupling ratio and appropriate waveguide parameters to ensure an asymmetry in the device it is possible to produce an intensity dependent relative phase shift between the counter propagating signals, thereby to vary the device output. Embodiments of the invention may be used to perform logic functions on, to amplify, switch or otherwise modify an input signal.

Abstract: An optical device comprises first and second optical waveguides connected between respective output and input ports of first and second optical couplers. The first coupler has at least one input port and is adapted to couple optical signals received at the input port into its output ports in a predetermined coupling ratio. The second coupler has at least one output port and is adapted to couple optical signals received at each input port into its output port in a predetermined coupling ratio. The first and second waveguides define respective optical paths with substantially the same optical length.