Abstract: An optical circuit comprises a bistable optical waveguide (34) having a first and a second transmission state. The waveguide is more transmissive to light of a given wavelength in the second state than in the first state. A first light source (11) and a second light source (21) emit light of a first and second wavelength respectively and are coupled to the waveguide at one end. Selective transmission of a sufficient amount of light of the first wavelength through the waveguide “sets” the waveguide, causing it to switch from the first into the second state, whereas transmission of a sufficient amount of light of the second wavelength “resets” the waveguide causing it to switch back from the second into the first state. A sensing or reading (“test”) light source (36) is arranged at the other end of the waveguide to transmit a sensing light signal through the waveguide (34) in the opposite propagation direction to that of light of the first and second wavelengths.

Abstract: A method of extracting a predetermined channel from an OTDM signal includes the steps of combining at the inlet of an SOA the OTDM signal and an impulsive signal with impulses temporally synchronized with the channel to be extracted to produce in the SOA FWM, XGM and XPM effects which shift to a length c the channel chosen for extraction with c outside the length d of the OTDM signal with the other channels outlet from the SOA and filtering the SOA outlet to extract components with c d that represent respectively the desired channel and the cleaned OTDM signal. A multiplexer in accordance with the method includes an inlet (14) of an OTDM signal sent to an SOA (24) together with an appropriate impulsive signal. The SOA outlet is filtered by filters (28, 29) to obtain the signal of the extracted channel (16) and the cleaned OTDM signal (15).

Abstract: An optical logic device comprising a first mirror confronting a second mirror, a saturable absorber located between the mirrors and radiation which is output from the device is output via the first mirror, and the reflectivity of the first mirror being such that, in use, for incident radiation which has an intensity that is above a given value, the intensity of exiting radiation is below a threshold, and for incident radiation that is below the given value, the intensity of exiting radiation is above the threshold.

Abstract: An all-optical contention manager includes at least two inputs and at least two outputs. The outputs are configured to output signals to a Banyan switch. The contention manager detects and resolves routing contentions between incoming optical signals prior to outputting the signals to the Banyan switch. The signals have tags that include routing information. A photonic comparator in the contention manager compares the tags of incoming optical signals in order to detect contention.

Abstract: An optical comparator circuit comprises a first stage comprising an optical gate which receives the signals applied to the two inputs and produces at its output an N bit signal with each bit being representative of the logical expression A XOR B for a respective pair of bits of the words A and B, a second stage which comprises an optical gate having at least two inputs, a first input being connected to the output of the first stage by an optical connection having a first time delay, and a second input being connected to the output of the first stage through (N?1) further optical connections, each further connection having a different associated time delay which is longer than the first time delay, the second stage providing at its output a signal comprising N bits, each bit corresponding to a respective bit of the signal output from the first stage at that time, and each bit having a first value if all of the inputs to the stage at that time are equal and a second value if and only if the first input differs

Abstract: An optical switch controller controls an optical interconnection network that variably connects at least one input data channel to a plurality of outputs channels via at least one switching element. An address reader module has at least one semiconductor optical amplifier optically processes an optical signal. The address reader module obtains information by reading a data tag from the input data channel, and outputs an address control signal based on the information. The address control signal can be used to control switching elements in the optical interconnection network.

Abstract: An optical sampler with high temporal resolution comprises a TOAD device (11) with a loop optical path (12) at the inlet of which is input an optical signal to be sampled Si of duration Tp and along which path is arranged a point (13) of input of an optical control signal Sc produced by a source (16) and appropriately delayed by a delay line (23) to change on command the temporal position of the TOAD transmittance window compared to the signal to be sampled. In the loop there is also a nonlinear device (14) The sampler also comprises control means (17) to command the delay line (23) to move step by step said transmittance window and make it run on the signal to be sampled. Measurement means (18) measure the mean power transmitted at the TOAD output for each window position and processing means (19) perform the derivative on the mean powers found for each window position thus finding samples representing the input signal Si.

Abstract: An optical logic gate (10) comprises: first and second optical inputs (11, 12) for receiving respective optical signals (A, B) and an optical output (15) for outputting an optical signal (Pout) which represents the result of applying a required logic function. The logic gate is characterised by optical combining means (13) for combining the optical signals to produce a corresponding combination signal whose power (Pi) is the combination of the powers (PA, PB) of the optical signals and non-linear optical means (14) for receiving the combination signal (Pi) and emitting the optical output signal (Pout) the logic function depending on the characteristic of the non-linear optical means wherein the characteristic is selected such that the power of the output signal is correlated to the power of the combination signal by the selected logic function.

Abstract: An optical logic gate (10) comprising inputs (12) for optical signals on which to perform a chosen logical operation. An SOA (11) element receives such input signals to be piloted thereby in saturation and its output is connected to at least one optical filter (14, 15, 16) that filters components of signals output from the SOA and which represent a desired logical result of the signals input at the gate so that at the output (13) of the filter there is an optical signal as the result of the desired logical operation. A probe signal (17) can also be provided. An appropriate combination of power of the input, power and probe signal wavelength and central wavelength of the filter allows obtaining a plurality of logic functions such as NOR, NOT, inverted XOR, AND, OR.

Abstract: A receiver scheme (10) for optical signals in Return-to-zero (RZ) systems comprises a conventional receiver (11) at the input of which is placed an all-optical decision element (12) realized with nonlinear optical elements. This allows obtaining a substantial increase in performance compared with a simple conventional receiver optimised for NRZ signals. In particular, an optical decision is made up advantageously of two non-linear optical loop mirrors (NOLMs) (15, 16) arranged in cascade with an optical amplifier (14) at the input and a pass-band filter (18) at the output. The loops lengths may be different, as may be the splitting ratios of the couplers of the NOLMs.

Abstract: A method and apparatus for restoration of operating conditions of a WDM optical ring network comprising a plurality of amplifiers linked together in a ring after a break or fault has occurred in the network. The method comprises in response to repair of the break or other fault, increasing output power or/and pump power of an amplifier in the network such that the output power or/and pump power increases substantially in accordance with a ramp function.

Abstract: A looped WDM optical network comprises an optical loop with optical amplifiers (12,16) between the sections of the loop (11) and with ASE recirculation in the loop. At a point of the loop a laser beam is injected and allowed to circulate in the loop with the laser beam being centered around a ?LINK wavelength where it is desired that a lasing peak be generated. This supplies high network strength in terms of section loss variations and greatly improves the OSNR of the WDM signal. High network survivability is also achievable.

Abstract: A method and device for sampling ultra-fast optical signals by generating a sampling signal comprising a train of short pulses and coupling the sampling signal together with an optical data signal to be sampled into a highly non-linear optical fibre. Four-wave mixing (FWM) occurs between the two signals resulting in a secondary signal output from the fibre consisting of pulsed components having energy proportional to the instantaneous power of points along the data signal. An analysis of this secondary signal can be carried out to create a normal trace or eye-diagram of the data signal.

Abstract: An optical 1-bit comparator has at least two inputs for receiving a respective first input signal A and a second input signal B, each comprising a single bit word, and at least three outputs, each of the three outputs providing a respective solution to the logical expressions: A>B, A<B and A=B, characterised in that each logical expression is obtained using at least one semiconductor optical amplifier (SOA) capable of providing cross gain modulation. Preferably the complete circuit requires only 3 identical SOAs to provide the three logical outputs, each operating with cross gain modulation.

Abstract: A pulsed optical signal regenerator device comprises three optical stages (11,12,13) arranged in cascade between an input (14) to which is applied a signal Si to be regenerated and an output (15) at which is available a regenerated signal Sr. The first stage (11) comprises a first noise suppressor on the zero for noise reduction in the spaces between the input signal pulses. The second stage (12) comprises an inverting converter for transferring to a clock signal (Ck) the information carried by the signal outgoing from the first stage and introducing a logical inversion of the signal for transformation of the pulses affected by noise in spaces affected by noise. The third stage (13) comprises a second noise suppressor on the zero for reduction of the noise in the spaces between the signal pulses output from the second stage. The clock signal can be at a tributary bit rate of the entering signal to obtain a demultiplexer function also.

Abstract: A looped WDM optical network comprises an optical loop with optical amplifiers (12,16) between the sections of the loop (11) and with ASE recirculation in the loop. At a point of the loop a laser beam is injected and allowed to circulate in the loop with the laser beam being centered around a ?LINK wavelength where it is desired that a lasing peak be generated. This supplies high network strength in terms of section loss variations and greatly improves the OSNR of the WDM signal. High network survivability is also achievable.

Abstract: A device wavelength division multiplex optical transmission system has the wavelengths of the optical carriers arranged so as to reduce the effect of in-band crosstalk which results from unwanted side bands to the carriers. Possible wavelengths are placed on an equally spaced wavelength grid, and the transmitted channels are organized into groups of three each of which is placed on four adjacent grid positions, one of which is unused. Adjacent groups are spaced apart by two or more vacant grid positions.

Abstract: A device wavelength division multiplex optical transmission system has the wavelengths of the optical carriers arranged so as to reduce the effect of in-band crosstalk which results from unwanted side bands to the carriers. Possible wavelengths are placed on an equally spaced wavelength grid, and the transmitted channels are organised into groups of three each of which is placed on four adjacent grid positions, one of which is unused. Adjacent groups are spaced apart by two or more vacant grid positions.