Abstract: Telecommunications switch architectures and switching methods based on the principle of replication/broadcasting some or all of the incoming data from each input-switch port to all output switch ports. The replicated data is transferred to the output ports either by the respective output port reading directly from a relevant address in an input memory, or by transferring the content of all or part of the input memory data simultaneously en bloc and in parallel to a plurality of output memories, with each output port then taking the data intended therefor. The input and output data is in serial form but transferred in parallel form. The data can be replicated optically or electronically. In particular, the input data can be formatted as spatially arranged pages in the optical domain by spatial light modulators (SLM) and switched by an image replicating optical switch, such as a matrix-matrix switch, to an output plane at which a second SLM device converts the data back to serial form.

Abstract: A holographic optical correlator includes a matched optical filter and control means therefor including a memory. In use searching for occurrences of an item to be found is carried out by the control means controlling the input and Fourier transform planes of the filter and a coherent light source for parallel optical processing of the memory content and the output plane of the filter provides information to the control means as to the location in the memory of occurrences of said item. The complexity of the detector means in the output plane can be reduced in comparison with previous proposals by moving the item to be sought step-wise across the input plane. The detector means then may comprise a single column of detectors which are required to detect a peak correlation signal within a predetermined range.

Abstract: An associative (content addressable) optical memory system is comprised by a matched optical holographic filter (10, 18, 21, L1, L2) coupled to a digital computing system (14, 15, 16) having a memory (15, 16). In order to search the computing system memory for occurrences of an item, a hologram of a binary representation of the item is formed in the Fourier transform plane (18) employing laser (11) as the light source. A page of the memory to be searched is subsequently displayed at the input plane (10), which for example is comprised by a liquid crystal over silicon display, and illuminated by the laser (11). The light is filtered at the Fourier transform plane (18). Any occurrences in the input plane display of the item result in a respective correlation spot at the output plane, which spot output is decoded and supplied to the processor (14), thus providing correlation information to the computing system as to the location in its memory of the occurrences of the item.

Abstract: In an optical fiber FDM system, the carriers are derived from the output of a high quality Master Oscillator, which output at frequency f.sub.0 is applied to a Raman Nath modulator (RNM1) whose other input is a frequency f.sub.0 this gives as its outputs (assuming a five channel system) f.sub.0 -2f, f.sub.0 -f, f.sub.0, f.sub.0 +f and f.sub.0 +2f. These are modulated by modulators (CM1, to CM5) with the signals to be sent, and the modulation results combined in a combiner CB for transmission to a remote station. The oscillator output is also sent to the remote stations where it is frequency-shifted by a Bragg modulator (BM) and the resultant similarly dealt with by a Raman Nath device (RNM2) to give five frequencies which are used to demodulate the channels. In an alternative the channel frequencies are switchable.