Abstract: An optical beam intensity modulator comprising a modulator element arranged to transmit an optical beam along a first path in a first modulator state as a first beam and along a second, deviated path in a second modulator state as a second beam, and a beam return element arranged to return a transmitted beam to the modulator element.

Abstract: A method and apparatus for generating and transmitting high energy optical pulses are described. Distributed temperature sensors usually use Raman scattering in optical fibres as the means to determine the temperature. Here, light from a laser source is sent down a fibre and the small amount of light that is scattered back towards the source is analysed. As the fibre length increases, the resolutions of the temperature and loss measurements become poorer. This is because losses in an optical fibre attenuate the signal. An obvious solution to this problem is to launch more light into the fibre to compensate for the losses but stimulated Raman scattering limits how much light may be launched. The present invention solves this problem by using a pulse conversion method to maximise the resultant pulse energy while the power is kept below SRS threshold.

Abstract: In a high bit rate optical communications system, a clock signal is recovered from a received optical data signal by comparison of the data signal with an optical pulse stream derived from a local oscillator running at a sub-multiple of the signal bit rate. The oscillator forms part of a phase locked loop, and the signal comparison is made via a two photon absorber element which responds to a combination of the photon energies of the data signal and the locally generated pulse signal. The oscillator output is then used as a local clock for de-multiplexing purposes.