Abstract: A TPON network in which the multiframe format includes a control portion, and a traffic portion. In the control portion the control word for each outstation is in the form of a respective group of contiguous bits. In the traffic portion, which is constituted by a series of traffic frames, the traffic information in each traffic frame for each outstation is in the form of a respective group of contiguous bits. Such a multiframe format enables the use of single-transducer transceiver in the outstations, and compared with known TPON multiframe formats increases the maximum operating range for the network beyond which transmit/receive conflict will occur.

Abstract: A spectral filtering optical sensor comprises a stationary zone plate and stationary co-terminous ends of input and output fibres with the interposition in the optical path between the zone plate and the optical fibre ends of a variable optical focussing arrangement the focussing characteristics of which change with changes in magnitude of the particular parameter being sensed and thereby vary the effective optical path length between the zone plate and the optical fibre ends and the wavelength of light impinging on the end of the output fibre.

Abstract: A differential delay optical coherent pulse generating arrangement, in which continuous wave light derived from a coherent light source is divided by beam splitting means into two optical paths, in which the light beam in one of said paths is delayed relative to the light beam in the other of said paths by differential delay means prior to the sequential selection of the light from the respective paths by optical switching means to produce two coherent pulses in predetermined time displaced relationship and in which a frequency difference may, if required, be produced between the frequencies of the two coherent pulses.

Abstract: An optical transmission system comprises a plurality of transducers located at intervals along a continuous optical fibre data transmission path. Data signals are derived from respective transmitters associated with the transducers and are applied to the transducers to produce mechanical stressing or deformation of the data transmission path optical fibre for imparting corresponding modulation of the polarization state of light being propagated along the optical fibre. A receiver connected to the far end of the transmission path includes means for determining the exact state of polarization of the received light and for extracting the modulation information and hence transmitted data therefrom.