Abstract: An optical grating includes a sequence of grating lines, the sequence being such that each grating line is centered on a position which is an integer multiple of a line spacing distance from a datum position on the grating, the sequence of grating lines is non-periodic and the sequence of the grating lines is formed from N concatenated sub-sequences. Each sub-sequence includes a series of one or more instances of a respective grating line pattern. Such an optical grating has a structure that is more amenable to calculation of the grating lines necessary to achieve a desired characteristic. A method of calculating and fabricating such a grating is also disclosed.

Abstract: An optical source for a communications system includes an optical signal source whose output is modulated to contain sidebands. The sidebands interact to produce beat frequencies and modifying apparatus, such as a length of dispersive optical fibre, is used to modify characteristics of the sidebands so that the beat frequency can be detected at a receiver such as a photodetector. In this way, high frequency signals can be generated and photodetected, the output of the receiver being suitable to drive a microwave antenna, thus providing an optically fed microwave communications link. Using a video signal generator a video signal can be superimposed on the received beat frequency and therefore carried by the microwave link.