Abstract: A broadband electrical signal spectrum analyser comprises a spatial light modulator such as a Bragg cell located within at least one resonant cavity and illuminated by a polychromatic source of light. The signal to be analysed is connected to the Bragg cell. The tuned cavity is arranged to lase the diffracted light to thereby enhance the signal before detection. In one arrangement the cavity is formed by opposed mirrors set at the Bragg angle and one of the mirrors is oscillated through a range of frequencies required by the broadband application. In a second arrangement a plurality of narrow band channels is formed by a fibre optic array. The fibres are arranged such that first ends of the fibres form a linear input array and the second ends form a linear output array. Light at the Bragg angle passes into an appropriate one or more of the output array fibres, passes around the looped fibres to the input array where the light (zero order) is transmitted through the Bragg cell and then back to the fibre loop.

Abstract: Light from a laser (10) is divided by a beam splitter (12) to provide signal (15) and reference (14) channels. The signal channel light is expanded (11) to illuminate an acousto-optic (AO) device (13). This leads to a spatial distribution of Doppler shifted frequencies. This spatial distribution then illuminates a spatial light modulator (SLM) (19) such that a number of parallel and discrete optical channels (112) emerge. In a local area network (LAN) the optical signal channels are coupled into a single mode optical fibre (22) and then heterodont to the reference laser light from a further optical fibre (23) in an optical coupler (25). In a receiver the modulated light is detected (32) and the detected signal connected to the transducer of an AO device (35). The AO device (35) is illuminated by a receiver laser light (36) and the emerging modulated light is incident on a focal plane detector array (39) where each detector (310) then receives light corresponding to each of the transmitted channels (311).