| 摘要 |
<p>A broadband electrical signal spectrum analyser comprises a spatial light modulator such as a Bragg cell (22) located within at least one resonant cavity and illuminated by a polychromatic source of light (20). The signal to be analysed is connected to the Bragg cell (22). 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 (23, 24) 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 (41) and the second ends form a linear output array (42). 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. A collimating lens (44) is provided on the input side of the Bragg cell and a Fourier transforming lens (45) is provided on the output side of the Bragg cell such that the position of the optical fibre in the array carrying the diffracted light is frequency dependent and the amount of light depends on the amplitude of that frequency in the electrical signal.</p> |
