Signal processing apparatus.

摘要

It is desirable for the change of frequency of a chirp pulse to be as linear as possible to improve the signal to noise ratio. Light from a light source (1) is sent to a first amplitude modulator (6) where it is modulated by a chirp signal from an oscillator (12). The modulated light travels along a fibre optic delay line (14) to a second amplitude modulator (15) where it is again modulated by the chirp signal. In effect the light leaving the second modulator (15) has been modulated by delayed and undelayed versions of the chirp signal. This results in a signal having a lower sideband which is representative of the frequency difference between the delayed and undelayed signals. The frequency difference remains constant if the chirp signal is linear, but any change varies the frequency difference. This variation can be used to improve linearity of the remaining part of the chirp signal still to be processed.