Optical Spectrum Analyzer.

An optical RF spectrum analyzer which is suitable for determining the real-time spectral frequency content of radar return signals. The optical RF spectrum analyzer includes a demodulator for demodulating an input RF signal to produce a time-varying voltage signal at its output and a sample and hold circuit for sampling the time-varying voltage signal to obtain and hold a prescribed number of samples of the time-varying voltage signal during each of successive prescribed frame intervals. At the conclusion of each frame interval, the samples obtained and held during that frame interval are applied to respective inputs of a laser array to drive respective ones of the lasers in the array, whereby the laser array produces a spatial pattern of infrared radiation having a spatial intensity distribution which is indicative of the amplitude distribution of the envelope of the input RE signal over a given frame interval. A first optical subsystem directs the spatial pattern of infrared radiation to strike an exposed surface of the electron trapping ET material of a spatial light modulator SLM. A second optical subsystem directs coherent blue light generated by an argon laser to illuminate the exposed surface of the ET material. The incident infrared radiation releases trapped electrons in the ET material at the exposed locations, resulting in the emission of incoherent visible light. The incident coherent blue light is selectively absorbed at these exposed locations as it acts to excite ground state electrons back into energy traps. The incoherent visible light which is emitted by the ET-SLM is filtered out by a blue light filter. The coherent blue light which passes through the ET-SLM is Fourier transformed by a Fourier lens, and then detected by a CCD detector.