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RF Spectral And Temporal Analysis With A Real Time Tunable Frequency Filter

This paper reports on a set of experiments involving an acousto-optic RF spectrum analyzer, an electro-optic tunable frequency filter, and a slit detection configuration. The system extracts in real time any wanted signal out of a multifrequency RF population and recovers its temporal modulation information. Its rise time is faster than the acoustic pulse transit time through the optical beam in the Bragg cell, yet its frequency resolution remains as fine as its A/O spectrum analyzer parameters dictate. The E/0 tunable frequency filter operates as a real time optical processor, hence significantly reducing digital processing of the RF spectrum. First, a conceptual system using the 5376 electrode Xerox linear Total Internal Reflection (TIR) spatial light modulator is described. Experimental results using a 10 channel TIR spatial light modulator are then presented which verify the concepts, demonstrate the retrieval of a weak signal, > 20 dB dynamic range, and real time selection of desired frequency signals. The recovery of temporal information is demonstrated using an imaging technique showing 5 1 μs modulation pulse rise time using a narrow slit at the photodetector. Tradeoffs exist between dynamic range, recovered rise time, laser power, Bragg cell efficiency, TIR efficiency and channels cross-talk, and photodetector/amplifier noise. These aspects will be discussed.