Video/Audio Photon "Noise" Converters
In this area helpful hints and circuits will be given for interfaces to go between the optical receiver and a video or audio system. With these interfaces, the detected photons can be viewed as "snow" on a video monitor or heard through an audio system. These simple interfaces are good for keeping an "eye" and/or an "ear" on the arriving photon stream, independent of any computer monitoring of the signal.
To convert the narrow output pulses produced by a photon-counter discriminator into an audible signal, the short TTL or ECL logic pulses are stretched by means of a NE555/556 timer chip.
The design for circuits to convert wideband PMT or APD signals into an audible signal will be given bellow. Human hearing provides a pretty sensitive way to spot non-white signals within the white-noise "hiss".
The circuit below is as simple as it gets. It is for use with analog wideband, direct-detection PMT and APD type optical receivers. It cuts off frequencies in the quantum noise above the audio range to prevent high-frequencies entering the audio amplifiers.
Circuit 1: Passive low-pass filter for use with analog wideband PMT and APD optical receivers
The circuit below stretches the narrow pulses produced by photon-counters so that sufficient energy falls within the audio band.
Circuit 2: NE555 timer circuit for use with photon-counters
Circuit diagrams and simulations produce by: