Design, modelling and testing of electro-optical transmitters for the central pixel of the MAGIC telescope camera

In this work we have built an electro-optical system for the transmission of low frequency analogue signals through optical fibre. The main goal was to achieve minimum pulse distortion with maximum dynamic range. The system has been used in the framework of the MAGIC telescope experiment for the transmission of the analogue output from a photo-multiplier dedicated to optical observation of astrophysical objects, in particular pulsars. The received signal polarizes an infrared LED ( =850 nm), which converts the pulse into an optical analogue pulse. The electro-optical pulse is transmitted by means of a multi-mode optic fibre and finally amplified and filtered by the optical receiver. The whole system has been tested using a pulse generator resembling the type of pulsed signal we expect from pulsars, that is with period of about tens of milli-seconds and few milli-seconds wide. The system was calibrated in order to: a) obtain a fixed relation between the received pulse and the final data and b) enhance the dynamic range and low distortion. In what follows, we show the behaviour of the optical transmitter under different pulse shapes, amplitude and frequencies up to several hundred Hz. The electro-optical system has been mounted on the MAGIC telescope and tested successfully with the observation of the pulsed optical signal from the Crab pulsar.