M. Asensio

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 (λ=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.

A simple blue light pulse generator with GaN/SiC light emitting diodes for the time response testing of PMTs

A simple and cost-effective integrated synthesizer of fast light pulses has been designed, analyzed and tested for the characterization of the time response of photo-multipliers (PMT). This synthesizer consists of an integrated pulse generator based on Schmidt Trigger Inverters, a broadband matching network and a high speed LED. It enables the generation of pulses as short as less than 10 ns with variable pulse width, amplitude and repetition frequency. In order to accurately know the shape of the pulses applied to the PMT under test, a circuital model of the LED has been developed and verified at frequencies up to 2 GHz. This model accounts for the nonlinear behavior of the LED capacitance as well as the package parasitics. The influence of the mismatch at the different frequency components of the synthesized pulse has been investigated. The pulse transmitter has been used to test the time response of MAGIC telescope pixels.