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fax: (33) I 47 46 04 I7 IntroductionHigh speed photodetectors are needed in optical communication systems and avalanche photodiodes are essential in highly sensitive photoreceivers at the 1.55 p m wavelength. Avalanche photodiodes (APDs), when compared to PIN photodiodes, provide higher responsivities due to their internal gain M. An improvement in the signal to noise ratio of about 10 dB is expected at 20 Gbit/s. Very good performances have already been demonstrated at 10 Gbit/s [ 11. For higher bit-rates, a side-illuminated structure has been proposed [2], to reach simultaneously high responsivity and high speed. The simulations allowing to design waveguide APD structures, their fabrication and their characteristics are reported in this paper.