Abstract
Recently, there has been a great deal of interest in the use of avalanche photodiodes (APD) for spatial light modulation,1-4 This interest steins from potential applications in optical processing and imaging. A full explanation of our system is provided elsewhere.4 In summary, when an incoming photon is absorbed by the APD under applied voltage, a localized avalanche of charge carriers is created. The electron avalanche causes localized heating, which alters the local optical properties (index of refraction) of the diode, allowing it to act as a spatial light modulator. Amplitude modulation may be easily achieved by using the from and backsurfaces of the APD to form a Fabry-Perot interferometer. This thermo-optic modulation is observed even when a single photon initiates the response. There are two distinct modes of operation. These are shown in Fig. 1. In the first mode, the modulation is both written and read with light at 1064 nm. In the second mode, the modulation is written with a beam at 850 nm and read with a beam at 1300 nm delayed 100 ns from the writing pulse.
© 1996 Optical Society of America
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