Hydrogenated amorphous silicon photodiodes for optical addressing of spatial light modulators

We discuss the use of hydrogenated amorphous silicon (a-Si:H) photodiodes as photosensors in high-performance optically addressed spatial light modulators (OASLM's). To find the performance limitations that result from the photodiode exclusively, a pseudo-OASLM is constructed; it is composed of an a-Si:H photodiode in series with a discrete capacitor and resistor to simulate an electrically ideal liquid-crystal modulator. The a-Si:H photodiode conduction regimes are identified, and the maximum and minimum frame rates that may be attained with an a-Si:H photodiode-driven OASLM are determined to be ~ 100 kHz and ~ 0 Hz, respectively. Optimum performance is obtained when the photodiode capacitance is equal to the light modulator capacitance.