ABSTRACT
An optically controlled reflection modulator has been demonstrated that consists of a combination of a GaAs-AlGaAs n-i-p-i doping structure with a multiple-quantum-well structure on top of a distributed Bragg reflector, all grown by molecular-beam epitaxy. A modulation of approximately 60% is obtained on our test structure, corresponding to a differential change of absorption coefficient in the quantum wells of approximately 7500/cm. Changes in reflectance can be observed with a control beam power as low as 1.5 microW. This device structure has the potential of being developed as an optically addressed spatial light modulator for optical information processing.
ABSTRACT
Promising approaches for achieving optically addressed spatial light modulators (O-SLMs) are investigated based on combining nipi and multiple quantum well structures. Theoretical aspects of photooptic effects achievable in such structures are treated. Test structures are grown by molecular beam epitaxy using two material systems, (In,Ga)As/GaAs and (Al,Ga)As/GaAs. Experiments show large optically controlled modulation of the absorption coefficient in the quantum well layers ( approximately 10(4) cm(-1)), a log power dependence on the control signal, millisecond and shorter time response, and generally predictable behavior. The results are encouraging for several different O-SLM device structures proposed.
ABSTRACT
A thin-film capacitive bolometer is described, which depends on a temperature sensitivity derived from electron trapping effects in thin amorphous dielectric films containing an ionic space charge. The theory of thisprocess is summarized and shown to be in good agreement with results obtained from anodized Nb(2)O(5) capacitors. The capacitive elements can be formed on thin-film supportingstructures to achieve large thermal detectivities D*. An analysis given for an optimized detector indicatesthat it is possible to reach the theoretical maximum D* at room temperature. Experimental detectors aredescribed which were fabricated from anodized Nb(2)O(5) and evaporated Al(2)O-TiO(2) capacitors. Their performance at room temperature indicates responsivities of at least 2 mV/microW, effective time constants of about 0.05 sec, and D*'s in excess of 10(9).
