WAVELENGTH SELECTIVE DETECTION USING EXCITONIC RESONANCES IN MULTIQUANTUM-WELL STRUCTURES

The wavelength and voltage dependence of photocurrent near excitonic resonances is used to study the wavelength selectivity of p-i(MQW)-n photodiode structures with a parallel sequence of optical bits, each with a different wavelength. The selectivity is considered good if the state of a lambda-i wavelength bit can be detected regardless of lamda-j(j not-equal i) state of the bits. Photocurrent is found to have very good selectivity only if lambda-j bits are all zero, i.e., the optical information is serial, but we find that differential photocurrent (DELTA-I(ph)/DELTA-V) provides a good selectivity for random states of lambda-j bits (i.e., parallel input). Four channel selectivity is demonstrated at 200 K. Specially designed quantum-well structures can greatly improve this selectivity.