Abstract
Dichroism - polarisation dependent absorption - can form the basis of a single-wavelength photonic switch in anisotropic materials such as CdS crystal platelets[1] or InGaAs quantum wells.[2] Whereas fibre-based switching devices rely on non-resonant nonlinearities in glasses and, consequently, require high irradiance-length products, Semiconductor All-optical Nonlinear Dichroic (SAND) devices need only be a few hundred micrometres long and can be operated with picosecond pulses of about 1 pJ.[2] To distinguish the control pulse from the signal pulse, the control is polarised so as to maximise its absorption and hence cause the maximum excitation of the semiconductor. The change in refractive index induced by the photogenerated free electron-hole pairs is sensed by the signal, which is polarised so as to minimise absorption losses. A switched signal can become a control pulse simply by rotating its polarisation and consequently the SAND devices are directly cascadable. When operating such a device the control acts as a pump pulse and the signal being switched is a probe pulse. These are the terms used in the remainder of this paper.
© 1996 Optical Society of America
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