Diffraction response of a low-temperature-grown photorefractive multiple quantum well modulator

Abstract

The transient diffraction response of a low-temperature-grown ͑LTG͒ photorefractive multiple quantum well ͑MQW͒ spatial light modulator ͑SLM͒ is studied experimentally as a function of the frequency and the on/off ratio of a single-sided applied voltage when a grating is written using a continuous-wave sinusoidal illumination. LTG MQW modulators have high spatial resolution, but their diffraction efficiency and speed are reduced. By varying the on/off ratio of the applied voltage, it is shown that the frequency response of the SLM can be optimized while maintaining its high spatial resolution. The flatness of the frequency response with respect to the peak diffracted signal is thus shown to increase by an order of magnitude. By temporally gating the diffracted signal, low and bandpass filtering capabilities of the SLM are experimentally demonstrated for applications such as speckle elimination and novelty filtering. When the diffracted signal is measured over an adjustable time window, it is shown that high frame rate operations in integrated optoelectronic systems can be achieved. A numerical model that includes the effect of high trap densities on the space-charge dynamics is developed. It is shown that the space-charge field grows nonuniformly along the MQW growth direction with the largest modulation in lateral field occurring only near the entrance face of the incident light, thus accounting partially for the low diffraction efficiency of LTG materials.

Overview of Nonlinear Optics

“…(Abeeluck, 2002). Pulsed pump and probe waves, with a time delay between them, is a particularly valuable way to measure transient phenomena, both excited state lifetimes and dephasing (Yang, 1994).…”