Photovoltaic and Pyroelectric Solitons

Abstract

This chapter presents the theory behind the observation of optical spatial solitons in photovoltaic photorefractive crystals. The bulk photovoltaic effect is different from the conventional “solar cell” photovoltaic effect and relates to anistropic probabilities of electron processes leading to a giant photovoltage. The band transport model is used to obtain the space charge field and the dynamical evolution equation for light beams propagating in biased photovoltaic photorefractive crystals. The general formulation presented here branches out to systems of photorefractive crystal which is open circuited or closed circuited and without the external bias field. Relevant example is taken to show the dark and grey soliton states. Consequently, the theoretical formulation for self trapping due to the pyroelectric effect is elucidated. The pyroelectric effect relates to a temperature change induced transient electric field. The temperature change can be externally controlled or due to incident beam energy absorption. This transient pyroelectric field can self trap a soliton in a photorefractive crystal. The space charge field and the dynamical evolution equation is obtained using simple considerations of charge transport and continuity equations. Finally, the interaction between the pyroelectric field, photovoltaic field and the external bias field is discussed.