R. S. Rana

Optical bistability from a thermodynamic phase transition in vanadium dioxide.

We demonstrate cw optical bistability at 1.06 μm using the large thermo-optical nonlinearity from the metal-semiconductor phase transition in a thin-film interference filter of vanadium dioxide. Highly stable and reproducible operation has been obtained. By biasing at the transition point, an all-optical external switching between the semiconducting and the metallic states has been demonstrated, with a contrast ratio of 15:1. The effective nonlinear index coefficient is n2 ≈ 1.6 cm2/W with a switching energy density of 135 pJ/μm2 and a speed of 15 ms. The tunability of the material properties of vanadium dioxide provides a means to make devices with a wide range of switching powers and speeds.

Faraday photorefractive effect in a diluted magnetic semiconductor

The Faraday photorefractive effect is demonstrated by combining photorefractive two-beam coupling with Faraday rotation in Cd1–xMnxTe, a diluted magnetic semiconductor. Two-wave mixing is monitored as a function of incident-beam polarization and magnetic-field strength with the grating vector parallel to a 〈111〉 axis. The photorefractive gain is an oscillatory function of the magnetic field. The magnetic field controls the direction and magnitude of photorefractive energy transfer by rotating the polarization inside the crystal.

OPTICAL PHASE CONJUGATION IN A MAGNETIC PHOTOREFRACTIVE SEMICONDUCTOR CDMNTE

Magneto-optical phase conjugation was performed in a diluted magnetic photorefractive semiconductor crystal CdMnTe under an applied magnetic field. The magnetic field removes time-reversal symmetry and quenches orthogonal components of the phase-conjugate signal for selected field strengths. The experimental results as functions of magnetic field and incident polarization angle are in good agreement with coupled-mode theory with transmission gratings during magneto-photorefractive mixing.

Voigt-photorefractive two-wave mixing in Cd0.9Mn0.1Te

Abstract Diluted magnetic semiconductors have pronounced magneto-optic effects. We have used the Voigt effect in a Cd 1 − x Mn x Te (x = 0.1) crystal to demonstrate that an external magnetic-field-induced linear birefringence can control the magnitude and the direction of energy transfer in photorefractive two-wave mixing. This behavior is distinctly different from the Faraday photorefractive effect studied previously. Two-wave mixing is monitored as a function of incident-beam polarization and magnetic-field strength for a grating vector along [ovbar|1 1 0]. A theoretical model is presented to describe the experimental results.