SINGLE-WAVELENGTH ALL-OPTICAL PHASE MODULATION IN A GAAS/ALAS HETERO-NIPI WAVE-GUIDE - TOWARDS AN OPTICAL TRANSISTOR

We propose and demonstrate a single-wavelength all-optical transistor-like device, exploiting the polarization-dependent absorption coefficient in quantum wells. The device is a GaAs/AlAs multiple-quantum-well hetero-nipi waveguide structure. A transverse-electric (TE)-polarized control beam is absorbed, changing the refractive index through carrier-induced effects. A transverse-magnetic-polarized probe beam at the same wavelength, to which the material is transparent, undergoes a phase shift, which can be converted to amplitude modulation if required. The probe can be more powerful than the control beam, so the device can exhibit gain. We obtained a 180-degrees phase shift in the probe beam with 4.2 mW of absorbed control light. The effect was greater with an applied dc bias. A 180-degrees phase shift was obtained at 831 nm with 2.8 mW absorbed TE light and 0.5 V bias.