Temperature-controlled beam steering in polymer waveguide arrays

Abstract

Inspired by the observation of Bloch oscillations of electrons in semiconductor supperlattices we recently predicted the existence of Wannier-Stark states as well as Wannier-Stark ladders and consequently the emergence of optical Bloch oscillations in evanescently coupled optical waveguide arrays. Here we show that the required linear variation of the propagation constant across the array can be realized by using the thermo-optic effect in polymers. Beyond the fundamental interest in waveguide arrays for the study of dynamical effects in discrete systems, they have a fair potential in all-optical signal processing. We demonstrate that waveguide arrays allow for temperature- controlled beam steering, while simultaneously minimizing the diffractive beam spreading. Homogeneous arrays of 75 waveguides are fabricated in an inorganic-organic polymer, with each waveguide guiding a single mode (<0.5 dB/cm) at a wavelength of 633 nm. By heating and cooling the opposite sides of the samples, a transverse linear temperature gradient is established. Exciting a few waveguides using a wide Gaussian beam we measure the oscillating transverse motion of the undiffracted output beam for an increasing temperature gradient.