Temperature controlled beam steering in polymer waveguide arrays

Inspired by the observation of Bloch oscillations of electrons in semiconductor supperlattices [C. Waschke et al., Phys. Rev. Lett. 70, 3319 (1993)] 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 [U. Peschel, T. Pertsch, and F. Lederer, Opt. Lett. 23, 1701 (1998)]. 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 6533 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.