Thermally induced optical beam steering in polymeric slab waveguide

Abstract

Routing and steering of optical beams in guiding structures is an attracting function, especially for the realization of inter-chip and intra-chip optical dynamic interconnections. Several physical mechanisms were used, in a huge variety of materials and device configuration. In this paper we propose a simple solution that allows efficient beam steering in a PMMA/PUR/PMMA slab waveguide, by means of thermal control. The operation principle is based on the generation of a 2D temperature distribution field in the slab waveguide cross section, which induces lateral confinement for the propagating optical radiation. In particular, the choice for core and cladding fabrication, of materials characterized by negative thermo-optic coefficient, allows to push away the optical beam from the hottest region and control the spatial position by tuning the temperature difference between hot and cold electrode. In this way, it is possible to achieve a sort of "analog" operation of the device, whose steering efficiency is proportional to the dissipated power. It has been evaluated a maximum lateral beam steering of about 40 micron, before that the lateral confinement at the cold side vanishes Propagation analysis confirms the results obtained from the modal simulations. The high thermal efficiency of the structure allows the desired behavior with an estimated power expense of few of milliwatts, due to the extremely high thermal insulating characteristic of PMMA and PUR. On the other hand, its dynamic is quite slow; this fact is confirmed by simulated switching time of hundreds of milliseconds. An alternative proposal, with a PUR slab waveguide directly realized on an oxidized silicon substrate, shows faster switching times below one millisecond, but higher driving power.