Polymeric waveguide optical switches based on electrooptic and thermooptic beam deflectors integrated with etched TIR mirrors
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We proposed and demonstrated a new type of optical switch incorporating a waveguide beam deflector with integrated total-internal-reflection mirrors. Waveguide beam deflectors based on both electrooptic and thermooptic effects were fabricated and characterized to evaluate their potential as a switching element in fully integrated devices. In the electrooptic beam deflector, an array of prism-shaped electrodes formed on the top of the waveguide induces selective refractive index change in the core polymer layer by Pockels effect, which results in the tilt of the propagation direction of the guided beam. The deflection sensitivity of 28.5mrad/kV, and the maximum deflection angle of ±8.4mrad at ±300V were obtained from the demonstrated device. In the thermooptic beam deflector, a similar prism array-shaped heating electrode is used to induce refractive index change by temperature tuning. A new design scheme of a polymeric waveguide thermooptic beam deflector was attempted in this work. Full sweep angle of 56.5mrad (3.24deg) and 1 × 8 switching capability at 1550nm wavelength were attained with power consumption of 247mW per resolvable spot by using dual folded-thin-strip heating electrodes. Switching from the zero-bias spot to the first resolvable spot exhibited response time of 2ms in both rising and falling. We fabricated a fully integrated 1xN switch in fluorinated polyimide by using the thermooptic beam deflector with integrated parabolic total-internal-reflection mirrors formed by reactive ion etching. The vertically etched sidewall of the planar waveguide works as a highly reflecting surface, which collimates and focuses the light signal. The estimated individual mirror insertion loss was 2.4dB or less. Nevertheless, the fabricated optical switch exhibited higher insertion loss than we expected, which was 16-17dB. The crosstalk was 8-11dB and the response time was ~10ms. This device is meaningful as the first demonstrated device of this kind. However, the beam deflector design method developed in this work and the polymeric waveguide TIR mirror fabrication technique have potential in other applications as well.