Switchable Waveguides for Novel Laser Displays and Scanners

The electro-optic Pockels and Kerr effect make it possible to tune the refractive index of a material with an applied electric field. Remarkably, these effects are reversible and show a very short reaction time. If it were possible to use these phenomena to extract light from the surface of a planar waveguide, this would provide laser displays, projectors, and scanners of unsurpassed performance.<br/>So far, tunable coupling between waveguide modes and free-space modes often relies on mechanical components or surface acoustic waves, limited in terms of reaction time. By placing a thin film resonator in the center of an electrooptic waveguide, we show that a continuum of waveguide modes can be tuned between zero and maximized coupling efficiency (80%) into free-space modes. We term this first phenomenon bound continuum coupled to the continuum (BCC), describing a continuum of waveguide modes with access to the continuum of free-space modes, showing zero coupling efficiency. Realized by the Pockels effect, this phenomenon is a promising way towards mechanics-free optics. Additionally, the proposed geometry allows for the absence of self-interference so that the electrooptic waveguide does not function as bandwidth-limiting second resonator. In addition, the symmetry enables switching in the entire visible spectrum.<br/>We demonstrate a local switching behavior and contrast ratios for red (C=1000) and green (C=500) light of our polymeric thin film resonator inside a symmetric lithium tantalate waveguide. Furthermore, we estimate the performance of laser displays and scanners based on the demonstrated concept.