Demonstration of a compact transmissive-reflective laser beam scanner enabled by a wire-grid polarizer on silicon

Polarization-selective metasurfaces can transmit, reflect, or alter incident light based on its polarization state. A widely used example of such a device is the wire-grid polarizer (WGP), which transmits light with an incident polarization state parallel to the polarizer pass axis and reflects light with an incident polarization state orthogonal to the pass axis. This essentially means that WGPs are polarization-dependent reflectors. We used this property to build an in-line laser beam scanner. The scanner is composed of two WGPs with pass axes offset by 45° and a thin-film Faraday rotator in between. Since the light path through the system is similar to a “z-fold” scanner in that the beam reflects once from each polarizer, the output beam angle can be controlled by the tilt angle of either polarizer. We have previously demonstrated this scanner concept using commercial off-the-shelf components and noted that the volumetric size of the scanner system could decrease if the actively tilted WGPs could be miniaturized to a microelectromechanical system (MEMS) platform. We now demonstrate the scanner system with a smaller nanofabricated silicon-based WGP as the tilting polarizer element. The optical throughput efficiency of the scanner was characterized as a function of scan angle and incident polarization state orientation. This system demonstrated greater than 58% transmission efficiency for a “single-layer” grating design and greater than 50% transmission efficiency for a “bilayer” grating design over an angular scan range of 90°. This scanner system demonstrates that our fabricated silicon-based nanostructures are capable of the polarization-selective behavior needed for this application. In addition, this demonstration presents realistic scanner efficiencies for a potential integrated device, as these polarizers were designed to be fabrication-compatible so that the polarizer and tilt actuation could be integrated into one MEMS element.