Abstract
Solid state beam steering devices are key elements in low cost, robust, and three-dimensional imaging systems. Here, we present a silicon photonic beam steering device based upon an 8 × 8 grating coupler focal plane array approach fed by a thermo-optic Mach–Zehnder switching tree. In this device, transmission of light from the grating couplers is made through the backside of the chip using topside mirrors allowing for both high-efficiency out-coupling and direct flip-chip integration of drive electronics, providing a path to scale to denser focal plane arrays with large numbers of points in the future. A −13.8 dB fiber-to-fiber transmission was achieved in our preliminary test around 1523 nm for the beam steering chip.
Highlights
In recent years there has been significant activity in the development of 3D imaging systems based upon LIDAR (Light Detection and Ranging) to accurately map the positions and even velocity of objects in a 3D space (Ref. 1-6)
We present a silicon photonic beam steering device based upon an 8 x 8 grating coupler focal plane array approach fed by a thermo-optic Mach Zehnder switching tree
Due to phase errors which are typical in submicron silicon photonic waveguides, the voltage required for the two switching states of each Mach Zehnder interferometer (MZI) in the circuit differed across the chip, and they needed to be accurately determined
Summary
In recent years there has been significant activity in the development of 3D imaging systems based upon LIDAR (Light Detection and Ranging) to accurately map the positions and even velocity of objects in a 3D space (Ref. 1-6). We presented an alternative approach to beam steering based upon a focal plane array (FPA) consisting of 16 grating couplers which are individually addressed using a thermo-optic Mach Zehnder interferometer (MZI) based switching tree (Ref. 18). The light in this case is routed to a single grating at a time, which in turn illuminates a small subset of the scene using a lens system. This work demonstrates the capability to realise a beam steering module using our backside emission and heterogeneous integration approach It can open up a range of manufacturing options and providing a path towards highly dense arrays of grating couplers. By optimizing the design parameters and assuming a perfect anti-reflection (AR) coating at the back side of the wafer, we can theoretically achieve 95% directionality to the backside of a wafer, and an 84% coupling efficiency to the fibre mode, which is about a 2dB improvement in coupling efficiency compared to top side coupling gratings fabricated on the same platform
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