On-Chip Optical and Analog Processing in 180nm CMOS for Holography

Abstract

Digital holography generally requires multiple measurements or complex post-processing, precise optical setups, and can suffer from aliasing and high noise. In this work we present a theoretical approach for a novel sensor and a complementary off-axis optical setup, which can perform wide-field capture in a single shot with less aliasing than conventional off-axis methods. By exploiting on-chip optical and analog processing enabled by advances in chip fabrication we are able to reduce the number of measurements required, and boost the signal-to-noise ratio. Using upper metal layers of the integrated circuit, we create gratings that block or pass light at 0, π/2, π, and 3π/2 radians of phase interference, converting phase information in the light field to intensity. In the analog circuitry of the sensor, we incorporate differential readout and feedback techniques to improve SNR. We simulate reconstructions demonstrating x-y spatial reconstruction at the size of the pixel (15µm × 15µm), and compare this to two fundamental approaches – phase-stepped and off-axis holography.