IQ Photonic Receiver for Coherent Imaging with a Scalable Aperture

Silicon photonics (SiP) integrated coherent image sensors offer higher sensitivity and improved range-resolution-product compared to direct detection image sensors such as CCD and CMOS devices. Previous generation of SiP coherent imagers suffer from relative optical phase fluctuations between the signal and reference paths, which results in random phase and amplitude fluctuations in the output signal. This limitation negatively impacts the SNR and signal acquisition times. Here we present a coherent imager system that suppresses the optical carrier signal and removes non-idealities from the relative optical path using a photonic in-phase (I) and quadrature (Q) receiver via a $90^\circ$ hybrid detector. Furthermore, we incorporate row-column read-out and row-column addressing schemes to address the electro-optical interconnect density challenge. Our novel row-column read-out architecture for the sensor array requires only $2N$ interconnects for $N^2$ sensors. An $8\times8$ IQ sensor array is presented as a proof-of-concept demonstration with $1.2\times 10^{-5}$ resolution over range accuracy. Free-space FMCW ranging with 250um resolution at 1m distance has been demonstrated using this sensor array.

Achieving Full Grating-Lobe-Free Field-of-View with Low-Complexity Co-prime Photonic Beamforming Transceivers

Integrated photonic active beamforming can significantly reduce the size and cost of coherent imagers for LiDAR and medical imaging applications. In current architectures, the complexity of photonic and electronic circuitry linearly increases with the desired imaging resolution. We propose a novel photonic transceiver architecture based on co-prime sampling techniques that breaks this trade-off and achieves the full (radiating-element-limited) field-of-view (FOV) for a 2D aperture with a single-frequency laser. Using only order-of-N radiating elements, this architecture achieves beamwidth and side-lobe level (SLL) performance equivalent to a transceiver with order-of-N-squared elements with half-wavelength spacing. Furthermore, we incorporate a pulse amplitude modulation (PAM) row-column drive methodology to reduce the number of required electrical drivers for this architecture from order of N to order of square root of N. A silicon photonics implementation of this architecture using two 64-element apertures, one for transmitting and one for receiving, requires only 34 PAM electrical drivers and achieves a transceiver SLL of -11.3dB with 1026 total resolvable spots, and 0.6 degree beamwidth within a 23x16.3 degree FOV.