Achieving full grating-lobe-free field of view with low-complexity co-prime photonic beamforming transceivers
Aroutin Khachaturian, Reza Fatemi, Ali Hajimiri
Abstract
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- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"><mml:mrow><mml:mi>N</mml:mi></mml:mrow></mml:math> radiating elements, this architecture achieves beamwidth and sidelobe level (SLL) performance equivalent to a transceiver with order-of- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"><mml:mrow><mml:msup><mml:mi>N</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"><mml:mrow><mml:mi>N</mml:mi></mml:mrow></mml:math> to order of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"><mml:mrow><mml:msqrt><mml:mi>N</mml:mi></mml:msqrt></mml:mrow></mml:math> . 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"><mml:mrow><mml:mo form="prefix">−</mml:mo><mml:mn>11.3</mml:mn><mml:mtext> </mml:mtext><mml:mi>dB</mml:mi></mml:mrow></mml:math> with 1026 total resolvable spots, and 0.6° beamwidth within a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m6"><mml:mrow><mml:mn>23</mml:mn><mml:mo>°</mml:mo><mml:mo>×</mml:mo><mml:mn>16.3</mml:mn><mml:mo>°</mml:mo></mml:mrow></mml:math> FOV.