Photonic technologies for autonomous cars: feature introduction.

Photonic technologies that support the low cost manufacturing needed for automotive sensors have experienced explosive developments in recent years. To date most commercially available lidar system have been direct detection time-of-flight (ToF) sensors operating at 905 nm using mechanical mirrors for beam steering. However, these sensors suffer from important drawbacks. One issue is eye-safety, which limits maximum laser powers and hence operating range. Direct detection systems must also content with potential interference issues when lots of cars operate lidar systems simultaneously. In addition, mechanical scanners are frequently bulky and may be difficult to integrate within the form factors allowed by modern vehicles.

Sub-wavelength-pitch silicon-photonic optical phased array for large field-of-regard coherent optical beam steering.

This paper reports on large field-of-regard, high-efficiency, and large aperture active optical phased arrays (OPAs) for optical beam steering in LIDAR systems. The fabricated 5 mm-long silicon photonic OPA with a 1.3 µm waveguide pitch achieved adjacent waveguide crosstalk below -12dB. A relatively large and uniform emission aperture has been achieved with a low-contrast silicon nitride assisted grating (~20 dB/cm) whose emission profile can be further optimized using an apodized design. The fabricated silicon-photonic OPA demonstrated > 40° lateral beam steering with no sidelobes in a ± 33° field-of-regard and 3.3° longitudinal beam steering via wavelength tuning by 20 nm centered at 1550 nm. We have fully integrated the silicon photonic OPA device with electronic controls and successfully demonstrated 2-dimensional coherent optical beam steering of pre-planned far-field patterns. Future improvements include placement of a distributed Bragg reflector (DBR) underneath the grating emitter in order to achieve nearly a factor of two improvement in emission efficiency.