Demonstration of low differential phase noise for optical phased arrays with optical amplification

Optical phased arrays (OPAs) are key enablers for light detection and ranging (LiDAR) in autonomous vehicles, free space optical communications, imaging and coherent beam combining. Active OPAs (with amplitude and phase control) allow the control of individual channel gains along with phases for enhanced control of far-field beam pattern. Path length variations and noise from amplifiers degrade the differential phase noise between the OPA channels, which is a key performance indicator that determines the far-field performance in terms of power in the main lobe, extinction of side lobes and pointing error. Conventionally, in fiber-based platforms, multiple phase locked loops are required to reduce the differential phase noise by locking the channels.
In this work, we investigate the differential phase noise in an InP active OPA and demonstrate less than 10 mrad differential phase noise corresponding to a stability better than λ/600. To the best of our knowledge, this is the first demonstration of low differential phase noise in an active OPA with amplification in a photonic integrated platform. This result enables on-chip OPA amplification in the InP platform without active locking, thus reducing the system complexity and power consumption.