Demonstration of inherently low differential phase noise across C-band in InP integrated, amplifying optical phased arrays

Optical phased arrays (OPAs) enable reliable and agile solid-state beam scanning for light detection and ranging (LiDAR), coherent beam combining, and free-space optical (FSO) communication systems. The performance of these systems strongly depends on the properties of the far-field pattern such as extinction ratio and side lobe suppression ratio, for maximizing the range and reliability of operation. Differential phase noise (DPN), a measure of the difference in time-varying phase fluctuations between the phased array channels, influences these characteristics, usually requiring the use of multiple phase-locked loops in fiber-based beam combining systems. In the present study, for the first time, we rigorously measure the differential phase noise between adjacent optical phased array channels integrated with phase modulators and in-line semiconductor optical amplifiers driven over a wide range of current densities in a generic InP photonic integrated platform. With the amplifiers driven at a current density of 5 kA/cm², the OPA channels generated an RMS differential phase noise of less than 10 mrad across the C-band, proving the capabilities of the InP photonic platform in inherently maintaining a high degree of temporal coherence between adjacent channels. The influence of the measured differential phase noise on the far-field pattern and the pointing error are analytically evaluated. The integrated platform's inherently low differential phase noise renders it suitable for implementing LiDAR and short-range FSO communication systems without active phase locking, significantly reducing system complexity.