Photonic Integrated Circuit Architecture and Modeling for Bidirectional Free-Space Optical Links with Independent Tx/Rx Beam Steering

We present a novel terminal design based on a 91-element optical phased array (OPA). This integrated architecture enables compact, bidirectional free-space optics (FSO) communication with independent transmit (Tx) and receive (Rx) beam steering. The system replaces the traditional telescope-based front end with a tiled large-lens array driven directly by a Photonic Integrated Circuit (PIC), eliminating the need for a telescope as well as circulators, beam splitters, or steering mirrors, and substantially improving form factor. The PIC architecture includes separate beamforming trees and phase-shifter arrays for Tx and Rx, followed by passive wavelength-selective routing that allows duplex operation through a shared optical aperture while maintaining independent pointing. The design supports point-ahead angles up to 50 μrad while mitigating micro-vibrations, suitable for inter-satellite and direct-to-Earth links under realistic orbital dynamics.Comprehensive end-to-end simulations and link-budget analyses demonstrate the feasibility of terabit-class performance. A 300 mm optical phased array composed of 91 elements, each 27 mm in diameter, achieves steering precision better than 0.5 μrad RMS and maintains approximately 50% of the optical power within the main lobe over its full steering range. Three representative scenarios are analyzed: an intra-plane LEO–LEO link at 1.6 Tbps (16×200G DP-QPSK) over 2,500 km, an inter-plane LEO–LEO link at 400 Gbps (2 × 200G DP-QPSK) over 5,000 km, and a GEO–LEO link at 100 Gbps (1×100G DP-QPSK) over 40,000 km. In all cases, the architecture meets the link-budget requirements while maintaining pointing margins sufficient for micro-vibration compensation.The results confirm that the integrated, large-aperture OPA approach enables scalable, alignment-tolerant optical terminals capable of supporting dynamic space geometries and multi-terabit throughput. By leveraging coherent combining of parallel EDFAs and low-loss SiN photonics, the system markedly reduces size, weight, and optical complexity, offering a clear path toward compact, high-performance laser communication payloads for next-generation space networks.