Integrated Multichannel Transceivers for Free-Space Optical Communication

Free-Space Optical Communication (FSOC) is an advanced wireless technology enabling high-speed data transmission without requiring physical fiber-optic infrastructure. Operating in unlicensed spectral bands, FSOC avoids spectrum congestion, offers immunity to electromagnetic interference, and provides high security due to narrow-beam transmission, making eavesdropping highly difficult. Its low latency, high energy efficiency, and rapid deployability make FSOC an attractive solution for last-mile access, temporary or emergency links, satellite communication, and high-capacity terrestrial or air-to-ground channels. These advantages position FSOC as a complementary or alternative technology to fiber systems, especially where cable deployment is impractical or cost-prohibitive. This work aims to combine the strengths of FSOC with the unique capabilities of InP-based photonic integrated circuits (PICs), which enable the compact, robust, and energy-efficient integration of multiple optical functions within a single chip. We present the design, fabrication, and experimental evaluation of multi-channel integrated transceivers developed using a generic InP platform and dedicated to FSOC applications. The transmitter circuits integrate distributed Bragg reflector (DBR) lasers, electro-absorption modulators (EAMs), and arrayed-waveguide gratings (AWGs), while the receiver comprises an array of photodiodes coupled to an AWG. Furthermore, we introduce a new FSOC-dedicated transceiver architecture featuring four wavelength channels and semiconductor optical amplifiers (SOAs) positioned at the AWG outputs to enhance optical power and improve the overall free-space link budget. Comprehensive characterization involved measurements of DBR lasers, modulators, and AWG spectral responses, as well as BER and eye-diagram analyses for single- and multi-channel transmission. Open eye diagrams were recorded at data rates up to 10 Gb/s. For a two-channel FSOC link over a 100 m distance, a received optical power of –17 dBm enabled error-free operation with a BER of 10⁻¹². Transmission experiments were carried out in both indoor and outdoor conditions using the designed integrated transmitter, confirming its robustness and stable performance in practical optical-wireless scenarios. This work was funded under the FENG programme, project “Integrated Photonics Systems for Free-Space Optical Communication (FSOC)”, FENG.01.01-IP.01-A0MR/24-00.