Chip-scale beam steering units, which would replace currently used mechanical gimbals, could revolutionize the field of free space optical communications. We review chip-scale technologies, which enable electronic beam reconfigurations and steering without mechanically moving parts. We assess the feasibility of using different electrically steerable apertures such as active metasurfaces and optical phased arrays for laser communications. Our optical link budget analysis shows that, for metasurface apertures of 1 cm in diameter and input powers of 5 W, the free space link range can approach ~ 10,000 km. We also provide an outlook how the link range can be increased further.

We demonstrate turbulence mitigation in a free-space optical link without adaptive optics. A module consisting of an 8-mode Multi-Plane Light Conversion (MPLC) device connected to a photonic integrated chip (PIC) collects a perturbed beam and converts it into a fundamental mode propagating in a standard single-mode fiber (SMF). Module is tested on a 200-meter optical link at 1550 nm under different D/r0 conditions. Results are compared to simulations and laboratory experiments using calibrated turbulent phase plates. We show increased coupling efficiency and lower fading compared to SMF coupling, demonstrating that MPLC and PIC are a viable turbulence mitigation option.

We demonstrate coherent on-chip combining for atmospheric turbulence mitigation using Multi-Plane Light Conversion (MPLC). A Niobate Lithium (LiNbO3) photonic integrated chip (PIC) was manufactured to optically combine via balancing and rephasing of 8 disturbed signals collected and demultiplexed by an MPLC. Cascaded on-chip Mach-Zehnders interferometers containing controllable phase shifters allow combining of optical inputs two at a time. Optical leaks are used as feedback loops. After 3 stages, all signals are coherently combined into a main output. We present efficiency, bandwidth, and compatibility with telecom operation of the PIC recombination.

Current satellite optical communications systems, e.g. EDRS, include a single optical terminal for point-to-point links. In case of a hand-over to a next available location, the optical terminal must actively repoint and reacquire the signal. We investigate a novel satellite telescope design covering multiple optical ground stations within its field-of-view. Additionally, orbital perturbations, mainly the ones due to inclination, distort the received optical field over the period of one day and must be compensated for each link individually. We present preliminary design of the space telescope and focal-plane-array and plan of the following breadboarding activity.

A module for spectral combination of five channels with an individual power of 20W each, designed for satellite-based communication, is presented. The channels are selected from the telecommunication ITU grid with a spectral spacing of 400 GHz. The combination is based on volume Bragg gratings, allowing for narrow spacing and combination without loss of near-diffraction-limited beam quality. Thermal effects due to high laser power are investigated. Due to the projected on-board satellite usage, volume and mass as well as vacuum conditions and radiation are considered in the module design.