Optical communication system using a photonic lantern for fine point tracking

A free-space optical communication system, comprising:

• a photonic lantern, the photonic lantern extending between a first open end and a second open end, wherein,
• the first open end comprises an opening to a single multi-mode fiber, the first open end being coupled to an external signal path arranged to transmit transmitted signals and receive received signals through free-space, and
• the second open end comprises a plurality of single mode fibers adiabatically coupled to the multi-mode fiber, the plurality of single-mode fibers include a single-mode fiber adapted to carry a fundamental optical mode and the remaining single-mode fibers adapted to carry higher-order optical modes, and
• at least one of the single-mode fibers is coupled to a signal transmitting path, and the remaining single-mode fibers are coupled to a signal receiving path;
• a signal processing unit coupled to the at least one single-mode fiber via an optical directional coupler, and to the remaining single-mode fibers via separate receiving path connections, wherein the signal processing unit includes one or more fiber splitters to sample a fraction of the received signal in each single mode fiber;
• one or more intensity sensors positioned in one arm of each fiber splitter, and used for monitoring fiber-specific intensity data associated with each of the single-mode fibers;
• a fine pointing assembly, disposed along the external signal path, and upstream of the photonic lantern, the fine pointing assembly comprising a fast steering optical element and a driver for controlling the fast steering optical element;
• a controller coupled to the one or more intensity sensors and the driver, the controller being configured to:
• receive, from the one or more intensity sensors, the fiber-specific intensity data associated with each of the single-mode fibers;
• based on the fiber-specific intensity data, determine a configuration of an incident wavefront on the fast steering mirror, wherein the configuration is determined using a neural network model trained to associate a non-linear relationship between fiber-specific intensity data and the incident wavefront configuration;
• and
• based on the determined incident wavefront configuration, transmit control data to the driver to control the fast steering mirror to stabilize the incident wavefront thereby applying an appropriate displacement angle to displace the received signals from the transmitted signals.