Systems and methods for remote detection and measurement of optical system misalignments in free-space optical communication terminals

A method for remotely detecting and measuring optical system misalignments, comprising:

• propagating an optical signal through a direction selective optical component;
• emitting the optical signal into free-space via a fiber end;
• collimating the optical signal emitted from the fiber end with a fiber collimator;
• controlling a pointing direction of the optical signal in free-space once emitted by the fiber end with a fast-steering mirror;
• relaying the emitted optical signal with an optical system;
• and
• transmitting the optical signal through an optical output element,
• wherein a portion of the optical signal is reflected from the optical output element, back-coupled through the fiber collimator, and routed through the direction selective optical component to detect a pointing misalignment.

A system for compact self-referenced alignment calibration in a free-space optical transmitter, comprising:

• a laser source configured to generate and transmit an optical signal;
• a direction selective optical component coupled to the laser source and configured to propagate the optical signal, the direction selective optical component comprising:
• an optical circulator configured to separate forward and backward propagating optical signals;
• and
• a fiber optic coupler configured to route a portion of a back-coupled optical signal to an optical power detector;
• a fiber end coupled to the direction selective optical component and configured to emit the optical signal into free-space;
• a fiber collimator positioned to collimate the optical signal emitted from the fiber end;
• a fast-steering mirror positioned to receive the collimated optical signal, the fast-steering mirror comprising an opto-mechanical device configured to scan and deflect the optical signal within two mutually orthogonal planes;
• an optical system comprising an optical telescope configured to relay and direct the scanned optical signal toward an optical output element comprising an optical window or an interference filter having a flat reflective surface upon which the transmitted optical signal is incident and from which a portion of the optical signal is reflected;
• and
• the optical power detector coupled to the direction selective optical component and configured to measure optical power back-coupled from the optical output element through the optical system, the fast-steering mirror, and the fiber collimator,
• wherein the optical power detector is further configured to generate an electrical signal corresponding to a measured amount of back-coupled optical power;
• wherein the laser source and the optical power detector are configured to determine a ratio of back-coupled optical power to transmitted optical power to evaluate changes in beam divergence, optical alignment, or an angular response of the fast-steering mirror, and
• wherein the system is configured to determine a position of maximum back-coupled optical power corresponding to a transmit beam direction that produces a maximum back-coupled response from the flat reflective surface of the optical output element and to detect deviations therefrom as optical misalignments.