Design and optimization of a self-referencing interferometer for effective wavefront sensing in adaptive optics systems

In this work, we consider the design of a self-referencing interferometer for wavefront sensing. The design is put forward as a key element for adaptive optics systems implementing laser-based (free-space optical) communication through the atmosphere. The self-referencing interferometer is pursued given its ability for operation under weak through strong atmospheric turbulence conditions. This sets it apart from traditional wavefront sensing systems, which can falter under strong turbulence conditions. The self-referencing interferometer takes the form of a traditional (Michelson) interferometer with the input beam, having wavefront/phase distortion across its transverse profile, split into signal and reference arms. The signal beam is subjected to a linear tilt, while the reference beam undergoes spatial filtering/aperturing to give it a sufficiently flat wavefront/phase profile. The signal and reference beams are then overlapped at the output of the interferometer, and the output beam is imaged on a camera. The image is processed to extract a profile of the distorted wavefront/phase across the input beam, with the conjugate of this distorted wavefront/phase profile applied to a deformable mirror for its correction. In this work, we consider the key design parameters for such a system, operating at a wavelength of 1550 nm, with particular thought given to the levels of linear tilt on the signal beam and spatial filtering/aperturing on the reference beam. We illustrate the sensitivity of the output characteristics to these levels and provide recommendations for optimal functioning of self-referencing interferometers in future laser-based (free-space optical) communication systems.