Lens-Based Adaptive Optics

Optical space-to-ground communication links are impacted by atmospheric turbulence, which results in optical scintillation effects at the receiver.  Adaptive optics (AO) techniques have been introduced to mitigate these optical aberrations, especially in the field of astronomy. These systems typically employ a deformable mirror (DM) and a wavefront sensor linked to a computer to control an array of mirror actuators, and dynamically correct for the above distortions.   AO systems are also applicable to free-space optical communications (FSOC) and provide improved fiber coupling at the receiver compared to simple tip/tilt correction schemes using a fast-steering mirror (FSM) alone.  This is especially the case when coupling into single-mode (SM) fiber, which is required for coherent modulation schemes.  A drawback to DM-based AO systems is their size, complexity and cost.  The goal of this proposed Phase II project is the integration and test of a novel lens-based AO solution in an optical terminal, resulting in a prototype design suitable for use in an optical ground station (OGS) and that could also integrate with existing SDA optical intersatellite link (OISL) designs due to its compact size. The effort aims to demonstrate how a lens-based approach can simplify and reduce the size of AO systems needed to mitigate atmospheric turbulence effects in an OGS.  The technology is also applicable for use in space terminals to correct for optical system aberrations, such as those induced by temperature variations from solar or cold-space loading. Eritek plans to test the effectiveness of a COTS multiactuator adaptive lens (MAL) for implementing an AO system in a small FSOC terminal as an alternative to a DM approach.  MALs are compact devices that use piezoelectric actuators to deform a thin glass double-pane window containing an index-matching liquid.  They exhibit performance similar to a DM (for similar actuator counts) but require far less volume as they can be directly inserted into an existing optical path, unlike DMs that require a reflective path to be added to the optical setup. As part of this SBIR effort, Eritek proposes to modify one of its company-owned FSOC terminals to include a lens-based AO system, test and demonstrate its performance over a terrestrial link, and prepare a deliverable final report.  By using an existing FSOC terminal and associated modem equipment, Eritek expects to produce a working AO prototype terminal with just a small investment to procure the MAL device, AO control elements, and miscellaneous optics.  This will avoid fabrication of a new terminal and allow the proposed effort to be completed with minimal SBIR award funds. If successful, this effort promises to lead to the development of compact FSOC terminals with AO capability for ground-to-ground, space-to-ground, and inter-satellite link (ISL) applications, all of which should be of interest to SDA, other government entities, and commercial telecom providers.