Adaptive Optics

Thousands of Individually Controlled Phase Elements

Until very recently, practical wavefront control systems have been limited by the lack of commercially-available, high-resolution, rapidly programmable spatial light modulators (SLMs). The application areas for high-resolution wavefront correction are varied, ranging from military imaging and laser communications to advanced ground-based telescopes and astronomy.

Liquid crystal on silicon devices provide a programmable phase shift at each pixel. Because the backplane of the device is a VLSI circuit, thousands of individually controlled elements are available, enabling not only low-order aberration control (e.g. tilt, power) but also extremely complicated wavefronts with high spatial frequency content. The devices capitalize on the fact that phase modulation is cyclical in nature, and uses phase resets to replicate phase distortion greater than a wavelength of the incident light. The total phase stroke of the SLM device is dependent on the number of pixels – with hundreds of waves of stroke possible.

Boulder Nonlinear Systems is currently investigating a liquid crystal “foveated imaging” concept – replacing heavy high-resolution lens systems with lightweight adaptive lenses. Although SLM devices are normally used to correct for wavefront aberrations, the devices can also be used to produce aberrations, providing a means to simulate atmospheric turbulence. In contrast to phase wheels, oil films or hot plates, the turbulence generated by SLMs can be calibrated with standard turbulence parameters, is repeatable, and dynamic. Segmentation or multiple SLM devices can be used to simulate a layered turbulent medium.