Adaptive Optical Systems

Adaptive Optical (AO) Systems

Adaptive optics have been integrated into systems for beam propagation, communications and microscopy. The traditional usage for AO was to correct for atmospheric turbulence during astronomical imaging. An incoming distorted wavefront is reflected off a Deformable Mirror (DM). After reflection, a fraction of the beam is split off and passed to a WaveFront Sensor (WFS). The WFS produces a 2D map of the distortions of the wavefront. These measurements are then used to generate the drive signals for the DM actuators. The system forms a closed loop driving the wavefront entering the WFS to null (flat). The flat wavefront will form a perfect diffraction limited image of the source.

Schematic of Traditional AO System

Deformable Mirror (DM)

A DM is a mirror whose surface shape can be accurately controlled via some method of actuation to control wavefront phase. AOA Xinetics is a leading provider of DMs, particularly for space and directed energy applications.

Wavefront Sensor (WFS)

A WFS measures the phase of an optical wavefront. A typical AO system uses a Shack-Hartmann WFS since these tend to have fast update rates and are less sensitive to environmental perturbations than other wavefront sensing methods. A reconstructor matrix is a mathematical object that converts data from the WFS into command signals to the DM. This matrix is usually determined by a calibration process. AOA Xinetics is a leading provider of custom wavefront sensors.

Driver Electronics

Deformable mirrors based on PMN technology, like those offered by AOA Xinetics, require high voltages to exercise the actuators. A mirror driver is an electronic device that converts signals from a computer processor into high voltage currents that are sent to the DM. Each actuator of the DM must have its own high voltage channel and corresponding physical wiring. AOA Xinetics offers the GEN III driver with up to 480 output channels.

Sensorless AO

Sensorless AO refers to a system without an explicit wavefront sensor, instead using the imaging camera as the detector that guides the shape of the DM. It is a catch-all term for "hill-climbing" techniques implemented by the direct optimization of a system performance metric applied through an active optical component. A specific example is Stochastic Parallel Gradient Descent (SPGD). Control is based on the maximization of system performance metric by small adjustments in actuator displacement in the mirror array, for instance the maximization of power through a pinhole. Sensorless AO techniques are less complex, less costly and more compact than traditional AO systems. However they tend to have poorer bandwidth and may not converge under certain circumstances. AOA Xinetics has direct experience with a variety of sensorless algorithms, including SPGD, phase diversity, and modal image optimization.