Wavefront sensor based on angle selectivity of an optical filter

The effectiveness of free-space laser communications is limited due to wavefront deformations caused by atmospheric optical turbulence. To determine these deformations, we propose a wavefront sensor that utilizes the angular selectivity of an optical transmission filter to measure the first derivative of the wavefront.

The transmission filter converts the gradients of the incident wavefront into an intensity distribution. For each direction (x and y) this distribution is captured twice, with different angles between filter and optical axis for each measurement. The contrast of both measurements (calculated for each pixel of the used detector) and the local gradients of the wavefront (averaged across each pixel) has a nearly linear relation. To reconstruct the wavefront from the obtained local gradients, algorithms developed for the Shack-Hartmann wavefront sensor are used. Simulations demonstrate the applicability of the sensor in atmospheric turbulence. For the experimental proof of concept, we have designed and fabricated volume Bragg gratings (VBG) as angular selective filters. The VBGs were implemented in an optical testbed to evaluate the sensor response to wavefront tilts.