Adaptable Shack-Hartmann wavefront sensor with diffractive lenslet arrays to mitigate the effects of scintillation

Abstract

Adaptive optics systems are used to compensate for distortions of the wavefront of light induced by turbulence in the atmosphere. Shack-Hartmann wavefront sensors are used to measure this wavefront distortion before correction. However, in turbulence conditions where strong scintillation (intensity fluctuation) is present, these sensors show considerably worse performance. This is partly because the lenslet arrays of the sensor are designed without regard to scintillation and are not adaptable to changes in turbulence strength. Therefore, we have developed an adaptable Shack-Hartmann wavefront sensor that can flexibly exchange its lenslet array by relying on diffractive lenses displayed on a spatial light modulator instead of utilizing a physical microlens array. This paper presents the principle of the sensor, the design of a deterministic turbulence simulation test-bed, and an analysis how different lenslet arrays perform in scintillation conditions. Our experiments with different turbulence conditions showed that it is advantageous to increase the lenslet size when scintillation is present. The residual phase variance for an array with 24 lenslets was up to 71% lower than for a 112 lenslet array. This shows that the measurement error of focal spots has a strong influence on the performance of a Shack-Hartmann wavefront sensor and that in many cases it makes sense to increase the lenslet size. With our adaptable wavefront sensor such changes in lenslet configurations can be done very quickly and flexibly.

Robust structured light in atmospheric turbulence

“…Importantly, our approach works even when the medium is long and the aberration strong, a regime where traditional adaptive optics often fails (beyond a Rytov variance of order 1). 98,99 A natural feature of the eigenmodes is that they are channelspecific. To be useful in a real-world setting, the transmission should be faster than the coherence time of the turbulence.…”

“…These modes are eigenmodes in their truest sense, i.e., they are fixed under the action of the channel. Importantly, our approach works even when the medium is long and the aberration strong, a regime where traditional adaptive optics often fails (beyond a Rytov variance of order 1) 98 , 99 …”

Influence of bandwidth error on the performance of adaptive optics systems for uncooperative beacons: plane wave and spherical wave analysis

“…Note that a real AO system is not going to achieve the performance levels quoted in this paper for several reasons. The main causes for this are the fact that practical wavefront sensors are susceptible to noise (from Poisson photon statistics, background, and the readout process) and they are especially vulnerable in the presence of scintillation 3,28 . The measurement error, which we neglect in our analysis, is therefore going to increase the residual phase variance.…”

Effect of Wavefront Distortion on the Performance of Coherent Detection Systems: Theoretical Analysis and Experimental Research

“…Zhong ZQ et al proposed a laser beam using a self-rotating wavefront to eliminate the degradation caused by turbulence and obtain a lower peakto-valley (PV) [11]. Among them, the introduction of AO technology further improved the mixing efficiency at the receiver side of the system, becoming an effective method to suppress the atmospheric turbulence effect [12][13][14]. The AO system corrected by the Zernike mode method can effectively compensate for the wavefront distortion effect caused by atmospheric turbulence on the reception sensitivity of the optical wireless coherent communication system [15][16][17][18].…”