A hybrid phase retrieval (HPR) method using a combination of linear phase retrieval (LPR) and iterative phase retrieval (IPR) is proposed for real-time wavefront sensing. Only the intensity information of a single defocused image is required by HPR. Low-order aberrations are estimated by classical LPR algorithm but using a “segmented” detector to provide design flexibility and better sensing accuracy. High-order aberrations are estimated by a kind of modified Gerchberg-Saxton (MGS) algorithm which uses the LPR result as a prior knowledge to significantly speed the convergence. The performance of HPR is tested under various seeing conditions by simulation. For atmospheric aberrations with D/r0=3, HPR containing LPR and ten-iteration IPR can achieve an averaged Strehl ratio of 0.88.
The Modified Hybrid-Input-Output (MHIO) phase retrieval algorithm is proposed for wavefront sensing. The results show that the MHIO algorithm significantly outperforms the Modified Gerchberg-Saxton algorithm (MGS) in large noise. However its dynamic-range is lower than MGS algorithm. It also shows that if combine the MGS algorithm with MHIO algorithm, which is called MGS+MHIO algorithm, then it can retain the property of MGS’s high dynamic-range and MHIO’s accuracy so that outperforms either MGS or MHIO algorithm. Repeating simulation results show that MGS+MHIO algorithm improves RMS of phase error obviously in high dynamic range and large noise.
Large-aperture segmented primary mirror will be widely used in next-generation space-based and ground-based telescopes. The effects of intersegment gaps, obstructions, position and figure errors of segments, which are all involved in the pupil plane, on the image quality metric should be analyzed using diffractive imaging theory. Traditional Fast Fourier Transform (FFT) method is very time-consuming and costs a lot of memory especially in dealing with large pupil-sampling matrix. A Partial Fourier Transform (PFT) method is first proposed to substantially speed up the computation and reduce memory usage for diffractive imaging analysis. Diffraction effects of a 6-meter segmented mirror including 18 hexagonal segments are simulated and analyzed using PFT method. The influence of intersegment gaps and position errors of segments on Strehl ratio is quantitatively analyzed by computing the Point Spread Function (PSF). By comparing simulation results with theoretical results, the correctness and feasibility of PFT method is confirmed.
In the process of high-resolution astronomical observation and space optical mapping, the wavefront aberrations caused by atmosphere turbulence effect lead to reduced resolution of optical imaging sensor. Firstly, on the base of influence of atmosphere turbulence effect for the optical observation system, this paper investigates and analyses the development and technical characteristics of deformable mirror, which is the key device of optical wavefront control technology. In this part, the paper describes the basic principles of wavefront control and measurement using the current production line of deformable mirror, including micro-electromechanical systems (MEMS) deformable mirror which is one of the most promising technology for wavefront modulation and Shack-Hartmann wavefront sensors. Secondly, a new method based on the technology of optical wavefront control and the data of optical path difference (OPD) for simulating the effect of optical transmission induced by turbulence is presented in this paper. The modeling and characteristics of atmosphere turbulence effect applied for optical imagery detector of astronomical observation and space optical mapping has been obtained. Finally, based on the theory model of atmosphere turbulence effects and digital simulation results, a preliminary experiment was done and the results verify the feasibility of the new method. The OPD data corresponding to optical propagation effect through turbulent atmosphere can be achieved by the calculation based on the method of ray-tracing and principle of physical optics. It is a common practice to decompose aberrated wavefronts in series over the Zernike polynomials. These data will be applied to the drive and control of the deformable mirror. This kind of simulation method can be applied to simulate the optical distortions effect, such as the dithering and excursion of light spot, in the space based earth observation with the influence of turbulent atmosphere. With the help of the optical wavefront control technology, the optical sensor and ability of space optical detection system for correcting the target image blurred by turbulence of atmosphere can be tested and evaluated in the laboratory.