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Hysteresis of piezoelectric deformable mirror (DM) reduces the closed-loop bandwidth and the open-loop correction accuracy of adaptive optics (AO) systems. In this work, a classical Prandtl–Ishlinskii (PI) model is employed to model the hysteresis behavior of a unimorph DM with 20 actuators. A modified control algorithm combined with the inverse PI model is developed for piezoelectric DMs. With the help of PI model, the hysteresis of the DM was reduced effectively from about 9% to 1%. Furthermore, open-loop regenerations of low-order aberrations with or without hysteresis compensation were carried out. The experimental results demonstrate that the regeneration accuracy with PI model compensation is significantly improved.

Introducing a reflective deformable mirror into an existing optical system for aberration correction requires a folded optical path and relay optics, increasing of the bulk and cost. This paper proposes a low-cost deformable lens (DL) that can be easily integrated into the existing system for correction of low-order aberrations. It is formed by a transparent medium layer sandwiched between a thick glass plate and a piezo-actuated thin glass plate with a transparent area in the middle. The thin glass plate presses the underlying transparent medium to produce optical path difference for correcting the aberrations of the transmitted light. The fabricated DL prototype accurately reproduced the first 9 Zernike mode shapes. Furthermore, the DL was integrated into a customized microscopy imaging system to correct the aberrations, significantly improving the quality of microscopic images.

Inherent hysteresis of piezoelectric deformable mirror (DM) limits the performance of adaptive optics (AO) systems including bandwidth and residual wavefront error. A charge control method based on switched capacitor charge pump was proposed to eliminate the hysteresis of piezoelectric DM. Experimental results show that the hysteresis of a unimorph DM was reduced from 11% to less than 1%. It indicates that the proposed charge control method has the potential to improve the deformation precision for one step correction as well as the bandwidth of the AO systems.

Adaptive optics (AO) systems greatly improve the resolution of retinal imaging instruments by actively correcting ocular aberrations. In this Letter, closed-loop correction as well as ocular aberration compensation of a 62-element silicon unimorph deformable mirror (DM) driven by only positive voltage is performed. The experimental results show that the root-mean square (RMS) wavefront of the initial mirror surface is reduced to 0.011 μm in a closed-loop AO system. The DM reproduces Zernike shapes from the third to 35th mode accurately. The simulated compensation of 200 ocular wavefronts shows that the average RMS value after correction is reduced to 0.017 μm.

This paper describes a piezoelectric deformable mirror (DM) for adaptive optics (AO) applications, with a 100 μm thick silicon mirror driven by 61 unimorph microactuators. Measurement results show that the stroke of the DM is ~ 7.4 μm at 100 V, and the resonance frequency is at 18 kHz. To demonstrate the correction capability of the DM, low-order Zernike modes up to 14th term were reproduced. Furthermore, a close-loop correction of laser beam in a 633 nm helium-neon laser system was performed. After system aberrations being compensated, a focal spot approximate to Airy disk was achieved.

This paper proposes a low-cost unimorph deformable mirror (DM) driven by positive voltages for ocular adaptive optics (AO). The DM consists of an inner actuators array and an outer ring actuator. The inner actuators array is used to correct aberrations, while the outer ring actuator is used to generate an overall defocus bias. The measurement results show that the maximum peak to valley defocus deformation is more than 14 μm. The DM has a satisfactory correction capability for up to the fifth order Zernike mode aberrations. Furthermore, a sample of 200 ocular wavefronts was simulated using a statistical model developed by Thibos. After correction with the developed DM, most of the simulated eyes achieved the diffraction-limited performance. These experimental and simulation results indicate that this DM is satisfactory for ocular applications.

Once a laser beam suffers from wavefront aberrations, the intensity of the focal spot degrades and the shape of the focus spot distorts. The same problem also exists in femtosecond laser fabrication system. The aberrations in the femtosecond laser fabrication system contain two main components: system aberrations and aberrations from the refractive index mismatch problem. Recently, adaptive optics (AO) has been used for laser beam aberrations correction to improve the light beam quality. In this paper, we introduce an adaptive optics system with double drive modes unimorph deformable mirror (DM) into the femtosecond laser fabrication system. In the experiments, the hill-climbing algorithm based on Zernike modes is used to control the DM to correct the aberrations in the close-loop manner. After correction for system aberrations and the refractive index mismatch aberrations, the shape and maximum intensity of the focal laser spot is much improved.

Unimorph deformable mirrors are attractive in adaptive optics system due to their advantages of simplicity, compact, low cost and large stroke. In this paper, a double drive modes unimorph deformable mirror is presented, which comprises a 200 μm thick PZT layer and a 400 μm thick silicon layer. This deformable has 214 inner actuators in the 50-mm active aperture, which are for the aberration correction and a outer ring actuator for generating an overall defocus bias. An analytical model based on the theory of plates and shells is built to predict the behavior of the deformable mirror. The stroke of the deformable mirror is tested in the experiments. In order to test the performance for aberration correction, the deformable mirror is used to correct the aberration from its imperfect initial mirror surface in the close-loop manner. The root-mean-square value of the mirror surface after the close-loop correction for ten iterations is about λ/40, which indicates this deformable mirror has a good aberration correction performance. This DM has the potential to be used for astronomical adaptive optics.

Unimorph deformable mirrors are attractive in adaptive optics system due to their advantages of simplicity, compact, low cost and large stroke. This paper reports the close-loop performance of a double drive modes unimorph deformable mirror.

The adaptive optics system (AO) without a wavefront sensor produces an alternative tool to correct the aberrations where the wavefront distortions are hard to be measured directly. This kind of adaptive optics system optimizes an evaluation parameter directly relevant to the wavefront quality to achieve the wavefront correction, and the optimization algorithms determines the efficiency of wavefront sensor-less AO system. In this paper, several frequently-used algorithms covering hill climbing algorithm, genetic algorithm, simulated annealing algorithm and two hybrid algorithms, known as hybrid genetic-hill climbing algorithm and hybrid simulated annealing-hill climbing algorithm (SAHC), have been investigated to improve the correction efficiency. The correction speeds and correction effects of the five kinds of algorithms have been compared in simulations and experiments for an adaptive optics system with 19-elements unimorph deformable mirror. The results show that hill climbing algorithm has the fastest correction speed, but suffered from the local optimum problem. The other four kinds of algorithms can get good correction results and have similar correction effects. Considering the correction effect and correction speed comprehensively, SAHC is the most efficient optimization algorithm in the five kinds of optimization algorithms.

Piezoelectric DM based on unimorph microactuator array has advantages of large stroke with low voltage and high operating bandwidth. In this paper, we estimate the correction capability of this DM by fitting Zernike polynomials shapes. First, the influences of actuator arrangement, actuator number and coupling on correction capability were investigated to optimize the correction performance. Then low-order Zernike shapes were reproduced by a fabricated DM using measured influence function matrix. Experiment and simulation results show that the DM has a satisfying correction performance.

This paper describes the characteristics of a 61 element piezoelectric deformable mirror (DM) based on bulk-PZT thick film and the generation of Zernike polynomials. This device consists of a continue silicon mirror supported by 61 element piezoelectric unimorph actuators which are arranged in a hexagonal grid with spacing of 5mm. Measurements of the displacement using a laser Doppler vibrometer demonstrated that the stroke of DM was 3.8μm at 100 volt with a displacement hysteresis of approximately 9% and the operating bandwidth was greater than 10KHz. A custom phasing-shifting interferometer based on Twyman-Green interferometer was developed to measure the mirror surface shape in response to the applied voltage. The influence function of the mirror measured accorded with Gaussian function with inter-actuator coupling of approximately 5%, which was similar to the traditional piezoelectric DM with stacked actuators. To examine the ability of the mirror to replicate optical aberrations described by the Zernike polynomials, low-order Zernike modes were reproduced by calculating the voltage on each actuator using an influence function matrix. The measurement demonstrated that the deformable mirror could produce the Zernike modes up to the ninth term. Considering the low-voltage actuation as well as the capability for miniaturization of the actuator size, deformable mirror actuated by bulk-PZT thick film has a potential application for low-cost adaptive optics.

A modified low-cost unimorph deformable mirror (DM) driven only by positive voltages for atmospheric turbulence compensation is presented. The 214 patterned inner actuators generate convex deformations for aberration correction, while one outer ring actuator generates an overall concave bias. To evaluate the aberration correction capability of the proposed DM, the iterative reconstruction of Zernike aberrations and correction were performed in an adaptive optics test system. The experimental results indicate that the fabricated DM has an excellent aberration correction capability, particularly matching the first 20 term Zernike aberrations with the normalized residual root-mean-square (RMS) error

This paper presents a low-cost silicon unimorph deformable mirror (DM) that will be used for astronomical adaptive optics. The device has a simple construction consisting of a 400-μm-thick silicon wafer and a 200-μm-thick lead zirconate titanate film, with 214 actuators and 50-mm active aperture. The actuator displacement of the fabricated device is about 1 μm at 50 V. And the resonance frequency is 550 Hz. The simula- tion and experimental generation of Zernike mode shapes indicate that the fabricated DM has an excellent correction performance for both low order and high order aberrations. © 2013 Society of Photo-Optical Instrumentation Engineers

To solve the local optimum problem, a modified hill-climbing algorithm based on Zernike modes is presented for wavefront sensorless adaptive optics. This algorithm adopts the Zernike mode coefficients, instead of the actuators' voltages in a traditional hill-climbing algorithm, as the adjustable variables to optimize the object function. First, the prin- ciple of the algorithm is described. Then the efficiency of the modified and traditional hill-climbing algorithms are analyzed numerically and experi- mentally using a He-Ne laser beam shaping system with a 37-element unimorph deformable mirror. The results of both simulations and experi- ments demonstrate that the modified hill-climbing algorithm can eliminate the local optimum problem with a fast speed of about 100 iterations. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.OE.52.1.016601) Subject terms: wavefront sensorless; adaptive optics; hill-climbing algorithm; Zernike modes; deformable mirror.

This paper reports the development and characterization of a low-cost thin unimorph deformable mirror (DM) driven by positive voltage. The developed DM consists of both an inner actuator array and an outer ring actuator, which works two drive modes: the inner actuator array is used for aberration correction, while the outer ring actuator is used to generate an overall defocus bias. An analytical model based on the theory of plates and shells is studied for predicting the behavior of the developed DM. Measurement results indicate that dual direction maximum defocus deformations of the developed DM are -14.3 and 14.9 μm, respectively, and the resonant frequency is 1.8 kHz. The root-mean-square deformation of the mirror surface after correction is better than λ/20 for λ=633 nm. The replication of Zernike mode shapes up to the fifth order demonstrates that this developed DM is satisfactory for low-order aberration correction.