Micromachined Membrane Deformable Mirror Research Articles

Membrane-based deformable mirror: intrinsic aberrations and alignment issues

A Deformable Mirror (DM) is an important component of an Adaptive Optics system. It is known that an on-axis spherical/parabolic optical component, placed at an angle to the incident beam introduces defocus as well as astigmatism in the image plane. Although the former can be compensated by changing the focal plane position, the latter cannot be removed by mere optical re-alignment. Since the DM is to be used to compensate a turbulence-induced curvature term in addition to other aberrations, it is necessary to determine the aberrations induced by such (curved DM surface) an optical element when placed at an angle (other than 0 degree) of incidence in the optical path. To this effect, we estimate to a first order, the aberrations introduced by a DM as a function of the incidence angle and deformation of the DM surface. We record images using a simple setup in which the incident beam is reflected by a 37 channel Micro-machined Membrane Deformable Mirror for various angles of incidence. It is observed that astigmatism is a dominant aberration which was determined by measuring the difference between the tangential and sagital focal planes. We justify our results on the basis of theoretical simulations and discuss the feasibility of using such a system for adaptive optics considering a trade-off between wavefront correction and astigmatism due to deformation.

A Novel Modal Wavefront Reconstruction Algorithm based on PSO Algorithm

Abstract The nonlinear response and strong coupling of control channels of micromachined membrane deformable mirror (MMDM) devices make it difficult to obtain the desired optimal surface shape of the MMDM. In order to overcome these limitations, the wavefront modal reconstruction algorithm based on particle swarm optimization (PSO) is proposed, which is used to find the optimal control voltages of the MMDM. It is initialized with a population of random solutions and searches for optima by updating generations. In this way the objective function can be optimum and influence of phase aberration can be reduced to minimum. The simulation results show that this algorithm could find the optimal MMDM shape which was applied to correct phase aberration.

微机械薄膜变形镜校正性能及控制算法

微机械薄膜变形镜校正性能及控制算法

Comparative analysis of Zernike aberrations generation with deformable mirrors for ocular adaptive optics

The micromachined membrane deformable mirror (MMDM) and piezoelectric deformable mirror (PDM) are two types of cost-effective deformable mirrors (DMs) that are widely used in ocular adaptive optics. In the current study, a 59ch MMDM and a 37ch PDM are tested and compared in generation of Zernike aberrations which are the most dominant of the human eye. The results reveal that although PDM performs better in larger scope, both DMs have almost similar performance if the individual generation coefficient is within the range of ±1 µm.

Variable View Imaging System: An Optomechatronic System for the Observation of Micro Objects with Variable View Direction

Insufficient vision information of conventional vision systems hinders the applications of vision-based microassembly and micromanipulation. In this article, an optomechatronic system with a variable view position and orientation is proposed to solve this problem, which is particularly suitable for observing three-dimensional micro objects in micromanipulation and microassembly. The integration of double wedge prisms and scanning mirrors gives a flexible view in a compact manner. In order to correct the variable aberrations induced by the wedge prisms and scanning mirror, a micromachined membrane deformable mirror (MMDM) is integrated in the system. Additionally, an optomechatronic design process for the proposed system is introduced. The view position and angle are analyzed by a ray tracing method. The proposed algorithm for MMDM can correct the aberrations in each Zernike mode without using a wavefront sensor instead of controlling each actuator. A series of experiments is conducted to investigate the validity of the prototype system.

Application of eigenmode in the adaptive optics system based on a micromachined membrane deformable mirror

The construction process and characteristics of a deformable mirror eigenmode are introduced. The eigenmode of a 37-element micromachined membrane deformable mirror (MMDM) from OKO, Ltd. is analyzed. The Gaussian-Seidel low-order aberrations are fitted with eigenmodes as basic functions. An experimental adaptive optics (AO) system is constructed with the MMDM as the wavefront corrector, a deformable mirror eigenmode as the wavefront control algorithm, and a Shack-Hartmann wavefront sensor as the wavefront detector. The experimental results demonstrate that the deformable mirror eigenmode can act as the wavefront control algorithm for the AO system based on the MMDM.

Retinal imaging with a low-cost micromachined membrane deformable mirror.

To study the retina in normal subjects with a high-resolution imaging system using adaptive optics for wave front aberration correction. We used a low-cost 37-element micromachined membrane deformable mirror (MMDM) with a continuous membrane as the reflective surface. A Hartmann-Shack wave front sensor with cooled charge coupled device camera was used to measure the wave front aberration. Zernike polynomials were used to describe the wave front shape. We developed a mirror control system to compensate for wave aberrations. We tested this instrument in normal subjects. We were able to image the retina in monochromatic laser light and document the increase in resolution. While it is hard to estimate the exact size of the smallest structures in the image, we were able to subjectively grade the image quality. The system is able to compensate for higher order aberrations present in the human eye. The capabilities of correcting ocular aberrations are limited by the number of adjustable elements in the mirror and the deflection range of the surface. The advantage of the MMDM system is its low cost when compared with other adaptive optics solutions such as piezodriven mirrors and spatial light modulators. This technique may allow for improved resolution for clinical fundus photography.

Intracavity control of a 200-W continuous-wave Nd:YAG laser by a micromachined deformable mirror

A silicon micromachined membrane deformable mirror with a diameter of 10 mm, reflectivity of better than 99.8%, and a surface deflection range of 3mum has been used for intracavity control of an industrial 200-W cw Nd:YAG laser. When it was placed in the resonator, the mirror demonstrated continuous (more than 40-h) stable operation under an ~550-W cw optical load, with beam diameters in the range 3-6 mm. Periodic modulation of the curvature of the deformable mirror with a frequency of 250 Hz produced quick switching between stable and unstable resonator configurations, which resulted in pulse-period Q -switched generation with average power in the range 50-200 W, modulation depth from 95% to 10%, and an M(2) parameter of 6.5 to 30.

Compact adaptive optical system based on blind optimization and a micromachined membrane deformable mirror

We describe and demonstrate an adaptive optical system based on the combination of a micromachined membrane deformable mirror and the stochastic parallel gradient descent control algorithm. This compact and relatively inexpensive adaptive optical system is used to maximize the coupling of a distorted laser beam into a single-mode optical fiber. The coupling efficiency is improved by 12 dB, and the coupling efficiency after correction is 64% of the diffraction-limited coupling efficiency.

Wave-front generation of Zernike polynomial modes with a micromachined membrane deformable mirror

We investigate the characteristics of a 37-channel micromachined membrane deformable mirror for wave-front generation. We demonstrate wave-front generation of the first 20 Zernike polynomial modes, using an iterative algorithm to adjust driving voltages. The results show that lower-order-mode wave fronts can be generated with good accuracy and large dynamic range, whereas the generation of higher-order modes is limited by the number of the actuator channels and the working range of the deformable mirror. The speed of wave-front generation can be as fast as several hundred hertz. Our results indicate that, in addition to generation of wave fronts with known aberrations, the characteristics of the micromachined membrane deformable mirror device can be useful in adaptive optics systems for compensating the first five orders of aberration.

Aberration-free dynamic focusing with a multichannel micromachined membrane deformable mirror

We demonstrate aberration-free dynamic focusing with a low-cost 19-channel continuous-surface micromachined membrane deformable mirror (MMDM). A lookup table of the optimum control voltages for various focal lengths is obtained with an adaptive optics algorithm. Diffraction-limited imaging resolution is achieved owing to the capability of the MMDM for aberration compensation. The measured speed of the MMDM supports dynamic focusing operations at several hundred hertz. Our dynamic focusing approach is shown to function with either monochromatic or broadband optical sources.

Adaptive control of a micromachined continuous-membrane deformable mirror for aberration compensation

The nonlinear response and strong coupling of control channels in micromachined membrane deformable mirror (MMDM) devices make it difficult for one to control the MMDM to obtain the desired mirror surface shapes. A closed-loop adaptive control algorithm is developed for a continuous-surface MMDM used for aberration compensation. The algorithm iteratively adjusts the control voltages of all electrodes to reduce the variance of the optical wave front measured with a Hartmann-Shack wave-front sensor. Zernike polynomials are used to represent the mirror surface shape as well as the optical wave front. An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels. The experimental results show that the algorithm can adaptively update control voltages to generate an optimum continuous mirror surface profile, compensating for the aberrations within the operating range of the deformable mirror.