Research On Voice Coil Deformable Mirror For Tip-tilt And High-order Aberration Correction

To obtain higher beam quality and imaging resolution,adaptive optics technology is applied in more and more optical systems.Deformable mirror（DM）is an important unit in adaptive optics system（AOS）,which can correct static dynamic aberration.Among all kinds of DMs,the voice coil deformable mirror compensates the wavefront distortion caused by atmospheric turbulence in large ground-based telescopes due to its low driving voltage and large phase stroke.However,voice coil deformable mirrors（VCDM）used for astronomical observation are difficult to popularize and applied in the fields of biological microscopy and visible light communication due to their large size and high cost.In addition,in traditional adaptive optics systems,tip tilt mirrors（TTM）are used to correct tip-tilt aberrations,and deformable mirrors are used to correct high-order aberrations.The cost of the entire AOS is high and its control process is complicated.To solve the above problems,a compact VCDM and a micro-deflection system were designed based on systematic theoretical analysis.At the same time,a structure of VCDM that can correct tip-tilt aberrations and higher-order aberrations on a single mirror was proposed.The specific research contents are as follows:（1）A compact VCDM is proposed.The deformable mirror adopted a micro voice coil actuator with a simple structure.The structural parameters of the voice coil actuator were optimized by ANSYS finite element software.The electromagnetic force of the voice coil actuator after optimization is 10%higher than that before optimization,and the efficiency is doubled.After the mirror material is determined,the optimal aperture and optimal coupling coefficient range of the 69-element VCDM were found by taking the wavefront fitting accuracy as the evaluation factor of metric（FOM）.The thermal analysis results show that the compact VCDM has good thermal stability.The temperature rise of the mirror is less than 0.4degrees Celsius at a current of 0.06 A,and the thermal distortion is only 12.36 nm.The compact voice coil has a fast response time of 0.65ms.The compact voice coil has a fast response time of 0.65ms.The fitting results of Zernike aberrations show that the wavefront fitting precision of the compact VCDM is 13%higher than that of the large-scale VCDM,which can meet the requirements of miniaturized adaptive optics system.（2）A micro-deflection system to correct the global tilt and tip is designed.The system adopted the composite transmission structure of a universal flexible hinge and a reed flexible hinge.By comparing the deflection table drift,the driving mode is determined to be the force couple.High-efficiency reluctance voice coil actuators were used for force couple.The structural parameters of the double-coil reluctance voice coil actuator were optimized.When the current is 0.03 A,the actuator can output an electromagnetic force of 1.34 N,and the corresponding efficiency is 5.72 N/W^1/2,which meets the application requirements of the micro-deflection system.Taking the deflection amplitude and normalized drift as the evaluation index,the structural parameters of the universal flexible hinge and the reed flexible hinge were optimized one by one.Driven by a force couple of±1 N,the optimized micro-deflection system has a deflection amplitude of 48.05μm（1.848mrad）and a normalized drift of only 0.0127%.The results show that when the micro-deflection system is unloaded,the first resonance frequency is 549 Hz,and its maximum effective load is 25 g.（3）Based on the principle of Zernike polynomial decoupling wavefront aberration,a VCDM for full-order aberration correction is proposed.The micro-deflection system in the deformable mirror is responsible for correcting tip-tilt aberrations,and the compact deformable mirror on the deflection stage is responsible for correcting high-order aberrations.The influence of the micro-deflection system on the compact deformable mirror responsible for high-order aberration correction was explored.It is found that the flux leakage of the reluctance voice coil actuator is very small,and the maximum parasitic force on the micro voice coil actuator is only 0.018 m N.This effect can be compensated in the control system.In addition,under the maximum working current,the micro-deflection system increases the mirror temperature by 0.59 degrees Celsius,and the PV of the thermal deformation is only24nm.A 97-element MEMS deformable mirror was used as a compact deformable mirror prototype to evaluate the correction capability of a voice coil deformable mirror.The results show that the VCDM can correct tip-tilt aberrations with a PV value as high as 24.94μm,and the RMS of the residual wavefront is less than 1.5 nm.For combined aberrations and random aberrations,the fitting precision of the voice coil deformable mirror is higher than that of the traditional deformable mirror.For random aberrations whose aberration components are within the fifth-order Zernike modes,the RMS reduction rate of the fitting residual wavefront of the VCDM is more than 9%compared with the traditional deformable mirror.The above results show that the VCDM can correct tip-tilt aberrations and high-order aberrations,and improve the compensation effect of the adaptive optics system.The VCDM for full-order aberration correction can reduce the complexity of the optical path and system cost,and has a good application prospect in retina imaging,airborne imaging,and other systems that require miniaturized adaptive optics equipment.