Conformal optical design with combination of static and dynamic aberration corrections

Conformal domes that are shaped to meet aerodynamic requirements can increase range and speed for the host platform. Because these domes typically deviate greatly from spherical surface descriptions, a variety of aberrations are induced which vary with the field-of-regard （FOR） angle. A system for correcting optical aberrations created by a conformal dome has an outer surface and an inner surface. Optimizing the inner surface is regard as static aberration correction. A deformable mirror is placed at the position of the secondary mirror in the two-mirror all reflective imaging system, which is the dynamic aberration correction. An ellipsoidal MgF2 conformal dome with a fineness ratio of 1.0 is designed as an example. The FOR angle is 0°-30°, and the design wavelength is 4μm. After the optimization at 7 zoom positions by using the design tools Code V, the root-mean-square （RMS） spot size is reduced to approximately 0.99 to 1.48 times the diffraction limit. The design results show that the performances of the conformal optical systems can be greatly improved by the combination of the static correction and the dynamic correction.

Derivative Form of Off-axis Aberration Correction Surface and Its Application in Solar Energy Concentration

By using the derivative method, we obtained the same result with that of the previous work of Chen et al. in 2006. Different from the integral form, the derivative form of the surface expression published in this paper is derived from differential equation and based on the theory of non-imaging focusing heliostat proposed by Chen et al. in 2001. The comparison of the derivative form of fixed aberration correction surface has been made with that of integral form surface as well as that of spherical surface in concentrating the solar ray.

Two-photon polymerization of femtosecond high-order Bessel beams with aberration correction

In the femtosecond two-photon polymerization(2PP)experimental system,optical aberrations degrade the fabrication quality.To solve this issue,a multichannel interferometric wavefront sensing technique is adopted in the adaptive laser processing system with a single phase-only spatial light modulator.2PP fabrications using corrected high-order Bessel beams with the above solution have been conducted,and high-quality microstructure arrays of microtubes with 20μm diameter have been rapidly manufactured.The effectiveness of the proposed scheme is demonstrated by comparing the beam intensity distributions and 2PP results before and after aberration corrections.

A coherence-based phase aberration correction method in medical ultrasound

A coherence-based correction method was proposed in order to improve the lateral resolution and enhance the contrast of medical ultrasound imaging in the presence of phase aberration. The averaged coherence factor was proposed at first and used as a metric to evaluate phase aberration correction. By maximizing the averaged coherence factor, the time delay parameter of each channel was adjusted. A new set of coherence factors was calculated and the corrected data was optimized to form the final B-mode image. The simulations on point targets and a cyst phantom showed that the proposed method outperformed the nearest neighboring cross correlation method and conventional coherence-weighting method, and the lateral resolution and contrast ratio was improved by approximately 0.24mm and 18dB respectively. The proposed method combined the advantages of phase error correction and coherence-weighting, which could improve imaging qualities effectively in medical ultrasound.

End-to-end optimization of a diffractive optical element and aberration correction for integral imaging

In the integral imaging light field display, the introduction of a diffractive optical element (DOE) can solve the problem of limited depth of field of the traditional lens. However, the strong aberration of the DOE significantly reduces the final display quality. Thus, herein, an end-to-end joint optimization method for optimizing DOE and aberration correction is proposed. The DOE model is established using thickness as the variable, and a deep learning network is built to preprocess the composite image loaded on the display panel. The simulation results show that the peak signal to noise ratio value of the optimized image increases by 8 dB, which confirms that the end-to-end joint optimization method can effectively reduce the aberration problem.

Magnetic fluid based deformable mirror for aberration correction of liquid telescope

A magnetic fluid based deformable mirror(MFDM) that could produce a large stroke more than 100 μm is designed and demonstrated experimentally with respect to the characteristics of the aberration of the liquid telescope. Its aberration correction performance is verified by the co-simulation using COMSOL and MATLAB. Furthermore, the stroke performance of the MFDM and the decentralized linear quadratic Gaussian(LQG) mirror surface control approach are experimentally evaluated with a prototype of MFDM in an adaptive optics system to show its potential application for the large aberration correction of liquid telescopes.

Digitalized Mirror Array and Its Application in Large Telescope:Principle and Case Studies

In this article, we report the principle and conceptual design of a fundamentally different technology in fabricating high precision aberration free optical devices. The tip-tilt of facet in a mirror array is produced by digitally controlled line-tilts of rows and columns. It has not only provided a cost-effective designing methodology in optical physics but also led to a much finer precision of 1 mili arc sec or less. As examples of the application of the proposed digitalised optics, two case studies have been given： a 10 m Schmidt telescope （off-axis） and an 8 m Cassegrain telescope （on-axis）.

Spatial light modulation for femtosecond laser manufacturing:Current developments and challenges

Since the invention of lasers,spatial-light-modulated laser processing has become a powerful tool for various applications.It enables multidimensional and dynamic modulation of the laser beam,which significantly improves the processing efficiency,accuracy,and flexibility,and presents wider prospects over traditional mechanical technologies for machining three-dimensional,hard,brittle,or transparent materials.In this review,we introduce:(1)The role of spatial light modulation technology in the development of femtosecond laser manufacturing;(2)the structured light generated by spatial light modulation and its generation methods;and(3)representative applications of spatial-light-modulated femtosecond laser manufacturing,including aberration correction,parallel processing,focal field engineering,and polarization control.Finally,we summarize the present challenges in the field and possible future research.

Light correcting light with nonlinear optics

Structured light,where complex optical fields are tailored in all their degrees of freedom,has become highly topical of late,advanced by a sophisticated toolkit comprising both linear and nonlinear optics.Removing undesired structure from light is far less developed,leveraging mostly on inverting the distortion,e.g.,with adaptive optics or the inverse transmission matrix of a complex channel,both requiring that the distortion be fully characterized through appropriate measurement.We show that distortions in spatially structured light can be corrected through difference-frequency generation in a nonlinear crystal without any need for the distortion to be known.We demonstrate the versatility of our approach using a wide range of aberrations and structured light modes,including higher-order orbital angular momentum(OAM)beams,showing excellent recovery of the original undistorted field.To highlight the efficacy of this process,we deploy the system in a prepare-and-measure communications link with OAM,showing minimal cross talk even when the transmission channel is highly aberrated,and outline how the approach could be extended to alternative experimental modalities and nonlinear processes.Our demonstration of light-correcting light without the need for measurement opens an approach to measurement-free error correction for classical and quantum structured light,with direct applications in imaging,sensing,and communication.

Accuracy characterization of Shack-Hartmann sensor with residual error removal in spherical wavefront calibration

The widely used Shack-Hartmann wavefront sensor(SHWFS)is a wavefront measurement system.Its measurement accuracy is limited by the reference wavefront used for calibration and also by various residual errors of the sensor itself.In this study,based on the principle of spherical wavefront calibration,a pinhole with a diameter of 1μm was used to generate spherical wavefronts with extremely small wavefront errors,with residual aberrations of 1.0×10^(−4)λRMS,providing a high-accuracy reference wavefront.In the first step of SHWFS calibration,we demonstrated a modified method to solve for three important parameters(f,the focal length of the microlens array(MLA),p,the sub-aperture size of the MLA,and s,the pixel size of the photodetector)to scale the measured SHWFS results.With only three iterations in the calculation,these parameters can be determined as exact values,with convergence to an acceptable accuracy.For a simple SHWFS with an MLA of 128×128 sub-apertures in a square configuration and a focal length of 2.8 mm,a measurement accuracy of 5.0×10^(−3)λRMS was achieved across the full pupil diameter of 13.8 mm with the proposed spherical wavefront calibration.The accuracy was dependent on the residual errors induced in manufacturing and assembly of the SHWFS.After removing these residual errors in the measured wavefront results,the accuracy of the SHWFS increased to 1.0×10^(−3)λRMS,with measured wavefronts in the range ofλ/4.Mid-term stability of wavefront measurements was confirmed,with residual deviations of 8.04×10^(−5)λPV and 7.94×10^(−5)λRMS.This study demonstrates that the modified calibration method for a high-accuracy spherical wavefront generated from a micrometer-scale pinhole can effectively improve the accuracy of an SHWFS.Further accuracy improvement was verified with correction of residual errors,making the method suitable for challenging wavefront measurements such as in lithography lenses,astronomical telescope systems,and adaptive optics.

Cascading optofluidic phase modulators for performance enhancement in refractive adaptive optics

We discuss the implementation and performance of an adaptive optics(AO)system that uses two cascaded deformable phase plates(DPPs),which are transparent optofluidic phase modulators,mimicking the common woofer/tweeter-type astronomical AO systems.One of the DPPs has 25 electrodes forming a keystone pattern best suited for the correction of low-order and radially symmetric modes;the second device has 37 hexagonally packed electrodes better suited for high-order correction.We also present simulation results and experimental validation for a new open-loop control strategy enabling simultaneous control of both DPPs,which ensures optimum correction for both large-amplitude low-order,and complex combinations of low-and high-order aberrations.The resulting system can reproduce Zernike modes up to the sixth radial order with stroke and fidelity up to twice better than what is attainable with either of the DPPs individually.The performance of the new AO configuration is also verified in a custom-developed fluorescence microscope with sensorless aberration correction.