The main postulates of adaptive correction of distortions of the wave front in large-size optical systems

In modeling space optical systems, an important property affecting the wave front error is the coefficient of thermal expansion (CTE) of the materials. The change of deformation that an optical element experiences due to thermal loads is proportional to both the CTE and the change in temperature gradient. This deformation affects the performance of the optical system by introducing error in the wave front. The deformation can be reduced in part by using materials with low CTE. Alternatively, using high conductivity materials to minimize temperature gradients through the mirror can also reduce deformation. Usually, a combination of these approaches is used to optimize the performance and meet the requirements of the system. Even with the utmost attention to thermal control, often the temperature gradients cannot be completely avoided. Low CTE materials have been developed to reduce thermal deformation, including ULE (Ultra-low Expansion), Zerodur, and Silicon Carbide. However, the manufacturing process can result in non-uniformities throughout the optics. For optical systems requiring highly precise performance, modeling these non-uniformities becomes important. The non-uniformity in the CTE of a material in effect compounds the deformation in the same manner as introducing additional temperature gradient through the optics. This paper describes the methodology for integrated thermal/mechanical modeling to predict the deformation response of an optical element with assumed CTE variations and thermal disturbances. A mirror with an assumed CTE variation was modeled in a changing thermal environment and using IDEAS/TMG analysis tools, thermal deformations were predicted. Results show excellent agreement with engineering predictions. Clearly knowing the CTE variation of the material is a critical step for modeling. However, measuring and specifying the material CTE is out of the scope of this paper.

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Multigrid Approach to Predictive Wave-Front Reconstruction in Adaptive Optical Systems

Applied Optics ◽

10.1364/ao.43.003708 ◽

2004 ◽

Vol 43 (18) ◽

pp. 3708 ◽

Cited By ~ 3

Author(s):

Jeffrey D. Barchers

Keyword(s):

Wave Front ◽

Optical Systems

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Using an Adaptive Filtration to Improve Adaptive Optical Systems Performance. Analytical Review

Mechanical Engineering and Computer Science ◽

10.24108/0219.0001461 ◽

2019 ◽

pp. 34-60

Author(s):

Yu. I. Shanin

Keyword(s):

Wave Front ◽

Adaptive Optics ◽

Adaptive Filtering ◽

Input Signal ◽

Least Square ◽

Optical Systems ◽

Control Algorithms ◽

Optical Wave ◽

Adaptive Filtration ◽

Laser Systems

For adaptive optical systems (AOS) installed in the optical path of aircraft-based laser systems, the presence of changing input light signals is typical. A wave-front sensor processes these signals. The quality of the radiation wave-front correction depends on how well the rapidly changing input signal is received and processed. When dealing with such signals, an adaptive filtration (AF) is used, which allows automatic adaptation to the changing input signal. The adaptive filtration is used in control algorithms for adaptive optical systems.The paper gives a brief theoretical AF background as applied to the AOS. The AF with feedback can be used for the following: a) predictions, b) identification of an unknown system, c) balancing of characteristics, d) disturbance rejection. The AF main point is to control the weighting factors of the input signal, which form the output signal. Under control, the difference between the reference and output signals is minimized. Mathematically, this comes down to defining the global minimum of the objective function. Among the search methods for this minimum, the paper considers the following ones: the Newton's method, the steepest-descent method and its modified version - the least square error method, and the recursive AF algorithm using the least squares criterion. The choice requirements for an adaptive algorithm are formulated.The paper considers direct application of the AF methods in the control algorithms of the AOS used in the airborne laser systems. Analyzes both the works on improving operation of classical AOS control loops (based on the PID-controllers with time-fixed gains) by adding various adaptive devices to the circuit, and the works on direct use of the adaptive filters and their relevant control algorithms. Adaptive filtering has shown the positive results both in suppressing the multiple narrow-band vibrations inherent in the aircraft and in broadband jitter due to the turbulent atmosphere, including the aero-optical wave-front aberrations of laser radiation.For more successful application of the adaptive filtering methods for AOS control, further interpretation and research into capabilities of their practical implementation for specific applications of adaptive optics is required.

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Method for optimizing the errors of the wavefront of recorded radiation for large-size information-measuring optical systems

Izmeritel`naya Tekhnika ◽

10.32446/0368-1025it.2021-2-57-61 ◽

2021 ◽

pp. 57-61

Author(s):

Victor V. Sychev ◽

Andrey I. Klem

Keyword(s):

Traditional Method ◽

Optimization Problem ◽

Optical Systems ◽

Field Variation ◽

Large Telescope ◽

Size Information ◽

Image Field ◽

Advantages And Disadvantages ◽

Large Size ◽

Secondary Mirror

The article proposes a new method for increasing the information content of the image by minimizing the errors of the optical system of a large telescope using the redistribution of errors over the image field. Variation of the parameters of the secondary mirror is carried out to solve the optimization problem of uniform distribution of aberrations over the image field of a large telescope using the example of a cryotelescope with a diameter of 12 m in the Zemax-EE package. The results of calculations of optical schemes by the traditional method and by the method of optimization of the errors of the radiation wavefront are presented. The advantages and disadvantages are considered.

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Automatic Control Systems for Adaptive Optical Systems: Analytical Review. Part 1: Adaptive Optical System Control of Onboard Laser Installations

Mechanical Engineering and Computer Science ◽

10.24108/0318.0001341 ◽

2018 ◽

pp. 51-68 ◽

Cited By ~ 1

Author(s):

Yu. I. Shanin ◽

A. V. Chernykh

Keyword(s):

Control System ◽

Laser Beam ◽

Automatic Control ◽

Wave Front ◽

Control Systems ◽

Turbulent Atmosphere ◽

Single Channel ◽

Optical Systems ◽

Automatic Control Systems ◽

Analytical Review

The first part of the analytical review presents an introduction to automatic control systems (ACS) for the adaptive optical systems (AOS) and control of tip-tilt correctors to eliminate a laser beam jitter. Considers a composition and a purpose of the AOS basic components. Also gives the AOS schemes to be used to form the sharper object images and focus radiation on a target when propagating a laser beam in a turbulent atmosphere. Briefly discusses the general issues of the AOS control, namely single-channel and multichannel linear control, bandwidth limitations of the control system, and possible signal paths in ACS of AOS.The article in-detail describes a path of the harmonic signal through the units of the feedback control loop as applied to the plane mirror of a two-channel corrector of the wave front tip-tilt. Provides guidelines to select the minimum quantization time for a propagating digital signal.Considers the certain problems of constructing ACS to be applied to AOS of the on-board laser installations. A simulated installation model where light passes through a turbulent atmosphere allowed us to develop a linear quadratic Gaussian controller (LQG-controller). Using this controller the optimal control (i.e. minimizing the dispersion of the output signal measured) with good robustness of the tip-tilt corrector is carried out.The concluding part of the review presents the certain research results of the AOS control when compensating the laser radiation wave front perturbations caused both by an aero-optical problem, arising when radiation propagates near the walls of an aircraft and by an atmospheric turbulence of free airflow. The influence of a small time delay (within one sampling step), when transmitting a control signal, on the control system operability was under special consideration.

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Pupil exploration and wave-front-polynomial fitting of optical systems

Applied Optics ◽

10.1364/ao.34.007986 ◽

1995 ◽

Vol 34 (34) ◽

pp. 7986 ◽

Cited By ~ 4

Author(s):

Ian Powell

Keyword(s):

Wave Front ◽

Optical Systems ◽

Polynomial Fitting

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Dynamic wave-front generation for the characterization and testing of optical systems

Optics Letters ◽

10.1364/ol.23.001849 ◽

1998 ◽

Vol 23 (23) ◽

pp. 1849 ◽

Cited By ~ 64

Author(s):

M. A. A. Neil ◽

M. J. Booth ◽

T. Wilson

Keyword(s):

Wave Front ◽

Optical Systems ◽

Dynamic Wave

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Broadband Ultrathin Transmission Quarter Waveplate with Rectangular Hole Array Based on Plasmonic Resonances

Nanoscale Research Letters ◽

10.1186/s11671-019-3200-y ◽

2019 ◽

Vol 14 (1) ◽

Author(s):

Yu Wang ◽

Yumin Liu ◽

Jing Li ◽

Chang Liu ◽

Zhongyuan Yu ◽

...

Keyword(s):

Near Infrared ◽

Silver Film ◽

Band System ◽

Optical Systems ◽

Hole Array ◽

Rectangular Hole ◽

Infrared Band ◽

Large Size ◽

Narrow Bandwidth ◽

Linearly Polarized

AbstractThe control of the polarization states of light plays an important role in modern optical systems. However, traditional polarization manipulating devices often have narrow bandwidth and their large size makes it difficult for them to achieve miniaturization and integration of optical systems. This work presents an ultrathin quarter waveplate with a periodic silver film 2 × 2 rectangular hole array with a thickness less than λ/50. Numerical simulation shows that the waveplate can efficiently transform a circular polarized wave into a linearly polarized one at the center of 1550 nm, and its bandwidth is 525 nm. Furthermore, the quarter waveplate can efficiently invert linear polarization into circular polarization at 1550 nm, which ellipticity is near unit. With an array of small holes on a metal film to enhance transmission, this structure can increase the transmission to 0.44. The broadband quarter waveplate can be used in communication system and near infrared band system, and be integrated with other optical devices at nanoscale to achieve polarization operation, detection, and sensing.

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