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

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.

Adaptive optics: wave-front correction by use of adaptive filtering and control

2000 ◽  
Vol 39 (16) ◽  
pp. 2525 ◽  
Author(s):  
James Steven Gibson ◽  
Chi-Chao Chang ◽  
Brent L. Ellerbroek
Keyword(s):  
Wave Front ◽  
Adaptive Optics ◽  
Adaptive Filtering ◽  
And Control

Laser Wave-Front Measuring Based on Quadri-Wave Lateral Shearing Interferometry

2014 ◽  
Vol 568-570 ◽  
pp. 50-54 ◽  
Author(s):  
Juan Ren ◽  
Xiu Juan Luo ◽  
Ai Li Xia ◽  
Yu Zhang
Keyword(s):  
Wave Front ◽  
Adaptive Optics ◽  
Least Square Method ◽  
Reconstruction Error ◽  
Least Square ◽  
Shearing Interferometry ◽  
Lateral Shearing Interferometer ◽  
Lateral Shearing ◽  
Laser Metrology ◽  
Lateral Shearing Interferometry

Quadri-wave lateral shearing interferometry (QWLSI) is a new and powerful technique for wave-front measurement. This paper deduced the principle of QWLSI in details, showed a Fourier analysis of the resulting interferogram, then obtained a wave-front with high accuracy and minimum reconstruction error by using the least square method. Finally a 532nm laser was measured to validate the reconstruction, and the error analysis was discussed in practical laser metrology. It is concluded that QWLSI provides a better choice for the adaptive optics as compared with traditional lateral shearing interferometer (TLSI) and Shack-Hartmann (S-H) wave-front sensor.

scholarly journals Adaptive Optical Systems in Air-Based Laser System. Analytical Review. Part 1. Current Status

2019 ◽  
pp. 1-23
Author(s):  
Yu. I. Shanin
Keyword(s):  
Laser Radiation ◽  
Adaptive Optics ◽  
Laser System ◽  
The United States ◽  
High Energy ◽  
Optical Systems ◽  
Current Status ◽  
Powerful Laser ◽  
Optical Elements ◽  
Laser Systems

Aviation-based laser complex is a complex technical object. Among its systems, we analyse only an adaptive optical system and issues related to its performance, and show that the effectiveness of the complex without an adaptive system is small. The analysis was carried out in terms of systems that were developed in the United States.Using the tilt corrector, an adaptive optics provides accurate tracking of the object. A deformable mirror performs correction of higher-order radiation wavefront aberrations caused by atmospheric turbulence for incoming light and outgoing laser radiation. The advantages of onboard laser systems are the beam propagation at the speed of light and the low price of a shot. The disadvantages are that the target should be in line-of-sight and there is a negative influence of the atmosphere. Another negative influences are vibrations of the aircraft and the aero-optical problem because of output radiation. An assured thermal target kill is possible at the range of 3-10 km. A functional kill and suppression are capable at ranges of 102-103 times longer than for the thermal target kill.Among the programs for the development of an onboard laser in the USA, the YAL, ATL and ABL programs are considered. The YAL program is an attempt to intercept short-and medium-range missiles with a powerful laser. The ATL system was to be installed on a heavily armed ground support aircraft. An airborne laser (ABL) is a demonstration of the U.S. Air Force of a high-energy laser system designed to destroy missiles on their boost phase. Over 30 years and several tens of billions of dollars were expended to develop the systems. Unfortunately, all onboard laser development programs have been closed.Experience of the flying laboratories is realized by Cessna Citations and Falcon 10s planes and is relevant, as it gives the chance to estimate adverse effects of aero-optics and vibrations directly in flight.Among the problems that need to be solved when creating adaptive optics for an onboard laser, the following are highlighted:-      loss of compensation capabilities;-      thermal effects of laser radiation on optical elements;-      creation of attenuators and radiation couplers;-    mitigating the negative effects of the onboard platform on radiation;-      operation reliability of the actuators of correction devices;-      technological working off of the uncooled optical elements which are affected by powerful laser radiation.For newly developed aviation-based laser systems, it is necessary to envision the niche in which their use will be most efficient.

Automatic Control Systems for Adaptive Optical Systems. Analytical review. Part 2: Application of the Adaptive Filtering and Control at the Spaced Frequencies

2018 ◽  
pp. 13-31
Author(s):  
Yu. I. Shanin ◽  
A. V. Chernykh
Keyword(s):  
Adaptive Optics ◽  
Adaptive Filtering ◽  
Free Stream ◽  
Signal Transmission ◽  
Low Frequency ◽  
Optical Systems ◽  
Free Stream Turbulence ◽  
Automatic Control Systems ◽  
Analytical Review ◽  
And Control

The second part of the analytical review considers in detail an adaptive filtering application in the systems of adaptive optical systems (AOS) from the perspective of the airborne laser platforms. Herein the AOS operates under aero-optical distortions and vibrations, which further complicate the propagation of the laser beam. Adaptive filtering is considered as a way to improve the efficiency of the control system of adaptive optical systems, allowing to improve running an adaptive optics control loop: by 1.5-2 times with compensation for only the aero-optical disturbances, by 1.5 times with compensation only for the free-stream turbulence, and by 2.5-3.5 times for the combination of aero-optics and free-stream turbulence.The article discusses implementation of a new type of the controller, which uses intellectual algorithms to predict (through an artificial neural network) a short-term horizon of evolution of aberrations due to aero-optical effect. This controller allows us to deal with a large time delay in signal transmission (up to 5 time steps of sampling).The application of two deformable mirrors in the adaptive optical system to provide control at the spaced frequencies is especially considered. A low-frequency mirror is used to correct the lower-order aberrations (tip-tilt, defocusing, astigmatism, coma) requiring large strokes of executive mechanisms (actuators) in the deformable mirror. A high-frequency mirror is used to correct the higher-order aberrations requiring small strokes of drives. Various control algorithms to control the system from two adaptive mirrors are briefly reviewed.The obtained results, conclusions, and recommendations are supposedly to be used in development of specification of requirements for systems of adaptive optics.

scholarly journals A micromirror array with annular partitioning for high-speed random-access axial focusing

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Nathan Tessema Ersumo ◽  
Cem Yalcin ◽  
Nick Antipa ◽  
Nicolas Pégard ◽  
Laura Waller ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Visual Information ◽  
High Speed ◽  
Random Access ◽  
General Purpose ◽  
Phase Shifting ◽  
Optical Systems ◽  
Piston Motion ◽  
Refresh Rate ◽  
Circular Symmetry

Abstract Dynamic axial focusing functionality has recently experienced widespread incorporation in microscopy, augmented/virtual reality (AR/VR), adaptive optics and material processing. However, the limitations of existing varifocal tools continue to beset the performance capabilities and operating overhead of the optical systems that mobilize such functionality. The varifocal tools that are the least burdensome to operate (e.g. liquid crystal, elastomeric or optofluidic lenses) suffer from low (≈100 Hz) refresh rates. Conversely, the fastest devices sacrifice either critical capabilities such as their dwelling capacity (e.g. acoustic gradient lenses or monolithic micromechanical mirrors) or low operating overhead (e.g. deformable mirrors). Here, we present a general-purpose random-access axial focusing device that bridges these previously conflicting features of high speed, dwelling capacity and lightweight drive by employing low-rigidity micromirrors that exploit the robustness of defocusing phase profiles. Geometrically, the device consists of an 8.2 mm diameter array of piston-motion and 48-μm-pitch micromirror pixels that provide 2π phase shifting for wavelengths shorter than 1100 nm with 10–90% settling in 64.8 μs (i.e., 15.44 kHz refresh rate). The pixels are electrically partitioned into 32 rings for a driving scheme that enables phase-wrapped operation with circular symmetry and requires <30 V per channel. Optical experiments demonstrated the array’s wide focusing range with a measured ability to target 29 distinct resolvable depth planes. Overall, the features of the proposed array offer the potential for compact, straightforward methods of tackling bottlenecked applications, including high-throughput single-cell targeting in neurobiology and the delivery of dense 3D visual information in AR/VR.

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