There are many research efforts around the world to develop adaptive optics technology, but only a few commercial efforts. This paper will investigate some of the boundaries that separate successful laboratory operation from successful commercialization of this technology and report on the progress Intellite has made toward the commercialization of adaptive optics.

Recent progress on deformable mirror systems made at Boston University and Boston Micromachines Corporation is described. The mirror's optical, electrical, and mechanical performance characteristics are summarized, and the effects of air damping on performance are described. Two applications that have employed the μDM in laser communications and retinal imaging are introduced.

We present experimental results for the adaptive compensation of atmospheric turbulence effects on a free-space laser communication links at near horizontal propagation paths over 2.5 km and 5 km lengths. A high-resolution micro-machined piston type mirror array (12x12 elements) and a fast beam steering mirror were used in an adaptive optics laser communication system based on the model-free stochastic parallel gradient descent (SPGD) optimization wavefront control technique. Control of the mirror was performed by a VLSI SPGD micro-controller. The experimental results demonstrate the improvement of the receiver performance (fiber coupling efficiency) on a summer day with a refractive index structure constant in the order of C_n²≈10^-14 m^-2/3.

We present here results using two novel active optic elements, an electro-static membrane mirror, and a dual frequency nematic liquid crystal. These devices have the advantage of low cost, low power consumption, and compact size. Possible applications of the devices are astronomical adaptive optics, laser beam control, laser cavity mode control, and real time holography. Field experiments were performed on the Air Force Research Laboratory 3.6 meter telescope on Maui, Hawaii.

The idea of using liquid crystal devices as an adaptive optics component has been proposed by several authors. In recent years a vigorous research effort has been carried out, and it is still flourishing, in several countries. Mainly the research and experimental work has been concentrated in the USA, U.K. and Russia. There are several reasons why liquid crystals may represent a valid alternative to the traditional deformable mirror technology that has been used for the past two decades or so. The main attractiveness of LC resides in the cost. Current deformable mirror technology has a range of price going from $2K to $15K per channel. LC technology promises to be at least a couple of orders of magnitude cheaper. Other reasons are connected with reliability, low power consumption and with a huge technological momentum based on a wide variety of industrial applications. In this paper we present some preliminary characterizations of a new, large format device. Such devices have the potential for extremely high-resolution wave-front control due to the over 10,000 corrective elements. The characterization of the device, so far, consists of measurements of the overall optical quality and of the phase control relationship.

High resolution devices, using liquid crystal phase modulators, have the ability to correct large phase variations across the aperture. These phase variations are corrected using discrete (pixelated) modulo-2π phase shifts, which simplifies the control scheme by eliminating inter-actuator influence and decreases the response time of the phase modulator by reducing the required stroke. Even with these advantages, modulo-2π phase correction is generally not used if the source is broadband due to degradation from chromatic dispersion. This paper discusses techniques for reducing the angular dispersion using new modulators which are being developed.

The experimental search of the shape of electrical voltage is presented for controlling the optical phase modulator based on dual frequency nematic liquid crystal. Two basic approaches were tested. One is based on universal relation between two driving frequencies, below and above inversion point, respectively. Another approach uses the combination of pulses of both frequencies, which allow us, at first, to provide the fast transition between chosen retardations and , at second, to hold final retardation for the necessary duration.

A 37-control-channel adaptive optics target-in-the loop system with phase correction of the outgoing wave capable of operating in the presence of speckle-field-induced strong intensity modulation is presented. System operation is based on speckle field metric optimization using the stochastic parallel gradient descent technique. A quadratic map that linearizes phase modulation response of deformable micromachined mirror to control variable perturbation is investigated. Results demonstrate that adaptive wavefront correction using speckle-field-based beam quality metrics can significantly improve laser beam concentration on extended objects. The use of the quadratic map improves both system convergence rate and magnitude of laser beam concentration on the target.

Telescope structures are typically required to attain a certain degree of mechanical rigidity in order to achieve the desired optical performance goals, yet there are many applications where weight is either at a premium or local conditions exist that pre-empt optimal mechanical stability requirements. What is needed is a system which can sense and compensate for the opto-mechanical instabilities and correct them in real-time, preferably without "stealing" light from the optical system. We propose using tiny MEMS-based inertial reference sensors to measure the structural dynamics, and, using an appropriate model and coordinate transformations, correct in real-time the tip/tilt, focus, and possibly higher order errors of the optical system aberrations using MEMS-based deformable mirrors and/or our own tip/tilt + piston mirrors.

Buiding a compact general-purpse adaptive optics system presents new challenges. By “compact” we mean a complete system less than 0.05 m³ in volume that contains all optics and processing electronics. By “general-purpose” we mean a system that can be used in astronomy, in laser communications, and in commercial and military applications with only minimal modifications specific to the application. This necssarily requires a robust control system that can be easily set-up, calibrated, and run by a minimally-trained operator. Knowing that transport or installation of such a system can misalign some components, we built a control system to accommodate those errors in a fast reconstructor reconfiguruing algorithm. A robust H-infinity control is implemented for closed-loop operation. Results of computer simulations and a series of laboratory demonstrations are presented.

Two generations of adaptive optical system for human retina imaging have been developed. The wavefront correcting elements are small PZT 19 and 37 element deformable mirrors (DM) with novel structure. The diameters of these DMs are 24 and 50mm respectively. By using these DMs, the size of whole optical system are rather small and can be fit on table. These systems are successfully used to correct the aberrations of living human eye. High-resolution images of microscopic structure in the scale of single photo-receptor cell and capillary in the human retina have been obtained by real-time correction of adaptive optical systems.

We performed architecture and design analyses of coupled-cavity laser systems to arrive at a concept for tracking distant objects. We also conducted an experimental study of such a system using a pulsed ruby laser as a prototype for the laboratory tests. Both laser cavities were coupled through the dynamic holographic grating. Special attention was paid to characterization of the coupled-cavity laser system and its operation. In particular, we studied the formation of holographic grating that serves to couple the cavity; the slope efficiency of the master and slave arms and their dependence upon cavity parameters. The resulted experimental data and analyses verified the tracking principle and proved the feasibility of the proposed phase-conjugate double cavity laser system for tracking moving object at distance with high accuracy.

Atmospheric aberrations reduce the resolution and contrast in surveillance images recorded over horizontal or slant paths. This paper describes our recent horizontal and slant-path imaging experiments of extended scenes as well as the results obtained using speckle imaging. The experiments were performed with an 8-inch diameter telescope placed on either a rooftop or hillside and cover ranges of interest from 0.5 km up to 10 km. The scenery includes resolution targets, people, vehicles, and other structures. The improvement in image quality using speckle imaging is dramatic in many cases, and depends significantly upon the atmospheric conditions. We quantify resolution improvement through modulation transfer function measurement comparisons.

In this paper, we use diffractive superresolution technology to design a pure-phase plate for realizing the smaller spot size than the usual Airy spot size. We have calculated 2,3,4,5 circulation zones for optimizing the highest energy compression (Strelratio) with the constraint of the Firstzero value G=0.8. Numerical results show that the 2-circular zone pure-phase plate can yield the highest Strelratio (S=0.59) with the constraint of G=0.8.The 3-circular zone pure-phase plate with the respective phases of φ₁φ₂φ₃ has also been calculated. At the same time the 4,5 circular zone binary phase (0,π) plates are calculated to yield the result of S = 0.57 with G=0.8. The usage of the superresolution phase plate aims to realize the smaller spot size instead of the usage of the higher numerical aperture lens, which is the main advantage of this superresolution technology. Therefore, in this constraint of G=0.8, we have selected the 2-circular zone with binary phase for ease of fabrication. At last, we use a 50 nanometer fiber tip detector to scan the diffractive superresolution light spot in order to compare it with the Airy spot. Detailed experiments are presented.

In this paper, the compensation effects of sub-aperture gradients of Hartmann-Shack wavefront sensor in an adaptive optics (AO) system with four different reconstruction algorithms were analyzed. A kind of optimal-gradient reconstruction algorithm was deduced from least-square (LS) reconstruction algorithm by consider the statistical characteristics of atmospheric turbulence and measurement noise. A kind of sensor-eigen (SE) modal reconstruction algorithm was deduced from LS reconstruction algorithm by orthogonalizing the statistical correlation matrix of drive voltages by means of singular value decomposition (SVD) method. Two kinds of zonal reconstruction algorithms, the LS reconstruction algorithm and the optimal-gradient reconstruction algorithm, along with two modal reconstruction algorithms, the Zernike modal reconstruction algorithm and the SE modal reconstruction algorithm, were compared together on a 61-element AO system working in atmospheric turbulence. Performances of the four reconstruction algorithms were calculated and analyzed in different work conditions. It is showed that zonal reconstruction algorithms can achieve better compensation, but the modal reconstruction algorithms can achieve better stability. Zonal reconstruction algorithms are suitable in general condition, but the modal reconstruction algorithm with ability of partial compensation will be better in lower signal-to-noise ratio (SNR) condition.

The Directed Energy Directorate is developing technologies for large space-based optical membrane telescopes. The goal is to develop technologies that will enable 20-meter or greater diameter telescopes, with areal densities of less than 1 kilogram per square meter. The challenge of building these precise structures is reduced by employing a diffractive wavefront controller, which will significantly relax the structural tolerances normally associated with conventional optical systems. A significant portion of the corrector's range and bandwidth can be consumed by structural disturbances. This survey will describe the relationship between the structural dynamics of a highly compliant, 11 inch diameter, planar optical aperture and the diffractive wavefront controller's ability to compensate for the resulting wavefront error. This overview should give the optical physicist and the opto-mechanical engineer a starting point to communicate system design and research needs.

A prototype programmable diffractive optics system demonstrates large aberration compensation and versatile laser wavefront control. This high-resolution phase modulator compensates large aberrations with high fidelity and high-optical efficiency via modulo-2π phase subtraction. Demonstrations include compensated imaging with monochromatic light, laser beam steering with aberration compensation, and both on-axis and off-axis aberration compensation in a telescope system. Compensated wavefront fidelities are near the diffraction limit.

During the last years, a considerable advance has been made in the development both of optical telescopes with the real-time image correction and of the concept of the light-weight telescope primary mirror. In spite of the progress in the design of the phase correctors, their parameters (such as spatial resolution, speed, accuracy of the correction, noise level, transverse dimensions, etc.) still do not completely satisfy the requirements to the distortion correctors for the light-weight mirrors of large diameter. At the same time, the optical nonideality of the light-weight mirror is an adjustable parameter depending, in the main, on the degree of lightening of the mirror weight. Thus, for optimization of the process of the distortion correction in telescopes of this type, parameters of the primary mirror (PM) and corrector should be matched with each other. As the first step towards this optimization, we will discuss, in this presentation, the so-called cross-requirements to the PM and corrector, i.e., the requirements imposed on the corrector from the viewpoint of ease of fabrication of the PM and the requirements of the PM quality from the viewpoint of the best nonlinear-optical correctors available nowadays.

High-fidelity wavefront control is demonstrated via programmable modulo-2π two-dimensional phase profiles displayed on a high-resolution computer-addressable phase modulator system. This prototype setup operates with 307,200 independently addressable elements and a fill-factor and interpixel influence function that are controlled via spatial filtering in a Fourier plane. Nonlinearities in the phase response are compensated computationally. Aberration compensation with better than 1/4-wave peak-to-peak fidelity is demonstrated.

Dynamic holography has been demonstrated as a method for correction aberrations in space deployable optics, and can also be used to achieve high-resolution beam steering in the same environment. In this paper we consider some of the factors affecting the efficiency of these devices. Specifically, the effect on the efficiency of a highly collimated beam from the number of discrete phase steps per period on steering resolution is also considered. We also present some results of Finite-Difference Time-Domain (FDTD) calculations of light propagating through liquid crystal blazed gratings. Liquid crystal gratings are shown to spatially modulate both phase and amplitude of propagating light.

Diffractive wavefront control has been demonstrated as a viable technique for high-dynamic-range laser wavefront control. Unfortunately, most conventional programmable diffractive elements, like liquid crystals and segmented mirror arrays, damage when illuminated with high-power laser light. Continuous reflective surfaces coated with multi-layer dielectric stacks have demonstrated high damage thresholds, but are not typically thought of as good diffractive wavefront control elements because of the inability to gneerate rapid spatial phase changes. In this paper, the investigation of a continuous reflective surface as a diffractive wavefront control element is presented.

The results of experimental and theoretical studies are presented on the development of optically addressed liquid crystal spatial light modulators (OA LC SLM) with clear aperture up to 50 mm and phase modulation depth up more than 2π. The optimization of electrical and optical characteristics of liquid crystal, photoconductor, dielectric mirror and blocking layers resulted in fabrication of samples of OA LC SLM that allowed writing diffraction gratings with the phase amplitude up to 2π and variable profile of grating fringes.

Phase-contrast wave front sensors that use a pixilated liquid crystal device as the Zernike filter have been demonstrated successfully in several laboratories. These systems are inherently very large. This paper presents design considerations and test results for a small, low-cost, portable, phase-contrast wave front sensor developed at New Mexico State University (NMSU). This sensor has measured wave fronts of optical systems and components in different laboratories.

A noise analysis is presented for complex field estimation using a self-referencing interferometer wave front sensor with an amplified reference. The wave front sensor is constructed from a phase-shifting, point diffraction interferometer. The reference field is created by coupling a part of the incident wave front into a single mode fiber where it is optically amplified. The noise characteristics of this wave front sensor are examined in terms of the field estimation Strehl. The effects of several system parameters are examined\nobreak—shot noise, read noise, quantization noise, spontaneous emission from the amplifier, the relative intensities of the signal and reference fields, and temporal phase shifting.

Before the design of adaptive optical system for the aberration correction in the proposed new generation laser driving Inertial Confinement Fusion (ICF) system, the spatial and temporal characteristics of aberration of this system should be studied and understood deeply. A single beam principle prototype of this ICF system has been built. The Shack-Hartmann wave-front sensors have been designed and constructed. Wave-front aberrations of this prototype are measured and studied.

A wavefront sensing detector array is presented with capabilities suited towards high-order adaptive optics systems. The phase of the wavefront is sensed by modulating and synchronously sampling the fringes of a white light interferogram imaged onto the array. The nature of the modulation is characterized by a voltage signal, which is delivered as an input to the array. As a fringe moves across an individual detector, the null is sensed, triggering a sampling of the modulation signal. The sampled signal represents the phase of the wavefront and is held until the next null is sensed. The signal makes it possible to directly send commands to a deformable mirror to correct the phasefront. This chip is optically mapped such that each pixel in the array corresponds to an actuator on the deformable mirror. The array outputs both the photodetector current and the sampled modulation signal voltage from individual pixels by means of bit parallel row and column inputs. A prototype of this array has been fabricated in a 0.5μm CMOS process with 21 × 21 detectors, suitable for (circular) deformable mirrors with up to 349 actuators. Experimental results suggest refresh rates in excess of 3kHz are attainable. This wavefront sensor could greatly simplify the process of controlling a deformable mirror for many applications, thereby increasing refresh rates and improving sensitivity.

We describe a novel technique for deriving wave-front aberrations from two defocused intensity measurements. The intensity defines a probability density function, and the method is based on the evolution of the cumulative density function of the intensity with light propagation. In one dimension, the problem is easily solved using a histogram specification procedure, with a linear relationship between the wave-front slope and the difference in the abscissas of the histograms. In two dimensions, the method requires the use of a Radon transform. Simulation results demonstrate that very good reconstructions can be attained down to 100 photons in each detector. In addition, the method is insensitive to scintillation at the aperture.

A calibration procedure is described for improved modeling of a continuous facesheet deformable mirror. A resistive force of each actuator as it attempts to move to its commanded position is modeled as a linear spring force. A force associated with the resistance of the facesheet to bending is modeled as a moment that exerts a force on the actuators. The resultant first order finite element model is parameterized by a gain on each actuator channel and a ratio relating the average actuator spring constant and the facesheet bending moment coefficient. Example experimental results are presented indicating that modeling accuracy is improved by use of the first order finite element model.

Approaches toward the fabrication of low-cost integrated micromachined spatial light modulators are presented. An optimized fabrication procedure minimizes requirements on integrated electronics and mechanical layers. This surface can rest on a viscoelastic carrier material under which an electrode array is placed. Under application of appropriate potentials on the underlying electrodes, localized sinusoidal phase gratings can be produced. The depth of modulation can be converted to an intensity value by using Schlieren bars and integrating properties of the projection lens. The pixel sizes can vary from 20μm to 1mm. In the fabrication procedure, a top chip is used, which is coated with a 50nm nitride layer and an 80nm Al layer. A droplet of the carrier layer is placed on the bottom chip, on which the top chip is then pressed, planarizing the surface. A 33 wt% KOH solution is used to bulk-etch the silicon of the top chip, using the thin nitride membrane as an etch stop, thus transferring the metal layer to the carrier substrate, a technique potentially also usable for adaptive deformable mirrors. A special elastomer based etch holder technology was developed to provide low stress protection of the sidewalls and aluminum bond pads during etching. Applications of these devices lie in the field of projection displays, optical lithography and optical communication networks.

Deformable mirror is a popular device in adaptive optics. The characterization of this deformable mirror becomes important in a closed loop system. A shack Hartmann based wavefront sensor using a proper combination of lenslet array and a CCD camera has been used for this purpose. The typical process sequence includes, acquisition of reference and distorted image, calculation of centroide for both images, calculation of shift along X and Y axis, calculation of slope data. Finally reconstruction of the wavefront to calculate phase is performed. Integrated software based on Windows 9X platform has been developed for all above steps. This paper describes a novel technique used in this software. A multithreaded approach is used to perform above steps in parallel. Threads are introduced to acquire image from CCD camera, to calculate slope and phase data for each captured image and to display real time graphs viz. Slope matrix, 3D-phase matrix. Phase matrix has been calculated based on standard least square iterative method.