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Showing papers on "Adaptive optics published in 2001"


Journal ArticleDOI
TL;DR: Calculations suggest that a perfect adaptive optics system with a closed-loop bandwidth of 1-2 Hz could correct these aberrations well enough to achieve diffraction-limited imaging over a dilated pupil.
Abstract: It is well known that the eye’s optics exhibit temporal instability in the form of microfluctuations in focus; however, almost nothing is known of the temporal properties of the eye’s other aberrations. We constructed a real-time Hartmann–Shack (HS) wave-front sensor to measure these dynamics at frequencies as high as 60 Hz. To reduce spatial inhomogeneities in the short-exposure HS images, we used a low-coherence source and a scanning system. HS images were collected on three normal subjects with natural and paralyzed accommodation. Average temporal power spectra were computed for the wave-front rms, the Seidel aberrations, and each of 32 Zernike coefficients. The results indicate the presence of fluctuations in all of the eye’s aberration, not just defocus. Fluctuations in higher-order aberrations share similar spectra and bandwidths both within and between subjects, dropping at a rate of approximately 4 dB per octave in temporal frequency. The spectrum shape for higher-order aberrations is generally different from that for microfluctuations of accommodation. The origin of these measured fluctuations is not known, and both corneal/lenticular and retinal causes are considered. Under the assumption that they are purely corneal or lenticular, calculations suggest that a perfect adaptive optics system with a closed-loop bandwidth of 1–2 Hz could correct these aberrations well enough to achieve diffraction-limited imaging over a dilated pupil.

395 citations


Journal Article
TL;DR: Wave aberrations of the eye increase with age, and this increase is consistent with the loss of contrast sensitivity with age observed by other investigators.
Abstract: PURPOSE To investigate the relations between age and the optical aberrations of the whole eye The eye’s optical quality, as measured by the modulation transfer function (MTF), degrades with age, but the MTF does not provide a means to assess the contributions of individual aberrations, such as coma, spherical aberration, and other higher order aberrations to changes in optical quality The method used in this study provides measures of individual aberrations and overall optical quality METHODS Wave aberrations in 38 subjects were measured psychophysically using a spatially resolved refractometer Data were fit with Zernike polynomials up to the seventh order to provide estimates of 35 individual aberration terms MTFs and root mean square (RMS) wavefront errors were calculated Subjects ranged in age from 229 to 645 years, with spherical equivalent corrections ranging from 105 to 260 D RESULTS Overall RMS wavefront error (excluding tilts, astigmatism, and defocus) was significantly positively correlated with age (r 5 033, P 5 0042) RMS error for the highest order aberrations measured (fifth through seventh order) showed a strong positive correlation with age (r 5 057, P 5 00002) Image quality, as quantified by the MTF, also degraded with age CONCLUSIONS Wave aberrations of the eye increase with age This increase is consistent with the loss of contrast sensitivity with age observed by other investigators (Invest Ophthalmol Vis Sci 2001;42:1390 ‐1395)

306 citations


Journal ArticleDOI
TL;DR: The results in a keratoconic subject showed that important benefits are obtained despite decentrations in highly aberrated eyes, and provided practical rules to implement a selective correction depending on the amount of decentration.
Abstract: An ideal correcting method, such as a customized contact lens, laser refractive surgery, or adaptive optics, that corrects higher-order aberrations as well as defocus and astigmatism could improve vision The benefit achieved with this ideal method will be limited by decentration To estimate the significance of this potential limitation we studied the effect on image quality expected when an ideal correcting method translates or rotates with respect to the eye’s pupil Actual wave aberrations were obtained from ten human eyes for a 73-mm pupil with a Shack–Hartmann sensor We computed the residual aberrations that appear as a result of translation or rotation of an otherwise ideal correction The model is valid for adaptive optics, contact lenses, and phase plates, but it constitutes only a first approximation to the laser refractive surgery case where tissue removal occurs Calculations suggest that the typical decentrations will reduce only slightly the optical benefits expected from an ideal correcting method For typical decentrations the ideal correcting method offers a benefit in modulation 2–4 times higher (15–2 times in white light) than with a standard correction of defocus and astigmatism We obtained analytical expressions that show the impact of translation and rotation on individual Zernike terms These calculations also reveal which aberrations are most beneficial to correct We provided practical rules to implement a selective correction depending on the amount of decentration An experimental study was performed with an aberrated artificial eye corrected with an adaptive optics system, validating the theoretical predictions The results in a keratoconic subject, also corrected with adaptive optics, showed that important benefits are obtained despite decentrations in highly aberrated eyes

291 citations


Journal ArticleDOI
TL;DR: Correcting the temporal variation in the eye's wave aberration increases the Strehl ratio of the point spread function nearly 3 times, and increases the contrast of images of cone photoreceptors by 33% compared with images taken with only static correction of the eyes' higher order aberrations.
Abstract: We measured the improvement in retinal image quality provided by correcting the temporal variation in the eye's wave aberration with a closed-loop adaptive optics system This system samples the eye's wave aberration at rates up to 30 Hz Correction of the eye's aberrations can be completed in 025-05 seconds, resulting in residual rms wave-front errors as low as 01 microns for 68 mm pupils Real-time wave-front measurements were used to determine how effectively the spatial and temporal components of the eye's wave aberration were corrected The system provides dynamic correction of fluctuations in Zernike modes up to 5 th order with temporal frequency components up to 08 Hz Temporal performance is in good agreement with predictions based on theory Correction of the temporal variation in the eye's wave aberration increases the Strehl ratio of the point spread function nearly 3 times, and increases the contrast of images of cone photoreceptors by 33% compared with images taken with only static correction of the eye's higher order aberrations

275 citations


Journal ArticleDOI
TL;DR: Results in living eyes showed effective closed-loop correction of aberrations, with a residual uncorrected wave front of 0.1microm for a 4.3-mm pupil diameter.
Abstract: We have developed a prototype apparatus for real-time closed-loop measurement and correction of aberrations in the human eye. The apparatus uses infrared light to measure the wave-front aberration at 25 Hz with a Hartmann–Shack sensor. Defocus is removed by a motorized optometer, and higher-order aberrations are corrected by a membrane deformable mirror. The device was first tested with an artificial eye. Correction of static aberrations takes approximately five iterations, making the system capable of following aberration changes at 5 Hz. This capability allows one to track most of the aberration dynamics in the eye. Results in living eyes showed effective closed-loop correction of aberrations, with a residual uncorrected wave front of 0.1 μm for a 4.3-mm pupil diameter. Retinal images of a point source in different subjects with and without adaptive correction of aberrations were estimated in real time. The results demonstrate real-time closed-loop correction of aberration in the living eye. An application of this device is as electro-optic “spectacles” to improve vision.

255 citations


Journal ArticleDOI
TL;DR: The Palomar High Angular Resolution Observer (PHARO) as discussed by the authors uses a HgCdTe HAWAII detector for observations between 1 and 2.5 mm wavelength.
Abstract: We describe Cornell's near-infrared camera system PHARO (Palomar High Angular Resolution Observer) built for use with the JPL Palomar Adaptive Optics System on the 5 m Hale telescope. PHARO uses a HgCdTe HAWAII detector for observations between 1 and 2.5 mm wavelength. An all-reflecting 1024 # 1024

226 citations


Patent
31 Aug 2001
TL;DR: In this paper, an improved ophthalmic instrument for in-vivo examination of a human eye including a wavefront sensor that estimates aberrations in reflections of the light formed as an image on the retina of the human eye and a phase compensator that spatially modulates the phase of incident light to compensate for the aberration estimated by the wavefront sensors.
Abstract: An improved ophthalmic instrument for in-vivo examination of a human eye including a wavefront sensor that estimates aberrations in reflections of the light formed as an image on the retina of the human eye and a phase compensator that spatially modulates the phase of incident light to compensate for the aberrations estimated by the wavefront sensor Optical elements create an image of a fixation target at the phase compensator, which produces a compensated image of the fixation target that compensates for aberrations estimated by the wavefront sensor. The compensated image of the fixation target produced by the phase compensator is recreated at the human eye to thereby provide the human eye with a view of compensation of the aberrations the human eye as estimated by the wavefront sensor. The phase compensator preferably comprises a variable focus lens that compensates for focusing errors and a deformable mirror that compensates for higher order aberrations. The optical elements preferably comprise a plurality of beam splitters and a plurality of lens groups each functioning as an afocal telescope. In addition, instruments and systems are provided that exploit these capabilities to enable efficient prescription and/or dispensing of corrective optics (e.g., contact lens and glasses).

202 citations


Journal ArticleDOI
TL;DR: An optimal approach for the phase reconstruction in a large field of view (FOV) for multiconjugate adaptive optics is proposed based on a minimum-mean-square-error estimator that minimizes the mean residual phase variance in the FOV of interest.
Abstract: We propose an optimal approach for the phase reconstruction in a large field of view (FOV) for multiconjugate adaptive optics. This optimal approach is based on a minimum-mean-square-error estimator that minimizes the mean residual phase variance in the FOV of interest. It accounts for the Cn2 profile in order to optimally estimate the correction wave front to be applied to each deformable mirror (DM). This optimal approach also accounts for the fact that the number of DMs will always be smaller than the number of turbulent layers, since the Cn2 profile is a continuous function of the altitude h. Links between this optimal approach and a tomographic reconstruction of the turbulence volume are established. In particular, it is shown that the optimal approach consists of a full tomographic reconstruction of the turbulence volume followed by a projection onto the DMs accounting for the considered FOV of interest. The case where the turbulent layers are assumed to match the mirror positions [model-approximation (MA) approach], which might be a crude approximation, is also considered for comparison. This MA approach will rely on the notion of equivalent turbulent layers. A comparison between the optimal and MA approaches is proposed. It is shown that the optimal approach provides very good performance even with a small number of DMs (typically, one or two). For instance, good Strehl ratios (greater than 20%) are obtained for a 4-m telescope on a 150-arc sec×150-arc sec FOV by using only three guide stars and two DMs.

176 citations


Journal ArticleDOI
TL;DR: Wave-front distortion caused by high-power lasers on transmissive optics is examined using a Shack-Hartmann wave-front sensor and the theoretical shape of the thermally induced optical phase aberration is compared with measurements made in a neutral-density filter glass, Faraday glass, and lithium niobate.
Abstract: We examine wave-front distortion caused by high-power lasers on transmissive optics using a Shack-Hartmann wave-front sensor. The coupling coefficient for a thermally aberrated Gaussian beam to the TEM(00) mode of a cavity was determined as a function of magnitude of the thermally induced aberration. One wave of thermally induced phase aberration between the Gaussian intensity peak and the 1/e(2) radius of the intensity profile reduces the power-coupling coefficient to the TEM(00) mode of the cavity to 4.5% with no compensation. With optimal focus compensation the power coupling is increased to 79%. The theoretical shape of the thermally induced optical phase aberration is compared with measurements made in a neutral-density filter glass, Faraday glass, and lithium niobate. The agreement between the theoretical and the measured thermal aberration profiles is within the rms wave-front measurement sensitivity of the Shack-Hartmann wave-front sensor, which is a few nanometers.

145 citations


Journal ArticleDOI
TL;DR: In this article, the authors present simulations of coronagraphs matched to adaptive optics (AO) systems on the Calypso 1.2 m, Palomar Hale 5 m, and Gemini 8 m telescopes under various atmospheric conditions and identify useful parameter ranges for AO coronagraphy.
Abstract: We summarize the theory of coronagraphic optics and identify a dimensionless —ne-tuning parameter, F, which we use to describe the Lyot stop size in the natural units of the coronagraphic optical train and the observing wavelength. We then present simulations of coronagraphs matched to adaptive optics (AO) systems on the Calypso 1.2 m, Palomar Hale 5 m, and Gemini 8 m telescopes under various atmospheric conditions and identify useful parameter ranges for AO coronagraphy on these telescopes. Our simulations employ a tapered, high-pass —lter in spatial frequency space to mimic the action of adaptive wave front correction. We test the validity of this representation of AO correction by comparing our simulations with recent K-band data from the 241 channel Palomar Hale AO system and its dedicated Palomar High Angular Resolution Observer (PHARO) science camera in coronagraphic mode. Our choice of monochromatic modeling enables us to distinguish between underlying halo suppression and ★ b)

141 citations


Patent
10 Apr 2001
TL;DR: An optical mirror system with multi-axis rotational control is described in this article, where an optical surface assembly, and at least one leg assembly coupled to the optical surface is used to support the optical surfaces above a substrate.
Abstract: An optical mirror system with multi-axis rotational control is disclosed The mirror system includes an optical surface assembly, and at least one leg assembly coupled to the optical surface assembly The at least one leg assembly supports the optical surface above a substrate A system and method in accordance with the present invention can operate with many different actuator mechanisms, including but not limited to, electrostatic, thermal, piezoelectric, and magnetic An optical mirror system in accordance with the present invention accommodates large mirrors and rotation angles Scanning mirrors can be made with this technique using standard surface-micromachining processes, or a deep RIE etch process A device in accordance with the present invention meets the requirements for a directly scalable, high port count optical switch, utilizing a two mirror per optical I/O port configuration An optical mirror in accordance with the present invention can be utilized in, but is not limited to, the following applications: optical add-drop multiplexers, wavelength routers, free-space optical interconnects, chip-level optical I/O, optical scanning displays, optical scanner (bar-codes, micro cameras), optical storage read/write heads, laser printers, medical replacement for glasses (incorporated with adaptive optics), medical diagnostic equipment, optical scanning for security applications

Journal ArticleDOI
TL;DR: In this paper, the authors evaluate the limiting magnitude for a pyramid sensor operating in a closed loop astronomical adaptive Optics system and show that when a point-like reference source is used, the pyramid sensor exhibits a significant gain in terms of limiting magnitude over the widely used Shack-Hartmann sensor.
Abstract: In this letter we evaluate the limiting magnitude for a Pyramid Sensor operating in a closed loop astronomical Adaptive Optics system. A first heuristic analysis has shown that, when a point-like reference source is used a pyramid sensor exhibits a significant gain in terms of limiting magnitude over the widely used Shack-Hartmann sensor. This when diffraction limited conditions are reached. However, in current astronomical Adaptive Optics, diffraction limited regime at the sensing wavelength is difficult to achieve. Our simulations quantify the pyramid sensor limiting magnitude considering an Adaptive Optics system working in a partial correction regime. The simulations show that the considered gain is retained even in partial correction. An average gain of two magnitude is found in the considered case. This feature of a pyramid sensor can be very important in reducing the fundamental limit of today's Astronomical Adaptive Optics systems using natural reference sources, i.e. the limited sky-coverage.

Patent
31 Aug 2001
TL;DR: ImprovedWavefront Coding Optics as mentioned in this paper apply a phase profile to the wavefront of an object to be imaged, retain their insensitivity to focus related aberration, while increasing the heights of the resulting MTFs and reducing the noise in the final images.
Abstract: Improved Wavefront Coding Optics, which apply a phase profile to the wavefront of light from an object to be imaged, retain their insensitivity to focus related aberration, while increasing the heights of the resulting MTFs and reducing the noise in the final images. Such improved Wavefront Coding Optics have the characteristic that the central portion of the applied phase profile is essentially flat (or constant), while a peripheral region of the phase profile around the central region alternately has positive and negative phase regions relative to the central region.

Proceedings ArticleDOI
10 Mar 2001
TL;DR: The Terrestrial Planet Finder (TPF) is a space-based astronomical telescope that will combine high sensitivity and spatial resolution to detect and characterize /spl sim/150 planetary systems within 15 pc of our Sun as mentioned in this paper.
Abstract: The Terrestrial Planet Finder (TPF) is a space-based astronomical telescope that will combine high sensitivity and spatial resolution to detect and characterize /spl sim/150 planetary systems within 15 pc of our Sun. In a five-year mission, currently expected to commence in 2012, TPF will look for the atmospheric signatures of life using the methods of planetary spectroscopy. This is only possible if implemented within a telescope or interferometer whose spatial resolution is capable of resolving the planet as distinct from its parent star, and yet being able to suppress the starlight to a level of 10/sup -6/ or better. The design of TPF that had been used to illustrate the feasibility of the mission was an interferometer composed of a four-element linear array of 3.5-m diameter telescopes situated in an orbit at L2 and observing over the spectral band of 3-30 /spl mu/m. At these wavelengths an Earth-like planet would be more easily detectable in the glare of the parent star, but the angular resolution required for planet detection implies telescope separations of between 75 and 200 m, and separations of up to 1000 m would be needed for general astrophysics. The interferometer had therefore been envisaged as an array of free-flying telescopes. More recent design studies for TPF have also considered the possibility of having it built as a single-aperture optical telescope. The required angular resolution for planet detection could then be achieved with a mirror spanning 8 or 10 m in diameter. Possible designs include coronagraphs with circular, square, rectangular, or other shaped entry pupils, with tapered transmission across the pupil to suppress unwanted sidelobes in the diffraction pattern. Coronagraphs with phase masks have also been proposed to more efficiently suppress starlight. For these coronagraphs the principal challenges include not only the suppression of scattered light but the design of adaptive optics systems with sub-nm control. The design requirements and the current status of research are reviewed.

Patent
23 Feb 2001
TL;DR: An apparatus for wavefront detection includes a wavefront source for the production of a wave front, an optical system transforming the wavefront, a diffraction grating through which the transformed wavefront passes, and a spatially resolving detector following the grating as mentioned in this paper.
Abstract: An apparatus for wavefront detection includes a wavefront source for the production of a wavefront, an optical system transforming the wavefront, a diffraction grating through which the transformed wavefront passes, and a spatially resolving detector following the diffraction grating. The wavefront source has a two-dimensional structure.

Journal ArticleDOI
TL;DR: Light microscopy of thick biological samples, such as tissues, is often limited by aberrations caused by refractive index variations within the sample itself, so this approach will open possibilities to study weakly labeled molecules in difficult-to-image live specimens.
Abstract: Light microscopy of thick biological samples, such as tissues, is often limited by aberrations caused by refractive index variations within the sample itself. This problem is particularly severe for live imaging, a field of great current excitement due to the development of inherently fluorescent proteins. We describe a method of removing such aberrations computationally by mapping the refractive index of the sample using differential interference contrast microscopy, modeling the aberrations by ray tracing through this index map, and using space-variant deconvolution to remove aberrations. This approach will open possibilities to study weakly labeled molecules in difficult-to-image live specimens.

Book
31 May 2001
TL;DR: In this paper, modern fringe pattern analysis in interferometry optical metrology of diffuse objects: full-field methods holography Fourier optics and optical image processing electro-optical and acousto-optic devices radiometry, incoherent light sources lasers spatial and spectral filters optical fibers and accessories isotropic amorphous optical materials anisotropic materials light-sensitive material optical fabrication.
Abstract: Basic ray optics basic wave optics basic photon optics refractive optical components reflective optical components diffractive optical components some lens optical devices telescopes spectrometers wavefront slope measurements in optical testing basic interferometers modern fringe pattern analysis in interferometry optical metrology: point methods optical metrology of diffuse objects: full-field methods holography Fourier optics and optical image processing electro-optical and acousto-optical devices radiometry, incoherent light sources lasers spatial and spectral filters optical fibers and accessories isotropic amorphous optical materials anisotropic materials light-sensitive material optical fabrication.


Patent
14 Nov 2001
TL;DR: In this article, the transverse ray intercept curves form substantially straight, sloped lines and wavefront coding corrects for known or unknown amounts of'misfocus-like' aberrations by altering the optical transfer function of the imaging apparatus in such a way that the altered optical transfer functions is substantially insensitive to aberration.
Abstract: The present invention provides improved Wavefront Coding imaging apparatus (100, 800, 1100) and methods composed of optics (102, 802, 1102), wavefront coding (104, 806, 1110), detection (106), and processing (112, 810, 1112) of the detected image The optics are constructed and arranged to have the characteristic that the transverse ray intercept curves form substantially straight, sloped lines The wavefront coding corrects for known or unknown amounts of 'misfocus-like' aberrations by altering the optical transfer function of the imaging apparatus in such a way that the altered optical transfer function is substantially insensitive to aberrations Post processing then removes the effect of the coding, except for the invariance with regard to aberrations, producing clear images

Journal ArticleDOI
TL;DR: The coupling between a turbulence-distorted optical beam and a single-mode waveguide is addressed and the coupling efficiency and the coupled phase are derived, both without aberrations and with small aberration.
Abstract: The coupling between a turbulence-distorted optical beam and a single-mode waveguide is addressed. The coupling efficiency and the coupled phase are derived, both without aberrations and with small aberrations. These analytical expressions are validated by numerical simulations. Correction with adaptive optics is investigated. In the general case, the Strehl ratio is a pessimistic estimator, and the coupled phase is different and has a smaller variance than the classical phase averaged over the pupil. Application fields are heterodyne detection and stellar interferometry, for which spatial and modal filtering are distinguished.

Journal ArticleDOI
20 Mar 2001
TL;DR: In this paper, a prototype of an electromagnetic miniature (O 50 mm) deformable mirror is developed, using available micro-technologies, composed of a thin polymer membrane (2-5 μm) covered with a matrix of permanent magnets, and of an array of planar micro-coils on a O 50 mm substrate.
Abstract: Ground-based telescopes suffer from atmospheric turbulences which perturb the quality of the light arriving from space. Astronomers use adaptive optics in order to correct the wavefront of oncoming light. In this context, a prototype of electromagnetic miniature (O 50 mm) deformable mirror is developed, using available microtechnologies. The mirror is composed of a thin polymer membrane (2–5 μm) covered with a matrix of permanent magnets, and of an array of planar microcoils on a O 50 mm substrate. The paper presents the various technologies used to build the actuator (membranes, coils, magnets). The mechanical behaviour of the mirror is tested. Deformations of up to 20 μm are achieved with currents in the range 1–3 A (6.6 μm/A). Resonance occurs at 485 Hz, with good linearity up to 200 Hz.

Journal ArticleDOI
TL;DR: A heuristic, low-order model for the principal source of tilt anisoplanatism is presented that suggests four possible approaches to eliminating this defect in LGS MCAO: tip/tilt measurements from multiple NGS, a solution to the LGS tilt uncertainty problem, additional higher-order WFS measurements from a single N GS, or higher-orders from both sodium and Rayleigh LGSs at different ranges.
Abstract: Multiconjugate adaptive optics (MCAO) is a technique for correcting turbulence-induced phase distortions in three dimensions instead of two, thereby greatly expanding the corrected field of view of an adaptive optics system. This is accomplished with use of multiple deformable mirrors conjugate to distinct ranges in the atmosphere, with actuator commands computed from wave-front sensor (WFS) measurements from multiple guide stars. Laser guide stars (LGSs) must be used (at least for the forseeable future) to achieve a useful degree of sky coverage in an astronomical MCAO system. Much as a single LGS cannot be used to measure overall wave-front tilt, a constellation of multiple LGSs at a common range cannot detect tilt anisoplanatism. This error alone will significantly degrade the performance of a MCAO system based on a single tilt-only natural guide star (NGS) and multiple tilt-removed LGSs at a common altitude. We present a heuristic, low-order model for the principal source of tilt anisoplanatism that suggests four possible approaches to eliminating this defect in LGS MCAO: (i) tip/tilt measurements from multiple NGS, (ii) a solution to the LGS tilt uncertainty problem, (iii) additional higher-order WFS measurements from a single NGS, or (iv) higher-order WFS measurements from both sodium and Rayleigh LGSs at different ranges. Sample numerical results for one particular MCAO system configuration indicate that approach (ii), if feasible, would provide the highest degree of tilt anisoplanatism compensation. Approaches (i) and (iv) also provide very useful levels of performance and do not require unrealistically low levels of WFS measurement noise. For a representative set of parameters for an 8-m telescope, the additional laser power required for approach (iv) is on the order of 2 W per Rayleigh LGS.

Journal ArticleDOI
TL;DR: In this article, the performance of modal multi-conjugate adaptive Optics systems correcting a finite number of Zernike modes using a second-order statistical analysis is studied, and an optimized command matrix is computed from the covariances of atmospheric signals and noise, to minimize the residual phase variance averaged over the field of view.
Abstract: The performance of modal Multi-Conjugate Adaptive Optics systems correcting a nite number of Zernike modes is studied using a second-order statistical analysis. Both natural and laser guide stars (GS) are considered. An optimized command matrix is computed from the covariances of atmospheric signals and noise, to minimize the residual phase variance averaged over the eld of view. An ecient way to calculate atmospheric covariances of Zernike modes and their projections is found. The modal covariance code is shown to reproduce the known results on anisoplanatism and the cone eect with single GS. It is then used to study the error of wave-front estimation from several o-axis GSs (tomography). With increasing radius of the GS constellation , the tomographic error increases quadratically at small , then linearly at larger when incomplete overlap of GS beams in the upper atmospheric layers provides the major contribution to this error, especially on low-order modes. It is demonstrated that the quality of turbulence correction with two deformable mirrors is practically independent of the conjugation altitude of the second mirror, as long as the command matrix is optimized for each conguration.

Journal ArticleDOI
TL;DR: A 1000mum-diameter silicon nitride deformable mirror for focus-control applications, using micro-optoelectromechanical systems technology, which achieved variable focal lengths from 36 to 360 mm while maintaining zero primary spherical aberration using a maximum control voltage of 100 V.
Abstract: We have built a 1000‐μm-diameter silicon nitride deformable mirror for focus-control applications, using micro-optoelectromechanical systems technology. We achieved variable focal lengths from 36 to 360 mm while maintaining zero primary spherical aberration, using a maximum control voltage of 100 V. Active control of spherical aberration of approximately two waves at 660 nm was demonstrated.

Patent
14 Nov 2001
TL;DR: An ophthalmic instrument for obtaining high resolution, wide field of area multi-spectral retinal images is described in this article, which includes a fundus retinal imager, which includes optics for illuminating and imaging the retina of the eye; apparatus for generating a reference beam coupled to the fundus optics to form a reference area on the retina; a wavefront sensor optically coupled to fundus optic sensors for measuring the wavefront produced by optical aberrations within the eye and the imager optics.
Abstract: An ophthalmic instrument (for obtaining high resolution, wide field of area multi-spectral retinal images) including a fundus retinal imager, (which includes optics for illuminating and imaging the retina of the eye); apparatus for generating a reference beam coupled to the fundus optics to form a reference area on the retina; a wavefront sensor optically coupled to the fundus optics for measuring the wavefront produced by optical aberrations within the eye and the imager optics; wavefront compensation optics coupled to the fundus optics for correcting large, low order aberrations in the wavefront; a high resolution detector optically coupled to the imager optics and the wavefront compensation optics; and a computer (which is connected to the wavefront sensor, the wavefront compensation optics, and the high resolution camera) including an algorithm for correcting, small, high order aberrations on the wavefront and residual low order aberrations.

Patent
13 Feb 2001
TL;DR: In this article, a wavefront sensor is combined with a digital micromirror device (DMD) to provide a sequence of two-dimensional arrays of values which together define the wavefront correction for the eye.
Abstract: A system (10) and method for performing corneal ablation or reshaping with a laser (22) in order to correct aberrations in the optical system of the eye (40) utilizes a wavefront sensor which defines a wavefront correction for the eye (40) and then, based upon that defined wavefront correction, drives a digital micromirror device (DMD) which modulates a laser beam to the eye (40) to perform the correction. As the DMD (26) is a 2-D array of individually controlled mirrors, and the wavefront sensor analysis can provide a sequence of two dimensional arrays of values which together define the wavefront correction for the eye (40), the combination of the two produces a method for correcting the corneal surface. The system (10) may be operated in either of two manners to achieve optimum refractive corrections: (1) off-line measurement of the eye optical system via the wavefront sensor followed by DMD-based laser refractive surgery, or (2) realtime measurement of the eye optical system via the wavefront sensor which directs a DMD-based laser refractive surgery system.

Journal ArticleDOI
TL;DR: The performance of adaptive systems that consist of microscale on-chip elements [microelectromechanical mirror (mu-mirror) arrays and a VLSI stochastic gradient descent microelectronic control system] is analyzed.
Abstract: The performance of adaptive systems that consist of microscale on-chip elements [microelectromechanical mirror (µ-mirror) arrays and a VLSI stochastic gradient descent microelectronic control system] is analyzed. The µ-mirror arrays with 5 × 5 and 6 × 6 actuators were driven with a control system composed of two mixed-mode VLSI chips implementing model-free beam-quality metric optimization by the stochastic parallel perturbative gradient descent technique. The adaptation rate achieved was near 6000 iterations/s. A secondary (learning) feedback loop was used to control system parameters during the adaptation process, further increasing the adaptation rate.

Journal ArticleDOI
TL;DR: This study was the first to demonstrate that the correction of higher-order aberrations can lead to supernormal visual performance in normal eyes, and spurred a ground swell of interest in wavefront sensing and the possibility of coupling it with wavefront correction in the form of customized corneal ablation.

Patent
28 Sep 2001
TL;DR: In this paper, a beam control system and method which utilizes the wavefront reversal property of nonlinear optical phase conjugation to permit incorporation of a liquid crystal OPA within the low power legs of the beam controller system, thereby affording the advantages of the OPA without the power limitations thereof.
Abstract: A beam control system and method which utilizes the wavefront reversal property of nonlinear optical phase conjugation to permit incorporation of a liquid crystal OPA within the low power legs of the beam control system, thereby affording the advantages of the OPA without the power limitations thereof. The invention is adapted for use with a beacon for illuminating a target with a first beam of electromagnetic energy. The system includes a telescope (1010) for receiving a target return comprising a reflection of the first beam from the target. An optical phased array (1050) is included for correcting for aberrations in the wavefront of the target return. A mechanism is included for ascertaining the correction applied by the optical phased array to the target return. The mechanism applies the correction to a third beam which ultimately is the output beam. In the illustrative embodiment, the first beam of electromagnetic energy is optical energy and the mechanism includes a first phase conjugate mirror (1091) adapted to conjugate electromagnetic energy output by the third mechanism and a second phase conjugate mirror (1092) adapted to conjugate the output of the first phase conjugate mirror. The fourth mechanism further includes an amplifier (1088) for boosting the signal output by the second phase conjugate mirror (1092) to provide the output beam.

Book ChapterDOI
01 Jan 2001
TL;DR: In this paper, a micromachined mirror array for adaptive optics is presented, where single-crystal-silicon mirrors are assembled onto electrostatic parallel-plate actuators.
Abstract: We present a micromachined mirror array for use in adaptive optics. Piston motions of more than 6 µm as well as tip/tilt motions of 11 mrad (0.65°) are demonstrated. Single-crystal-silicon mirrors are assembled onto electrostatic parallel-plate actuators. The actuators lift off the substrate after microstructure release as a consequence of residual stresses in nickel-polysilicon bimorph flexures. The assembled mirrors provide fill factors of 95%. Peak-to-valley surface variations are smaller than 30 nm over a 464 µm-diameter (vertex-to-vertex) mirror segment.