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Neglecting pupil irradiance fluctuations using a Hartmann Shack wavefront sensor leads to phase reconstruction bias. This bias depends on the pupil irradiance profile, the Hartmann Shack geometry and the amplitude and structure of the aberrations. In order to quantify the impact on real eye aberrations measurement, pupil irradiance and ocular aberrations of three trained subjects have been acquired on the LESIA testbed at Hospital des Quinze-Vingts. The pure WFS error is quantified with these data sets, on various lenslet array geometries. The propagation of this pure WFS error on actual systems, namely a static aberro- meter and an AO imager, is addressed. We find that, for a large enough lenslet array and with a reasonably clean optical path, the induced error is negligible.

GNOSIS is an OH suppression unit to be used in conjunction with existing spectrographs. The OH suppression is achieved using fibre Bragg gratings (FBGs), and will deliver the darkest near-infrared background of any ground-based instrument. Laboratory and on-sky tests demonstrate that FBGs can suppress OH lines by 30dB whilst maintaing > 90% throughput between the lines, resulting in a 4 mag decrease in the background. In the first implementation GNOSIS will feed IRIS2 on the AAT. It will consist of a seven element lenslet array, covering 1.4" on the sky, and will suppress the 103 brightest OH lines between 1.47 and 1.70 μm. Future upgrades will include J-band suppression and implementation on an 8m telescope.

Today it is still clinical practice to determine burns wounds and their depth by visual inspection. However, it was recently shown that burns develop differently from their initial grade depending on the contact time of the source. As this contact time varies it is difficult to assess the burn severity relaying only on a naked eye. Parameters such as oxygen saturation, hematocrit, water presence, and perfusion, can offer a more quantitative approach to wound assessment hence improving diagnosis and treatment. These parameters can be obtained with spectroscopic and flow sensitive techniques. We propose a study of burns dynamic using a combination of spectroscopic and thermal imaging techniques. A spectral camera based on a lenslet array architecture was used to obtain 18 images of the skin, each lenslet was interfaced with a narrowband filter hence 18 spectrally sensitive images were obtained. In this paper the results of a preliminary electrical burns study are presented.

We describe the use of a lenslet-array-based device for interconnections in optical digital computing systems. This new device, the digital lenslet array processor, operates in polychromatic and spatially incoherent light, so it can use a wide spectrum of electro-optical light sources. An experimental example is presented.

There has been very limited study on the stability of a Shack-Hartmann wavefront sensor (SHWS) since its emergence in the early 1970s. In this paper, through experimental study of the system stability of a digital SHWS, a special lenslet array with long focal range is designed and implemented with a spatial light modulator to improve the system performance. Diffractive lenses with long focal length range can provide pseudo-nondiffracting beams and a long range of focusing plane. The performance and effect of the modified SHWS with this lenslet array are investigated, and the experimental results show that the system stability and measurement repeatability are not sensitive to the sensing distance and stay at an acceptable level.

The sensitivity and dynamic range of a Shack-Hartmann wavefront sensor is enhanced when the spots produced by the lenslet array are allowed to shift more than one lenslet radius from their on-axis positions. However, this presents the problem of accurately and robustly associating the spots with their respective subapertures. This paper describes a method for sorting spots that takes advantage of the local spot position distortions to unwrap the spot pattern. The described algorithm is both simple and robust and also applicable to any lenslet array geometry that can be described as a two-dimensional lattice, including hexagonal arrays, which are shown here to be more efficient than square arrays.

We have been testing at laboratory commercial variable attenuators commonly used in telecommunication applications for their used in astronomy. Such variable attenuators are going to be included in the central fibers of the integral field unit (IFU) of the prototype instrument EDiFiSE (Equalized and Diffraction-limited Field Spectrograph Experiment). The EDiFiSE IFU is conformed by a lenslet array of 331 lenses, 331 fibers and seven variable attenuators (inserted in the seven central fibers of the bundle). We present here the characterization of the attenuator devices tested for their use in astronomy and, in particular, to their application in the observation of object of large dynamic range using equalized integral field spectroscopy. We also present the optical tests we have carried out to characterize the performances of two lenslet arrays acquired in the framework of the EDiFiSE project.

In this paper, a magnification display of three-dimensional images in one-dimensional integral imaging system using lenslet array is proposed. To show the feasibility of proposed system, some experiments are carried out and results are presented.

It is generally believed that very fast cameras imaging large Fields of View translate into huge optomechanicsand mosaics of very large contiguous CCDs. It has already been suggested that seeing limited imaging camerasfor telescopes whose diameters are larger than 20m are considered virtually impossible for a reasonable cost.It has also been suggested that using existing technology and at a moderate price, one can build a Smart FastCamera, a device that placed on aberrated Field of View, including those of slow focal ratios, is able to provideimaging at an equivalent focal ratio as low as F/1, with a size that is identical to the large focal ratio focal planesize. The design allows for easy correction of aberrations over the Field of View. It has low weight and sizewith respect to any focal reducer or prime focus station o f the same performance. It can be applied to existing8m-class telescopes to provide a wide “eld fast focal plane or to achieve seeing-limited imaging on ExtremelyLarge Telescopes. As it oers inherently fast read-o ut in a massive parallel mode, the SFC can be used as apupil or focal plane camera for pupil-plane or Shack-Har tmann wavefront sensing for 30-100m class telescopes.Basing upon Smart Fast Camera concept, we present a study turned to explain the pliability of this instrumentfor dierent existing telescopes.Keywords: Wide-“eld camera, seeing limited , lenslet array, wavefront sensi ng, Extremely Large Telescope,Smart Focal Plane

In this paper, we present the characteristics of integral imaging systems with large depth when using plane illumination and diffusing illumination. For each system, we perform ray analysis based on ray optics. To check visual quality through optical experiments, we use an average image of observed images pickuped at various positions within large depth. Experimental results show that the use of diffusing illumination can improve visual quality of reconstruction 3-D images in large depth integral imaging system.

We have designed and built a multi-aperture thin imager using a lenslet array and a CCD imager. The thickness of the imager is significantly reduced. We will present experimental results that demonstrate high resolution imaging.

It is generally believed that very fast cameras imaging large Fields of View translate into huge optomechanics and mosaics of very large contiguous CCDs. It has already been suggested that seeing limited imaging cameras for telescopes whose diameters are larger than 20m are considered virtually impossible for a reasonable cost. We show here that, using existing technology and at a moderate price, one can build a Smart Fast Camera, a device that placed on aberrated Field of View, including those of slow focal ratios, is able to provide imaging at an equivalent focal ratio as low as F/1, with a size that is identical to the large focal ratio focal plane size. The design allows for easy correction of aberrations over the Field of View. It has low weight and size with respect to any focal reducer or prime focus station of the same performance. It can be applied to existing 8m-class telescopes to provide a wide field fast focal plane or to achieve seeing-limited imaging on Extremely Large Telescopes. As it offers inherently fast read-out in a massive parallel mode, the SFC can be used as a pupil or focal plane camera for pupil-plane or Shack-Hartmann wavefront sensing for 30-100m class telescopes.

Criss-crossing of focal images is the cause of a narrow dynamic range in Shack-Hartmann sensors. Practically, aberration range wider than ±3 diopters can not be measured. A method has been proposed for ophthalmologic applications using a rarefied lenslet array through which a wave front is projected with the successive step-by-step changing of the global tilt. The data acquired in each step are accumulated and processed. In experimental setup, a doubled dynamic range was achieved with four steps of wave front tilting.

Historically, the spots produced by a Shack-Hartmann wavefront sensor are expected to stay in a region immediately behind their respective lenslets. Valuable sensitivity and dynamic range can be recovered if the spots are allowed to wander. A new algorithm is presented for resolving this issue for a hex-packed lenslet geometry.

A new optical neuron device has been developed. The device can perform both summation and thresholding operations in optics, and consists of a PIN a-Si:H photoreceptor, aluminum neuron electrodes and a ferroelectric liquid crystal light modulator. The a-Si:H photoreceptor shows characteristics of an ideal quantum efficiency (η∼1) and a good linearity (γ∼1). The optical neuron device exhibits a response time of ∼30 µs for incident light power of 9 µW and a contrast ratio of 300:1. Using this neuron device, a lenslet array and a memory mask, an all-optical neural network has been constructed. The network demonstrates an associative memory function on purely optical parallel processing without any help from electric computation.

The paper discusses how phase retrieval can be employed as a robust technique for estimating the wavefront distortion using a lenslet array. It is shown that the principal problem of phase retrieval, namely divergence is considerably reduced when the aperture is subdivided. The results obtained compare favorably with the alternative approach of phase diversity. Furthermore, the introduction of prior information, in the form of statistical information of the distortion, is shown to considerably enhance the success of the phase retrieval.

The Shack-Hartmann wavefront sensor is a powerful tool for optical analysis. A vital step in the data analysis chain involves reconstructing the wavefront incident upon the lenslet array from hundreds or thousands of slope measurements. We discuss here the basics of reconstruction and the differences in reconstruction for the case of Hartmann and Shack-Hartmann sensors. Hartmann sensors take point samples of the wavefront but Shack-Hartmann sensors measure the average slope over small regions. This results in subtle differences in the reconstruction.

The dynamic range and accuracy of an ophthalmic wavefront sensor system are the important performance criteria. The resolution of the lenslet array, in terms of the number of lenslet samples across the ocular pupil, is the key element in determining this performance. Higher performance lenslet arrays can be used to increase both the dynamic range and accuracy of the system in most applications.

We have integrated an 850-nm VCSEL, its driver, and diffractive lenslet array onto a single substrate to produce an integrated opto-electronic multi-chip module. The diffractive element fans the output from the VCSEL into an array of approximately 60 focal spots at a plane 1416 µm from the surface of the VCSEL. Experimental results are presented.

Excimer lasers are the preferred source of illumination for photolithographic systems. Lenslet array optical integrators are very frequently used to achieve good uniformity of illumination at the plane of the mask--the target to be recorded by the photolithographic system. Lenslet arrays break the incident beam up into subapertures and the resulting beams are overlapped at the plane of the target with variable incident angles. The overlapping of the tilted beams segments results in coherent interference effects leading to fine-scale intensity modulation called orange peel. We show that the ideal method of characterization of excimer lasers for this application is the Young's double hole test with hole spacing set to the lenslet element separation. This method to be superior to other common measures of laser quality such as angular divergence and M2.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The spatial resolution of Hartmann-type sensors can be increased by moving a wavefront being sensed relative to the sensor by a non-integral number of apertures. The apertures may have a tilt on at least one side thereof. The lenslets themselves in a lenslet array may serve as the apertures or material may be provided on the lenslet array to create the apertures.

An optoelectronic multistage compact interconnection network using polarizing beam splitters, polarizing switch arrays, lenslet array and free-space optics is proposed. It is capable of realizing a interconnection of a large number of data pattern images with the total data throughput up to 1 Pbit/s and a reconfiguration time up to 10 ns.

Quadratic aberration is successfully corrected with a segmented microelectromechanical deformable mirror in conjunction with a refractive lenslet array. Use of the lenslet array greatly improves the effective fill factor of the correcting element. Experimental results show correction approaching the diffraction limit for an extreme spherical aberration.

In the last two decades, three-dimensional sensors based on misfocusing have been suggested. This research addresses the question of measuring several focal depths simultaneously. Two options for generating the necessary array of spots are analyzed: the use of a lenslet array and the use of a Dammann grating. Finally, a combination of the two approaches is proposed. Such a combination enables tailoring the system performance to the exact needs of the user.

Optical implementation of a large-scale neural network with 32 × 32 neurons is reported. The experimental setup is described, error caused by limited precision of hardware is analyzed, and experimental results are presented.

Although electronic systems continue to shrink in size, optical processors, particularly correlators/convolvers, remain relatively bulky. Here a compact holographic correlator/convolver, based on the use of multiple lenslet arrays, is presented. This compact lenslet-array holographic correlator/convolver approach offers most of the advantages of conventional optical correlators, including fully parallel high-speed operation, yet its physical size is comparable with that of monolithic optoelectronic units such as VLSI spatial light modulators and CCD's. Thus hybrid optoelectronic systems based on the lenslet-array holographic correlator/convolver (pattern recognition, optically interconnected computers, artificial neural networks, etc.) can be both compact and fast.

A theoretical limitation on the neuron numbers (N x N) of a spatial interconnection system based on a lenslet array is analyzed. To improve the limitation, we propose a submatrix coaxial interconnection architecture. Off-axial aberration is decreased, and high light efficiency is achieved. A detailed analysis is given.

A novel optical encryption method is proposed in this paper to achieve 3-D image encryption. This proposed encryption algorithm combines the use of computational integral imaging (CII) and linear-complemented maximum-length cellular automata (LC-MLCA) to encrypt a 3D image. In the encryption process, the 2-D elemental image array (EIA) recorded by light rays of the 3-D image are mapped inversely through the lenslet array according the ray tracing theory. Next, the 2-D EIA is encrypted by LC-MLCA algorithm. When decrypting the encrypted image, the 2-D EIA is recovered by the LC-MLCA. Using the computational integral imaging reconstruction (CIIR) technique and a 3-D object is subsequently reconstructed on the output plane from the 2-D recovered EIA. Because the 2-D EIA is composed of a number of elemental images having their own perspectives of a 3-D image, even if the encrypted image is seriously harmed, the 3-D image can be successfully reconstructed only with partial data. To verify the usefulness of the proposed algorithm, we perform computational experiments and present the experimental results for various attacks. The experiments demonstrate that the proposed encryption method is valid and exhibits strong robustness and security.

This presentation deals with the use of an incoherent optical processing device for optical interconnections in digital systems. Our device is based on a lenslet-array/mask assembly. The lenslet array creates multiple images of the input. The mask controls the interconnections pattern by blocking parts of these images. The device can operate with polychromatic and spatially incoherent light, so it can use many electro-optical light sources. Device limitations and capabilities are analyzed. This analysis shows that up to 107 elements may be connected by such devices. A demonstration of a simple digital circuit is presented.

By combining a lenslet array with masks it is possible to obtain a noncoherent optical processor capable of computing in parallel generalized 2-D discrete linear transformations. We present here an analysis of such lenslet array processors (LAP). The effect of several errors, including optical aberrations, diffraction, vignetting, and geometrical and mask errors, are calculated, and guidelines to optical design of LAP are derived. Using these results, both ultimate and practical performances of LAP are compared with those of competing techniques.