The security of sensitive information exchange has become a major topic in recent years. Quantum Key Distribution (QKD) provides a highly secure approach to share random encryption keys between two communication terminals. In contrast with traditional public cryptography methods, QKD security relies on the foundations of quantum mechanics and not on computational capabilities. This makes QKD unconditionally secure (if properly implemented) and it is envisaged as a main component in the next–generation cryptographic technology. QKD has already been successfully demonstrated in different contexts such as fibre-to- fibre, and free-space ground-toground as well as ground-to-air communications. However, Size, Weight and Power (SWaP) constraints have prevented previous implementations to be demonstrated on small form airborne platforms such as Unmanned Aircraft Systems (UAS) and High Altitude Pseudo-Satellites (HAPS). Project Q-DOS aims to deliver a QKD module using compact, cutting-edge photonic waveguide technology, which will allow low-SWaP aerospace requirements to be met. This module uses 1550 nm single photons to implement a BB84 protocol, and will enable the demonstration of a secure, high-speed optical communication data link (~0.5 Gbps) between a drone and a ground station. The targeted link range is 1 km. The airborne communications module, including the QKD terminal, tracking modules, traditional communications systems, optics and control electronics, must not exceed a mass of 5 kg and a power consumption of 20 W.
The advent of the Unmanned Aerial Vehicle (UAV) has generated the need for reduced size, weight and power (SWaP)
requirements for communications systems with a high data rate, enhanced security and quality of service. This paper
presents the current results of the DAZZLE project run by Airbus Group Innovations. The specifications, integration
steps and initial performance of a UAV to ground communication system using a laser and a modulated retro-reflector
are detailed. The laser operates at the wavelength of 1550nm and at power levels that keep it eye safe. It is directed using
a FLIR pan and tilt unit driven by an image processing-based system that tracks the UAV in flight at a range of a few
kilometers. The modulated retro-reflector is capable of a data rate of 20Mbps over short distances, using 200mW of
electrical power. The communication system was tested at the Pershore Laser Range in July 2014. Video data from a
flying Octocopter was successfully transmitted over 1200m. During the next phase of the DAZZLE project, the team
will attempt to produce a modulated retro-reflector capable of 1Gbps in partnership with the research institute Acreo1
based in Sweden. A high speed laser beam steering capability based on a Spatial Light Modulator will also be added to
the system to improve beam pointing accuracy.
The new generation of UAVs (Unmanned Aerial Vehicles) require high speed data links to offload all its sensors data.
RFSO (Reflective Free Space Optics) has become an important alternative to RF systems because it is robust against
interception and jamming, enhancing data security. Moreover, the weight and power consumption of the RFSO coms
module is reduced, making it suitable for SWaP (Size, Weight, and Power) constrained applications.
In this paper, we present the design of a tracking module based on a non-mechanical holographic beam steering system.
A highly accurate position sensing unit is required to accomplish a good tracking process and therefore guarantee the
data link stability. Different localization methods such as centroid, centroid windowed or centroid squared are tested and
compared using real data captured in a turbulent scenario. Errors below 8cm are reported in a double pass 1km link.
Optical Coherence Tomography (OCT) is a technique that allows imaging tissue in three spatial dimensions. Such a
technique makes it possible to examine the subsurface of the tissue. The depth of penetration into the tissue can be
tailored by tuning the wavelength of the light source. While in some cases it is desirable to obtain deep penetration of
the sample, when scanning for cancerous changes, it may only be necessary to penetrate the first few hundred
micrometres. The use of a shorter wavelength, while decreasing the penetration depth, will improve the resolution of the
instrument. While images from OCT systems contain speckle and other artefacts, there are methods of evaluating the
information by using image processing techniques. Of particular interest is the scattering coefficient that can be derived
from the OCT data. Using discriminant techniques on the scattering data (such as principal components analysis), gives
a sensitive way of differentiating between changes in structure in the tissue. An extensive data collection was performed
on cervical tissue using samples that ranged from normal to invasive cancer. The histopathology of each sample was
gathered and was classified from normal to cancer. The scattering profiles of the data were averaged and gradient
analysis was performed, showing that for small distances into the sample there is a significant difference between
scattering profiles between cancerous and normal tissue. PCA was also performed on the data showing grouping into
various stages of cancer.
The spatial resolution of retinal images is limited by the presence of static and time-varying aberrations present within the eye. An updated High Resolution Adaptive Optics Fundus Imager (HRAOFI) has been built based on the development from the first prototype unit. This entirely new unit was designed and fabricated to increase opto-mechanical integration and ease-of-use through a new user interface. Improved camera systems for the Shack-Hartmann sensor and for the scene image were implemented to enhance the image quality and the frequency of the Adaptive Optics (AO) control loop. An optimized illumination system that uses specific wavelength bands was applied to increase the specificity of the images. Sample images of clinical trials of retinas, taken with and without the system, are shown. Data on the performance of this system will be presented, demonstrating the ability to calculate near diffraction-limited images.
Kestrel Corporation has previously demonstrated that the Distorted Grating Wavefront Sensor (DGWFS) can successfully reconstruct wavefronts in severely scintillated conditions, and has an ongoing experiment investigating aberrations in the eye using a DGWFS. Existing aberrometers cannot accurately reconstruct wavefronts when large amounts of scattering or scintillation are present and so cannot be used with subjects who have conditions such as cataracts (opacification of the ocular lens). Consequently a large proportion of the population cannot utilize today's diagnostic aberrometers and so do not benefit from otherwise available treatments. As previously reported, a DGWFS has been integrated into an Shack-Hartmann based aberrometer provided by the International Laser Center, Moscow State University, however several issues became apparent regarding data collection from the human eye. Results from laboratory experiments intended to investigate and resolve these data collection issues will be discussed.
A new significantly redesigned version of clinically applicable adaptive optics multispectral fundus imager is presented. Along with greatly improve adaptive system loop rate, the device performs reliably and is convenient for use in clinical practice. This new imager has allowed us to use new approaches for retina image analysis and obtain original results on the distribution of aberrations in the human eye.
Diagnosis and treatment of retinal diseases such as diabetic retinopathy commonly rely on a clear view of the retina. High quality retinal images are essential in early detection and more accurate diagnosis of many retinal diseases. Conventional fundus cameras usually lack the ability to provide high resolution details required for diagnostic accuracy. Major factors contributing to the degradation of retinal image quality are the aberrations from the eye and the imaging device. The challenge in obtaining high quality retinal image lies in the design of the imaging system that can reduce the strong aberrations of the human eye. Since the amplitudes of human eye aberrations decrease rapidly as the aberration order goes up, it is more cost-effective to correct low order aberrations with adaptive optical devices while process high order aberrations through image processing. A cost effective fundus imaging device that can capture high quality retinal images with 2-5 times higher resolution than conventional retinal images has been designed. This imager improves image quality by attaching complementary adaptive optical components to a conventional fundus camera. However, images obtained with the high resolution camera are still blurred due to some uncorrected aberrations as well as defocusing resulting from non-isoplanatic effect. Therefore, advanced image restoration algorithms have been employed for further improvement in image quality. In this paper, we use wavefront-based and self-extracted blind deconvolution techniques to restore images captured by the high resolution fundus camera. We demonstrate that through such techniques, pathologies that are critical to retinal disease diagnosis but not clear or not observable in the original image can be observed clearly in the restored images. Image quality evaluation is also used to finalize the development of a cost-effective, fast, and automated diagnostic system that can be used clinically.
Aim: The objective of this project was to evaluate high resolution images from an adaptive optics retinal imager through comparisons with standard film-based and standard digital fundus imagers. Methods: A clinical prototype adaptive optics fundus imager (AOFI) was used to collect retinal images from subjects with various forms of retinopathy to determine whether improved visibility into the disease could be provided to the clinician. The AOFI achieves low-order correction of aberrations through a closed-loop wavefront sensor and an adaptive optics system. The remaining high-order aberrations are removed by direct deconvolution using the point spread function (PSF) or by blind deconvolution when the PSF is not available. An ophthalmologist compared the AOFI images with standard fundus images and provided a clinical evaluation of all the modalities and processing techniques. All images were also analyzed using a quantitative image quality index. Results: This system has been tested on three human subjects (one normal and two with retinopathy). In the diabetic patient vascular abnormalities were detected with the AOFI that cannot be resolved with the standard fundus camera. Very small features, such as the fine vascular structures on the optic disc and the individual nerve fiber bundles are easily resolved by the AOFI. Conclusion: This project demonstrated that adaptive optic images have great potential in providing clinically significant detail of anatomical and pathological structures to the ophthalmologist.
A key element in any adaptive optics system is the deformable mirror used to introduce the conjugate correction. In this paper we will present the results from characterizing a pair of custom 20 element, 38 mm diameter, bimorph deformable mirrors that were specifically designed to provide unusually large stroke to allow correction of significant focus and astigmatism terms in a human fundus adaptive optics imager. Data on the measured correction capability and inherent hysteresis of the mirror shown that the mirrors have 40 μm waves of defocus correction and 20 μm waves of astigmatism correction at 760 nm, with a typical hysteresis at full deflection of 15%. This technology is patented under Patent # 6,331,059 B1.
Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL's ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.
The concept of a curvature-based wavefront sensor using a distorted grating as the imaging element to capture images of two spatially separated planes onto a single detector has been reported previously. This presentation reports on simulations comparing a Shack-Hartmann (S-H) sensor with a distorted grating wavefront sensor (DGWFS) for a generic adaptive optics (AO) system using a Clear-1 atmospheric model. Using WaveTrainTM simulation software a model of the DGWFS has been developed and integrated into the software. A simulation of a complete AO system including a tip/tilt system, high order correction system, atmospheric model, and a back-propagating laser system has been constructed. The model has then been exercised using various seeing conditions, noise levels, WFS sensitivities, camera systems, and other parameters. A comparison between the performance of the AO system using the S-H sensor and the DGWFS is presented, both in terms of wavefront measurement accuracy, image quality, and as a beam delivery system.
Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL’s ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.
An adaptive optics system usually has three basic elements, a wavefront sensor, a deformable element, and a feedback scheme. Typically these components are a Shack-Hartmann sensor, a bimorph or segmented mirror, and a DSP solution for performing the necessary calculations. These components are expensive, and give rise to a complex optical and computational system. In this paper a novel implementation of an adaptive optics system will be discussed. The wavefront sensor is based on an IMP grating to measure the curvature of the incoming light. This sensor has been found to be robust to scintillation, so is applicable to horizontal propagation paths. An OKO technologies deformable mirror is used, and the feedback loop calculations run on a standard Pentium III computer using Windows 2000. Results from recent trials of the system correcting for errors over various horizontal propagation lengths will be shown. Additionally results using this system for laser beam propagation will also be discussed.
A comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS) has been completed. The DGWFS is a phase diversity/wavefront curvature type of sensor using a grating to generate the multiple image planes. Data were collected under simulated propagation conditions using the Advanced Concept Laboratory at Lincoln Laboratory. The sensors were arranged such that both recorded a time varying sample of the wavefront at exactly the same time. Dynamic and static comparisons of the two sensors under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =50, were completed.
The data show that the two techniques measure static, low amplitude, on the order of a few waves, aberrations with little difference. Under conditions where there are significant aberrations, the wavefronts measured by the two sensors show notable differences with the DGWFS exhibiting a smoothed, low passed, rendition of the wavefront. As the aberrations increase to produce scintillated condition the differences become more pronounced.
Phase-diversity wavefront sensing has been implemented for the measurement of turbulence-distorted atmospheric wavefronts in applications of adaptive optics for essentially-horizontal propagation paths. The selected implementation of phase-diversity provides a wavefront sensor capable of estimating atmospheric distortions when observing extended scenes and provides a range-weighted sensing of the atmospheric distortions dependent on the angular region of the scene used for measurement. The data inversion, based on a Green's function analysis, is fast and robust enough for real-time implementation. For measurements of the atmospheric properties this wavefront sensor is being used with bright, compact sources to give high signal to noise measurements for integrated atmospheric effects along defined optical paths. The implementation used facilitates measurements of the atmospheric distortions along separate propagation paths. By simultaneous measurements along 3 separate paths a library of spatio-temporal atmospheric distortions and information about the isoplanicity of the distortions will be compiled for use in assessing applications of adaptive optics in horizontal propagation conditions. The principles of measurement, the details of implementation and some preliminary results will be described.
Turbulence effects close to the air-ground interface may be expected to be non-Kolmogorov, even if that model is an adequate description of free-air turbulence effects. Direct measurements of the optical effects of propagation through the boundary layer are therefore required and are being undertaken as part of a program in which various potential applications of adaptive optics are being examined. The measurements are intended to characterize the spatio- temporal characteristics of optical wavefronts after propagation through the air-ground boundary layer. The objective in these measurements is to describe the level of performance that will be required in an adaptive system intended to mitigate the deleterious effects of atmospheric propagation on image formation and on other optical measurements. The principles of measurements and the preliminary results are presented.
Optical fibre interferometric strain sensors embedded into structures offer a very accurate and robust method for shape measurement [1]. Many schemes have been demonstrated in which strain and/or temperature in a structure are inferred from monochromatic optical phase delay [2].
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