Active Optics Research Papers - Academia.edu (original) (raw)

During the last two decades, optical stellar interferometry has become an important tool in astronomical investigations requiring spatial resolution well beyond that of traditional telescopes. This book, first published in 2006, was the... more

During the last two decades, optical stellar interferometry has become an important tool in astronomical investigations requiring spatial resolution well beyond that of traditional telescopes. This book, first published in 2006, was the first to be written on the subject. The authors provide an extended introduction discussing basic physical and atmospheric optics, which establishes the framework necessary to present the ideas and practice of interferometry as applied to the astronomical scene. They follow with an overview of historical, operational and planned interferometric observatories, and a selection of important astrophysical discoveries made with them. Finally, they present some as-yet untested ideas for instruments both on the ground and in space which may allow us to image details of planetary systems beyond our own.

The Outer Banks barrier islands of North Carolina, USA, contain a geologic record of inlet activity that extends from ca. 2200 cal yr BP to the present, and can be used as a proxy for storm activity. Optically stimulated luminescence... more

The Outer Banks barrier islands of North Carolina, USA, contain a geologic record of inlet activity that extends from ca. 2200 cal yr BP to the present, and can be used as a proxy for storm activity. Optically stimulated luminescence (OSL) dating (26 samples) of inlet-fill and flood tide delta deposits, recognized in cores and geophysical data, provides the basis for understanding the chronology of storm impacts and comparison to other paleoclimate proxy data. OSL ages of historical inlet fill compare favorably to historical documentation of inlet activity, providing confidence in the technique. Comparison suggests that the Medieval Warm Period (MWP) and Little Ice Age (LIA) were both characterized by elevated storm conditions as indicated by much greater inlet activity relative to today. Given present understanding of atmospheric circulation patterns and sea-surface temperatures during the MWP and LIA, we suggest that increased inlet activity during the MWP responded to intensified hurricane impacts, while elevated inlet activity during the LIA was in response to increased nor'easter activity. A general decrease in storminess at mid-latitudes in the North Atlantic over the last 300 yr has allowed the system to evolve into a more continuous barrier with few inlets.

This work presents first in-vivo results of beating heart tracking with a surgical robot arm in off-pump cardiac surgery. The tracking is performed in a 2D visual servoing scheme using a 500 frame per second video camera. Heart motion is... more

This work presents first in-vivo results of beating heart tracking with a surgical robot arm in off-pump cardiac surgery. The tracking is performed in a 2D visual servoing scheme using a 500 frame per second video camera. Heart motion is measured by means of active optical markers that are put onto the heart surface. Amplitude of the motion is evaluated along the two axis of the image reference frame. This is a complex and fast motion that mainly reflects the influence of both the respiratory motion and the electro-mechanical activity of the myocardium. A model predictive controller is setup to track the two degrees of freedom of the observed motion by computing velocities for two of the robot joints. The servoing scheme takes advantage of the ability of predictive control to anticipate over future references provided they are known or they can be predicted. An adaptive observer is defined along with a simple cardiac model to estimate the two components of the heart motion. The predictions are then fed into the controller references and it is shown that the tracking behaviour is greatly improved.

With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control... more

With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control variables. In severely aberrated systems, the Zernike modes are not orthogonal to each other with respect to this merit function. Using wavefront maps, the PSF, and the MTF, we discuss the physical causes for the non-orthogonality of the Zernike modes with respect to the merit function. We show that for combinations of Zernike modes with the same azimuthal order, a flatter wavefront in the central region of the aperture is more important than the RMS wavefront error across the full aperture for achieving a better merit function. The non-orthogonality of the Zernike modes with respect to the merit function should be taken into account when designing the algorithm for image-based wavefront correction, because it may slow down the process or lead to premature convergence.

With a view to the next generation of large space telescopes, we investigate guide-star-free, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror. We designed and built a... more

With a view to the next generation of large space telescopes, we investigate guide-star-free, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror. We designed and built a high-resolution imaging testbed to evaluate control algorithms. In this paper we use an algorithm based on the heuristic hill climbing technique and compare the correction in three different domains, namely the voltage domain, the domain of the Zernike modes, and the domain of the singular modes of the deformable mirror. Through our systematic experimental study, we found that successive control in two domains effectively counteracts uncompensated hysteresis of the deformable mirror.

In this paper, we present active optical flex module aimed for mobile device applications. The module utilizes flexible optical waveguides on electrical printed circuit board for data links between high-speed interface devices, such as... more

In this paper, we present active optical flex module aimed for mobile device applications. The module utilizes flexible optical waveguides on electrical printed circuit board for data links between high-speed interface devices, such as application processor-to-camera or display module. In this study, flexible and rigid-flex optical electrical circuit boards are used in product emulator designed for in-device optical data links with aggregate data rate up to 120 Gbps (12-ch × 10 Gbps). This paper describes design and fabrication of OE-R/F HDI engine boards with flexible optical interconnect FPCs (OE-FPC); optical coupling methods; chip embedding and assembly procedures; optical engines with 850-nm vertical cavity surface emitting lasers, photo-detectors, and multichannel integrated ICs. Characterization results are given on optical waveguides, I/O couplers, transceiver units, thermal simulations and on selected life-time performance and reliability tests. Low-loss acrylate-based waveguides (~0.0 5dB/cm at 850 nm) are used for OFPCs. Efficient light in/out coupling structures including integrated and embedded 45° mirrors are characterized to meet the target link budget of 10-15 dB at 5-10 Gbps data rate with bit-error-rate (BER) of 10-12. With the chip set used in the test vehicle, the power consumption is approx. 1350 mW for the bi-directional 12-channel 10 Gbit/s/ch optical link (Tx+Rx). This is 112.5 mW per link or 11.25 mW/Gbit/s/link. Bending loss measurements shows that the optical slide flex can be bent down to 2 mm with insignificant increase in loss. Repeatable folding tests indicate of high bend endurance and stability. These results show that our active optical flex module could replace electrical slide or hinge flex and provide high-speed data links free of electromagnetic noise inside typical mobile device configurations.

We construct a model of an excitable medium with elastic rather than the usual diffusive coupling. We explore the dynamics of elastic excitable media, which we find to be dominated by low dimensional structures, including global... more

We construct a model of an excitable medium with elastic rather than the usual diffusive coupling. We explore the dynamics of elastic excitable media, which we find to be dominated by low dimensional structures, including global oscillations, period-doubled pacemakers, and propagating fronts. We suggest that examples of elastic excitable media are to be found in such diverse physical systems as Burridge-Knopoff models of frictional sliding, electronic transmission lines, and active optical waveguides.

This article presents a review of active optical devices. We examine different technologies that can be used for active wavefront modulation in a large range of applications including displays, electronic paper and adaptive optics. We... more

This article presents a review of active optical devices. We examine different technologies that can be used for active wavefront modulation in a large range of applications including displays, electronic paper and adaptive optics. We introduce this review by describing the different light modulations that can be achieved namely amplitude, phase or wavelength modulation. We then examine the different criteria

With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control... more

With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control variables. In severely aberrated systems, the Zernike modes are not orthogonal to each other with respect to this merit function. Using wavefront maps, the PSF, and the MTF, we discuss the physical causes for the non-orthogonality of the Zernike modes with respect to the merit function. We show that for combinations of Zernike modes with the same azimuthal order, a flatter wavefront in the central region of the aperture is more important than the RMS wavefront error across the full aperture for achieving a better merit function. The non-orthogonality of the Zernike modes with respect to the merit function should be taken into account when designing the algorithm for image-based wavefront correction, because it may slow down the process or lead to premature c...

Quantifying spatial variation in pasture and crop biomass can help to direct management practices and improve farm productivity, through accurate and informed movements of grazing rotations, crop and pasture nutrient management and yield... more

Quantifying spatial variation in pasture and crop biomass can help to direct management practices and improve farm productivity, through accurate and informed movements of grazing rotations, crop and pasture nutrient management and yield prediction. Visual pasture assessments are often subjective, and require a degree of expert knowledge/experience. Quadrat-based plant harvesting determinations of biomass is labour intensive and costly when accurate

With a view to the next generation of large space telescopes, we investigate guide-star-free, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror. We designed and built a... more

With a view to the next generation of large space telescopes, we investigate guide-star-free, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror. We designed and built a high-resolution imaging testbed to evaluate control algorithms. In this paper we use an algorithm based on the heuristic hill climbing technique and compare the correction in three different domains, namely the voltage domain, the domain of the Zernike modes, and the domain of the singular modes of the deformable mirror. Through our systematic experimental study, we found that successive control in two domains effectively counteracts uncompensated hysteresis of the deformable mirror.

1. INTRODUCTION Fiber lasers are resolutely entering the market of lasers and this requires the development of fibers dedicated to specific applications. High-power lasers and some active fibers already demonstrate very large effective... more

1. INTRODUCTION Fiber lasers are resolutely entering the market of lasers and this requires the development of fibers dedicated to specific applications. High-power lasers and some active fibers already demonstrate very large effective area and singlemode operation [1]. ...

We analyse the feasibility of a new configuration for the astrometric payload of the GAIA mission, based on active optics, high precision linear metrology, and the baseline CCD detectors. The design approach of both baseline and backup... more

We analyse the feasibility of a new configuration for the astrometric payload of the GAIA mission, based on active optics, high precision linear metrology, and the baseline CCD detectors. The design approach of both baseline and backup configurations is reviewed, and the requirements for the new concept are discussed. We derive the optical parameters (aperture geometry, ef- fective focal length)

Within our project for wide-field telescopes, we discuss the researchs that would particularly benefit of observations at the Concordia Station: discovery and follow up of potentially hazardous near-Earth asteroids, search for extrasolar... more

Within our project for wide-field telescopes, we discuss the researchs that would particularly benefit of observations at the Concordia Station: discovery and follow up of potentially hazardous near-Earth asteroids, search for extrasolar planet transits, and ...

The importance of research in optical nano-engineering today is comparable to that of research in semiconductors 60 years ago. Biologically inspired photoactive isomers are being engineered and incorporated into substrates to construct... more

The importance of research in optical nano-engineering today is comparable to that of research in semiconductors 60 years ago. Biologically inspired photoactive isomers are being engineered and incorporated into substrates to construct optically addressable nanomachine "laser controlled molecular actuators" which will provide non-contact active figure control, allowing a robust response of lightweight optics to pointing slewing, thermal perturbations, and misalignment.