Showing papers on "Lens (optics) published in 2008"

The Solar Optical Telescope of Solar-B (Hinode): The Optical Telescope Assembly

Abstract: The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388 – 668 nm) with a spatial resolution of 0.2 – 0.3 arcsec. The SOT consists of two optically separable components: the Optical Telescope Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope yet flown in space.

Freeform LED lens for uniform illumination

Abstract: Light flux from LED must be redistributed to meet the needs of lighting in most cases, a new method is proposed for its secondary optic design. Based on refractive equation and energy conservation, a set of first-order partial differential equations which represent the characters of LED source and desired illumination were presented. The freeform lens was constructed by solving these equations numerically. The numerical results showed that we can get a freeform lens for the illumination of uniformity near to 90%, with considerable high computation speed. This method can shorten the designing time of the freeform lens with high accepted tolerance.

LED with phosphor tile and overmolded phosphor in lens

Abstract: Overmolded lenses and certain fabrication techniques are described for LED structures. In one embodiment, thin YAG phosphor plates are formed and affixed over blue LEDs mounted on a submount wafer. A clear lens is then molded over each LED structure during a single molding process. The LEDs are then separated from the wafer. The molded lens may include red phosphor to generate a warmer white light. In another embodiment, the phosphor plates are first temporarily mounted on a backplate, and a lens containing a red phosphor is molded over the phosphor plates. The plates with overmolded lenses are removed from the backplate and affixed to the top of an energizing LED. A clear lens is then molded over each LED structure. The shape of the molded phosphor-loaded lenses may be designed to improve the color vs. angle uniformity. Multiple dies may be encapsulated by a single lens. In another embodiment, a prefabricated collimating lens is glued to the flat top of an overmolded lens.

Optical coherence tomography

Abstract: This invention relates to an optical coherence tomography, in which a light source and an optical linear beam forming system are adopted to obtain two dimensional image of high quality resolution within short time without affection by any mechanical movements. For such purpose, the optical linear beam forming system(20) comprises semicy Under lens(21), convex lens(22) and slit(23) to implement the frequency domain optical coherence tomography. Parallel light beam from the light source is incident on the surface of the semicylinder lens(21), and focal line of the semicylinder lens (21) is located in front of the convex lens (22). The convex lens (22) has short focal point where the parallel light component converges and long focal point where the diverging light component converges. The slit(23) is located between the short focal point and the long focal point.

Ultra wide-field lens-free monitoring of cells on-chip.

Abstract: We experimentally and theoretically demonstrate the proof-of-principle of a new lens-free cell monitoring platform that involves using an opto-electronic sensor array to record the shadow image of cells onto the sensor plane This technology can monitor/count cells over a field-of-view that is more than two orders of magnitude larger than that of a conventional light microscope Furthermore, it does not require any mechanical scanning or optical elements, such as microscope objectives or lenses We also show that this optical approach can conveniently be combined with microfluidic channels, enabling parallel on-chip monitoring of various different cell types, eg, blood cells, NIH-3T3 fibroblasts, murine embryonic stem cells, AML-12 hepatocytes An important application of this approach could be a miniaturized point-of-care technology to obtain CD4 T lymphocyte counts of HIV infected patients in resource limited settings

Transformation optical designs for wave collimators, flat lenses and right-angle bends

Abstract: The transformation optics technique is applied to design three novel devices—a wave collimator, far-zone and near-zone focusing flat optical lenses and a right-angle bend for propagating beam fields. The structures presented in this paper are all two-dimensional (2D), however, the transformation optics design methodologies can be easily extended to develop 3D versions of these optical devices. The required values of the permittivity and the permeability tensors are derived for each of the three devices considered here. Furthermore, the functional performance of each device is verified using full-wave electromagnetic simulations. A wave collimator consists of a 2D rectangular cylinder where the fields (cylindrical waves) radiated by an embedded line source emerge normal to the top and bottom planar interfaces thereby producing highly directive collimated fields. Next, a far-zone focusing lens for a 2D line source is created by transforming the equi-amplitude equi- phase contour to a planar surface. It is also demonstrated that by aligning two far- zone focusing flat lenses in a back-to-back configuration, a near-zone focusing lens is obtained. Finally, a 2D square cylindrical volume is transformed into a cylinder with a fan-shaped cross section to design a right-angle bend device for propagating beam fields.

Biometry and intraocular lens power calculation

Abstract: Purpose of review Heightened patient expectations for precise postoperative refractive results have spurred the continued improvements in biometry and intraocular lens calculations. In order to meet these expectations, attention to proper patient selection, accurate keratometry and biometry, and appropriate intraocular lens power formula selection with optimized lens constants are required. The article reviews recent studies and advances in the field of biometry and intraocular lens power calculations. Recent findings Several noncontact optical-based devices compare favorably, if not superiorly, to older ultrasonic biometric and keratometric techniques. With additional improvements in the internal acquisition algorithm, the new IOL Master software version 5 upgrade should lessen operator variability and further enhance signal acquisition. The modern Haigis-L and Holladay 2 formulas more accurately determine the position and the shape of the intraocular lens power prediction curve. Summary Postoperative refractive results depend on the precision of multiple factors and measurements. The element with the highest variability and inaccuracy is, ultimately, going to determine the outcome. By understanding the advantages and limitations of the current technology, it is possible to consistently achieve highly accurate results.

Optical lens system for taking image

Abstract: An optical lens system for taking image comprises, in order from the object side to the image side: a first lens element with positive refractive power having a convex object-side surface; an aperture stop; a second lens element with negative refractive power; a third lens element having a convex object-side surface; and a fourth lens element with negative refractive power having a concave object-side surface, an image-side surface of the fourth lens element being aspheric and formed with inflection points. A distance from the image-side surface of the fourth lens element to an image plane along an optical axis being BFL, a total track length of the optical lens system for taking image being TTL, and they satisfy the relation: BFL/TTL>0.12. In the optical lens system for taking image, the number of lens elements with refractive power being limited to four.

Bessel beam spectral-domain high-resolution optical coherence tomography with micro-optic axicon providing extended focusing range

Abstract: Endoscopic imaging in tubular structures, such as the tracheobronchial tree, could benefit from imaging optics with an extended depth of focus (DOF) to accommodate the varying sizes of tubular structures across patients and along the tree within the same patient. Yet the extended DOF needs to be accomplished without sacrificing resolution while maintaining sufficient sensitivity and speed of imaging. In this Letter, we report on the measured resolution and sensitivity achieved with a custom-made micro-optic axicon lens designed to theoretically achieve an 8 mm DOF. A measured invariant resolution of ~8 μm is demonstrated across a 4 mm measured DOF using the micro-optic axicon while achieving an invariant sensitivity of ~80 dB with a 25 mW input power. Double-pass Bessel beam spectral-domain optical coherence tomography with an axicon micro-optic lens (i.e., <1 mm in diameter) is, for the first time to our knowledge, demonstrated in a biological sample demonstrating invariant resolution and signal-to-noise ratio across a 4 mm measured DOF, which is compared to Gaussian beam imaging.

Engineering space for light via transformation optics

Abstract: Conceptual studies and numerical simulations are performed for imaging devices that transform a near-field pattern into magnified far-zone images and are based on high-order spatial transformation in cylindrical domains. A lens translating a near-field pattern from an almost circular input boundary onto a magnified far-field image at a flat output boundary is considered. The lens is made of a metamaterial with anisotropic permittivity and permeability both depending on a single "scaling" parameter of the transformation. Open designs of the lens with a truncated body (3/4-body and 1/4-body lenses) are suggested and analyzed. It is shown that the ideal full lens and the 3/4-body lens produce identical images. Numerical simulations of 1/4-body designs indicate that further truncation of the lens could limit its performance. A light concentrator "focusing" far-zone fields into a nanometer-scale area is also considered.

Flexible electro-active lens

Abstract: A lens including a flexible refractive optic having a fixed refractive index, an electro-active element embedded within the flexible refractive optic, wherein the electro-active element has an alterable refractive index, and a controller electrically connected to the electro-active element wherein when power is applied thereto the refractive index of the electro-active element is altered.

Subwavelength colour imaging with a metallic nanolens

Abstract: Early research into metamaterials by other scientists has shown that nanostructured metamaterials can focus incident light and act as a lens. Although such structures are capable of subwavelength imaging, they have two major restrictions: they can only work at one particular wavelength, and the image can only be transferred for a short distance within the limits of the near field and is therefore undetectable in the far field. Here, we propose a lens made of stacked silver nanorods that is capable of colour imaging at subwavelength resolution in the visible range. The subwavelength image can be transferred over distances of at least micrometre scale and magnified before detection by conventional optics devices. Such a nanorod lens has the potential to be an indispensable imaging tool, with particular application to biomedical applications, where individual viruses and other nano-entities could be imaged in colour in the far field. A stack of silver nanorods could, according to calculations, be the answer to performing subwavelength colour imaging over far-field distances. The metallic nanolens is designed to operate in the visible wavelength range and by tapering the nanorods, image magnification is also shown to be feasible. If realized such a lens could be useful for imaging applications in the biomedical sciences and other fields.

Focusing of hard x-rays to 16 nanometers with a multilayer Laue lens

Abstract: We report improved results for hard x-ray focusing using a multilayer Laue lens MLL. We have measured a line focus of 16 nm width with an efficiency of 31% at a wavelength =0.064 nm 19.5 keV using a partial MLL structure with an outermost zone width of 5 nm. The results are in good agreement with the theoretically predicted performance. © 2008 American Institute of

High-speed varifocal imaging with a tunable acoustic gradient index of refraction lens

Abstract: Fluidic lenses allow for varifocal optical elements, but current approaches are limited by the speed at which focal length can be changed. Here we demonstrate the use of a tunable acoustic gradient (TAG) index of refraction lens as a fast varifocal element. The optical power of the TAG lens varies continuously, allowing for rapid selection and modification of the effective focal length at time scales of 1 μs and shorter. The wavefront curvature applied to the incident light is experimentally quantified as a function of time, and single-frame imaging is demonstrated. Results indicate that the TAG lens can successfully be employed to perform high-rate imaging at multiple locations.

Eyeglass lens processing apparatus

Abstract: In an eyeglass lens processing apparatus, a roughing tool for roughing a periphery of an eyeglass lens cuts the periphery up to a roughing path without rotating an eyeglass lens in a first stage and the roughing tool moves along the roughing path while rotating the eyeglass lens in a second stage. A calculating unit for obtaining control data of the lens rotating unit at the second stage. The calculating unit obtains a first load torque applied to a lens chuck shaft at every rotation angle of the lens based on condition data, and obtains a rotation speed of the lens at which the first load torque per unit time becomes equal to or lower than a predetermined reference value.

Thermal Behavior and Microstructural Evolution during Laser Deposition with Laser-Engineered Net Shaping: Part I. Numerical Calculations

Abstract: Laser-engineered net shaping (LENS) is a rapid direct manufacturing process. The LENS process can be analyzed as a sequence of discrete events, given that it is a layer-by-layer process. The thermal history associated with the LENS process involves numerous reheating cycles. In this article, the thermal behavior during laser deposition with LENS is simulated numerically by using the alternate-direction explicit (ADE) finite difference method (FDM). The simulation results showed that deposited material experiences a significant rapid quenching effect during the initial stages of deposition and can attain a very high cooling rate. With an increase in deposit thickness, the rapid quenching effect decreases and eventually disappears. The effects of the processing parameters on the thermal behavior of deposited materials were also simulated and analyzed. The objective of this study is to provide insight into the thermal history during the LENS process, where the ability to correlate process parameters to microstructural evolution is a motivating force.

Time Reversal and Negative Refraction

Abstract: Time reversal and negative refraction have been shown to be intimately linked processes. We propose a scheme that exploits transitions between positive and negative frequencies to mimic negative refraction at an interface and hence to make a negatively refracting lens. The theory applies equally to electromagnetic and acoustic waves. We also propose an experimental realization, and under ideal circumstances this lens can exhibit subwavelength resolution, limited only by the strength of the time-reversed signal.

Bayesian Strong Gravitational-Lens Modeling on Adaptive Grids: Objective Detection of Mass Substructure in Galaxies

Abstract: We introduce a new adaptive and fully Bayesian grid-based method to model strong gravitational lenses with extended images. The primary goal of this method is to quantify the level of luminous and dark-mass substructure in massive galaxies, through their effect on highly-magnified arcs and Einstein rings. The method is adaptive on the source plane, where a Delaunay tessellation is defined according to the lens mapping of a regular grid onto the source plane. The Bayesian penalty function allows us to recover the best non-linear potential-model parameters and/or a grid-based potential correction and to objectively quantify the level of regularization for both the source and the potential. In addition, we implement a Nested-Sampling technique to quantify the errors on all non-linear mass model parameters -- ... -- and allow an objective ranking of different potential models in terms of the marginalized evidence. In particular, we are interested in comparing very smooth lens mass models with ones that contain mass-substructures. The algorithm has been tested on a range of simulated data sets, created from a model of a realistic lens system. One of the lens systems is characterized by a smooth potential with a power-law density profile, twelve include a NFW dark-matter substructure of different masses and at different positions and one contains two NFW dark substructures with the same mass but with different positions. Reconstruction of the source and of the lens potential for all of these systems shows the method is able, in a realistic scenario, to identify perturbations with masses >=10^7 solar mass when located on the Einstein ring. For positions both inside and outside of the ring, masses of at least 10^9 solar mass are required (...).

Experimental demonstration of a mu=-1 metamaterial lens for magnetic resonance imaging

Abstract: In this work a mu=-1 metamaterial (MM) lens for magnetic resonance imaging (MRI) is demonstrated. MRI uses surface coils to detect the radiofrequency(RF) energy absorbed and emitted by the nuclear spins in the imaged object. The proposed MM lens manipulates the RF field detected by these surface coils, so that the coil sensitivity and spatial localization is substantially improved. Beyond this specific application, we feel that the reported results are the experimental confirmation of a new concept for the manipulation of RF field in MRI, which paves the way to many other interesting applications.

Optical time lens based on four-wave mixing on a silicon chip

Abstract: We propose a new technique to realize an optical time lens for ultrafast temporal processing that is based on four-wave mixing in a silicon nanowaveguide. The demonstrated time lens produces more than 100 pi of phase shift, which is not readily achievable using electro-optic phase modulators. Using this method we demonstrate 20x magnification of a signal consisting of two 3 ps pulses, which allows for temporal measurements using a detector with a 20 GHz bandwidth. Our technique offers the capability of ultrafast temporal characterization and processing in a chip-scale device.

Holographic microscopy of holographically trapped three-dimensional structures

Abstract: A method and system for performing three-dimensional holographic microscopy of an optically trapped structure. The method and system use an inverted optical microscope, a laser source which generates a trapping laser beam wherein the laser beam is focused by an objective lens into a plurality of optical traps. The method and system also use a collimated laser at an imaging wavelength to illuminate the structure created by the optical traps. Imaging light scattered by the optically tapped structure forms holograms that are imaged by a video camera and analyzed by optical formalisms to determine light field to reconstruct 3-D images for analysis and evaluation.

The sloan lens ACS survey. VI. Discovery and analysis of a double Einstein ring

Abstract: We report the discovery of two concentric partial Einstein rings around the gravitational lens SDSSJ0946+1006, as part of the Sloan Lens ACS Survey. The main lens is at redshift zl = 0.222, while the inner ring (1) is at redshift zs1 = 0.609 and Einstein radius REin1 = 1.43 ± 0.01 00 . The wider image separation (REin2 = 2.07±0.02 00 ) of the outer ring (2) implies that it is at higher redshift than Ring 1. Although no spectroscopic feature was detected in » 9 hours of spectroscopy at the Keck I Telescope, the detection of Ring 2 in the F814W ACS filter implies an upper limit on the redshift of zs2 . 6.9. The lens configuration can be well described by a power law total mass density profile for the main lens ‰tot / r i∞ 0 with logarithmic slope ∞ 0 = 2.00±0.03 (i.e. close to isothermal), velocity dispersion aeSIE = 287 ± 5kms i1 (in good agreement with the stellar velocity dispersion aev,⁄ = 284 ± 24kms i1 ) with little dependence upon cosmological parameters or the redshift of Ring 2. Using strong lensing constraints only we show that the enclosed mass to light ratio increases as a function of radius, inconsistent with mass following light. Adopting a prior on the stellar mass to light ratio from previous SLACS work we infer that 73 ± 9% of the mass is in form of dark matter within the cylinder of radius equal to the eective radius of the lens. We consider whether the double source plane configuration can be used to constrain cosmological parameters exploiting the ratios of angular distance ratios entering the set of lens equations. We find that constraints for SDSSJ0946+1006 are uninteresting due to the sub-optimal lens and source redshifts for this application. We then consider the perturbing eect of the mass associated with Ring 1 (modeled as a singular isothermal sphere) building a double lens plane compound lens model. This introduces minor changes to the mass of the main lens, allows to estimate the redshift of the Ring 2 (zs2 = 3.1 +2.0 i1.0 ), and the mass of the source responsible for Ring 1 (aeSIE,s1 = 94 +2747 kms i1 ). We conclude by examining the prospects of doing cosmography with a sample of 50 double source plane gravitational lenses, expected from future space based surveys such as DUNE or JDEM. Taking full account of the uncertainty in the mass density profile of the main lens, and of the eect of the perturber, and assuming known redshifts for both sources, we find that such a sample could be used to measure ›m and w with 10% accuracy, assuming a flat cosmological model. Subject headings: Gravitational lensing ‐ galaxies : Ellipticals and lenticulars, cD ‐ galaxies: structure ‐ galaxies: halos ‐ cosmology: dark matter ‐ cosmology: cosmological parameters

Effect of radial polarization and apodization on spot size under tight focusing conditions.

Abstract: We study the effect of polarization and aperture geometry on the focal spot size of a high numerical aperture (NA) aplanatic lens. We show that for a clear aperture geometry, illuminating the lens by linear or circular polarization is preferable over radial polarization for spot size reduction applications. For annular aperture and objective lenses of 0.85 NA and above we give the sizes of the inner annulus which constitute the transition points to a state where the radial polarization illumination gives smaller spot size. We analyze the evolution, the profile and the effect of transverse and longitudinal field components in the focal plane, and show that they play an opposite role on the spot size in the cases of circular and radial polarization illumination. We show that in the limit of a very thin annulus the radial polarization approaches the prediction of the scalar theory at high NA, whereas the linear and circular polarizations deviate from it. We verify that the longitudinal component generated by radially polarized illumination produces the narrowest spot size for wide range of geometries. Finally, we discuss the effects of tight focusing on a dielectric interface and provide some ideas for circumventing the effects of the interface and even utilize them for spot size reduction.

Ultrahigh-resolution optical coherence tomography with monochromatic and chromatic aberration correction

Abstract: We have developed an improved adaptive optics - optical coherence tomography (AO-OCT) system and evaluated its performance for in vivo imaging of normal and pathologic retina. The instrument provides unprecedented image quality at the retina with isotropic 3D resolution of 3.5 x 3.5 x 3.5 microm(3). Critical to the instrument's resolution is a customized achromatizing lens that corrects for the eye's longitudinal chromatic aberration and an ultra broadband light source (Delta lambda=112 nm lambda(0)= approximately 836 nm). The eye's transverse chromatic aberrations is modeled and predicted to be sufficiently small for the imaging conditions considered. The achromatizing lens was strategically placed at the light input of the AO-OCT sample arm. This location simplifies use of the achromatizing lens and allows straightforward implementation into existing OCT systems. Lateral resolution was achieved with an AO system that cascades two wavefront correctors, a large stroke bimorph deformable mirror (DM) and a micro-electromechanical system (MEMS) DM with a high number of actuators. This combination yielded diffraction-limited imaging in the eyes examined. An added benefit of the broadband light source is the reduction of speckle size in the axial dimension. Additionally, speckle contrast was reduced by averaging multiple B-scans of the same proximal patch of retina. The combination of improved micron-scale 3D resolution, and reduced speckle size and contrast were found to significantly improve visibility of microscopic structures in the retina.

Nanohole Array as a Lens

Abstract: We demonstrate that a quasi-crystal array of nanoholes in a metal screen can mimic a function of the lens: one-to-one imaging of a point source located a few tens of wavelengths away from the array to a point on the other side of the array. A displacement of the point source leads to a linear displacement of the image point. Complex structures composed of multiple point sources can be faithfully imaged with resolutions comparable to those of high numerical aperture lenses.

Active contact lens

Abstract: An active contact lens system (100) and method for fabricating an active contact lens (200) are disclosed. The system comprises an active contact lens (110) worn like a conventional contact lens, and comprising a transparent substrate (112) having a circuit formed of one or more of a semi-transparent display (114), a display drive circuit (116), a data communications circuit (118), one or more biosensors (122), an energy transfer antenna (120) and an interconnect network (124). The substrate may be a conventional contact lens material, such as PMMA or RGP, and the display may be formed from a plurality LEDs. A method for fabricating the active contact lens includes fabricating the template (202), forming solder compatible pads (204), assembling the circuit elements (206) and micro-molding the lens (208). The template is fabricated with an interconnect network and shape-specific recesses for receiving the circuit elements. Preferably, the assembly is done using fluidic self-assembly.

Digital Single Lens Reflex Camera Identification From Traces of Sensor Dust

Abstract: Digital single lens reflex cameras suffer from a well-known sensor dust problem due to interchangeable lenses that they deploy. The dust particles that settle in front of the imaging sensor create a persistent pattern in all captured images. In this paper, we propose a novel source camera identification method based on detection and matching of these dust-spot characteristics. Dust spots in the image are detected based on a (Gaussian) intensity loss model and shape properties. To prevent false detections, lens parameter-dependent characteristics of dust spots are also taken into consideration. Experimental results show that the proposed detection scheme can be used in identification of the source digital single lens reflex camera at low false positive rates, even under heavy compression and downsampling.