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Showing papers on "Lens (optics) published in 2014"


Journal ArticleDOI
TL;DR: In this article, a planar lens without chromatic aberrations at three wavelengths is presented, which is based on low-loss dielectric resonators which introduce a dense spectrum of optical modes to enable dispersive phase compensation.
Abstract: The replacement of bulk refractive optical elements with diffractive planar components enables the miniaturization of optical systems. However, diffractive optics suffers from large chromatic aberrations due to the dispersion of the phase accumulated by light during propagation. We show that this limitation can be overcome with an engineered wavelength-dependent phase shift imparted by a metasurface and demonstrate a design that deflects three wavelengths without dispersion. A planar lens without chromatic aberrations at three wavelengths is also presented. Our design is based on low-loss dielectric resonators which introduce a dense spectrum of optical modes to enable dispersive phase compensation. The suppression of chromatic aberrations in metasurface-based planar photonics will find applications in lightweight collimators for displays, and chromatically-corrected imaging systems.

773 citations


Journal ArticleDOI
TL;DR: The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification.
Abstract: Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.

586 citations


Patent
09 Jan 2014
TL;DR: In this article, the distance on an optical axis from a most-object-side lens surface in an entire system to an image-plane, maximum image height, distance on the optical-axis from an imaging lens surface to a mostimage-side surface in the first lens-group, and focal length of the entire system are satisfied.
Abstract: An imaging lens substantially consists of a first lens-group, a stop and a second lens-group in this order from an object-side. The first lens-group substantially consists of three or less lenses including at least one negative lens and a positive lens. The second lens-group substantially consists of a 21st lens-group and a 22nd lens-group in this order from the object-side. The 21st lens-group substantially consists of three or less lenses and has positive refractive-power. The 22nd lens-group substantially consists of two lenses of a negative lens and a positive lens in this order from the object-side. Predetermined conditional formulas about distance on an optical-axis from a most-object-side lens surface in an entire system to an image-plane, maximum image height, distance on the optical-axis from a most-object-side lens surface in the first lens-group to a most-image-side lens surface in the second lens-group, and focal-length of the entire system are satisfied.

377 citations


Patent
16 Apr 2014
TL;DR: In this article, one or more tapered feeds can be provided as part of or interconnected to a conductive top plate, and an aperture over the lens region can be covered or filled by an impedance surface.
Abstract: Conformal antennas and methods for radiating radio frequency energy using conformal antennas are provided. In particular, one or more tapered feeds can be provided as part of or interconnected to a conductive top plate. The one or more tapered feeds have a depth that decreases from a feed point to a tip. The tip of the one or more tapered feeds is adjacent a cavity formed over a lens region. An aperture over the lens region can be covered or filled by an impedance surface. This impedance surface may comprise a frequency selective surface. Alternatively, a frequency selective surface can be provided over the lens region of an antenna incorporating one or more stripline feeds.

276 citations


Journal ArticleDOI
TL;DR: A set of lens designs with reduced reflection and tailorable phase gradients have been developed and tested, demonstrating focal distances of a few hundred microns, beam area contraction ratio up to three, and insertion losses as low as 11%.
Abstract: We have proposed, designed, manufactured and tested low loss dielectric micro-lenses for infrared (IR) radiation based on a dielectric metamaterial layer. This metamaterial layer was created by patterning a dielectric surface and etching to sub-micron depths. For a proof-of-concept lens demonstration, we have chosen a fine patterned array of nano-pillars with variable diameters. Gradient index (GRIN) properties were achieved by engineering the nano-pattern characteristics across the lens, so that the effective optical density of the dielectric metamaterial layer peaks around the lens center, and gradually drops at the lens periphery. A set of lens designs with reduced reflection and tailorable phase gradients have been developed and tested, demonstrating focal distances of a few hundred microns, beam area contraction ratio up to three, and insertion losses as low as 11%.

270 citations


Journal ArticleDOI
TL;DR: The performance of a computational lens-free, holographic on-chip microscope that uses the transport-of-intensity equation, multi-height iterative phase retrieval, and rotational field transformations to perform wide-FOV imaging of pathology samples with comparable image quality to a traditional transmission lens-based microscope is illustrated.
Abstract: Optical examination of microscale features in pathology slides is one of the gold standards to diagnose disease. However, the use of conventional light microscopes is partially limited owing to their relatively high cost, bulkiness of lens-based optics, small field of view (FOV), and requirements for lateral scanning and three-dimensional (3D) focus adjustment. We illustrate the performance of a computational lens-free, holographic on-chip microscope that uses the transport-of-intensity equation, multi-height iterative phase retrieval, and rotational field transformations to perform wide-FOV imaging of pathology samples with comparable image quality to a traditional transmission lens-based microscope. The holographically reconstructed image can be digitally focused at any depth within the object FOV (after image capture) without the need for mechanical focus adjustment and is also digitally corrected for artifacts arising from uncontrolled tilting and height variations between the sample and sensor planes. Using this lens-free on-chip microscope, we successfully imaged invasive carcinoma cells within human breast sections, Papanicolaou smears revealing a high-grade squamous intraepithelial lesion, and sickle cell anemia blood smears over a FOV of 20.5 mm(2). The resulting wide-field lens-free images had sufficient image resolution and contrast for clinical evaluation, as demonstrated by a pathologist's blinded diagnosis of breast cancer tissue samples, achieving an overall accuracy of ~99%. By providing high-resolution images of large-area pathology samples with 3D digital focus adjustment, lens-free on-chip microscopy can be useful in resource-limited and point-of-care settings.

257 citations


Patent
29 Apr 2014
TL;DR: In this paper, a focusing module with two adjustable polymeric surfaces (e.g., two adjustable-surface lenses in a back-to-back configuration) is used to adjust the curvature of the surfaces to change focus.
Abstract: An autofocus lens system includes no conventional moving parts and has excellent speed and low power consumption. The system includes a small electronically-controlled focusing-module lens. The focusing-module lens includes two adjustable polymeric surfaces (e.g., two adjustable-surface lenses in a back-to-back configuration). The curvature of the surfaces can be adjusted to change focus. The performance of the autofocus lens system is extended by adding a conventional first and second lens, or lens group, on either side of the focusing-module lens. What results is an autofocus lens system with excellent near field and far field performance.

242 citations


Journal ArticleDOI
Min Liang1, Wei-Ren Ng1, Kihun Chang1, Kokou Gbele1, Michael E. Gehm1, Hao Xin1 
TL;DR: In this article, a low-gain 20 dBi Luneburg lens antenna using a rapid prototyping machine as a proof-of-concept demonstrator was designed, built, and tested.
Abstract: In this work, we designed, built, and tested a low-gain 20 dBi Luneburg Lens antenna using a rapid prototyping machine as a proof of concept demonstrator. The required continuously varying relative permittivity profile was implemented by changing the size of plastic blocks centered on the junctions of a plastic rod space frame. A 12-cm ( 4λ0 at 10 GHz) diameter lens is designed to work at X-band. The effective permittivity of the unit cell is calculated by effective medium theory and simulated by full-wave finite-element simulations. The fabrication is implemented by a polymer jetting rapid prototyping method. In the measurement, the lens antenna is fed by an X-band waveguide. The measured gain of the antenna at X-band is from 17.3 to 20.3 dB. The measured half-power beam width is from 19° to 12.7° while the side lobes are about 25 dB below the main peak. Good agreement between simulation and experimental results is obtained.

239 citations


Journal ArticleDOI
TL;DR: The Dragonfly Telephoto Array as discussed by the authors is a robotic imaging system optimized for the detection of extended ultra-low surface brightness structures, which is capable of imaging extended structures to surface brightness levels below μB = 30 mag arcsec-2 in ~10 h integrations.
Abstract: We describe the Dragonfly Telephoto Array, a robotic imaging system optimized for the detection of extended ultra-low surface brightness structures. The array consists of eight Canon 400 mm f/2.8 L IS II USM telephoto lenses coupled to eight science-grade commercial CCD cameras. The lenses are mounted on a common framework and are coaligned to simultaneously image the same position on the sky. The system provides an imaging capability equivalent to a 0.4 m aperture f/1.0 refractor with a 2.6° × 1.9° field of view. The system is driven by custom software for instrument control and robotic operation. Data is collected with noncommon optical paths through each lens, and with careful tracking of sky variations in order to minimize systematic errors that limit the accuracy of background estimation and flat-fielding. The system has no obstructions in the light path, optimized baffling, and internal optical surfaces coated with a new generation of antireflection coatings based on subwavelength nanostructures. As a result, the array's point-spread function has a factor of ~10 less scattered light at large radii than well-baffled reflecting telescopes. The Dragonfly Telephoto Array is capable of imaging extended structures to surface brightness levels below μB = 30 mag arcsec-2 in ~10 h integrations (without binning or foreground star removal). This is considerably deeper than the surface brightness limit of any existing wide-field telescope. At present, no systematic errors limiting the usefulness of much longer integration times have been identified. With longer integrations (50-100 h), foreground star removal, and modest binning, the Dragonfly Telephoto Array is capable of probing structures with surface brightnesses below μB = 32 mag arcsec-2. The detection of structures at these surface brightness levels may hold the key to solving the "missing substructure" and "missing satellite" problems of conventional hierarchical galaxy formation models. The Dragonfly Telephoto Array is therefore executing a fully automated multiyear imaging survey of a complete sample of nearby galaxies in order to undertake the first census of ultrafaint substructures in the nearby universe.

214 citations


Journal ArticleDOI
TL;DR: The use of scleral lenses for non-pathological eyes is discussed in this paper, and the current applications of different ScCL (all types), their fitting methods, and their clinical outcomes including potential adverse events are presented.

185 citations


Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a highly efficient, sub-wavelength thick, transmissive grating lens configuration using symmetrical resonant posts to achieve polarization-independent operation, and demonstrate the generation of high-order orbital angular momentum beams and their use in an optical mode-isolator application.
Abstract: Dielectric high-contrast sub-wavelength grating (SWG) structures have received much attention in recent years, offering a new paradigm for the integration of optical systems. Their nanoscale resonant properties can result in a complex and unintuitive far-field behavior that, if carefully crafted, allows the full control of the optical phase front from a thin sub-wavelength planar layer. To date, experimental demonstrations of these new devices have only been realized with polarized light in a reflective mode, greatly limiting their use for practical systems. In this letter, we demonstrate a highly efficient, sub-wavelength thick, transmissive grating lens configuration using symmetrical resonant posts to achieve polarization-independent operation. Our transmissive SWG lenses are easily fabricated using low-cost scalable semiconductor process technology. To illustrate their performance, we demonstrate the generation of high-order orbital angular momentum beams and their use in an optical mode-isolator application that achieves a suppression ratio of over 25 dB.

Journal ArticleDOI
12 Feb 2014-ACS Nano
TL;DR: A nanodiamond (ND)-embedded contact lens capable of lysozyme-triggered release of TM for sustained therapy is presented and it is found that ND-embedded lenses composed of enzyme-cleavable polymers allow for controlled and sustained release ofTM in the presence of Lysozyme.
Abstract: Temporarily implanted devices, such as drug-loaded contact lenses, are emerging as the preferred treatment method for ocular diseases like glaucoma. Localizing the delivery of glaucoma drugs, such as timolol maleate (TM), can minimize adverse effects caused by systemic administration. Although eye drops and drug-soaked lenses allow for local treatment, their utility is limited by burst release and a lack of sustained therapeutic delivery. Additionally, wet transportation and storage of drug-soaked lenses result in drug loss due to elution from the lenses. Here we present a nanodiamond (ND)-embedded contact lens capable of lysozyme-triggered release of TM for sustained therapy. We find that ND-embedded lenses composed of enzyme-cleavable polymers allow for controlled and sustained release of TM in the presence of lysozyme. Retention of drug activity is verified in primary human trabecular meshwork cells. These results demonstrate the translational potential of an ND-embedded lens capable of drug sequestrat...

Patent
23 Jul 2014
TL;DR: In this paper, a LIDAR device may include a lens that both (i) collimates the light from the one or more light sources to provide collimated light for transmission into an environment of the LidAR device and (ii) focuses the reflected light onto the detectors.
Abstract: A LIDAR device may transmit light pulses originating from one or more light sources and may receive reflected light pulses that are then detected by one or more detectors. The LIDAR device may include a lens that both (i) collimates the light from the one or more light sources to provide collimated light for transmission into an environment of the LIDAR device and (ii) focuses the reflected light onto the one or more detectors. The lens may define a curved focal surface in a transmit path of the light from the one or more light sources and a curved focal surface in a receive path of the one or more detectors. The one or more light sources may be arranged along the curved focal surface in the transmit path. The one or more detectors may be arranged along the curved focal surface in the receive path.

Journal ArticleDOI
TL;DR: This paper presents a novel lens detection algorithm that can be used to reduce the effect of contact lenses and outperforms other lens detection algorithms on the two databases and shows improved iris recognition performance.
Abstract: The presence of a contact lens, particularly a textured cosmetic lens, poses a challenge to iris recognition as it obfuscates the natural iris patterns. The main contribution of this paper is to present an in-depth analysis of the effect of contact lenses on iris recognition. Two databases, namely, the IIIT-D Iris Contact Lens database and the ND-Contact Lens database, are prepared to analyze the variations caused due to contact lenses. We also present a novel lens detection algorithm that can be used to reduce the effect of contact lenses. The proposed approach outperforms other lens detection algorithms on the two databases and shows improved iris recognition performance.

Journal ArticleDOI
TL;DR: A highly efficient gradient metasurface lens based on a metal-dielectric-metal structure that operates in the terahertz regime is proposed, which is polarization insensitive, works efficiently even at wide angles of incidence and enables new applications in optical device design such as ultrathin flat lenses.
Abstract: Metamaterials offer exciting opportunities that enable precise control of amplitude, polarization and phase of the light beam at a subwavelength scale. A gradient metasurface consists of a class of anisotropic subwavelength metamaterial resonators that offer abrupt amplitude and phase changes, thus enabling new applications in optical device design such as ultrathin flat lenses. We propose a highly efficient gradient metasurface lens based on a metal-dielectric-metal structure that operates in the terahertz regime. The proposed structure consists of slotted metallic resonator arrays on two sides of a thin dielectric spacer. By varying the geometrical parameters, the metasurface lens efficiently manipulates the spatial distribution of the terahertz field and focuses the beam to a spot size on the order of a wavelength. The proposed flat metasurface lens design is polarization insensitive and works efficiently even at wide angles of incidence.

Patent
05 Jan 2014
TL;DR: In this article, the authors describe a method for capturing or generating images using multiple optical chains operating in parallel, where pixel values captured by individual optical chains corresponding to the same scene area are combined to provide an image with at least some of the benefits which would have been provided by capturing an image of the scene using a larger lens than that of the individual lenses of the optical chain modules.
Abstract: Methods and apparatus for capturing or generating images using multiple optical chains operating in parallel are described. Pixel values captured by individual optical chains corresponding to the same scene area are combined to provide an image with at least some of the benefits which would have been provided by capturing an image of the scene using a larger lens than that of the individual lenses of the optical chain modules. By using multiple optical chains in parallel at least some benefits normally obtained from using a large lens can be obtained without the need for a large lens. Furthermore in at least some embodiments, a wide dynamic range can be supported through the use of multiple sensors with the overall supported dynamic range being potentially larger than that of the individual sensors. Some lens and/or optical chain configurations are designed for use in small handheld devices, e.g., cell phones.

Journal ArticleDOI
TL;DR: In this article, a superoscillatory focusing lens has been demonstrated by optimizing Fresnel zone plates (FZP), with limited physical insight as to how the lens feature contributes to the focal formation.
Abstract: A superoscillatory focusing lens has been experimen- tally demonstrated by optimizing Fresnel zone plates (FZP), with limited physical insight as to how the lens feature contributes to the focal formation. It is therefore imperative to establish a generalized viable account for both FZP (amplitude mask) and binary optics (phase mask). Arbitrary superoscillatory spots can now be customized and realized by a realistic optical device, without using optimization. It is counterintuitively found that high spatial frequency with small amplitude and destructive interfer- ence are favorable in superfocusing of a superoscillation pat- tern. The inevitably high sidelobe is pushed 15λ away from the central subwavelength spot, resulting in significantly enlarged field of view for viable imaging applications. This work therefore not only reveals the explicit physical role of any given metallic/

Journal ArticleDOI
TL;DR: A transformational metasurface Luneburg lens based on the quasi-conformal mapping method, which has weakly anisotropic constitutive parameters, is presented in this article.
Abstract: We present a transformational metasurface Luneburg lens based on the quasi-conformal mapping method, which has weakly anisotropic constitutive parameters. We design the metasurface lens using inhomogeneous artificial structures to realize the required surface refractive indexes. The transformational metasurface Luneburg lens is fabricated and the measurement results demonstrate very good performance in controlling the radiated surface waves.

Journal ArticleDOI
TL;DR: To outline the refractive problems associated with presbyopia and to review the basis and relative merits of currently‐available methods for their correction, with detailed consideration of spectacle and contact lens approaches.

Journal ArticleDOI
TL;DR: Sun et al. as mentioned in this paper used femtosecond laser direct writing (FsLDW) to fabricate flexible and biocompatible optical elements from a protein hydrogel, which could be useful for use in photonic implants or as stretchable optical devices.
Abstract: In this work, we report a novel soft diffractive micro-optics, called ‘microscale kinoform phase-type lens (micro-KPL)’, which is fabricated by femtosecond laser direct writing (FsLDW) using bovine serum albumin (BSA) as building blocks and flexible polydimethylsiloxane (PDMS) slices as substrates. By carefully optimizing various process parameters of FsLDW (e.g., average laser power density, scanning step, exposure time on a single point and protein concentration), the as-formed protein micro-KPLs exhibit excellent surface quality, well-defined three-dimensional (3D) geometry and distinctive optical properties, even in relatively harsh operation environments (for instance, in strong acid or base). Laser shaping, imaging and other optical performances can be easily achieved. More importantly, micro-KPLs also have unique flexible and stretchable properties as well as good biocompatibility and biodegradability. Therefore, such protein hydrogel-based micro-optics may have great potential applications, such as in flexible and stretchable photonics and optics, soft integrated optical microsystems and bioimplantable devices. Scientists have used direct laser writing to fabricate flexible and biocompatible optical elements from a protein hydrogel. Yun-Lu Sun and co-workers from Jilin University in China and Pohang University of Science and Technology in Korea say that the miniature optical components produced using this approach could be useful for use in photonic implants or as stretchable optical devices. They fabricated soft, phase-type diffractive lenses with diameters of 50–100 µm by focusing femtosecond pulses from a Ti:sapphire laser into an aqueous ‘protein ink’ comprising a mixture of bovine serum albumin and the photosensitizer methylene blue. Irradiated regions underwent two-photon polymerization to form a soft protein hydrogel. By moving both the laser beam and the sample, the researchers successfully fabricated a three-dimensional optic featuring the desired series of concentric rings needed to act as a phase-type lens.

Patent
11 Jun 2014
TL;DR: In this paper, an image comparator is used to estimate the yaw of an HMD from images captured by an upward facing camera at different points in time, using a wide angle fisheye lens.
Abstract: Ahead mountable display (HMD) has an upward facing camera associated with a wide angle (such as a fisheye) lens arranged to capture images of the environment of the HMD, and an image comparator arranged to derive an indication of yaw of the HMD from images captured by the upward facing camera at different points in time.

Journal ArticleDOI
TL;DR: In this paper, the authors develop a framework for multiplane lensing that can handle an arbitrary combination of tidal planes treated with shear and convergence and planes treated exactly (i.e., including higher order terms).
Abstract: In strong gravitational lens systems, the light bending is usually dominated by one main galaxy, but may be affected by other mass along the line of sight (LOS). Shear and convergence can be used to approximate the contributions from less significant perturbers (e.g. those that are projected far from the lens or have a small mass), but higher order effects need to be included for objects that are closer or more massive. We develop a framework for multiplane lensing that can handle an arbitrary combination of tidal planes treated with shear and convergence and planes treated exactly (i.e., including higher order terms). This framework addresses all of the traditional lensing observables including image positions, fluxes, and time delays to facilitate lens modelling that includes the non-linear effects due to mass along the LOS. It balances accuracy (accounting for higher-order terms when necessary) with efficiency (compressing all other LOS effects into a set of matrices that can be calculated up front and cached for lens modelling). We identify a generalized multiplane mass sheet degeneracy, in which the effective shear and convergence are sums over the lensing planes with specific, redshift-dependent weighting factors.

Patent
09 Dec 2014
TL;DR: In this article, a photographing optical lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element and a third lens element.
Abstract: A photographing optical lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element. The first lens element with positive refractive power has an object-side surface being convex in a paraxial region. The second lens element has refractive power. The third lens element has positive refractive power. The fourth lens element has refractive power. The fifth lens element with positive refractive power has an object-side surface being convex in a paraxial region and an image-side surface being convex in a paraxial region. The sixth lens element with positive refractive power has an object-side surface being convex in a paraxial region and an image-side surface being concave in a paraxial region, and the image-side surface thereof has at least one inflection point.

Patent
28 Jul 2014
TL;DR: In this paper, a camera array comprising camera modules, the camera modules comprising a master camera that includes a processor, a memory, a sensor, a lens, a status indicator, and a switch, the switch configured to initiate a start operation to start recording video data using the lens and the sensor in the other camera modules.
Abstract: The disclosure includes a camera array comprising camera modules, the camera modules comprising a master camera that includes a processor, a memory, a sensor, a lens, a status indicator, and a switch, the switch configured to instruct each of the camera modules to initiate a start operation to start recording video data using the lens and the sensor in the other camera modules and the switch configured to instruct each of the camera modules to initiate a stop operation to stop recording, the status indicator configured to indicate a status of at least one of the camera modules.

Journal ArticleDOI
TL;DR: The various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances are discussed.

Proceedings ArticleDOI
TL;DR: Bicep3 as discussed by the authors is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz, with a focal plane area 5x larger than a Bicep2/Keck Array receiver.
Abstract: Bicep3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of Bicep1, Bicep2 and the Keck Array experiments | it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, Bicep3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5x larger than a Bicep2/Keck Array receiver and faster optics (f=1:6 vs. f=2:4). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, Bicep3 will have survey speed comparable to Keck Array 150 GHz (2013), and will signifcantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the Bicep2 observation patch.

Journal ArticleDOI
TL;DR: In this article, a planar bifunctional Luneburg-fisheye lens made of an anisotropic metasurface is presented, which features as a Lunesburg along the horizontal optical axis, while as a fisheyes along the vertical optical axis.
Abstract: Luneburg lens and Maxwell-fisheye lens are well-known microwave and optical devices with distinct focusing properties. Here, a planar bifunctional Luneburg-fisheye lens made of an anisotropic metasurface is presented, which features as a Luneburg along the horizontal optical axis, while as a fisheye along the vertical optical axis. A method to control the inhomogeneous indices of refraction along the two optical axes independently is proposed by designing an anisotropic and nonuniform metasurface, which can provide the required distributions of refractive indices approximately for Luneburg and fisheye lenses viewing from the two optical axes. Experiments in the microwave frequency range demonstrate very good performance of the planar bifunctional Luneburg-fisheye lens. The proposed method opens up an avenue to design other kinds of bifunctional devices using metasurfaces in the microwave, terahertz, and even optical ranges.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated numerically and experimentally highly efficient acoustic lenses based on the principle of extraordinary acoustic transmission, which can transmit up to 83% of the incident energy and generate sharp focusing with very high amplification.
Abstract: We investigate numerically and experimentally highly efficient acoustic lenses based on the principle of extraordinary acoustic transmission. We study circular, flat lenses composed of perforated air channels. The geometry is similar to binary Fresnel lenses, and the lenses exploit several resonance mechanisms to enhance the transmission, such as Fabry–Perot resonances in the channels and cavity resonances on the lens surface. The proposed lenses are able to transmit up to 83% of the incident energy and generate sharp focusing with very high amplification (up to 16 dB experimentally). Furthermore, the resulting lenses are thinner than other designs providing similar performance, making them ideal candidates for application in acoustic imaging and medical diagnostics.

Journal ArticleDOI
TL;DR: The use and characterization of an electrically focus tunable lens to perform axial scanning in a confocal microscope has potential to enhance in vivo three-dimensional imaging in confocal endomicroscopy.
Abstract: This paper presents the use and characterization of an electrically focus tunable lens to perform axial scanning in a confocal microscope Lateral and axial resolution are characterized over a >250 µm axial scan range Confocal microscopy using optical axial scanning is demonstrated in epithelial tissue and compared to traditional stage scanning By enabling rapid axial scanning, minimizing motion artifacts, and reducing mechanical complexity, this technique has potential to enhance in vivo three-dimensional imaging in confocal endomicroscopy

01 Jan 2014
TL;DR: It is demonstrated that sub-diffraction focal spots can actually be formed without any evanescent waves, making far-field, label-free super-resolution imaging possible and extending the super-oscillatory concept into the vectorial-field regime to work with circularly polarized light.
Abstract: Planar optical lenses are fundamental elements of miniaturized photonic devices. However, conventional planar optical lenses are constrained by the diffraction limit in the optical far-field due to the band-limited wavevectors supported by free-space and loss of high-spatial-frequency evanescent components. As inspired by Einstein’s radiation ‘needle stick’, electromagnetic energy can be delivered into an arbitrarily small solid angle. Such sub-diffraction optical needles have been numerically investigated using diffractive optical elements (DOEs) together with specially polarized optical beams, but experimental demonstration is extremely difficult due to the bulky size of DOEs and the required alignment precision. Planar super-oscillatory lenses (SOLs) were proposed to overcome these constraints and demonstrated that sub-diffraction focal spots can actually be formed without any evanescent waves, making far-field, label-free super-resolution imaging possible. Here we extend the super-oscillation concept into the vectorial-field regime to work with circularly polarized light, and experimentally demonstrate, for the first time, a circularly polarized optical needle with sub-diffraction transverse spot size (0.45l) and axial long depth of focus (DOF) of 15l using a planar SOL at a violet wavelength of 405 nm. This sub-diffraction circularly polarized optical needle has potential applications in circular dichroism spectroscopy, super-resolution imaging, high-density optical storage, heat-assisted magnetic recording, nano-manufacturing and nano-metrology.