Optical Device [TOP]
Low vision optical devices include a variety of devices, such as stand and handheld magnifiers, strong magnifying reading glasses, loupes, and small telescopes. Magnifying devices are generally either handheld or mounted on a stand, with zoom ranges from 2x to 10x. Monoculars and binoculars are intended to help the user see items at a distance, often 15-30 feet away. These handheld telescopes are usually small enough to fit in the user's pocket.
Low vision optical devices are task-specific. A low vision specialist may prescribe several different low vision optical devices for various tasks or help determine the right type of device or devices that will help a user with the tasks her or she wants to perform.
Acrylic Full-Page MagnifierLarge 10" x 12" magnifier for reading newspapers, books, or magazines. The 2x Fresnel magnifier lens is made of optical-grade acrylic which will not bend or distort words or images.
Optivisor Binocular MagnifiersBinocular magnifiers with optical glass lenses mounted on a frame on a comfortable headband that can be tilted out of the way when magnification is not needed. Designed for close work, such as reading, writing or crafting projects. May be worn over eyeglasses or alone. Available in varying diopters and magnifications.
Anterior chamber depth was measured with the IOLMaster and compared with measures from an A-scan applanation ultrasound device (Storz Omega Compu-Scan Biometric Ruler, Storz International, St Louis, MO, USA). The IOLMaster directs a 0.7 mm width slit beam of light through the anterior segment of the eye at an angle of 38 degrees to the visual axis. The instrument camera is aligned so that the light beam forms an optical section and the internal software measures the distance between the anterior corneal pole and the anterior crystalline lens surface to calculate the anterior chamber depth. The A-scan applanation device calculates anterior chamber depth from the time taken for ultrasound waves to reflect back to its receiver from an optical surface.13 One drop of topical anaesthetic, benoxinate hydrochloride 0.4% (Minims, Chauvin Pharmaceuticals Ltd), was instilled in each of the subject's eyes 2 minutes before ultrasound measurement. Special care was taken in aligning the transducer beam probe along the optical axis and to exert minimal corneal pressure. Ten measurements were taken for each eye and the mean calculated.
Measurements with this device are not affected by longitudinal eye motion.3,9 The calculation of axial length is dependent on the refractive index of the medium in which the light travels, and therefore the optical path length is divided by the mean group refractive index (taken as n = 1.3549) in order to obtain the geometrical axial length.9,14 Laser light is reflected from the retinal pigment epithelium, in contrast with ultrasound waves which are reflected from the internal limiting membrane. Hence, in order to make the IOLMaster results comparable with previous ultrasound measures, a conversion factor has been incorporated into the instrument software.8,9 The A-scan applanation device calculates axial length from the time taken for ultrasound waves to reflect back to its receiver from the internal limiting membrane.13
Nanophotonic circuit layout. (a) Optical micrograph of a nanophotonic circuit for the characterization of 3D photonic components, including focusing grating couplers (b: SEM image), Y-splitters and tapered waveguides (c SEM micrograph). The 3D optical component is written into the gap between two facing tapers using DLW. (d) Transmission spectrum of a reference photonic circuit. Two types of grating couplers are employed, where each couples to either TE-like (black curve) or TM-like (red curve) waveguide mode efficiently. DLW, direct laser writing; SEM, scanning electron microscope; TE, transverse electric; TM, transverse magnetic; 3D, three-dimensional.
The structures we fabricate are several voxel sizes large in all three dimensions. Therefore, we cannot write the whole 3D device (e.g., a 3D bridge waveguide) using a single DLW trajectory. Instead, we decompose the volume of the 3D device to be written into slices less than a voxel size apart from each other. These slices are then filled up using a rectangular spiral pattern. By writing the spiral patterns slice by slice using DLW, we finally obtain the designed 3D structure.
In order to transfer light from planar waveguides to arbitrary 3D components, efficient coupling between the nanophotonic circuit and a 3D waveguide is crucial. Low insertion loss can be achieved by employing inverted tapers which are conveniently used for coupling nanophotonic waveguides to optical fibers in order to overcome the large insertion loss due to modal size mismatch. Such an approach is ideally suited for interconnecting planar and 3D waveguides written by DLW. Therefore, the transmission characteristics of a 3D bridge waveguide are studied.
With access to 3D form shaping on a submicron-scale, waveguide geometries that cannot be achieved by traditional nanofabrication techniques can readily be produced. This additional degree of freedom is of particular interest for achieving control of the polarization of propagating optical modes on a chip, which is non-trivial with planar architectures.
Using 3D waveguides to achieve polarization rotation of a propagating mode, we employ DLW to twist the waveguide along the propagation direction. Such devices can be integrated into planar circuits using the polymer-inverted tapers described above. The twist, however, induces coupling among all waveguide modes. Thus, in order to optimize polarization rotation of a given mode, two properties of the rotator can be tuned. First, the number of guided modes should be ideally one and the propagation constants of the remaining modes should differ from each other as much as possible. The latter can be achieved by employing a rectangular waveguide with a large aspect ratio. Second, for a given cross-section of the waveguide, increasing the twist length will improve polarization rotation.31
In addition, we repeat the experiment on the same device, but use port 3 (TE) as input and port 2 (TM) and port 4 (TE) as outputs this time. Ignoring propagation losses in the planar waveguides, the following transmittances (relative to the laser output power) can be measured:
Further applications of interest that could prospectively be investigated include on-chip coupling to ultra-high Q resonators like microspheres59 or convenient on-chip access to 3D photonic crystals.22,23 Also, the approach could be extended to the visible regime. For the silicon nitride devices, this is readily done by adjusting grating coupler period and waveguide geometry. For the polymer structures, however, resolution is limited by the DLW voxel size. Thus, in order to fabricate monomode waveguides for visible light, usage of more advanced 3D lithography techniques like stimulated-emission-depletion DLW60 could be required.
Direct laser writing is a popular scheme for constructing three-dimensional integrated optical structures. Martin Schumann and co-workers from the Karlsruhe Institute of Technology and the Institute of Nanotechnology in Germany used two-photon polymerization to create three-dimensional polymer objects such as bridge waveguides, a twisted-waveguide polarization rotator and free-standing disk resonators. The structures, which would be difficult or impossible to construct using planar lithography, were successfully integrated with silicon optical chips featuring silicon nitride waveguides that guide light in the 1,550 nm telecommunications wavelength window. The researchers say that their approach could also be used to provide convenient access to three-dimensional photonic crystals. An advanced form of this approach that exploits higher resolutions would allow the construction of structures that are compatible with visible wavelengths.
The image above depicts a new device for surface enhanced infrared absorption spectroscopy. Infrared light (the white beams) is trapped by tiny gaps in the metal surface, where it can be used to detect trace amounts of matter.More about this imageWhen searching for traces of drugs, bomb-making components and other chemicals, researchers use a method called spectroscopy in which they shine light on the materials they're analyzing. Spectroscopy involves studying how light interacts with trace amounts of matter.Infrared absorption is one of the most effective types of spectroscopy; scientists use it when they check for performance-enhancing drugs in blood samples and for tiny particles of explosives in the air. Researchers are working to make the technology more sensitive, inexpensive and versatile and now, a new light-trapping sensor, developed by a University at Buffalo (UB)-led team of engineers, is making progress in all three areas."This new optical device has the potential to improve our abilities to detect all sorts of biological and chemical samples," says Qiaoqiang Gan, an associate professor of electrical engineering in the School of Engineering and Applied Sciences at UB, and lead author of the published study.The new sensor, which works with light in the mid-infrared band of the electromagnetic spectrum -- the part of the spectrum used for most remote controls, night-vision and other applications, consists of two layers of metal with an insulator sandwiched in between. The researchers used a fabrication technique called atomic layer deposition to create a device with gaps less than 5 nanometers (a human hair is roughly 75,000 nanometers in diameter) between two metal layers. These gaps allow the sensor to absorb up to 81 percent of infrared light, a significant improvement from the 3 percent that similar devices absorb.This process is known as surface-enhanced infrared absorption (SEIRA) spectroscopy. The sensor, which acts as a substrate for the materials being examined, boosts the sensitivity of SEIRA devices to detect molecules at 100 to 1,000 times greater resolution than previously reported results. SEIRA could be used to find traces of molecules, including but not limited to drug detection in blood, bomb-making materials, fraudulent art and tracking diseases.This research was supported in part by a grant from the National Science Foundation's Nanomanufacturing Program (grant CMMI 15-62057).Read more about this research in the UB news story Beware doping athletes! This sensor may be your downfall. (Date image taken: July 2017; date originally posted to NSF Multimedia Gallery: July 20, 2018) 041b061a72