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PubMed2004

Theoretical and experimental study of the surface plasmon resonance effect on a recordable compact disk.

The surface plasmon resonance (SPR) effect on noble-metal surfaces has been explored by several investigators for the development of chemical and biological sensors as well as for the design of optical devices for other applications. The effect can be observed by use of prism couplers, diffraction gratings, and specially configured optical fibers. In an attempt to seek a new configuration that minimizes costs of fabricating media that support SPR in conjunction with designing a new format suitable for large-scale chemical and biological sensing, I have investigated the feasibility of using a commercially available, gold-type, recordable compact disk for observation of the SPR phenomenon. Experimental and theoretical results of this investigation are reported.

Journal Article↗
PubMed2000

Successive approximations for charged particle motion

Single-particle dynamics in electron microscopes, ion or electron lithographic instruments, particle accelerators, and particle spectrographs is described by weakly nonlinear ordinary differential equations. Therefore, the linear part of the equation of motion is usually solved and the nonlinear effects are then found in successive order by iteration methods. When synchrotron radiation is not important, the equation can be derived from a Hamiltonian or a Lagrangian. The Hamiltonian nature can lead to simplified computations of particle transport through an optical device when a suitable computational method is used. H. Rose and his school have contributed to these techniques by developing and intensively using the eikonal method [1-3]. Many ingenious microscopic and lithographic devices were found by Rose and his group due to the simple structure of this method [4-6]. The particle optical eikonal method is either derived by propagating the electron wave or by the principle of Maupertuis for time-independent fields. Maybe because of the time-dependent fields which are often required, in the area of accelerator physics the eikonal method has never become popular, although Lagrange methods had been used sometimes already in early days [7]. In this area classical Hamilitonian dynamics is usually used to compute nonlinear particle motion. Here the author will therefore derive the eikonal method from a Hamiltonian quite familiar to the accelerator physics community and reformulate it in a simplifying way. With the event of high-energy polarized electron beams [8] and plans for high-energy proton beams [9], nonlinear effects in spin motion have become important in high-energy accelerators. The author introduces a successive approximation for the nonlinear effects in the coupled spin and orbit motion of charged particles which resembles some of the simplifications resulting from the eikonal method for the pure orbit motion.

Journal Article↗
PubMed2003

Eugen Bircher (1882-1956) the first knee surgeon to use diagnostic arthroscopy.

Eugen Bircher was a strong advocate of diagnostic arthroscopy as shown in several papers on the topic of internal derangements of the knee published between 1921 and 1926. During that time, he performed about 60 endoscopic procedures, which usually preceded a meniscectomy. We believe that this was the first time arthroscopy was used in a large scale for clinical purposes. Bircher was the head surgeon of the busy provincial Aarau General Hospital, a right-wing politician, and a highly ranked army officer. His interest in knee surgery was supported by his friend Fritz Steinmann, who was the "man of the pin" and an early promoter of skeletal traction for fracture treatment. Bircher believed in the early surgical treatment of meniscal lesions and, later, in the reconstruction of cruciate ligament lesions. He used the Jacobaeus thoracolaparoscope for arthroscopy, but it had poor endoscopic qualities. The electric lamp at the tip of the optical device was not mechanically protected and was therefore endangered by every manipulation within the joint space. Also, the 90 degrees optical system delivered a dark image. By the late 1920s, Bircher had developed the technique of double-contrast arthrography, and he gave up endoscopy by 1930. In 1935, he left surgery and took a military command in the Swiss army; later he was a representative of the Farmers Party in the National Parliament until his death.

Arthrography↗
PubMed2005

Reduction of polarization-induced artifacts in grating-based spectrometers.

An optical device that converts unpolarized light into a single polarization state is described. The device is based on a polarizing beam splitter that separates the two polarization directions. The beam splitter is combined with two pairs of equilateral prisms that are used to collimate the two beams in terms of both propagation and polarization directions. When it is used in combination with a blazed diffraction grating, this device is shown to effectively remove the polarization dependence of the first-order diffracted power. The device has an insertion loss of approximately 14% for purely s-polarized light. However, for unpolarized light incident upon the two gratings studied here, the increased throughput of the p-polarized component leads to an average relative gain in overall efficiency of 13%-19%, depending on the grating. In collimating the two polarization directions, the device may cause a reduction in spectral resolution for a rectangular entrance slit. As a result, the device is more likely to find use in spectrometers that have a circular aperture, such as that provided by an optical fiber.

Journal Article↗
PubMed2001

Capillary blood flow in acute branch retinal vein occlusion.

PURPOSE: To study retinal capillary blood flow during the acute stage of induced branch retinal vein occlusion (BRVO) in the feline retina and the effect of systemic blood pressure during this event. METHODS: Known fractions of the animal blood cells were labeled by a fluorescent marker and tracked by an electro-optical device as they flowed within the retinal microcirculation. Branch retinal vein occlusion was induced by photocoagulation of a large vein at the optic disk rim. The findings were video recorded and analyzed by computerized image processing. RESULTS: Reversed capillary blood cell flow from the blocked vein was noted immediately following occlusion of the vein. Two patterns of reversed capillary flow were identified: one from the blocked vein to a terminal arteriole and the other from a blocked vein to another vein via a junction with a terminal arteriole. Increased systemic blood pressure decreased the reversed flow in both flow patterns. CONCLUSIONS: 1) Flow deviation to nearby retinal arterioles or veins (shunting) through the normal capillary system is an immediate hemodynamic event following acute BRVO. 2) The reversed capillary flow is affected by the systemic blood pressure.

Acute Disease↗
PubMed2002

Fiber optic multi-channel protein detector for use in preparative continuous annular chromatography.

Continuous annular chromatography is an effective method in the separation of preparative scale quantities of biological compounds including proteins where established batch chromatography borders on it. The need for identification or quantification of proteins triggered the development of respective detection units. Here, we describe two types of optical multi-channel detectors. The first is a fiber optic multi-channel detector suitable for the separation of aqueous protein solutions. The second is a technically improved (circular optic) device suitable for application in multi-channel detection. Specifically, UV-absorption measurements of proteins at 280 nm were carried out using newly designed fiber optic detectors having eight and 16 channels. Calibration plots were established for a series of stock solutions of known concentrations of proteins. Mathematical functions were derived from these calibration data to simulate the response of the detector. Limits of detection and the ranges of validity of the fit functions were determined. The 16-channel detector has a theoretical limit of detection that is equivalent to absorbance changes of 10(-4) units.

Chromatography, Liquid↗
PubMed1987

A new optical treatment for oscillopsia.

A simple optical device (spectacles plus contact lens) enabling viewing of the real world with either partial or almost-complete retinal image stabilisation has been tested in patients with oscillopsia caused by nystagmus. The device gave a useful improvement in vision in two of 14 patients. Reasons for success and failure were clear and are discussed. Obvious contraindications include severe optic atrophy, titubation and dementia. Net benefit is also unlikely if there is a good null point or area to the nystagmus, or if acuity (corrected but unstabilized) is 6/9 or better. It is not suitable for the treatment of oscillopsia caused by failure of the vestibulo-ocular reflex.

Adult↗
PubMed2005

Exploration of the retinal nerve fiber layer thickness by measurement of the linear dichroism.

An electro-optic device mounted on a slit lamp to assess the degree of polarization of a light beam that has double passed through the retina about the optic-nerve head in the living human eye is described. The asymmetric structure of the retinal nerve's fiber layer possesses a linear-form dichroism and will partially polarize an unpolarized light beam that is scattered at the fundus of the eye and has double passed the ocular media (cornea, lens, retina). This partial polarization is a function of the retinal nerve's fiber layer thickness, and its measurement may be used for exploring glaucoma and other retinal neuropathies. Experimental conditions allow us to neglect corneal dichroism. The first clinical measurements show a different degree of polarization between normal and glaucomatous eyes and a good correlation with the results obtained by optical coherence tomography.

Algorithms↗
PubMed2003

Micropatterning of organic semiconductor microcrystalline materials and OFET fabrication by "hot lift off".

Considerable progress toward the development of electronic devices that rely on organic semiconductors as the active material component has been made in recent years. The key step for realization of the advanced organic electronic, or optical, device is the ability to micropattern different kinds of electronic materials, such as organic semiconductor/conducting materials, over large areas with micrometer-sized resolution. Here we demonstrate a simple and direct method for micropatterning small-molecule microcrystalline films using an epoxy stamp. The "hot lift off" method is highly selective, creating patterns with high resolution and relies on straightforwardly tailoring the adhesive properties between the epoxy and the film. This process is well suited for patterning many types of materials.

Journal Article↗
PubMed1997

The influence of demographic factors on phase-modulated spectroscopy in adults.

The increased complexity of phase-modulated spectroscopy (PMS) compared with incoherent light techniques of near-infrared spectroscopy is justified if measurement of path length is necessary. In order to assess the variability of optical transmission in the head of adults, 96 subjects of varying age, gender and skin pigmentation were studied using an experimental three-wavelength time-shared PMS device. Optical path length was measured at each wavelength, and saturation and haemoglobin-free path length were calculated. Path length varied linearly with the separation of the optical probes, but gender, age or skin pigmentation were not associated with differences in path length. Haemoglobin saturation averaged 68% and varied with age in a non-uniform fashion. Haemoglobin-free path length differed between genders, being 8% longer in women than in men. Measurements could not be performed at 5 cm due to optical attenuation in 36% of subjects. These subjects were more often young, but they were not otherwise distinguished by gender or pigmentation differences. Subjects in whom measurements could be obtained at 5 cm had longer haemoglobin-free path lengths than did subjects in whom optical attenuation prevented these measurements. These data confirm the occurrence of significant differences in optical transmission in adults and support the use of PMS techniques that measure path length.

Adult↗
PubMed2001

Updating the classical approach to visual acuity.

The classical account of visual acuity incorporates optical, anatomical and physiological components. Knowledge of these helps to put into perspective recent scientific advances that have clinical implications. They include the development of active optical devices for neutralising aberrations in peripheral zones of the pupil, with the potential of improving the eye's imagery beyond its customary limit. In another application of modern optical and electronic instrumentation, the quality of retinal images in young eyes has been compared with that in the aged. This has led to a better understanding of the choice of contrast patterns to enhance visual acuity in older patients.

Journal Article↗
PubMed2006

Optical trapping and integration of semiconductor nanowire assemblies in water.

Semiconductor nanowires have received much attention owing to their potential use as building blocks of miniaturized electrical, nanofluidic and optical devices. Although chemical nanowire synthesis procedures have matured and now yield nanowires with specific compositions and growth directions, the use of these materials in scientific, biomedical and microelectronic applications is greatly restricted owing to a lack of methods to assemble nanowires into complex heterostructures with high spatial and angular precision. Here we show that an infrared single-beam optical trap can be used to individually trap, transfer and assemble high-aspect-ratio semiconductor nanowires into arbitrary structures in a fluid environment. Nanowires with diameters as small as 20 nm and aspect ratios of more than 100 can be trapped and transported in three dimensions, enabling the construction of nanowire architectures that may function as active photonic devices. Moreover, nanowire structures can now be assembled in physiological environments, offering new forms of chemical, mechanical and optical stimulation of living cells.

Journal Article↗
PubMed2005

Closed-form inversion of the reflection ellipsometric function of a film-substrate system: absorbing-substrate optical constant.

A closed-form inversion expression for obtaining the optical constant (complex refractive index) of the substrate of an absorbing-film-absorbing-substrate system from one reflection ellipsometry measurement is derived. If, in addition, the film thickness is to be determined, a second measurement at another angle of incidence may or may not be used. The derived formula does not introduce errors itself, and tolerates errors in input variables very well. Random and systematic errors in the measured ellipsometric parameters do not affect the value obtained for the optical constant of the substrate: it is always the true value to two decimal places. Two examples in ellipsometry and in the design of reflection-type optical devices, one each, are presented and discussed. In addition, experimental results for a commercially available wafer are also presented. Two other closed-form inversion expressions for obtaining the optical constant of the substrate from two and three measurements are also presented and briefly discussed.

Journal Article↗
PubMed2004

Fiber optic in vivo imaging in the mammalian nervous system.

The compact size, mechanical flexibility, and growing functionality of optical fiber and fiber optic devices are enabling several new modalities for imaging the mammalian nervous system in vivo. Fluorescence microendoscopy is a minimally invasive fiber modality that provides cellular resolution in deep brain areas. Diffuse optical tomography is a non-invasive modality that uses assemblies of fiber optic emitters and detectors on the cranium for volumetric imaging of brain activation. Optical coherence tomography is a sensitive interferometric imaging technique that can be implemented in a variety of fiber based formats and that might allow intrinsic optical detection of brain activity at a high resolution. Miniaturized fiber optic microscopy permits cellular level imaging in the brains of behaving animals. Together, these modalities will enable new uses of imaging in the intact nervous system for both research and clinical applications.

Animals↗
PubMed2005

Micrometre-scale silicon electro-optic modulator.

Metal interconnections are expected to become the limiting factor for the performance of electronic systems as transistors continue to shrink in size. Replacing them by optical interconnections, at different levels ranging from rack-to-rack down to chip-to-chip and intra-chip interconnections, could provide the low power dissipation, low latencies and high bandwidths that are needed. The implementation of optical interconnections relies on the development of micro-optical devices that are integrated with the microelectronics on chips. Recent demonstrations of silicon low-loss waveguides, light emitters, amplifiers and lasers approach this goal, but a small silicon electro-optic modulator with a size small enough for chip-scale integration has not yet been demonstrated. Here we experimentally demonstrate a high-speed electro-optical modulator in compact silicon structures. The modulator is based on a resonant light-confining structure that enhances the sensitivity of light to small changes in refractive index of the silicon and also enables high-speed operation. The modulator is 12 micrometres in diameter, three orders of magnitude smaller than previously demonstrated. Electro-optic modulators are one of the most critical components in optoelectronic integration, and decreasing their size may enable novel chip architectures.

Journal Article↗
PubMed2004

Irreversible coupling by use of dissipative optics.

The time reversibility of optical propagation impedes the definite performance of many optical devices, such as couplers, polarization converters, etc. We suggest a novel concept in which we use media with loss and gain, thus breaking the time-reversal characteristics, to achieve a unidirectional optical mode interference and coupling, which is a desirable feature for light-wave circuits. Using a matched periodic modulation of both the index of refraction and loss (gain) of the medium, we implement a spatially single sideband perturbation, which breaks the symmetry to allow only a unidirectional energy transfer from mode m to mode n of the optical structure. We elaborate on this phenomenon in coupling between two modes of a multimode optical waveguide.

Journal Article↗
PubMed2005

Demonstration of systematic photonic crystal device design and optimization by low-rank adjustments: an extremely compact mode separator.

We present a powerful design and optimization method for devices in a photonic crystal. The method is based on a Wannier basis field expansion and efficient matrix analysis techniques for searching through a vast number of designs. The method permits the design of many compact optical devices with complex and novel functions. We present a design example of a very compact mode separator that is 8.2 microm x 13.3 microm in size that demultiplexes the three modes of an input photonic crystal multimode waveguide into three single-mode output waveguides. We verify the method with finite-difference time-domain calculations.

Journal Article↗
PubMedDate not supplied

[Why is the eye round?].

By an unsophisticated experiment, published data on the anatomy of the eye, wave theory of light, and the laws of geometrical optics the author tries to prove that a spherical concave screen is the optimal variant of a screen on which spherical wave front is projected, formed by a single lens. The shape of the wave front and of the concave screen are in complete agreement. Such optical imperfections as the field curvature, distortion, coma (partially), and astigmatism of the oblique light beams are compensated for. These optical drawbacks are undetectable on a concave screen, and hence they are proposed to be the shortcomings of a flat screen. The author compares this to a spherical shape of the eye, the posterior wall of which represents a concave screen, an indisputable fact, and assumes that the before-named optic imperfections are completely compensated for in human eye due to concavity of the posterior optic wall. Based on the anatomy and practical results of using aspherical refracting surfaces in artificial optic devices, the author draws a parallel with the anatomical structures of the eye possessing aspherical refracting surfaces in order to demonstrate that higher and lower-order spherical aberrations (Zeidel's aberrations) are fully compensated for in human eye, as are the position and enlargement chromatism. Analysis of published data permitted the author to assert that the eye of man is characterized by a method for compensation of spherical aberrations, which has no analogs in man-made practice. Hence, the Nature has imparted the eye with such a collection of compact, universal, and highly effective methods for compensation of optic imperfections, which is not to be found in any of the man-made devices of today.

Eye↗