Change In Optical Power Research Articles

Characterization of the Effects of Hyperbaric Oxygen on the Biochemical and Optical Properties of the Bovine Lens.

To assess the morphologic, biochemical, and optical properties of bovine lenses treated with hyperbaric oxygen. Lenses were exposed to hyperbaric nitrogen (HBN) or hyperbaric oxygen (HBO) for 5 or 15 hours, lens transparency was assessed using bright field microscopy and lens morphology was visualized using confocal microscopy. Lenses were dissected into the outer cortex, inner cortex, and core, and glutathione (GSH) and malondialdehyde (MDA) measured. Gel electrophoresis and Western blotting were used to detect high molecular weight aggregates (HMW) and glutathione mixed protein disulfides (PSSG). T2-weighted MRI was used to measure lens geometry and map the water/protein ratio to allow gradient refractive index (GRIN) profiles to be calculated. Optical modeling software calculated the change in lens optical power, and an anatomically correct model of the light pathway of the bovine eye was used to determine the effects of HBN and HBO on focal length and overall image quality. Lenses were transparent and lens morphology similar between HBN- and HBO-treated lenses. At 5- and 15-hour HBO exposure, GSH and GSSG were depleted and MDA increased in the core. Glutathione mixed protein disulfides were detected in the outer and inner cortex only with no appearance of HMW. Optical changes were detectable only with 15-hour HBO treatment with a decrease in the refractive index of the core, slightly reduced lens thickness, and an increase in optimal focal length, consistent with a hyperopic shift. This system may serve as a model to study changes that occur with advanced aging rather than nuclear cataract formation per se.

Graphene electrodes for adaptive liquid crystal contact lenses.

The superlatives of graphene cover a whole range of properties: electrical, chemical, mechanical, thermal and others. These special properties earn graphene a place in current or future applications. Here we demonstrate one such application - adaptive contact lenses based on liquid crystals, where simultaneously the high electrical conductivity, transparency, flexibility and elasticity of graphene are being utilised. In our devices graphene is used as a transparent conductive coating on curved PMMA substrates. The adaptive lenses provide a + 0.7 D change in optical power with an applied voltage of 7.1 Vrms - perfect to correct presbyopia, the age-related condition that limits the near focus ability of the eye.

Analytical modeling of power detection-based interrogation methods for fiber Bragg grating sensors for system optimization

We present an analytical model to investigate power detection-based interrogation methods for optical fiber Bragg grating (FBG) sensors. This model is used to facilitate the optimization of interrogation systems in terms of sensitivity and dynamic range. In general, power detection methods are passive intensity-based interrogation schemes, where the spectral shift in the FBG due to the applied measurand is converted into a change in optical power due to the spectral properties of the light source. The analytical model developed herein assumes that the FBG and light source are Gaussian shaped. As such, the filtering of the light source by the FBG results in the reflection of a Gaussian spectrum governed by the properties of both the light source and FBG. The further investigation of the model has enabled analytical expressions to be developed for the sensitivity and dynamic range of the different power detection methods considered. The different power detection methods investigated include linear edge source and narrow bandwidth source (utilizing the reflected component, transmitted components, and both the transmitted and reflected components). Results show how the dynamic range and sensitivity of the power detection methods vary for different FBG sensor widths and different light source properties, specifically the width and optical power. This facilitates a direct comparison between the interrogation methods and also enables system optimization based on either a given light source or FBG.

A pre-tensioned finite element model of ocular accommodation and presbyopia

Accommodation is the ability of the eye to dynamically alter its optical power. Presbyopia is the progressive loss of this ability with age. We have developed the first pre-tensioned finite element model of accommodation and used it to address the question of whether increasing lens stiffness alone is sufficient to cause presbyopia. Intrinsic resting forces and accommodative displacement were calibrated for a 20 year-old lens’ stiffness over a 7 D optical power change. Accommodation was simulated by displacing the distal zonule attachments towards the optical axis, mimicking the movement of the ciliary body when the ciliary muscle contracts. The optical power, capsule strain, and radial zonule forces were extracted for one full cycle of accommodation. These responses were compared for lenses having elastic moduli corresponding to 14, 20, 39.5, and 62.7-year-old human lenses. Accommodative power decreased from 20 to 62.5 years of age from 7 to 2 D. This change was less than in experiments where changes in lens power go to zero around age 50. Thus, lens elasticity contributes significantly to presbyopia but is not the sole cause. Lens diameter and thickness changes were within 20 % of reported values, indicating that the present model yields a good approximation of the changes in lens shape during accommodation.

Novel switching mode in a vertically aligned liquid crystal contact lens.

Liquid crystal (LC) contact lenses are emerging as an exciting technology for vision correction. A homeotropically (vertical) aligned LC lens is reported that offers improved optical quality and simplified construction techniques over previously reported LC contact lens designs. The lens has no polarization dependence in the off state and produces a continuous change in optical power of up to 2.00 ± 0.25 D with a voltage applied. The variation in optical power results from the voltage-induced change in refractive index of the nematic LC layer, from 1.52 to a maximum of 1.72. One device substrate is treated with an alignment layer that is a mixture of planar and homeotropic polyimides, rubbed to induce a preferred director orientation in the switched state. Defects that could occur during switching are thus avoided and the lens exhibits excellent optical quality with a continuous variation in focal power.

Glucose oxidase immobilized PANI cladding modified fiber optic intrinsic biosensor for detection of glucose

In the present study, we report design, development and study of polyaniline (PANI) cladding modified fiber optic intrinsic glucose biosensor (FOIGB) for glucose sensing applications. Chemically and biologically sensitive material PANI has been exploited for the preparation of sensing element by cladding modification technique. Enzyme-glucose oxidase (GOx) was immobilized on porous supportive matrix of PANI using glutaraldehyde as a cross-linking agent. As-synthesized and deposited PANI film on fiber optic core was characterized by ultraviolet–visible and Fourier transform infra-red spectroscopies. X-ray diffraction and field emission scanning electron microscopy were employed to study structure and morphology of modified cladding. Sensing parameters, such as modal power distribution (MPD), sensing response, selectivity and stability were analyzed in order to study the performance of sensor. These parameters were determined by measuring change in optical power and MPD. The sensor, stored at a temperature 4°C, showed lowest detection limit of 10nM and found stable up to 36 days. It also showed good selectivity toward glucose and stability with high result reproducibility.

A quantitative geometric mechanics lens model: Insights into the mechanisms of accommodation and presbyopia

This study expands on a geometric model of ocular accommodation (Reilly and Ravi, Vision Res. 50:330-336; 2010) by relaxing assumptions regarding lens symmetry about the equator. A method for predicting stretching force was derived. Two models were then developed: Model 1 held the equatorial geometry constant at all stages of accommodation, while Model 2 allowed localized deformation at the equator. Both models were compared to recent data for axial thickness, anterior and posterior radii of curvature, surface area, cross-sectional area, volume, and stretching force for the 29-year-old lens. Age-related changes in accommodation were also simulated. Model 1 gave predictions which agreed with the Helmholtz theory of accommodation, while Model 2's predictions agreed with the Schachar mechanism of accommodation. Trends predicted by Model 1 agreed with all available experimental data, while Model 2 disagreed with recent surface area measurements. Further analysis indicated that Model 1 was fundamentally more efficient in that it required less force per diopter change in optical power than Model 2. Model 1 more accurately predicted age-related changes in accommodation amplitude. This implies that the zero-force (fully accommodated) state geometry changes with age due to a shifting balance in residual stresses between the lens and capsule.

Measurement of minimum angle of resolution (MAR) in the stereoscopic display using the optotype of stereoscopic stimuli

AbstractIn stereoscopic images, the crossing point of the viewing directions of the two eyes determines the perceived depth. Assuming that accommodation is affected by the positions of the crossing point, the effect of crossing point on minimum angle of resolution (MAR) was investigated. For 40 participants, MAR was measured by two‐alternative forced choice where Snellen optotype E of up and down directions were used as two kinds of stimuli. As the crossing point of the viewing direction of the left and right eyes moves farther from the sample display, the ability to identify the direction of letter E decreases at the optotype of the same line thickness. The change of MAR shows linear trends with respect to the optical power change that are the reciprocal of the distance from the participant to the crossing points located out of screen and on screen.

Multilayered relaxor ferroelectric polymer actuators for low-voltage operation fabricated with an adhesion-mediated film transfer technique

We designed and fabricated multilayered relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-clorotrifluoroethylene) [P(VDF-TrFE-CTFE)] actuators in this study. To minimize the driving voltage of the P(VDF-TrFE-CTFE) actuator, which produces bending deformation, we designed a multilayered structure and analyzed the structure using composite beam theory. We developed a new adhesion-mediated film transfer technique to fabricate 1.5μm-thick P(VDF-TrFE-CTFE) films and laminate them onto a micromachined silicon substrate. Metal electrodes were deposited on top of each P(VDF-TrFE-CTFE) film to obtain a multilayer structure with alternating electrodes. We show that with an applied voltage of only 40V, the multilayered P(VDF-TrFE-CTFE) actuators fabricated in this study produced deflections of about 9μm, and their transient behavior faded out within 10ms. When the actuators were integrated onto a varifocal liquid-filled microlens, an optical power change of more than 50 diopters was obtained. This is the first report of a method to fabricate and stack 1–2μm-thick PVDF-based films.

A High-Temperature Fiber Sensor Using a Low Cost Interrogation Scheme

Regenerated Fibre Bragg Gratings have the potential for high-temperature monitoring. In this paper, the inscription of Fibre Bragg Gratings (FBGs) and the later regeneration process to obtain Regenerated Fiber Bragg Gratings (RFBGs) in high-birefringence optical fiber is reported. The obtained RFBGs show two Bragg resonances corresponding to the slow and fast axis that are characterized in temperature terms. As the temperature increases the separation between the two Bragg resonances is reduced, which can be used for low cost interrogation. The proposed interrogation setup is based in the use of optical filters in order to convert the wavelength shift of each of the Bragg resonances into optical power changes. The design of the optical filters is also studied in this article. In first place, the ideal filter is calculated using a recursive method and defining the boundary conditions. This ideal filter linearizes the output of the interrogation setup but is limited by the large wavelength shift of the RFBG with temperature and the maximum attenuation. The response of modal interferometers as optical filters is also analyzed. They can be easily tuned shifting the optical spectrum. The output of the proposed interrogation scheme is simulated in these conditions improving the sensitivity.

Cross-layerly embedded FBG in carbon fiber composites for self-modulated, intensity referenced and temperature insensitive microdisplacement measurement

A novel temperature insensitive and intensity modulated microdisplacement sensor is demonstrated by cross-layerly embedding an FBG in carbon fiber composites. The reflection spectrum of the FBG is selfmodulated to be chirped spectrum if a microdisplacement is applied to the center of the sensor structure. By monitoring the optical power change due to the above chirped spectrum variation, the microdisplacement can be measured. Experimental results show that there are quasilinear relationships between the microdisplacement and optical power, the maximum measurement resolution of the sensor reaches 10.7μm within the displacement range of 0–1050μm, and the dynamic measurement range is within the range of 0–200Hz.

The Measurement on Transmission Characteristic of Fiber Raman Amplifier

The interaction between the pump and pump, the signal and signal ,the pump and signal in Fiber Raman amplifiers are measured. Three-wavelength pumping at 1427nm, 1445nm and 1466nm, it show that the pump energy transfers from short wavelength to long wavelength, that is, Raman effect exists between the different pumping lights. When the different wavelength signals input at the same time, the output optical power change, which is also caused due to the Raman interactions between different signals. When three-wavelength pumping, the input signal power, respectively 0.03dBm 5.04dBm 15.08dBm, the signal gain values are measured. A significant gain saturation phenomenon in 15.08 dBm appears, and it will intensify as the power increases.

Influence of Anterior Segment Power on the Scan Path and RNFL Thickness Using SD-OCT

Retinal nerve fiber layer (RNFL) thickness measures with spectral domain-optical coherence tomography (SD-OCT) provide important information on the health of the optic nerve. As with most retinal imaging technologies, ocular magnification characteristics of the eye must be considered for accurate analysis. While effects of axial length have been reported, the effects of anterior segment optical power on RNFL thickness measures have not been described fully to our knowledge. The purpose of our study was to determine the influence of the optical power change at the anterior corneal surface, using contact lenses, on the location of the scan path and measurements of RNFL thickness in normal healthy eyes. We recruited 15 normal subjects with less than 6 diopters (D) of ametropia and no ocular pathology. One eye of each subject was selected randomly for scanning. Baseline SD-OCT scans included raster cubes centered on the optic nerve and macula, and a standard 12-degree diameter RNFL scan. Standard 12-degree RNFL scans were repeated with 10 separate contact lenses, (Proclear daily, Omafilcon A/60%) ranging from +8 to -12 D in 2-D steps. The extent of the retinal scan, and RNFL thickness and area measures were quantified using custom MATLAB programs that included ocular biometry measures (IOL Master). RNFL thickness decreased (0.52 μm/D, r = -0.33, P < 0.01) and the retinal region scanned increased (0.52%/D, r = 0.97, P < 0.01) with increase in contact lens power (-12 to +8). The normalized/percentage rates of change of RNFL thickness (-0.11/mm, r = -0.67, P < 0.01) and image size (0.11/mm, r = 0.96, P < 0.01) were related to axial length. Changes in the retinal region scanned were in agreement with transverse scaling, computed with a three surface schematic eye (R(2) = 0.97, P < 0.01). RNFL area measures, that incorporated the computed transverse scaling, were not related significantly to contact lens power (863 μm(2)/D, r = 0.06, P = 0.47). Measurements of RNFL thickness by SD-OCT are dependent on the optics of the eye, including anterior segment power and axial length. The relationships between RNFL thickness measures and optical power are a direct reflection of scan path location with respect to the optic nerve head rim, caused by relative magnification. An incorporation of transverse scaling to RNFL area measures, based on individualized ocular biometry, eliminated the magnification effect.

Pig Lenses in a Lens Stretcher

To investigate porcine lenses in a lens stretcher with regard to presbyopia corrective procedures. A lens stretching device was designed, which allows to simultaneously determine all relevant geometrical and optical parameters at each stretch position. The setup was used to compare the optical and geometrical lens properties of young slaughter pigs (n = 5) with older sows (n = 7). The change of optical power with stretching is about five times larger for young porcine lenses than for sows. For young pigs, the gradient index profile of the crystalline lens significantly contributes to the induced accommodation amplitude. We have shown that sow lenses are a suitable model for in vitro experiments on possible treatments for presbyopia. The rapid decrease in the induced accommodation amplitude with age may be explained by a reduced change of all geometrical lens parameters, which in turn leads to a smaller contribution of the gradient index profile to accommodation.

Surface Loading Sensitivity Characterization of a Resonant Planar Optical Waveguide Stack

Detuning of a coupled planar waveguide pair through surface loading of the top waveguide that is in contact with the analyte serves as a transducer for a Stacked Planar Affinity-Regulated Resonant Optical Waveguide (SPARROW) sensor. Here we investigate the surface loading detection sensitivity of a SPARROW transducer composed of a stack of two planar alumina waveguides grown using ion beam assisted e-beam deposition. Using a sucrose analyte solution introduced to the stack surface in a poly-di-methyl-siloxane (PDMS) microfluidic channel, the change in optical output power through the coupled waveguide pair as a function of sucrose analyte solution concentration was experimentally determined. Based on the analyte in the evanescent field penetration depth volume, the effective minimum detectable surface loading of the stack was determined to be 20 with a bulk index sensitivity of 5.6 refractive index units (RIU) for this stack configuration and experimental setup.

Response of the Internal Electric Field in CdZnTe to Illumination at Multiple Optical Powers

Manipulation of CdZnTe (CZT) crystals using illumination is a useful tool for altering the internal electric field present under normal bias conditions. The interactions with carriers that are trapped at either terminal are visualized by the electric field distribution through polarization. In this report, we demonstrate an ability to selectively manipulate the internal electric field of CZT using multiple-wavelength light illumination at various optical powers. The internal electric field polarization can be controlled using changes in optical power. We also investigate the electric field distributions using multiple optical powers to examine the light response as a function of light penetration depth.

Application of Quasi-Distributed and Dynamic Length and Power Change Measurement Using Optical Frequency Domain Reflectometry

Application results of a dynamic technique for simultaneous measurement of length changes and optical power changes between multiple reflection points in an optical fiber are presented. The technique is based on incoherent optical frequency domain reflectometry (I-OFDR) and allows for measuring for example length changes and optical power changes quasi-distributed at repetition rates up to 2 kHz. Precise measurement with length change resolutions in the -range can be conducted using standard single-mode or multi-mode fibers. Previous results of dynamic refractive index change measurement and the use of polymer optical fibers for high-strain measurement are concluded and possible sources of measurement inaccuracies are discussed. Field test results with sensors installed on a masonry building during a seismic shake test are presented. The versatility and simplicity of this technique makes it potentially interesting for application in the structural health monitoring sector and chemical process control.

A WDM Capable Integrated Optical Readout of a MEMS Sensor

We present experimental validation of an integrated readout technique for interrogating the suspension height of micro-electro-mechanical systems (MEMS) structures using a doubly clamped beam as the demonstration structure. This readout technique is envisaged to be useful in applications such as MEMS-based chemical sensing, where it is necessary to obtain the accurate position of a MEMS beam. The approach is based on the suspended MEMS structure modulating light transmission in an underlying optical waveguide via Fabry-Perrot phenomena. Our experimental results show that changing the doubly clamped beam suspension height by 100 nm can result in an up to 20 dB change in optical power transmitted through an underlying optical waveguide.

Varifocal liquid lenses with integrated actuator, high focusing power and low operating voltage fabricated on 200 mm wafers

We developed an innovative type of varifocal liquid lens actuated by electrostatic parallel plates. The 3mm diameter lens is made of a polymer membrane that encapsulates a high permittivity liquid in a cavity on top of a glass wafer. Annular electrodes situated below the membrane and on the glass wafer form the electrostatic parallel plates actuator. By applying a voltage between the electrodes, the electrostatic actuation generated reduces the gap and pushes the liquid towards the center of the lens changing the curvature of the membrane.Compared to previous liquid lenses, very compact devices (≤6mm×6mm×0.7mm) working at a reduced supply voltage (<25V) are demonstrated. Wave front measurements indicate an optical power change of 8m−1 at 22VRMS that can be further improved. The lenses were fabricated on 200mm wafers using standard microelectronics processes that make our solution a promising small outline, low voltage and low cost candidate for auto-focus devices in camera phones.

Fallstricke bei der Bestimmung von Nahbrillen

People in the second half of their lives often require reading glasses. A basic requirement for determining suitable reading glasses is measurement of the patient's accommodation, which describes the change in the eye's optical power caused by the attempt to clearly focus on an object at a certain distance. The maximum accommodation performance of a person already begins to decline from the age of 40 onwards. When it becomes increasingly difficult to adjust to the typical reading distance of 40 cm, one speaks of presbyopia: age-related farsightedness. This contribution describes two appropriate methods for determining the strength of reading glasses: determination of the maximum accommodation performance by measuring the near point distance and determination of the maximum accommodation effort by measuring the relative positive and negative accommodation. Optimal reading glasses enable the patient to focus sharply on something from the working distance that is closer but also on something that is further away.