The double sliding-door effect.
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Astigmatism↗
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Results for “Optics and Refraction”
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Bifocal implants: clinical results.
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Aged↗
Accuracy of Zernike polynomials in characterizing optical aberrations and the corneal surface of the eye.
PURPOSE: Zernike polynomials have been successfully used for approximately 70 years in many different fields of optics. Nevertheless, there are some recent discussions regarding the precision and accuracy of these polynomials when applied to surfaces such as the human cornea. The main objective of this work was to investigate the absolute accuracy of Zernike polynomials of different orders when fitting several types of theoretical corneal and wave-front surface data. METHODS: A set of synthetic surfaces resembling several common corneal anomalies was sampled by using cylindrical coordinates to simulate the height output files of commercial videokeratography systems. The same surfaces were used to compute the optical path difference (wave-front [WF] error), by using a simple ray-tracing procedure. Corneal surface and WF error was fit by using a least-squares algorithm and Zernike polynomials of different orders, varying from 1 to 36 OSA-VSIA convention terms. RESULTS: The root mean square error (RMSE) ranged-from the most symmetric corneal surface (spherical shape) through the most complex shape (after radial keratotomy [RK]) for both the optical path difference and the surface elevation for 1 through 36 Zernike terms-from 421.4 to 0.8 microm and 421.4 to 8.2 microm, respectively. The mean RMSE for the maximum Zernike terms for both surfaces was 4.5 microm. CONCLUSIONS: These results suggest that, for surfaces such as that present after RK, in keratoconus, or after keratoplasty, even more than 36 terms may be necessary to obtain minimum accuracy requirements. The author suggests that the number of Zernike polynomials should not be a global fixed conventional or generally accepted value but rather a number based on specific surface properties and desired accuracy.
Cornea↗
512-channel vertical-cavity surface-emitting laser based free-space optical link.
A vertical-cavity surface-emitting laser based bidirectional free-space optical interconnect has been implemented to interconnect two printed circuit boards. A total of 512 clustered channels with a density of 2844 channels/cm2 are transmitted over a distance of 83 mm. The optical interconnect is a combination of refractive microlenses and diffractive minilens relays.
Journal Article↗
Sputtered Si:H alloys for edge filters: application to thermophotovoltaics.
Si:H alloys are being investigated for the high-index material in an interference filter to provide spectral control in an application of thermophotovoltaic energy conversion. In particular, a multilayer edge filter is being developed to provide high transmission of photons with wavelengths between 1.0 and 2.4 microm and high reflectance for wavelengths outside this range. Thin films of Si:H were deposited by means of rf reactive sputtering. Deposition parameters were varied to optimize the H content in Si:H coatings such that the refractive index was greater than 3. Optical absorption near 1 microm and Si:H infrared absorptions near 5 and 12 microm were minimized.
Journal Article↗
Antireflection coating formed by plasma-enhanced chemical-vapor deposition for terahertz-frequency germanium optics.
A method of manufacturing optical coatings for germanium optics used at terahertz frequencies has been developed. The various optical coatings used at terahertz frequencies are difficult to manufacture conventionally because these coatings must be as thick as several tens of micrometers, which is far thicker than those used in the optical region. One way to overcome this problem is to form a silicon oxide layer through plasma-enhanced chemical-vapor deposition, with silane (SiH4) as a source gas. Using this method, I formed 21-microm-thick silicon oxide films as antireflection (AR) layers for germanium optics and obtained low reflection at 1.7 THz (wavelength, lambda = 175 microm). This method is easily applied to large-aperture optics and micro-optics as well as to optics with a complex surface form. The AR coatings can also be formed for photoconductive detectors made from germanium doped with gallium at a low temperature (160 degrees C); this low temperature ensures that the doped impurities in the germanium do not diffuse. Fabrication of optical coatings upon substrates that have refractive indices of 3.84-11.7 may also be possible by control of the refractive indices of the deposited layers.
Journal Article↗
Enhanced solar irradiance across the atmosphere-sea ice interface: a quantitative numerical study.
A radiative transfer model for the coupled atmosphere-sea ice system is used to study the change in downward irradiance across the air-ice interface. Computations demonstrate that the downward solar irradiance can be significantly enhanced across the air-ice interface. The enhancement is mainly due to light in the ice that is scattered upward and then totally reflected by the air-ice interface. It depends primarily on the change in the index of refraction across this interface and the optical properties of the sea ice, but also on the direct solar and sky illumination of the interface.
Journal Article↗
Assessment of the accuracy of the crossed-cylinder aberroscope technique.
Simulations of the optics of the Howland crossed-cylinder aberroscope technique show that errors in alignment, data collection, and analysis can lead to unexpected asymmetries of the determined aberrations in a rotationally symmetric system. In particular, coma can be incorrectly indicated. The magnitude of the error in aberration measurement depends on the magnitude of the alignment, data collection, and alignment errors. These findings indicate that the tolerances for setting up the technique and data collection should be analyzed thoroughly before quantitative significance is given to the determined aberration coefficients.
Computer Simulation↗
Lie algebraic treatment of dioptric power and optical aberrations.
The dioptric power of an optical system can be expressed as a four-component dioptric power matrix. We generalize and reformulate the standard matrix approach by utilizing the methods of Lie algebra. This generalization helps one deal with nonlinear problems (such as aberrations) and further extends the standard matrix formulation. Explicit formulas giving the relationship between the incident and the emergent rays are presented. Examples include the general case of thick and thin lenses. The treatment of a graded-index medium is outlined.
Humans↗
Correction of the aberrations in the human eye with a liquid-crystal spatial light modulator: limits to performance.
We evaluated the performance of a liquid-crystal spatial light modulator for static correction of the aberrations in the human eye. By applying phase-retrieval techniques to pairs of double-pass images we first estimated the wave aberration of the eye to be corrected. Then we introduced the opposite phase map in the modulator, which was placed in a plane conjugated with the eye's pupil, and we recorded double-pass images of a point source before and after correction of the aberrations. In a slightly aberrated artificial eye a clear improvement was obtained after correction, and, although diffraction-limited performance was not achieved, the results were close to the theoretical predictions. In the two living eyes that we studied some benefit also appeared in the correction, but the performance was worse than that expected. We evaluated possible explanations for the relatively poor performance that was obtained in the human eye: an incorrect estimate of the ocular aberration, the limited spatial resolution of the modulator, and the dynamic changes in the ocular aberrations. Based on the results in the artificial eye, the first problem was not considered to be a major source of error. However, we showed that the spatial resolution of the liquid-crystal spatial light modulator limits the maximum correction to be attained. In addition, the changes in the ocular optics over time also impose a limit in the performance of static corrections.
Adult↗
Study on the effects of monochromatic aberrations in the accommodation response by using adaptive optics.
The effect of asymmetric monochromatic aberrations in the accommodation response was studied by using an adaptive optics (AO) system. This approach permits the precise modification of ocular aberrations during accommodation. The AO system is composed of a real-time Hartmann-Shack wavefront sensor and a membrane deformable mirror with 37 independent actuators. The accommodation response was measured in two subjects with their normal aberrations and with the asymmetric aberrations terms corrected. We found a significant and systematic increase in the response accommodation time, and a reduction in the peak velocity, in both subjects when the aberrations were corrected in real time. However, neither the latency time nor the precision of the accommodation were affected. These results may indicate that the monochromatic aberrations play a role in driving the accommodation response.
Accommodation, Ocular↗
Evolution of the vortex and the asymmetrical parts of orbital angular momentum in separable first-order optical systems.
We analyze the evolution of the vortex and the asymmetrical parts of orbital angular momentum during its propagation through separable first-order optical systems. We find that the evolution of the vortex part depends on only parameters a(x), a(y), b(x), and b(y) of the ray transformation matrix and that isotropic systems with the same ratio b/a produce the same change of the vortex part of the orbital angular momentum. Finally, it is shown that, when light propagates through an optical fiber with a quadratic refractive-index profile, the vortex part of the orbital angular momentum cannot change its sign more than four times per period.
Journal Article↗
Imaging and sizing of diamond nanoparticles.
Typical disturbances of biological environment such as background scatter and refractive index variations have little effect on the size-dependent scattering property of highly refractive nanocrystals, which are potentially attractive optical labels. We report on what is to our knowledge the first investigation of these scattering optical labels, and their sizing, in particular, by imaging at subvideo frame rates and analyzing samples of diamond nanocrystals deposited on a glass substrate in air and in a matrix of weakly scattering polymer. The brightness of a diffraction-limited spot appears to serve as a reliable measure of the particle size in the Rayleigh scattering limit.
Algorithms↗
Analytical relation between effective mode field area and waveguide dispersion in microstructure fibers.
For optical fibers exhibiting a radially symmetric refractive index profile, there exists an analytical relation that connects waveguide dispersion and the Petermann-II mode field radius. We extend the usefulness of this relation to the nonradially symmetric case of microstructure fibers in the anomalous dispersion regime, yielding a simple relation between dispersion and effective mode field area. Assuming a Gaussian mode distribution, we derive a fundamental upper limit for the effective mode field area that is required to obtain a certain amount of anomalous waveguide dispersion. This relation is demonstrated to show excellent agreement for fiber designs suited for supercontinuum generation and soliton lasers in the near infrared.
Journal Article↗
Polarization modulation imaging ellipsometer.
The polarization modulation technique was successfully combined with parallel synchronous detection using a switching light source and a CCD camera to realize full-frame measurement of ellipsometric parameters. The detected thickness of a monolayer film of n-octadecylsiloxane agreed well with theoretical and reported experimental values. The thickness resolution for imaging and the temporal noise in parallel thickness measurements were smaller than +/-0.1 nm and smaller than +/-0.02 nm, respectively.
Biophysical Phenomena↗
Television captions for hearing-impaired people: a study of key factors that affect reading performance.
Closed captions are broadcast with television programs for special-needs viewers such as hearing-impaired people. We examined how caption presentation rate, small amounts of induced dioptric blur, and English learned as a second language affect the reading performance of good readers. Thirty-two college graduates with normal hearing and vision, half of whom learned English as a second language, read television captions that consisted of white capital letters equivalent in size to 20/92 Snellen letters on a black background. Text was presented at rates of 55, 120, and 216 words/min. Lenses of 0, 0.5, 1.0, or 1.5 diopters (D) were worn over the person's best refractive correction. The fastest text rate and small amounts of blur significantly disrupted reading performance. People who learned English as a second language were hindered more by presentation rate than by dioptric blur. Surprisingly, people with refractive errors (even though they were optically corrected) were hindered less by induced blur than were people with normally clear vision.
Adult↗
[Development of ophthalmologic software for handheld devices].
INTRODUCTION: The formulas for calculation of intraocular lenses have evolved since the first theoretical formulas by Fyodorov. Among the second generation formulas, the SRK-I formula has a simple calculation, taking into account a calculation that only involved anteroposterior length, IOL constant and average keratometry. With the evolution of those formulas, complexicity increased making the reconfiguration of parameters in special situations impracticable. In this way the production and development of software for such a purpose, can help surgeons to recalculate those values if needed. PURPOSE: To idealize, develop and test a Brazilian software for calculation of IOL dioptric power for handheld computers. METHODS: For the development and programming of software for calculation of IOL, we used PocketC program (OrbWorks Concentrated Software, USA). We compared the results collected from a gold-standard device (Ultrascan/Alcon Labs) with the simulation of 100 fictitious patients, using the same IOL parameters. The results were grouped for ULTRASCAN data and SOFTWARE data. Using SRK/T formula the range of those parameters included a keratometry varying between 35 and 55D, axial length between 20 and 28 mm, IOL constants of 118.7, 118.3 and 115.8. RESULTS: Using Wilcoxon test, it was shown that the groups do not differ (p=0.314). We had a variation in the Ultrascan sample between 11.82 and 27.97. In the tested program sample the variation was practically similar (11.83-27.98). The average of the Ultrascan group was 20.93. The software group had a similar average. The standard deviation of the samples was also similar (4.53). CONCLUSION: The precision of IOL software for handheld devices was similar to that of the standard devices using the SRK/T formula. The software worked properly, was steady without bugs in tested models of operational system.
Computers, Handheld↗
[Construction of optometric scales in the light of philosophy].
It is by walking that the new arises. This study aims at establishing new issues in the construciton of optometric scales of pictures accordingly to their shape and content. It is a reflection (bibliographic-analytical) based on Danta's dissertation. It is observed that the matter is the optonometric scale ready for use. The shape, in turn, is what was developed until the generation of the matter, the optical calculations and the law of refraction, apart from the ocular anatomy and physiology. The new aspect developed is culture. The philosophical question shows the infinity of knowledge and reveals that the view of certain research at a certain time can be rebuilt in another.
Optometry↗