Inherent Spherical Aberration Research Articles

A simple strategy for increasing optical waveguide performance using spherical aberration

Femtosecond Laser Writing (FLW) has some advantages over competing techniques; it is a direct, highly flexible, and maskless process that can inscribe waveguides in almost any type of transparent material. FLW has proven to produce photonic integrated circuits with innovative design in a deterministic way for several applications, including quantum photonics and microfluidics. Although direct laser writing of waveguides has been extensively studied, there is still an intense search for methods to produce waveguides with lower losses and higher optical quality, because improvements in this sense will impact photonic research and technology. In this work, straight waveguides were directly inscribed into Eagle XG glass samples in a single process step at fabrication depths up to 370 µm. The propagation loss and the mode profile for single-mode waveguides were obtained. The laser pulse energy threshold that triggers the optical breakdown as a function of the depth was measured and used to study its relationship with the resulting waveguide optical properties. A trend between the waveguide losses and the observed pulse energy threshold for optical breakdown was found, which is connected with the microscope objective spherical aberration. It can be useful for finding the best conditions for producing low-loss waveguides. Compared to the waveguides written with the corrected pulses, propagation losses up to 2.5 times smaller were observed in our experiments when applying the strategy presented here. Therefore, by taking advantage of the inherent spherical aberration, the FLW technique can be made capable of much more at even higher intensities than previously possible.

Effect of spherical aberration in trefoil phase plates on color wavefront coding

Wavefront coding is a technique that makes use of aspheric phase masks and image processing to greatly increase the depth of focus and/or reduce the cost of imaging systems. The phase mask adds a controlled amount of aberrations to the optical system in such a way that invariant imaging properties are achieved over a wide range of defocus. When aspheric phase plates are fabricated, their shape has to be carefully designed to avoid introducing other aberrations into the optical system, which could reduce its performance. In this work, we will show how inherent spherical aberration for trefoil-shaped phase plates reduces the quality of color images. Results will be illustrated with numerical simulations. We will show that a fourth-order polynomial added to a trefoil shaped phase mask can avoid the plate generating undesired spherical aberration that will affect the final quality of the decoded color images.

Population spherical aberration: associations with ametropia, age, corneal curvature, and image quality

PurposeThe aim of this analysis was to determine the total ocular wavefront aberration values of a large phakic population of physiologically normal, ametropic eyes, gathered under the same clinical protocol using the same diagnostic wavefront sensor.Materials and methodsStudies were conducted at multiple sites in Asia, North America, Europe, and Australia. A Bausch + Lomb Zywave II Wavefront Aberrometer (Rochester, NY, USA) was used to measure the lower and higher order aberrations of each eye. Data analysis was conducted using linear regression analysis to determine the relationship between total spherical aberration, ametropia, age, corneal curvature, and image quality.ResultsLinear regression analysis showed no correlation (r = 0.0207, P = 0.4874) between degree of ametropia and the amount of spherical aberration. There was also no correlation when the population was stratified into myopic and hyperopic refractive groups (rm = 0.0529, Pm = 0.0804 and rh = 0.1572, Ph = 0.2754). There was a statistically significant and weak positive correlation (r = 0.1962, P < 0.001) between age and the amount of spherical aberration measured in the eye; spherical aberration became more positive with increasing age. Also, there was a statistically significant and moderately positive correlation (r = 0.3611, P < 0.001) with steepness of corneal curvature; spherical aberration became more positive with increasing power of the anterior corneal surface. Assessment of image quality using optical design software (Zemax™, Bellevue, WA < USA) showed that there was an overall benefit in correcting the average spherical aberration of this population.ConclusionAnalysis of this dataset provides insights into the inherent spherical aberration of a typical phakic, pre-presbyopic, population and provides the ability to determine what drives the spherical aberration of the eye, as well as what potential benefit a person could gain by compensating for that average spherical aberration.

Inherent Ocular Spherical Aberration and Multifocal Contact Lens Optical Performance

The role of inherent spherical aberration (SA) in the optical performance of presbyopic eyes corrected with simultaneous vision multifocal contact lenses was investigated. Presbyopic schematic eyes were modeled with partial accommodative function to represent 45- and 55-year olds and were further classified into five categories based on their magnitude of inherent SA. Two representative ametropic models of each category were corrected with four multifocal contact lens iterations. High-add designs were used to correct 55-year olds, whereas low-add designs served 45-year ones. The overall performances were gauged in terms of visual Strehl ratio and area under through-focus modulation transfer function. The root mean square error of higher order aberrations of the eye and correcting lens combination were significantly different (p < 0.05) within the five inherent SA models, for all pupils and accommodative states. Area under through-focus modulation transfer function at all three spatial frequencies tested was found to be significantly different (p < 0.05) within the five SA models. Visual Strehl ratio measures were also different but statistically insignificant. Eyes having the same refractive prescriptions but diverse levels of inherent SA perform differently even when corrected with identical multifocal designs, and the performance is dependent on pupil size and level of residual accommodation. Overall, the distinct performances within the five SA models were optically relevant for pupils ∼4 mm and greater. Among the designs investigated, the low-add multizone iteration demonstrated performance relatively independent of the inherent SA because of the favorable interactions of defocus with primary, secondary, and tertiary SA. These findings confirm that the coupling of ocular SA and correcting lens aberrations contributes to the multifocal functionality.

A compensated spherical reflector antenna using sub‐reflectarrays

AbstractSpherical reflectors have been used as wide‐angle scanning antennas due to the unique geometric properties of the sphere. The inherent spherical aberration, however, causes considerable performance degradation. This article presents a novel sub‐reflectarray compensating technique to correct it. A microstrip reflectarray is a planar, inexpensive, passive device with unique capabilities of controlling reflection phases. By exploiting this feasible property, it is employed as an auxiliary phase corrector, and the phase errors caused by spherical aberration are compensated. Two examples, a 35‐m spherical reflector antenna at Ka‐band and a 1.5‐m breadboard spherical reflector, are presented, and simulation results show great performance improvement for both no scan and large scan cases. Because of the difficulty in measuring large reflector antennas at UCLA, it is part of future plan to collaborate with other institutions for the verification of the concept. However, we believe that the simulation results generated in this article should provide acceptable performance prediction of the proposed antenna design. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 577–582, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24088

Optical performance of 3 intraocular lens designs in the presence of decentration

To study the theoretical optical performance of 3 intraocular lens (IOL) designs in the presence of IOL decentration. Optics Center, Bausch & Lomb, Rochester, New York, USA. A ray-tracing program was used to evaluate the effect of IOL decentration on the optical performance of 3 silicone IOLs (LI61U, Bausch & Lomb; Tecnis Z9000, Advanced Medical Optics; and a new aberration-free IOL [SofPort AO, Bausch & Lomb]) in an experimental model eye. The study was done using pupil diameters of 3.0 mm, 4.0 mm, and 5.0 mm and IOL decentrations of 0 mm, 0.25 mm, 0.50 mm, 0.75 mm, and 1.00 mm. The modulation transfer functions were computed and plotted. A Monte Carlo simulation analysis with 1000 trials with IOL decentration randomly varying for each pupil size was performed. Decentration of LI61U and Tecnis Z9000 IOLs led to asymmetrical higher-order aberrations that adversely affected the optical performance of the model eye; performance was not affected with the aberration-free IOL because it lacks inherent spherical aberration. Optical performance with the aberration-free IOL was better than with the LI61U IOL as the former has less spherical aberration and did not introduce other aberrations when decentered. Performance with the aberration-free IOL was better than with the Tecnis Z9000 IOL for 3.0 mm, 4.0 mm, and 5.0 mm pupils when decentration exceeded 0.15 mm, 0.30 mm, and 0.38 mm, respectively. Performance with the LI61U IOL was better than with the Tecnis Z9000 IOL for 3.0 mm, 4.0 mm, and 5.0 mm pupils when decentration exceeded 0.3 mm, 0.5 mm, and 0.5 mm, respectively. Monte Carlo simulations showed the expected postoperative results of the LI61U IOL and aberration-free IOL would be repeatable and predictable, whereas the outcomes with the Tecnis Z9000 IOL would vary widely. The optical performance of the model eye was not affected by decentration of an aspheric IOL designed to have no inherent spherical aberration. With decentration, the performance with the new IOL was better than with a conventional spherical IOL and an aspheric IOL designed to offset the spherical aberration of an average cornea.

Imaging of Silicon Naphthalocyanine in Toluene

AbstractPulsed-laser shadowgraphs and images of scattered light are combined with limiting and scattering data to build a model of the response of silicon napthalocyanine (SiNc) at concentrations on the order of 10−3 M in toluene to 12–16 ns 532 nm laser pulses over an energy range from 10 nJ to 2 mJ. The inherent spherical aberration induced by the sample has a profound effect on the response. The scattering is extremely intense above pulse energies of 100 μJ. The data indicates the response at pulse energies below 300 mJ is due to reverse saturable absorption. Full absorbance is not observed until the agglomerates vaporize. At fluences approaching 1 J/cm2 a plasma begins to form and the liquid near the window starts to boil. Intense scatter from the boiling liquid combined with plasma absorption produces hard clamping.

A Gregorian corrector for spherical reflectors

The inherent spherical aberration of a spherical reflector antenna is corrected by using an auxiliary Gregorian reflector feed system that rotates about the center of curvature of the reflector. Tests at both X - and K -band frequencies demonstrate feasibility of the design for wide-angle scanning.

Wide-angle scanning with microwave double-layer pillboxes

The double-layer pillbox is a microwave parallel-plate system in which the image space and the object space relative to a two-dimensional internal reflector are electrically separated by a metal septum. The double-layer prevents the shadowing effects and impedance mismatch that result in a single-layer pillbox when energy from the reflector reenters the primary feed. It also allows correction of the optical aberrations of the system in the image space, the object space, or both. The pillbox with semicircular reflector has wide-angle scanning properties. Its inherent spherical aberration can be reduced by such elements as dielectric lenses, geodesic contours, quasi point-source feeds, and auxiliary reflectors. These techniques have been applied to the construction of pillboxes whose wide-angle scanning properties and improved radiation characteristics substantiate the theory.

Apparatus for Determining Spherical Aberration of Convex Surface of Paraboloid of Revolution

In the production of 60-inch anti-aircraft searchlight reflectors by the electroforming process, convex parabolic forms are used as molds. To avoid production of reflectors with excessive spherical aberration, it is necessary to know the inherent spherical aberration of each mold. To obtain this information, an apparatus has been devised to measure the spherical aberrations of the convex surface of a paraboloid of revolution. The optical system of the apparatus consists essentially of a collimator, a plane mirror, and a photographic plate used in the following manner. A narrow beam of light parallel to the optical axis of the mold to be tested is projected from the collimator onto a designated spot of a particular zone on the mold which is in a horizontal position. The beam of light is reflected from the mold as if it were coming from the virtual focus for the designated spot. The reflected light strikes the plane mirror, vertically placed in a predetermined position and is re-reflected so that the beam of light intersects the optical axis of the mold at a distance above the mold equal to the focal length for the designated spot in the mold being examined. The photographic plate is placed horizontally at a distance above the mold equal to the nominal focal length of the mold. The beam of light intercepts the photographic plate and produces a specified image. Eight such images are photographed on one plate at equally spaced intervals around the periphery of the zone being tested. A required number of zones are tested. Simple interpretation of the photographs yield the amount of aberration present. An important feature of this apparatus is that the interpretations of the photographs are identical to those obtained for testing concave parabolic reflectors. This apparatus aids reflector production in that it determines the abberation characteristics of the convex mold directly, thus eliminating the previous practice of making a reflector from a mold to determine the mold’s accuracy indirectly.