Designing DWDM multiplexers on SiON wafers

The popular treatment of cloudy eyes (cataracts) replaces the cloudy natural lens with an artificial intraocular lens (IOL). The spherical and chromatic aberration are the main factors that affect the IOL image quality. This paper uses hybrid (refractive-diffractive) intraocular lenses with an aspherical surface to minimize chromatic and spherical aberrations. Three types of hybrid IOLs are selected to replace the eye crystal lens, and their performances are evaluated and compared with the healthy eye, based on the results estimated from Liou and Brennan eye model (LBEM). The vision is assessed by calculating the polychromatic modulation transfer function (MTF), the point spread function (PSF), the longitudinal chromatic aberration (LchC), and the encircled energy (EE) using the ray-tracing Zemax program. The results indicate that the polychromatic vision with PMMA hybrid IOL gives the best optical performance compared with other hybrid IOLs and provides a magnitude of (LchC) comparable with a healthy eye.

Focusing of ultrashort light pulses with single lenses is analyzed by taking into account the unavoidable interplay between chromatic and spherical aberration simultaneously for the first time to our knowledge. The spatial intensity distribution is mainly affected by spherical aberration, whereas the temporal distribution is determined by both aberrations. The impact on second-harmonic generation for femtosecond pulse measurements is discussed. For example, the presence of spherical aberration allows one to record the correct autocorrelation of a 10-fs pulse even if chromatic aberration alone would cause a half-width of the autocorrelation function of 40 fs.

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In this work, Point Spread Function (PSF) for triangular aperture was studied, in case of ideal optical system, also in case of presence first order aberrations )focal error and tilt aberration) and third order aberrations (spherical ,coma, and astigmatism aberrations) individually, and for the same values of aberration factor )W=0.1λ …..0.5 λ ) for angle of rotation (ѱ =0). First order aberrations were added to third order aberrations, to obtain the best balance and to reduce the curve width of the (PSF), and to increase the Strehl ratio, like adding a tilt aberration to the coma aberration and adding focal error to spherical aberration and astigmatism aberration. There are some aberrations effects impact negatively on point spread function, such as focal error with coma aberration and tilt aberration with spherical aberration.

An infrared-optical zoom system using binary element is proposed in this paper. The two main advantages of the zoom system introducing here are: bigger F-number and lower cost. The primary optical properties are: F/#=1,zoom ratio =1:4,and dual field are 26.6°and 5.6°respectively. Wider field of view is used for search and the smaller one is used for imaging details. This system uses un-cooled infrared detector with 320×240 pixels and 45μm pixel size. The F-number matches the sensitivity range of the detector array. Three aspects are considered during design process to make the system more satisfactory and more achievable. First, the manner of zoom is accomplished by exchanging tow lenses into the smaller field of view system layout. The lens exchange manner faces the requirement of simple system structure and good image quality in both focal points. It can also make the system more feasible in the alignment process than mechanical-zooming manner and optical-zooming manner; Second, binary element is used to correct the chromatical aberration by taking the advantage of negative dispersion characteristics and the cost of the system is lower than that of conventional ones with Zinc Selenide (Znse) material at the same level. In the binary element is rotational symmetric with one step which is easy to fabricate; Others, in order to balance 5th spherical aberration, 5th coma aberration and 5th astigmatic aberration, high-order asphere surfaces with 2th order to 10thorder are also hired in the system. Asphere surface is useful in compressing the system and improving optical system transmittance. This kind asphere surface is on industrial level featuring low cost and easy to fabricate. It is shown that good image quality can achieved by implementing five Germanium lenses and the transmittance of system is 72%. All aberrations are diffraction-limited, both spherical aberration and astigmatic aberration are corrected. When the field of view(FOV) is 26.6°and the focal length is 152mm, MTF at Nyquist frequency(11lp/mm) is great than 0.7. The spherical aberration is -0.0073. The coma aberration is 0.0978 and the astigmatic aberration is -0.013. When the field of view(FOV) is 5.6°and the focal length is 38mm, MTF at Nyquist frequency is great than 0.8 with spherical aberration -0.0046,the coma aberration 0.055 and astigmatic aberration 0.034.

SummaryRelative modulation transfer is defined as contrast sensitivity under blur normalised to contrast sensitivity at optimum focus. Measured relative modulation transfer exceeds relative modulation transfer as calculated for aberration free optics at higher spatial frequencies (>2 cpd). The contribution of spherical aberration to this discrepancy was studied. In the case of positive blur, spherical aberration increases relative modulation transfer for spatial frequencies of approximately 4 cpd and over. However, spherical aberration does not explain the entire difference between measured and calculated relative modulation transfer. Chromatic aberration does not provide a noticeable additional explanation. With negative blur, spherical aberration increases the relative modulation transfer much more. The effect of other monochromatic aberrations on relative modulation transfer is discussed.

For the transmission electron aberration-corrected microscope (TEAM) initiative of five U.S. Department of Energy laboratories in the United States, a correction system for the simultaneous compensation of the primary axial aberrations, the spherical aberration Cs, and the chromatic aberration Cc has been developed and successfully installed. The performance of the resulting Cc /Cs-corrected TEAM instrument has been investigated thoroughly. A significant improvement of the linear contrast transfer can be demonstrated. The information about the instrument one obtains using Young's fringe method is compared for uncorrected, Cs-corrected, and Cc /Cs-corrected instruments. The experimental results agree well with simulations. The conclusions might be useful to others in understanding the process of image formation in a Cc /Cs-corrected transmission electron microscope.

Measuring and correcting aberrations of a cathode objective lens

In general, the correction of cemented doublets is based on the convergence condition and the correction of spherical and chromatic aberrations. This can be achieved by a suitable assignation of values to the lenses radii. Moreover, if during the correction process a change of glass is introduced, it is possible for another aberration to be in tolerance. The result is a two lens system which, in spite of its simplicity, is free of many aberrations. The current presentation describes a method to obtain aplanatic cemented doublets, with the spherical, coma, and chromatic aberrations in tolerance, by an appropriate selection of glasses before the project. Some maps of glasses with lines which provide this election are presented. These lines are valid for both telescope and microscope objectives. Besides, with this method it is possible to easily project aplanatic cemented doublets with a residual value of the spherical aberration. Finally, it is also shown that certain combinations of glasses are impossible to be corrected simultaneously of spherical and chromatic aberrations.

Spherical and chromatic aberration coefficients Cs and C of various immersion lenses forlow voltage SEM and LEEM are calculated. The minimun values of magnetic immersion lens are C5Cl mm. For the combined electrostatic and magnetic lenses, those values are at most C5=1 mm and CO.7 mm, when the specimen is free from the electrostatic field. Whenthe specimen is immersed in the electrostatic field, those values reduce to C50.2 mm and Cc=o.1 mm at 1 kV. Key words: SEM, LEEM, Objective lens, Spherical aberration, Chromatic aberration, Immersion lens, Cathode lens, Computer aided design 1. INTRODUCTION Importance of low accelerating voltage in scanning electron microscopy (SEM) increasesrecently for semiconductor and biological applications. A main difficulty of low voltage SEM(LVSEM) is its low spacial resolution due to the increase of the wave length and the increaseof AVIV0 ratio where AV is the energy spread and V0 the incident energy. The immersionobjective lens as well as the field emission electron gun is very useful in realizing the highresolution LVSEM. Low energy electron microscopy (LEEM) instruments are very useful forsurface studies of metals and semiconductors. The electrostatic immersion objective lensis essentially necessary for LEEM to get a low landing voltage and low aberrations.There are three kind of immersion lenses: the magnetic immersion lens, the retardingelectrostatic immersion lens and the combination of immersion electrostatic and magneticlenses. The latter two lenses are reviewed by Mullerova and Lenc (1992)1. Here we have to

Chromatic and spherical aberration correction with hexapole and quadrupole fields.

For the middle wave 640×512 cooled thermal IR focal plane array with 15 μm pixel pitch, a design of 3.7～4.8 μm refractive infrared switchable dual-field-of-view imaging system is described, which makes use of a mechanical holder to switch two lenses into and out of the whole optical system to change the focal length from 45mm to 135mm. The system includes a telescope and a relay sub-system to avoid vignetting caused by the presence of the cold shield. Preliminary calculations are carried out first to determine the focal powers and first-order parameters of each lens and then the aberration equations are solved to achieve the initial configuration of the system as the starting point. During the optimization, in order to correct varied aberrations, such as spherical aberrations, coma, astigmatism, and chromatic aberrations, more lenses, glasses and aspherical surfaces are employed. In consideration of decreasing the manufacture cost and fabrication difficulties, only germ, silicon and one ZnS single lens are allowed to make use of, and the highest order of aspherical coefficients is no more than 8 th . Meanwhile, the separation between the two lenses fixed in the mechanical holder must be controlled strictly to make sure no ray will be obscured by them when they are switched out of the system. Between the telescope and the relay system, the relay system and the image plane, there are two mirrors to fold the system, so reserved space must be valued in the optical path. Finally, a total of ten lenses with two aspherical surfaces and two mirrors are used in the design, making the system cost effective and compact. At the end, the design results are given. The modulation transfer function (MTF) of each field-of-view is above 0.5 in all focal positions at the spatial frequency of 33lp/mm, which approaches the diffraction limits and the energy permeance ratio is greater than 80%, showing excellent performance.

To measure and compare the optical quality of spherical and aspheric toric intraocular lenses (IOLs). Wavefront aberrations of AcrySof Toric and IQ Toric IOLs (Alcon Laboratories) for different powers were measured at 3- and 5-mm pupils by Nimo TR0805 instrument. The Zernike coefficients of trefoil, coma, tetrafoil, secondary astigmatism, and spherical aberration were evaluated. The point spread functions (PSFs) of each IOL evaluated were calculated from the wavefront aberrations. The PSF images also were calculated from the IOL wavefront aberrations, adding the cornea's aberrations to simulate the optical quality after their implantation. Spherical toric IOLs showed positive and aspheric toric IOLs negative spherical aberrations. Statistically significant differences were found in spherical aberration root mean square (RMS) values between spherical and aspheric IOLs for both pupil sizes (p<0.05). Aspheric toric IOLs showed higher spherical aberration RMS values. We found differences in PSF images between both IOL designs at 5-mm pupil. The PSFs corresponding to the aspheric toric IOLs showed more spread out than the PSFs corresponding to the spherical toric IOLs. However, when corneal aberrations were added, aspheric toric IOLs showed better optical quality than spherical toric IOLs. At 3-mm pupil, the optical quality between the IOL designs was similar, but at 5-mm pupil the optical quality was higher for spherical IOLs than aspheric IOLs. However, when theoretical corneal aberrations were added, aspheric toric IOLs showed better optical quality than spherical toric IOLs, due to the compensation between aspheric toric IOL negative spherical aberration and corneal positive spherical aberration.

Background: Rigid gas permeable (RGP) and silicone hydrogel (SH) contact lenses with specific designs are currently being used to improve visual function in patients with keratoconus. However, there are minimal data available comparing the effects of these lenses on visual function in patients with keratoconus. The objectives of this study were to compare visual acuity and contrast sensitivity using spectacles, RGP lenses, and SH lenses, and to evaluate the effects of RGP and SH lenses on higher-order aberrations and visual quality in eyes with keratoconus. The relationship between visual outcomes, aberration, and visual quality were also examined. Methods: This was a pilot study involving 13 eyes from nine subjects with keratoconus. Subjects were fitted with RGP and SH contact lenses. Visual acuity and contrast sensitivity were measured using Snellen and Pelli-Robson charts, respectively. Ocular aberrations and visual quality were measured using an OPD-Scan II device. All measurements were conducted before and after contact lens wear. Results: Significantly better visual acuity was obtained with RGP lenses than with spectacles or SH lenses ( P <0.001). No significant difference in contrast sensitivity values was detected between RGP and SH lenses ( P =0.06). Both SH and RGP lenses significantly reduced total ocular and higher-order aberrations ( P <0.001) when compared with spectacles, but RGP lenses reduced trefoil, coma, and spherical aberrations more than SH lenses. No significant difference in astigmatic aberrations was found between RGP and SH lenses ( P =0.12). Negative correlations were found between visual acuity and coma aberration and contrast sensitivity with higher-order aberrations and coma, trefoil, and astigmatic aberrations. Regarding visual quality, no significant difference was found between RGP and SH lenses, but RGP significantly improved visual quality when compared with spectacles ( P =0.04). Conclusion: RGP lenses provided better visual acuity and greater reduction of aberrations than spectacles or SH lenses in patients with keratoconus. However, more data are needed to confirm these findings. Keywords: visual acuity, contrast sensitivity, aberration, visual quality, keratoconus

Optical systems with integrated tunable lenses allow for rapid axial-scanning without mechanical translation of the components. However, changing the power of the tunable lens typically upsets aberration balancing across the system, introducing spherical and chromatic aberrations that limit the usable axial range. This study develops an analytical approximation for the tuning-induced spherical and axial chromatic aberration of a general optical system containing a tunable lens element. The resulting model indicates that systems can be simultaneously corrected for both tuning-induced spherical and chromatic aberrations by controlling the lateral magnification, coma, and pupil lateral color prior to the tunable surface. These insights are then used to design a realizable axial-scanning microscope system with a high numerical aperture and diffraction-limited performance over a wide field of view and deep axial range.