Apodized multilevel diffractive lenses that produce desired diffraction-limited focal spots

An apodized, multilevel diffractive lens that can produce a desired diffraction-limited focal spot is proposed for many applications, such as focusing, imaging, optical storage, and optical trapping. The three key points for the design are the innovative idea of complex conjugate subzones, the use of Babinet's principle, and the equivalent-pupil (or aperture) function theory of diffractive focusing elements composed of concentric transparent rings. As a concrete example, we numerically design a mixed multilevel diffractive lens (the highest phase level is 8) to produce a diffraction-limited Gaussian focal spot. Some related problems, such as the validity range and the combination with high-numerical-aperture refractive lenses, are also discussed.     

Design and tolerancing of achromatic and anastigmatic diffractive-refractive lens systems compared with equivalent conventional lens systems

Since focal diffractive optics have been introduced, designing them has flourished, particularly as the manufacturing technology has developed to meet the performance requirements. My purpose is to introduce to hybrid diffractive-refractive optical systems not only the design procedure but also the optical and the mechanical aspects of optical tolerancing. A comparison is made with equivalent conventional (purely refractive) systems in the visible wave band (rather than the infrared wave band where there are many published designs) to seek advantages and disadvantages that systems with diffractive optics bring. The results of tolerancing comparisons show that for small-field systems the introduction of diffractive components has a powerful desensitizing effect, whereas for a wide-field anastigmatic system that has been investigated the desensitization effect of the inclusion of diffractive surfaces is less marked. These results come mainly from the fact that an achromatizing diffractive surface has little focal power, whereas an achromatizing refractive component has to have a large focal power.     

Reduction of the spherical aberration effect in high-numerical-aperture optical scanning instruments

In modern high-numerical-aperture (NA) optical scanning instruments, such as scanning microscopes, optical data storage systems, or laser trapping technology, the beam emerging from the high-NA objective focuses deeply through an interface between two media of different refractive index. Such a refractive index mismatch introduces an important amount of spherical aberration, which increases dynamically when scanning at increasing depths. This effect strongly degrades the instrument performance. Although in the past few years many different techniques have been reported to reduce the spherical aberration effect, no optimum solution has been found. Here we concentrate on a technique whose main feature is its simplicity. We refer to the use of purely absorbing beam-shaping elements, which with a minimum modification of optical architecture will allow a significant reduction of the spherical aberration effect. Specifically, we will show that an adequately designed reversed-Gaussian aperture permits the production of a focal spot whose form changes very slowly with the spherical aberration.     

Transition between diffractive and refractive micro-optical components

Optical components are usually classified into diffractive and refractive elements. In this classification, refractive components are defined as elements that are sufficiently described by geometrical optics. For micro-optics this distinction is very often not applicable. Our goal is to understand which parameters control the transition from elements that can be interpreted as refractive to those elements that are called diffractive. We investigate the linear blazed grating and focus on the wavelength dependence of its properties. For this we adopt an approach well known from the theory of echelette gratings. Our results can easily be transferred to other blazed components, such as Fresnel lenses.     

Photon-sieve lithography

We present the first lithography results that use high-numerical-aperture photon sieves as focusing elements in a scanning-optical-beam-lithography system [J. Vac. Sci. Technol. B 21, 2810 (2003)]. Photon sieves are novel optical elements that offer the advantages of higher resolution and improved image contrast compared with traditional diffractive optics such as zone plates [Nature 414, 184 (2001)]. We fabricated the highest-numerical-aperture photon sieves reported to date and experimentally verified their focusing characteristics. We propose two new designs of the photon sieve that have the potential to significantly increase focusing efficiency.     

Diffractive,refractive optics or anything more? Comparative analysis and trends of development

Abstract

The development of diffractive and refractive optics from ancient times (2000 years ago) to the present is traced from a theoretical and practical point of view. A comparative analysis of the possibilities of the two fields in optics is presented. The possibility for achromatization and corrections that exceed the boundary of diffractive and refractive optical elements is pointed out.     

Integrated diffractive andrefractive elements for spectrum shaping

Diffractive elements can be designed for spectrum shaping in the Fourier or Fresnel plane by iterative methods. It is necessary to use a Fourier lens and the wavelength for which the diffractive elements were designed to get the required spectrum shaping at the Fourier plane. Using a different wavelength will cause chromatic aberration. We deal with the combination of refractive and diffractive elements and two or more different diffractive elements on the same element to get appropriate beam shaping of light sources with a multiple spectral output. Simulations are preformed that transform the profile of a He-Ne laser with a Nd:YAG laser source, and shape the trapezoidal beam profile of an excimer laser into a Gaussian beam is also considered.     

对衍射光学元件温度特性的研究

大多数空间光学仪器的工作环境温度变化范围都较大。对折射元件和衍射元件的温度特性进行了分析,建立了透镜焦距和衍射效率随环境温度的变化关系,并论述了利用衍射光学元件的温度特性实现光学系统消热差的原理和设计方法。     

Two-dimensionally-periodic diffractive optical elements: limitations of scalar analysis

The range of validity of the scalar diffraction analysis is quantified for the case of two-dimensionally-periodic diffractive optical elements (crossed gratings). Three canonical classes of two-dimensionally-periodic grating structures are analyzed by using the rigorous coupled-wave analysis as well as the scalar diffraction analysis. In all cases the scalar-analysis diffraction efficiencies are compared with the exact diffraction efficiencies. The error in using the scalar analysis is then determined as a function of the grating-period(s)-to-wavelength ratio(s), the minimum feature size, the grating depth, the refractive index of the grating, the incident polarization, and the number of phase levels. The three classes of two-dimensional (2-D) unit cells are as follows: (1) a rectangular pillar, (2) an elliptical pillar, and (3) an arbitrarily pixellated multilevel 2-D unit cell that is representative of more complicated diffractive optical elements such as computer-generated holograms. In all cases a normally incident electromagnetic plane wave is considered. It is shown that the error of the scalar diffraction analysis in the case of two-dimensionally-periodic diffractive optical elements is greater than that for the corresponding one-dimensionally-periodic counterparts. In addition, the accuracy of the scalar diffraction analysis degrades with increasing refractive index, grating thickness, and asymmetry of the 2-D unit cell and with decreasing grating-period-to-wavelength ratio and feature size.     

Diffractive element design for resonant scanner angular correction: a beam retardation approach

A new approach for designing diffractive optical corrective elements with zooming capability to convert nonlinear sinusoidal scanning into linear scanning is proposed. Such a device will be useful for linearizing the angular scan of a resonant mirror scanner. The design methodology is to create a graded index of a refraction device as the reference design with its index of refraction parameters based on beam retardation through propagation in an inhomogeneous medium. The diffractive element is designed by utilizing a binarizing algorithm of the accumulated phase from transmission through the refractive element. In contrast to a prior approach, which was introduced based on the beam propagation through inhomogeneous media, the new approach takes beam diameters into consideration. This makes both the refractive element and its associated diffractive element more robust against beam fanning.     

Diffractive-refractive behavior of kinoform lenses

The connection between the diffractive behavior and the refractive behavior of kinoform lenses is investigated. The image-forming capabilities of the diffractive element are found to be expressed as an interference pattern that is due to a set of associated refractive lenses corresponding to each zone of the kinoform. The coefficient modulating the contribution of each refracting zone is determined. The term linking the point-spread function of a refractive lens and a diffractive lens is also obtained. Spectral and spatial aspects are compared as the diffractive element approaches the refractive limit.     

Compact wavelength division multiplexers and demultiplexers

Compact devices for wavelength division multiplexing and demultiplexing, believed to be novel, are presented. These devices are based on planar optics configurations, comprising multiplexed diffractive optical elements. The principle, design, and recording of these planar devices are described, including the fact that the recording is done at a single wavelength in the green region. Experimental procedures and results for planar devices that can handle three wavelengths in the visible as well as in the near infrared are presented.     

Coupling of light from an LED into a thin light guide by diffractive gratings

Ring-shaped and radial diffractive gratings are designed with rigorous diffraction theory to couple light of a nearly monochromatic LED into a thin planar light guide on the bottom side. The theoretical coupling efficiencies for ring-shaped and radial gratings are 41% and 66%, respectively. Optimized diffractive elements are manufactured with direct electron-beam lithography and reactive-ion-etching into SiO2 substrates. Good agreement between experimental and theoretical results for selected radial gratings is reached. Furthermore, the mass production tests using injection molding are carried out with good replicability.     

Focusing of ultrashort laser pulses by the combination of diffractive and refractive elements

Hybrid elements, containing optical power with both diffractive (holographic) and refractive components, are shown to be able to eliminate the effect of propagation time difference. The consideration is provided through a paraxial approximation of diffraction theory.     

Design of diffractive optical elements for multiple wavelengths

A method for producing diffractive optical elements (DOE's) for multiple wavelengths without chromatic aberration is described. These DOE's can be designed for any distinct wavelength. The DOE's are produced from two different optical materials, taking advantage of their different refractive indices and dispersions.     

Planar-optic-disk pickup with diffractive micro-optics

An integrated optical-disk pickup with a diffractive planar micro-optic system is proposed. In this device, the beam follows a zigzag optical path inside a glass substrate that is used as a light guide. To fabricate off-axis diffractive optical elements, we have recently developed an electron-beam writing system with a curve-pattern generator. It is demonstrated that a transmission off-axis objective microlens, a reflection twin-focusing beam splitter, and reflection layers were integrated on a glass substrate, and such a diffractive planar micro-optic system exhibited an excellent focusing performance and operated forfocus-error signal detection, as designed.     

二元光学折/衍混合消色差望远物镜设计

首先从光栅衍射理论出发导出衍射光学元件的色散公式，并进一步推导出用一种材料进行折／衍混合消色差望远物镜设计的公式。最后给出全折射型、一个混合型消色差和一个改进型消色差望远物镜的例子，并进行了比较。结果说明，混合型透镜的性能优于全折射型透镜，而改进型消色差物镜的总体性能优于原混合消色差物镜     

Sapphire-GaN-based planar integrated free-space optical system

We report on the design and fabrication of a planar integrated free-space optical system working on the basis of binary phase diffractive optical elements (DOEs) realized in GaN on a sapphire substrate. Group III-nitride/sapphire substrates enable the parallel monolithic integration of passive microoptical elements like lenses and gratings as demonstrated here and optoelectronic devices like light emitters and photodetectors on a single wafer. We present an approach for the simultaneous optimization of the efficiency of transmissive and reflective diffractive optical elements processed in a single lithographic etching step.     

Implementation of ordinary and extraordinary beams interference by application of diffractive optical elements

Abstract

We apply diffractive optical elements in problems of transformation of Bessel beams in a birefringent crystal. Using plane waves expansion we show a significant interference between the ordinary and extraordinary beams due to the energy transfer in the orthogonal transverse components in the nonparaxial mode. A comparative analysis of the merits and lack of diffractive and refractive axicons in problems of formation non-paraxial Bessel beams has shown the preferability of diffractive optics application in crystal optics. The transformation of uniformly polarised Bessel beams in the crystal of Iceland spar in the nonparaxial mode by application of a diffractive axicon is investigated numerically and experimentally.