Diffractive Micro-optical Elements Research Articles

Non-dispersion boundary conditions of micro-optical element illuminated by broadband light source

With the development of the microstructure fabrication process and the integration of micro-optical elements, diffractive micro-optical elements are widely used in broadband light sources, such as the integrated light guide plate (ILGP). And with the structural feature size of the ILGP decreasing from tens of microns to microns and even sub-microns, the diffraction dispersion phenomenon will inevitably become a prominent problem in research and design of non-dispersion elements. Nevertheless, under the broadband light source illumination, the analysis of the dispersion characteristic of diffraction spectrum of the microstructure array has not been reported in detail. Therefore a theoretical model of micro-optical element with a typical one-dimensional rectangular phase grating (RPG) and a widely used white LED source is established in this paper. The dispersion characteristic of the diffraction spectrum is studied, that is, with the increase of period of the RGP or the cone angle of incident beam, the dispersion of diffraction spectrum weakens. Dispersion parameter C and its formula are proposed, which can precisely measure the chromatic dispersion degree of the diffraction spectrum. Furthermore, the boundary criterion point of non-dispersion <i>C</i> = 0.3 is given explicitly. It is explored that no matter whether the cone angle of incident beam or the RPG period increases, the non-dispersion output light can be obtained only by matching the two parameters to make the dispersion parameter <i>C</i> less than 0.3. Then an RPG sample, of which the structural parameters are consistent with the designed ones, is fabricated by using micro-nano processing technology. By changing the cone angle of incident beam, the luminance and the chromaticity coordinates of the diffraction beam are tested. The analyses of the test results of the fabricated RPG sample show that the spectrum dispersion regularity is in accord with the theoretical analysis. The consistency verifies the correctness of dispersion parameter <i>C</i>, its formula and the non-dispersion boundary criterion point. The dispersion parameter <i>C</i> and non-dispersion boundary criterion point presented in this paper provide a guidance for analyzing the dispersion characteristics when the structural parameters of the integrated light guide plate and other broadband micro-optical element are designed.

Soft glasses for photonic crystal fibers and microstructured optical components

Thermally stable tellurite, lead-bismuth-gallium oxides based boron-silicate and lead-silicate glasses dedicated for multiple thermal processing are presented. The glasses are successfully used for the development of photonic crystal fibers, nanostructured gradient index lenses, all-solid microstructured fibers as well as refractive or diffractive micro-optical elements with ultra-broadband transmission.

Tunable protein harmonic diffractive micro-optical elements

Herein, tunable protein harmonic diffractive microlenses (PHDMs) have been constructed by femtosecond laser direct writing from bovine serum albumin. With excellent three-dimensional topography, PHDMs show distinct harmonic diffractive features, such as similarly good imaging performance with smaller thickness than refractive lenses and well controlled minus chromatic dispersion compared with simple diffractive lenses (∼5% focal length shift against ∼21% of the protein Fresnel zone plate with the same radius under light with wavelength 450-659 nm). Owing to the nature of protein molecules as "building blocks," the focal length of the PHDM can be facilely tuned within seconds by changing the pH value (focal length tunability of up to ∼20%).

Wafer-scale micro-optics fabrication

Abstract Micro-optics is an indispensable key enabling technology for many products and applications today. Probably the most prestigious examples are the diffractive light shaping elements used in high-end DUV lithography steppers. Highly-efficient refractive and diffractive micro-optical elements are used for precise beam and pupil shaping. Micro-optics had a major impact on the reduction of aberrations and diffraction effects in projection lithography, allowing a resolution enhancement from 250 nm to 45 nm within the past decade. Micro-optics also plays a decisive role in medical devices (endoscopes, ophthalmology), in all laser-based devices and fiber communication networks, bringing high-speed internet to our homes. Even our modern smart phones contain a variety of micro-optical elements. For example, LED flash light shaping elements, the secondary camera, ambient light and proximity sensors. Wherever light is involved, micro-optics offers the chance to further miniaturize a device, to improve its performance, or to reduce manufacturing and packaging costs. Wafer-scale micro-optics fabrication is based on technology established by the semiconductor industry. Thousands of components are fabricated in parallel on a wafer. This review paper recapitulates major steps and inventions in wafer-scale micro-optics technology. The state-of-the-art of fabrication, testing and packaging technology is summarized.

Diffractive micro-optical elements for implementing hollow beam and bi-focus simultaneously

We design diffractive micro-optical elements (DMOEs) with sub-wavelength characteristic size based on a half- π-phase shifting scheme, with the aim of realizing a hollow beam and bi-focus simultaneously. The optical properties of DMOEs, such as the positions of the real focal planes, the aspect ratio of the hollow beam and the diffraction efficiency, are investigated by using the rigorous electromagnetic theory and the boundary element method. The numerical results show that a well-defined hollow beam and bi-focus are achieved simultaneously. Further analysis of the interference between dual-DMOE shows that the interference is much less than that of a conventional dual-microlens. It is indicated that the designed micro-optical element array can not only implement hollow beam and dual focus, but also suppress the interference effect significantly.

Application of an approximate vectorial diffraction model to analysing diffractive micro-optical elements

Scalar diffraction theory, although simple and efficient, is too rough for analysing diffractive micro-optical elements. Rigorous vectorial diffraction theory requires extensive numerical efforts and is not a convenient design tool. In this paper we employ a simple approximate vectorial diffraction model which combines the principle of the scalar diffraction theory with an approximate local field model to analyse the diffraction of optical waves by some typical two-dimensional diffractive micro-optical elements. The TE and TM polarization modes are both considered. We have found that the approximate vectorial diffraction model can agree much better with the rigorous electromagnetic simulation results than the scalar diffraction theory for these micro-optical elements.

Design and fabrication of continuous-profile diffractive micro-optical elements as a beam splitter

An optimization algorithm that combines a rigorous electromagnetic computation model with an effective iterative method is utilized to design diffractive micro-optical elements that exhibit fast convergence and better design quality. The design example is a two-dimensional 1-to-2 beam splitter that can symmetrically generate two focal lines separated by 80 microm at the observation plane with a small angle separation of +/- 16 degrees. Experimental results are presented for an element with continuous profiles fabricated into a monocrystalline silicon substrate that has a width of 160 microm and a focal length of 140 microm at a free-space wavelength of 10.6 microm.

Phase-only optical decryption in a planar integrated micro-optics system

We present a compact optical decryption system using the generalized phase contrast (GPC) method implemented in a planar integrated micro-optical (PO) device. An encrypted phase pattern is deciphered by the application of a decrypting phase key and visualized using a miniaturized implementation of the GPC method. The current proof-of-principle demonstration makes use of a PO device composed of diffractive micro-optical elements to form a 4-f lens imaging setup with a spatial phase-only filter at the Fourier plane. Successful decryption of a 17×9-pixel encrypted phase mask is achieved with high-contrast visualization of the original pattern.

Replication technology for optical microsystems

Replication technology is playing an increasingly important role in the production of optical microsystems and micro-optical elements. Hot embossing, injection moulding and UV-embossing all can produce high-quality optical elements in very cost-effective processes. New sol–gel materials allow the combination of replication with lithography to leave selected areas material-free for sawing and bonding. The development of wafer-scale replication technology using UV-curable sol–gel and polymer materials enables refractive and diffractive micro-optical elements as well as micro-mechanical alignment features to be replicated directly onto glass substrates or onto semiconductor device wafers. Grating nanostructures with linewidths less than 100nm have been replicated into polymer and sol–gel materials for the cost-effective fabrication of large area subwavelength structures for applications such as polarisers and buried grating security features.

Iterative optimization algorithm based on electromagnetic model for designing diffractive micro-optical elements

An iterative optimization algorithm for designing two dimensions, finite aperture, aperiodic diffractive micro-optical elements based on rigorous electromagnetic computation model––the finite-difference time-domain method has been proposed. All aspects relating to the algorithm such as the finite-difference time-domain method, and the optimization process have been discussed in detail. Without any approximation based on scalar theory, the algorithm can present rigorous design results with reasonable computational cost. An aspherical surface lens and four kinds of off-axis lenses for normally incident TE mode have been designed to illustrate our algorithm. Meanwhile, we also consider the influence of quantized-lenses profiles on their diffraction performance.

Electromagnetic effects for the resonance-domain IR diffractive optics

Binary optics technology enables the manufacture of arrays of diffractive micro-optical elements which are used in many optoelectronic devices, e.g. the focal plane collection optics. The first-order diffraction grating efficiency decreases in the best part of the resonance-domain region of diffraction, i.e. when the grating period is close to the optical wavelength in the substrate material. A large fraction of the fast binary lens surface relief is built of staircase annular structures whose width is of wavelength scale. Therefore, the rigorous electromagnetic theory of gratings has been applied in this paper to calculate and analyze the diffraction effects for the resonance-domain longwave (8–12 μm) infrared (LWIR) binary optics. It is shown that electromagnetic effects limit the speed of the LWIR first-order diffractive lenses and the optical gain achievable with the diffractive lenses used as the focal plane collection optics in the IR detection systems.

Simple technique for replication of micro-optical elements

Keywords: microlens ; replication ; micro-optics Reference EPFL-ARTICLE-183156doi:10.1117/1.601799 Record created on 2013-01-17, modified on 2017-05-10

Sol-Gel Prepared Glass for Refractive and Diffractive Micro-Optical Elements and Arrays

The fast sol-gel method enables facile preparation of siloxane-based glassy matrices, in which polymerization is completed within minutes and volume changes 10 mm thick. Minimizing shrinkage and enabling relaxation of the drying sol-gel are key factors in the elimination of cracking. These features and the resulting optical quality of the glass make this method technologically and economically attractive for replication-produced micro-lenses and micro-optical arrays.