Focusing anomalies with binary diffractive optical elements.

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.

The design and fabrication of two binary phase diffractive optical elements are presented. We used iterative design procedures and performed numerical two-dimensional Fourier transforms in order to evaluate the reconstruction pattern. Fraunhofer and Fresnel diffraction patterns for the same intensity distribution are compared, using computer simulations. The elements were fabricated by configuring either thermally grown silicon dioxide on silicon substrate or aluminium layers. The experimental results are shown to be close to the results obtained by simulations.

Laser brightness is crucial in many optical processes, and is optimized by high power, high beam quality (low M2) beams. Here we show how to improve the laser beam quality factor (reducing the M2) of arbitrary structured light fields in a lossless manner using continuous phase-only elements, thus allowing for the increase in brightness by a simple linear optical transformation. We demonstrate the principle with four high M2 initial beams, converting each to a Gaussian (M2≈1) with a dramatic increase in brightness of >10×. This work puts a new (to the best of our knowledge) perspective on the old debate of improving laser beam quality with binary diffractive optics, while providing a practical approach to enhancing laser brightness for arbitrary input beams.

A novel technique to improve the focus depth of a Gaussian beam is presented in this paper. The improvement is based on two-step beam shaping using a cascade of binary phase diffractive optical elements (BPDOEs). The first BPDOE transforms the incident Gaussian beam into a high-order radial Laguerre-Gaussian beam (LGp0). Then the second BPDOE rectifies the obtained LGp0 beam and gives rise to a quasi-Gaussian one in the focal plane of a converging lens. This resulting quasi-Gaussian beam exhibits a lower divergence and larger focus depth compared to the pure Gaussian beam having the same beam waist. These results open new possibilities in laser beam manufacturing and micromachining, and in applications that need an extended focus depth.

Near-field shaping with two binary diffractive optical elements in tandem

Holography is a powerful method for achieving 3D images of objects. Extending this method to short wavelengths potentially offers significantly higher resolution than visible light holography. However, current X-ray holography setups employ nanoscale pinholes to form the reference wave. This approach is relatively inefficient and limited to very small sample size. Here, we propose a new setup for X-ray holography based on a binary diffractive optical element (DOE), which forms at the same time the object illumination and the reference wave. This optic is located separately from the sample plane, which permits investigation of larger sample areas. Using an extended test sample, we demonstrate a resolution of 90 nm (half-pitch) at an undulator beamline at BESSY II. The new holography setup can be directly transferred to free electron laser sources enabling time-resolved nanoscale imaging for ultra-fast processes.

Liquid crystal spatial light modulators are used in a wide range of modern problems in science and technology. These modulators are used to control the amplitude, phase, and direction of propagation of coherent optical radiation in optical information processing systems. However, the influence of the characteristics of the temporal dynamics of liquid crystal spatial light modulators on the performance of information optical systems, including diffractive neural networks, has not been sufficiently studied. The article presents the results of a study of the temporal dynamics of phase modulation of the liquid crystal spatial light modulator SLM-200 (Santec, Japan). Computer-synthesized binary phase diffractive optical elements were used in the experiments, and the characteristics of the temporal dynamics of the optical modulator were measured: 125 ms is the rise time of the diffraction efficiency when displaying diffractive optical elements on the screen; 61.9 ms is the decay time when switching frames. With these characteristics, it is possible to ensure the formation of a variable optical field at a frame display frequency of 2 Hz with an interference level of –17.1 dB. Increasing the frame display frequency leads to the appearance of unavoidable interframe interference, which in turn limits the effective performance of the information system. The results obtained can be useful in designing high-performance optical information processing systems and diffraction neural networks

Many optical systems used in the infrared spectrum have, so far, adopted binary optical elements (BOE) to achieve a better performance. Especially, in the middle and long infrared spectrum, binary optical elements are commonly used. Thus, limited by the manufacture technology, the applications of binary optics in the visible spectrum are rare. This tentative research aims at finding the practicability of applying BOEs in the visible spectrum. We attempted to replace the reference lens group in the interferometer with a harmonic diffractive/refractive hybrid lens group, expecting that the wave aberration be well-corrected. In this paper, the main procedure of designing a hybrid optical system is introduced with an example of “F2” lens group. After the analysis on the interference pattern and wave front, the comparison between the tested result and theoretical result can be made. It demonstrates that the hybrid optical system is capable of being applied in the visible spectrum. The analysis also discloses that raising the diffractive efficiency is the next step for us to take.

Using a laser light source in imaging devices provides a wide color gamut, high brightness, resolution, and efficiency. At the same time, it creates a speckle pattern that deteriorates the image quality. This paper is related to the application of the moving binary code diffractive optical element (DOE) for speckle suppression in a laser display. Analytical optimization of DOE parameters is made in this paper. The optimal DOE pitch is found analytically. Limitation of the DOE code length is shown, and the highest possible code length is estimated. Application of the compound Barker code for the DOE design is suggested. As an alternative, the M-sequence and minimum peak side-lobe codes are considered. The expected residual speckle contrast ratio after application of those codes is estimated for the number of codes. A comparison of the different codes is done, and recommendations for speckle suppression DOE design are provided.

The liquid crystal spatial light modulator (SLM) is an effective active beam-shaping device through adjusting each pixel transmittance to improve the spatial beam quality of the output laser, which can also be used as a binary optical element (BOE) with each pixel transmittance 0 or 1 to realize spatial beam shaping for high-power lasers. We present and demonstrate an efficient shaping method of the SLM used as BOE based on diffraction principle. The method can be used to control the output nearfield actively by compensating the spatial nonuniformity of transmission and amplification in the high-power laser system. Results show the output nearfield beam quality improves significantly after shaping by using this method with the fluence contrast changing from 22% to 11.3% within only two shots in the single-shot operation laser.

Liquid crystal spatial light modulators for precise dynamic manipulation of coherent light fields, used in diffractive optoelectronic optical data processing systems, are considered. This paper presents the results of a study of the temporal dynamics of the HoloEye PLUTO-2 VIS-016 liquid crystal spatial light modulator for analysis of light fields rate modulation. Experiments using binary phase computer generated holograms and binary focusing phase diffractive optical elements were conducted. Based on experimental data, the time characteristics of the modulator response were determined. It was found that when the rise time of the diffraction efficiency was 146 ms after the hologram displaying onto the SLM, and when switching to a new hologram, the decay time was 97 ms. These results allowed the dynamic generation of an alternating holograms at a refresh rate of 2 Hz with an interference level of –16 dB. Increasing the frequency of fringe pattern updates increases the level of interframe noise in the generated holograms, and when updated at the specification frequency, the generated distributions cannot be separated. Determining the actual frame rate based on the rise and decay times of the diffraction efficiency makes it possible to correctly calculate the minimum operating time of an information optical system containing a liquid crystal spatial light modulator.

Binary and continuous phase-only surface relief diffractive optical elements can be fabricated on hybrid sol-gel glass based on a single-step microfabrication process. We report on the fabrication and characterization of an inorganic-organic hybrid SiO2/TiO2 sol-gel glass by UV light exposure. Preliminary results of binary and continuous surface relief structures fabricated on sol-gel glass with UV exposure using holographic technique and a high-energy-beam-sensitive (HEBS) glass mask are demonstrated. The effects of the fabrication parameters such as doping concentration, bake temperature, and UV light exposure time on the film characteristics (thickness and refractive index) are studied.

Recording of binary volumetric diffractive optical elements within a 13 μm thick photosensitive chalcogenide layer using an innovative exposure set-up based on digital micro-mirrors devices is demonstrated. Different examples of beam transformations are shown such as the conversion of Gaussian beam into higher order modes or top-hat beam shapers.

In recent years surface-relief Diffractive Optical Elements (DOEs), a specialized class of diffractive optical elements, have revolutionized design of optical systems and instruments. Surface-relief diffractive optical components improve performance of the existing optical systems and increase systems compactness and reliability. Surface-relief DOEs can be fabricated as multilevel binary optical elements, or as continuous surface-relief optical elements. A surface-relief DOE is being designed such that incident light interacts with the topography of the surface-relief microstructure including the size and shape characteristics of surface profile features such as indentations and projections as well as their dimensional relationship, to perform a desired optical function. Binary optical elements are being made by the same microlithographic and ion etching techniques used to produce VLSI circuits. Computer-generated continuous surface-relief DOE is recorded by direct laser-beam or e-beam writing in photoresist. Continuous surface-relief DOE can be also recorded in photoresist by interferometric (holographic) technique. After development recorded in photoresist surface-relief microstructures are being ion-beam etched into quartz or other inorganic optical substrates.

Binary optical elements are finding increased use in a wide range of applications. Fabrication of binary optical elements generally remains a time consuming and expensive process. Even in high volume, costs can be prohibitive, especially for elements larger than a few millimeters in diameter. Replications techniques, such as injection molding, have recently begun to show promise as a means of manufacturing binary optical elements, and doing so at a significant cost reduction over conventional photolithographic means. We report on recent improvements in the application of injection molding techniques to the replication of binary optical elements. Several examples of binary elements fabricated by these techniques, as well as present process capability, will be discussed.