Rotational varifocal moiré metalens made of single-crystal silicon meta-atoms for visible wavelengths

Metasurface lenses (metalenses) offer an ultrathin and simple optical system with dynamic functions that include focal length tuning. In this study, a rotational varifocal (i.e., moiré) metalens based on octagonal single-crystal silicon pillars was designed and fabricated to realize a high transmittance, whole 2π phase coverage, and polarization insensitivity for visible wavelengths. The moiré metalens consists of a pair of cascaded metasurface-based phase lattices and the focal length can be adjusted from negative to positive by mutual rotation. The fabricated moiré metalens demonstrated a focal length that can be tuned from −36 mm to −2 mm and from 2 to 12 mm by mutual rotation from −90° to 90°, and the experimental measurements agreed well with theoretical values at the design wavelength of 633 nm. Imaging was demonstrated at three distinct wavelengths of 633, 532, and 440 nm.

Optical Hydrogel Detector for pH Measurements

Measuring pH has become a major key for determining health conditions, and food safety. The traditional pH assessment approaches are costly and offer low sensitivity. Here, a novel pH sensor based on a pH-responsive hydrogel has been developed. A Fresnel lens pattern was replicated on the surface of the pH-responsive hydrogel using the replica mould method. The pH sensors were tested in a pH range of 4–7. Introducing various pH solutions to the pH sensor led to volumetric shifts as the hydrogel swelled with pH. Consequently, the dimensions of the replicated Fresnel lens changed, modifying the focal length and the focus efficiency of the optical sensor. As a result, the measured optical power at a fixed distance from the sensor changed with pH. The optical sensor showed the best performance in the acidic region when pH changed from 4.5 to 5.5, in which the recorded power increased by 13%. The sensor exhibited high sensitivity to pH changes with a short respond time in a reversible manner. The developed pH optical sensor may have applications in medical point-of-care diagnostics and wearable continuous pH detection devices.

Relationship between liquid crystal layer thickness and variable-focusing characteristics of an ultrasound liquid crystal lens

The effect of the liquid crystal (LC) layer thickness on the optical characteristics of an ultrasound LC lens was explored. Three LC lenses with differing LC layer thicknesses (100, 200, and 300 µm) were fabricated, and the optical focal lengths were measured by an optical microscope with a varying driving voltage. For the lens with a 200-µm-thick LC layer, a larger change in the focal length was observed for a smaller driving voltage compared with that of the other two lenses, indicating that the LC layer thickness is appropriate for a variable-focus lens.

Samsun İlinde Hayvansal Kaynaklı Kompost Potansiyeli ve Optimum Tesis Konumları

Compared to industrial wastes, the recycling of agricultural wastes is more efficient because they are organic. The low organic matter content of Anatolian agricultural lands makes the recycling of agricultural wastes even more important. In the Samsun region, compost centres are recommended in order to help increase productivity in agricultural production, develop agricultural activities and ensure rural development. It is very important to use natural fertilizers because it is to protect and improve the organic structure of the soil. The low production costs of organic fertilizers compared to chemical fertilizers provide an advantage to farmers and prevent foreign exchange loss. In this study, it is aimed to determine the animal existence and optimum facility locations for evaluation of animal wastes as compost in Samsun. For this purpose, the number of animals of the enterprises in the region was determined by using the data obtained from Samsun Provincial Directorate of Agriculture and Forestry. The coordinates of the settlements of 1,284 enterprises with bovine capacity of 40 or more in Samsun were determined according to the rectangular coordinate system. In terms of animal distribution in Samsun province, 27 cluster numbers were preferred through Elbow method and f(K) Function method. The location of most suitable compost production centres according to the distance and the total number of animals was determined by the K-Means clustering analysis method using geographical coordinates. For Samsun, the group size was taken as 2,000-10,000 cattle and the enterprises with a focal length less than 15 km were included in the compost production clusters. In line with these criteria, 10 compost production clusters for compost production have been determined in Samsun and the locations of these cluster centres are shown on the map in a way that will provide the most efficient information to investors and relevant institutions.

Silk Microlens Array

Optics that are capable of merging with biomaterials create a variety of opportunities for sensing disease, for therapeutics, and for augmenting brain-machine interface. The FDA has approved silk devices for sutures and reconstructive surgery. Recently, a silk product made from regenerated silk protein is FDA approved for orthopedic application, as the understanding of structure and processing technologies of silk fibroin has been improved. Here, we report a facile fabrication process to construct silk microlens array. The process includes preparation of regenerated silk solution and casting on a micropatterned poly(dimethylsiloxane) (PDMS) master. Due to the identical surface area of a unit patterned regime, the silk solution exhibits a partial wetting state in the vicinity of the silk solution–PDMS–vapor interface with same contact angle, and after drying, produces consistent radius of curvature within the microlens array. This in turn provides highly uniform focal length, focal spot diameter, and imaging performance of individual lens. Our results provide the foundation for biophotonic microlens adding new capabilities for implantable and degradable devices from regenerated silk protein.

Coherence Properties and Intensity Distribution of a Partially Coherent Lorentz–Gauss Beam Emerging from the Axicon

The propagation of a partially Lorentz–Gauss beam in a uniform-intensity diffractive axicon is studied according to the Huygens–Fresnel principle, the Hermite–Gaussian expansion of a Lorentz function, and using the stationary phase method. We have derived the intensity equation of a partially coherent Lorentz-Gauss beams propagating through uniform-intensity diffractive axicon, and we proved mathematically that it is the superposition of Bessel beams of various orders after emerging from axicon, using Hermite’s function series and the Bessel function integral formulas. The results show that the intensity distribution of the diffracted beam is the intensity pattern evolved from a Lorentz–Gauss shaped spot into a Gaussian-shaped spot at any position on the focal length of the axicon, and the intensity distribution of a partially Lorentz–Gauss beam generated by an axicon becomes uniform by increasing the beam width and more uniform and constant with the larger coherence width.

Liquid crystal lens with four driving voltages and its applications in imaging system with rectangular aperture

Liquid crystal lens has the characteristic of variable focal length. Many studies have demonstrated that electronically controlled focusing without mechanical movements can be realized by using liquid crystal lenses in imaging system. In this paper, a four-electrodes liquid crystal lens with a rectangular aperture is applied to focus. The aperture’s aspect ratio of the liquid crystal lens can be designed arbitrarily so that installing it with the periscope lens in phones becomes possible.