High Refractive Index Lens Research Articles

Ultrathin Ge-YF3 antireflective coating with 0.5 % reflectivity on high-index substrate for long-wavelength infrared cameras

Abstract Achieving long-wavelength infrared (LWIR) cameras with high sensitivity and shorter exposure times faces challenges due to series reflections from high-refractive index lenses within compact optical systems. However, designing effective antireflective coatings to maximize light throughput in these systems is complicated by the limited range of transparent materials available for the LWIR. This scarcity narrows the degrees of freedom in design, complicating the optimization process for a system that aims to minimize the number of physical layers and address the inherent large refractive mismatch from high-index lenses. In this study, we use discrete-to-continuous optimization to design a subwavelength-thick antireflective multilayer coating on high-refractive index Si substrate for LWIR cameras, where the coating consists of few (e.g., five) alternating stacks of high- and low-refractive-index thin films (e.g., Ge-YF3, Ge-ZnS, or ZnS-YF3). Discrete optimization efficiently reveals the configuration of physical layers through binary optimization supported by a machine learning model. Continuous optimization identifies the optimal thickness of each coating layer using the conventional gradient method. As a result, considering the responsivity of a LWIR camera, the discrete-to-continuous strategy finds the optimal design of a 2.3-μm-thick antireflective coating on Si substrate consisting of five physical layers based on the Ge-YF3 high-low index pair, showing an average reflectance of 0.54 % within the wavelength range of 8–13 μm. Moreover, conventional thin-film deposition (e.g., electron-beam evaporator) techniques successfully realize the designed structure, and Fourier-transform infrared spectroscopy (FTIR) and thermography confirm the high performance of the antireflective function.

Hemispherical Rutile Solid Immersion Lens for Terahertz Microscopy with Superior 0.06–0.11λ Resolution

AbstractSolid immersion microscopy is a near‐field imaging modality that overcomes the Abbe diffraction limit by focusing the light beam behind a high refractive index lens. It offers high energy efficiency, thanks to the absence of any sub‐wavelength probes or apertures in the optical path. A favorable combination of superresolution and high optical throughput opens up a variety of imaging applications in different branches of science and technology. The spatial resolution of solid immersion microscopy is mostly limited by the refractive index value of the lens, with optically denser lenses offering higher resolutions. In this paper, bulk rutile (TiO2) crystal is used as a material for the solid immersion lens, which offers an impressive refractive index of ≈10 in the terahertz range. This is the highest value of refractive index ever used in solid immersion microscopy. A continuous wave impact ionization avalanche transit‐time diode‐emitter at the 0.2 THz frequency (the λ = 1.5 mm wavelength) and a Golay detector are used for building a solid immersion microscope. Numerical and experimental studies reveal 0.06–0.11λ resolution of the developed microscope. This is the highest normalized resolution ever reported for any solid immersion imaging systems.

Inverted with power efficiency over 220 lm W–1

The white organic light-emitting diodes (WOLEDs) have great potential in the fields of solid-state lighting. Continued efforts have been made to catch up with the power efficiency (PE) of inorganic light-emitting diodes. Apart from low operating voltage and near unity internal quantum efficiency, improvement the efficiency of light extraction, especially suppression of surface plasmon (SP) modes is essential for realizing ultimate PE. In contrast to corrugated structure which could suffer from spectral selectivity, higher leakage current and potential degradation issue stemmed from the rough structure, increasing the distance between the emitter and the metallic electrode becomes an effective avenue towards suppressing SP modes while maintaining the planar structure. In this work, an inverted bottom-emitting structure with thick hole transport layer (HTL) composed of multi-period organic heterojunctions is demonstrated to effectively extract the SP modes without any electrical property degradation in the current density range for lighting. Investigation on electrical properties of thickened HTL with increased count of organic heterojunctions indicates no increase of driving voltage at same current density in lighting application condition. By attaching an matched high refractive index lens, a record maximum forward-viewing PE of 228.4 lm W-1 is obtained for the thick WOLED fabricated on high refractive index glass substrate, exhibiting significant enhancements of 57% compared to the counterpart of the conventional thin WOLEDs. An unambiguous picture is given to depict the regularity derived from increase of emitter-to-metal distance by combination of a full optical simulation and experimental measurements excluded the influence of electrical property degradation.

Recent progress in thermally stable and photosensitive polymers

Thermally stable and photosensitive polymers (TSPSPs), such as photosensitive polyimides (PSPIs) and polybenzoxazoles (PSPBOs), have been widely developed in recent years for their applications in electronic packaging (for example, buffer coating, passivation layers, and insulation layers) and redistribution in microelectronics due to their excellent thermal and reasonable dielectric properties. This review describes recent advances in TSPSPs during the last decade and focuses on related design concepts. Following a brief introduction of the basic patterning procedure, various chemistries used for the design of TSPSPs are highlighted along with two major patterning methodologies: positive- and negative-working PSPIs/PSPBOs. Furthermore, new applications of TSPSPs (for example, low dielectric materials, high refractive index lenses, resists for indium tin oxide patterning, and π-conjugated polymers for organic-field effect transistors) are introduced. Thermally stable and photosensitive polymers have been widely developed in recent years for their applications in the electronic packaging such as buffer coating, passivation layers, and insulation layers for redistribution in microelectronics due to their excellent thermal and reasonable dielectric properties. This review describes the recent progress of TSPSPs in the last decade and focuses on their design concept. After a brief introduction of the basic patterning procedure, various chemistries on the design of TSPSPs are highlighted along with two major patterning methodologies such as positive- and negative-working polymers. Furthermore, new applications of TSPSPs, such as low dielectric materials, high refractive index lenses, resists for ITO patterning, and π-conjugated polymers for organic-field effect transistors, are also introduced.

온도에 의한 고분자 렌즈의 재질별 코팅 박막의 변화

목적: 플라스틱 렌즈의 온도에 의한 영향을 조사하고자 열 충격을 주어 렌즈 재질과 코팅의 변화를 살펴보았다. 방법: 본 연구에서는 굴절률이 다른 3 가지의 렌즈(2 종류의 thiourethane계열 렌즈, 한 종류의 allyl diglycol carbonate, ADC 렌즈)를 5 시간 동안 고온(50, 80, 그리고 <TEX>$100^{\circ}C$</TEX>)에 노출시켰을 때 각각의 코팅(반사방지코팅, 하드 코팅, 그리고 수막방지코팅)의 변화를 측정하였다. 결과: 그 결과 고굴절률 렌즈들에서는 경도의 변화가 미미하였으나 중굴절률 렌즈는 고온의 열에 노출될수록 경도가 점차 감소하여 하드코팅이 손상됨을 확인하였다. 모든 렌즈의 광투과율이 <TEX>$80^{\circ}C$</TEX> 이상의 열 충격 시 큰 감소가 나타나 멀티코팅 층이 파괴됨을 유추할 수 있었다. 렌즈에 열 충격이 가해질수록 표면 접촉각이 작아져 <TEX>$80^{\circ}C$</TEX> 이상 가열 시 수막발수코팅이 손상되기 시작함을 보였다. 결론: 굴절률이 다른 3가지 렌즈 모두에서 <TEX>$80^{\circ}C$</TEX> 이상의 열 충격을 받았을 때 발수코팅을 포함한 멀티코팅이 손상되었고 고분자 재료 소재에 따라 기계적, 물리적 특성 변화정도가 다르게 나타났다. Purpose: To observe changes of coatings and lens materials with varying temperature to understand effect of temperature on plastic lens. Methods: In this study, three lenses of different refractive indices (2 of thiourethane oriented lenses, an allyl diglycol carbonate oriented lens) were exposed to high temperature (50, 80, and 100 degree) for 5 hours and changes of individual coating (anti-refractive coating, hard coating, and water repellent coating) were measured. Results: As a result, high-refractive index lenses did not exhibit significant variation of hardness. However, hardness of mid-refractive index lens were decreased when exposed to high temperature and destructions of hard coating layer was inferred. Surface contact angles of lens were decreased with increasing temperature and water repellent coating layer were damaged at higher than 80 degree. Conclusions: Multi including water repellent coatings on all three lenses with different refractive indices were damaged when exposed to at or higher than 80 degree. The degree of changes in mechanical and physical properties were depended on polymer material type.

Tinting of Plastic Eyeglass Lens using Laser

This paper reports about tinting of polycarbonate (PC) eyeglass lens with laser. We have developed laser tinting using violet laser diode (VLD) and a CO2 laser. In order to dye eyeglass lens uniformly, it is important to spread disperse dyestuff on lens and plates. We selected the sublimation transfer tinting without contact, which was used as one of the technologies that spread dyestuff on the PC surface thinly. We have tested line tinting (200um) of PC plate(t=2 mm) with the sublimation transfer tinting without contact using VLD. Uniform tinting in small area(approximately 1x2 mm2) was achieved by scanning VLD light. The uniform tinting of large area was expected, so we tried to dye PC lens which is used widely. In order to dye wide area, we used a CO2 laser while eliminating the melt of the lens surface by the defocus. Recently, high refractive index lens are widely used, but it is very difficult to dye high refractive index lens uniformly. The dyestuff layer was thinly spread on the surface of the high refractive index lens by using the sublimation transfer tinting without contact, and uniform tinting on the lens were achieved by the CO2 laser.

High Refractive Index Polymers for Optical Applications

High refractive index (RI) materials are extremely important in many optical applications. Polymers traditionally have relatively low refractive indices, but they can be raised to technologically useful values. Our group has prepared RI tunable materials up to 1.68 using brominated and aromatic monomers in a copolymer synthesis method. These copolymers are transparent in the technologically important near-IR, have high glass transition temperatures, and are good film formers. These attributes make them useful in optical quality composites where a RI-controlled matrix material is used to match the RI of the incorporated phase to avoid scattering. In addition to composites, applications of these high RI materials include antireflective coatings and high RI lenses, among others.