Nanowire Grid Polarizer Research Articles

Shear-Rolling Process for Unidirectionally and Perpendicularly Oriented Sub-10-nm Block Copolymer Patterns on the 4 in Scale.

Shear alignment of the block copolymer (BCP) thin film is one of the promising directed self-assembly (DSA) methodologies for the unidirectional alignment of sub-10 nm microdomains of BCPs for next-generation nanolithography and nanowire-grid polarizers. However, because of the differences in the surface/interfacial energies at the top surface/bottom interface, the shear-induced ordering of BCP nanopatterns has been restricted to BCPs with spherical and cylindrical nanopatterns and cannot be realized for high-aspect-ratio perpendicular lamellar structures, which is essential for practical application to semiconductor pattern processes. It is still a difficult challenge to fabricate the unidirectional alignment in a short time over a large area. In this study, we propose an approach for combining the shear-rolling process with the filtered plasma treatment of BCP films for the fabrication of unidirectionally aligned and perpendicularly oriented lamellar nanostructures. This approach enables fabrication within 1 min on a 4 in scale. We treated filtered plasma on the BCP film for perpendicular orientation and executed the hot-rolling process with different roller and stage speeds. Large-scale shear was generated only at the location where the BCP film was in contact with both the roller and stage, effectively applying shear stress to a large area of the BCP film within a short time. The repeated application of this shear-rolling process can achieve a higher level of unidirectional alignment. Our aligned BCP vertical lamellae were used to fabricate a high-aspect-ratio sub-10-nm-wide metallic nanowire array via dry/wet processes. In addition, shear-rolling with chemoepitaxy patterns can achieve higher orientational order and lower defectivity.

Unidirectionally Oriented Multi-Layered Carbon Nanotubes Film for Polarizer

Nanowire-grid polarizer (WGP) that is generally used for a linearly polarized UV light that required for photo-alignment requires to have a very short pitch of about 100 nm to make, which is highly cost process due to nanopattern of metals. Therefore, we propose multi-layered CNT (Carbon nanotube) sheet that can replace the conventional WGPs. In this regard, unidirectionally oriented CNT bundles are proposed which shows a strong optical activity and anisotropic behavior with visible and ultraviolet wavelengths. In addition, a film prepared by oriented CNT bundles shows a high transparency at shorter wavelengths of 380 nm and even less. Furthermore, oriented CNT film exhibits 75-80% of DOP in the region of 350nm ~ 800 nm, especially ~91% in ultraviolet region, and provides wide absorption spectrum due to the π -plasmon of graphite. Moreover, the DOP and optical activity of aligned SWCNT can be further enhanced by improving the degree of alignment of CNT by stretching the polyvinyl alcohol substrate. We prepare a multi-layer CNT polarizer by depositing CNT layers one over another on a Silicon substrate by chemical vapor deposition technique. And then a bundle of CNTs are unidirectionally stretched to make the CNT sheet by using a mechanical rotation tool. The long axis of CNT rods in each sheet is orient parallel to the stretching direction. Then the stacked CNT sheet is transferred to a glass substrate as indicated in Fig 1. (a).The final multi-layered CNT polarizer consists of 3, 5, 8 and 12 CNT sheets stacked together with matching orientations. The relative transmittance of CNT polarizer within visible region is decreasing with increasing number of CNT layers. The incident light with its electric vector parallel (perpendicular) to the stretched CNT axis is effectively absorbed (transmitted) by the multi-layered CNT polarizers. Wavelength-dependent transmittance is showing a good correlation with optical microscopic results, as shown in Fig 1. (b). The transmittance of CNT polarizer at 365 nm is measured to be >10%, 6.5%, 1.0% and 0.5% for 3, 5, 8 and 12 CNT layers, respectively, whereas the iodine polarizer is exhibiting almost zero transmittance. Moreover, the proposed CNT polarizer is capable to extend the absorption of incident light up to deep UV region providing a wider operating wavelength range from 300 nm to400 nm and all multi-layered CNT polarizers exhibit high stability against long time UV exposure. To measure the multi-layer CNT polarizer’s performance, we have employed fringe field switching (FFS) cell with 3.4 μm with film spacers (passivation layer = 0.5 µm / gap between pixel electrodes = 4.5 µm / pixel electrode width = 3.5 µm). As shown in Fig. 1(c), obtained multi-layer CNT polarizer exhibits higher DOP of 91% by matching orientation of stacked CNTs in each layer. Inserted left image in the graph is the FFS cells exposed with 3 CNT layers. It exhibits slight nonuniformity in brightness of low grey scales called mura at 3 V, whereas the cells exposed with 12 CNT layers (right insert image of Fig. 1 (c)) do not show such mura. The proposed CNT polarizer film is expected to be applied as photomask with low-cost. we believe it has strong potentiality to utilize in future photonic and electro-optic devices with broad band gap from UV to infrared. Figure 1

Maskless Fabrication of Film-Patterned-Retarder (FPR) Using Wedged Liquid Crystal Cell

Film-patterned-retarder (FPR) is an optical film used in the stereoscopic 3D display and is fabricated using an expensive photomask and nano-wire grid polarizer. This method is expensive and the pitch of FPR is fixed for a given photomask. Here, we introduce a maskless fabrication method for FPR using a wedged liquid crystal (LC) cell. The retardation of the wedged LC cell is continuously increased from one edge to the other. When the polarized monochromatic laser beam (450 nm) passes through the cell, periodically undulated polarization pattern of light is obtained, and can be used to produce FPR by combining with the photo-alignment method. The method does not require the expensive photomask and nano-wire grid polarizer, and the pitch of FPR can be simply controllable by changing the birefringence of LC material with temperature or using a light source of different wavelengths. Thus, this method can provide a simple and cost-effective method for FPR fabrication.

A bilayer Al nanowire-grid polarizer integrated with an IR-cut filter

A bilayer Al nanowire-grid polarizer integrated with an IR-cut filter has been developed to exhibit high polarization sensitivity in a visible region. The IR-cut filter consisting of Ti3O5/SiO2 multilayer oxide film completely blocks the incoming light over 680 nm wavelength and shows high transmittance over 95% in the visible range. By incorporating the reversible nanostructures molding lithography and the two-step oblique angle deposition of the e-beam evaporator, we are able to secure the nanowire-grid patterning with 50-nm resolution in a form of bilayer Al grating. Then, it is found that the plasmonic coupling between the nearby Al layers leads to the high transmittance of TM-mode light passing through the IR-cut filter, while there is no plasmonic coupling between them for TE-mode case. Both the Finite-Difference Time-Domain simulation and experimental results show that the transmittance of the TM polarization for the grid height of 110 nm reaches up to 90% and the extinction ratio is around 300∶1 in the visible range. Therefore, the observed results can provide an insight in designing the bilayer Al based plasmonic polarizer combined with the IR-cut filter in order to achieve better performance utilizing the plasmonic coupling effect.

Near-infrared bilayer nanowire grid polarizer array fabricated using soft nanoimprint lithography

We fabricated a cost-effective and tractable near-infrared nanowire grid polarizer array with six different directional grating elements on a Borofloat 33 glass substrate at once using a soft nanoimprint and metal thermal evaporation process. Each element consists of a 200-nm period bilayer Al grating with an area of 1.3 × 1.3 mm2. Scanning electron microscopy images reveal that each unit of the polarizer array has an intact nanostructure without large-area damage. Meanwhile, the TM transmittance of each element exceeds 65% in the wavelength range of 1 to 2.5 μm, and of particular note, it is >70 % in the wavelength range of 1.2 to 2.5 μm. The extinction ratio is more than 20 dB in 1.38- to 2.5-μm wavelength range, proving that the polarizer array has good polarization characteristics. Such a polarizer array has low costs and better compatibility with microfabrication processes, which can be used as an element of near-infrared polarization image detection equipment.

Large-area flexible infrared nanowire grid polarizer fabricated using nanoimprint lithography.

We fabricated a 4-in large-area flexible infrared nanowire grid polarizer using a nanoimprint and metal thermal evaporation process. To protect the Si master template, as well as to prolong the service life of it, we first fabricated a nickel template as an alternative by an electroforming process. Then, the nanowire grid structure was transferred from this template to IPS substrate by a thermal nanoimprint process. Finally, Al was deposited on the IPS nanowire structure by vertical thermal evaporation technology. The results of the infrared optical test reveal that the TM transmittance of the polarizer is greater than 60% in the 4-5.71μm and 5.73-6.7μm wavelength ranges, and, especially, it is greater than 70% in the wavelength ranges of 4.70-5.69μm and 5.75-6.59μm. The extinction ratio is more than 20dB in the wavelength range of 3.6-6.7μm, proving that the polarizer has good polarization characteristics. The flexible infrared nanowire grid polarizer has potential applications in the fields of curved surface monitoring equipment and polarized imaging equipment.

Quasi-Resonant Enhancement of the Extinction Ratio in the Amorphous Silicon Nanowire Grid Polarizer

Spectral characteristics of thin-film nanowire grid polarizers based on amorphous silicon are numerically investigated. The extinction ratio, transmission coefficients, and reflection coefficients are calculated using the MC Grating code based on the rigorous coupled-wave analysis. It is found out that at particular structure parameters of the nanowire grid polarizer the extinction ratio increases to 106 at the optical radiation wavelength of about 380 nm, which is characterized as a quasi-resonance effect. A dissipative-interference qualitative interpretation of this effect within the waveguide model is proposed. This interpretation is confirmed by the calculated field distribution patterns in the vicinity of the quasiresonance.

Fill factor controlled nanoimprinted ZnO nanowires based on atomic layer deposition

Enhanced diffraction by sub-wavelength nanostructures to convert incident electromagnetic radiation into waveguide modes has applications in anti-reflective coatings for optoelectronic devices. We propose a metal oxide (ZnO) nanowire grid polarizer as such a nanostructure, fabricated by ultraviolet nanoimprint lithography and whose fill factor (FF) is controlled by atomic layer deposition. Using finite difference time domain simulations, we investigated the polarization-dependent optical transmittance of the structures and calculated the polarizing efficiency. Optical profiles such as electric and magnetic field intensity and current density distributions of specific FF nanopatterns were determined for the transverse magnetic and transverse electric modes. The effects of geometrical parameters including the wire-grid period, fill ratio, and spacing between the wire-grid layers on diffraction wavelength were characterized. Respective FF-controlled ZnO nanowire structures were fabricated and their experimental optical transmittances were measured for nanowire grid polarizer applications.

Tunable structure of nanowire-grid polarizer for deep ultraviolet region

As the performance of nanowire-grid polarizer is determined by the characteristic size of nanowire, the polarizer for full ultraviolet (UV) region requires the characteristic size less than 50 nm, which is challengeable to the current fabrication level. In this letter, two pieces of nanowire-grid polarizers sandwiching a layer of polymer-dispersed liquid crystal (PDLC) was proposed as a tunable structure of nanowire-grid polarizer for high performance in deep ultraviolet region with 100 nm of nanowire period. In this structure, the transmittance of transverse electric (TE) mode (TTE) and transverse magnetic (TM) mode (TTM), and also the transmission extinction ratio (Ex) could be tuned by the optical path of the PDLC layer. Assuming the refractive index of PDLC layer could be varied from 1.5 to 1.6 as its applied voltage changed from saturation voltage to zero, we calculated the TTM and Ex, which varies periodically as the PDLC layer refractive index increasing. For a given incident wavelength, the maximums of TTM and Ex could be attained easily by tuning the applied voltage on PDLC layer. The simulation results show that the tunable structure has a short starting wavelength than that of single layer and double-layer structure nanowire-grid polarizer at a given transmission or extinction requirement with same characteristic size of nanowire, because of the constructive interference of TM polarization and the destructive interference of TE polarization in these two layers of nanowire, similar to a Fabry-Perot cavity, which makes it excellent to be applied in deep UV region.

Performance comparison of polarized white light emitting diodes using wire-grid polarizers with polymeric and glass substrates

Polarized white light emitting diodes (WLEDs) packaged with reflective metal wire-grid polarizer of polymeric and glass substrates were investigated. The performance comparison of polymeric wire-grid polarizer film (WGF) and nano wire-grid polarizer (NWGP) with glass substrate was evaluated. The transverse electric field (TE) polarization transmittance of WGF is less than that of NWGP due to its smaller grid parameters. Despite of the higher duty cycle of WGF, the angular-dependent extinction ratio (ER) of the polarized WLEDs (PWLEDs) with WGF is higher than that of with NWGP. Regarding increasing drive currents, the PWLEDs with NWGP had better color stability than that with WGF due to better substrate thermal stability. In summary, linewidth, period and substrate material are the crucial factors for the PWLED packaging using wire grid polarizer.

Selection of absorptive materials for non-reflective wire grid polarizers

Wire grid polarizers often have reflective characteristics, such that some incident light is transmitted through the polarizer, while the rest is reflected. For some applications, such as anti-reflective films in OLEDs, non-reflective (or absorptive) wire grid polarizers are necessary; these can be realized by the deposition of an absorptive material on the nanoscale metal wire grid. However, because this deposited absorptive layer can severely affect the polarization characteristics, its material must be selected carefully. The polarization characteristics of a given nanowire grid polarizer can be simulated using rigorous coupled-wave analysis (RCWA). In this study, several types of metal oxides and nitrides were tested as candidate materials for the absorptive layer of a non-reflective polarizer. Nanopatterned double layers with absorptive and reflective functions were modeled using RCWA. Simulations were conducted for various pattern widths, depths, and periodicities. CuO and Fe3O4 showed optimal polarization characteristics among the simulated absorptive layers. Simulations indicated that the performance of non-reflective wire grid polarizers could be enhanced using CuO or Fe3O4. The design of absorptive polarizers was fully characterized by simulation for future experimental research.

Progress on bio-inspired polarized skylight navigation sensor

Navigation technology is indispensable for both animal and human. Navigation sensor plays an important role in emergency rescue, precision-guided weapons, ship exploration, aircraft navigation, and satellites positioning system. To reach nests or favorable grounds, many insects have evolved navigational ability that can obtain the solar azimuth by detecting the polarized skylight. This polarized pattern in the sky arises, due to the sunlight scattering in the atmosphere. In the single-scattering Rayleigh atmosphere, the direction of polarization is perpendicular to the scattering plane determined by the observer, the observed celestial point and the sun. Some insects can finish long-distance migration to survive in the seasonal changing environments. Inspired by the amazing capacity, kinds of sensors have been developed depending on the structure of the insects’compound eyes and the insects’ visual mechanism. Integrated polarization dependent sensors have the features of compact structure, high precision, strong robustness, and simple fabrication process. This kind of sensor is composed of a complementary-metal-oxide-semiconductor sensor integrating with a multiorientation nanowire grid polarizer, and also the working principle of the sensor is described. The astronomy navigation technology based on polarized skylight has already become the innovation and research focus, even though the navigational mechanism of insects is still not very clear. In the meantime, the miniaturization and integration are new directions for the future research of navigation sensors. Additionally, to prevent navigational errors, it is necessary to calibrate orientation compass. Modern navigation technologies such as GPS have made themselves straightforward for mankind to locate global positions. These techniques are classified as satellite navigation, radio navigation, inertia navigation or celestial navigation. Unfortunately each of these techniques has their own weakness. For example, satellite navigation has the possibility of jamming and satellite signal loss. Radio navigation cannot work without base stations. Inertia navigation needs to correct its peculiar accumulated errors. And celestial navigation is complex and very expensive. The existing researches show that the astronomy navigation technology is real-time and autonomous and can work without accumulation of errors. Polarized skylight is one of the multitude of sensory information used by animals, thus there is much future work waiting for researchers to develop.

나노 금속 격자형 편광필름 제작에서 증착 두께에 따른 광 특성 연구

본 연구에서는 대면적 나노 금속 격자형 편광 필름 제작에서 증착 두께에 따른 광 특성 연구를 수행하였다. 나노 금속 격자형 편광필름은 PET(Polyethylene phthalate)기판 위에 알루미늄 선 격자 구조로 구성된다. 본 연구에서는 대면적 편광필름 제작을 위한 증착공정을 통한 금속 격자 형성을 목표로 하였으며, 금속 격자형 편광 필름 제작에 있어 최적의 투과율과 소광비를 가지는 금속 박막 형성 조건을 도출하였다. 최적화 공정에 의해 나노 금속 격자형 편광필름은 140 nm 주기, 70 nm 선폭, 70 nm의 금속층 높이를 가지는 금속 격자 구조로 제작 되었다. 분석결과 600 nm 파장에서 80% 이상의 최고 투과율 및 <TEX>$10^6$</TEX> 이상의 소광비를 가지는 나노 금속 격자 편광필름의 높은 광 특성을 확인하였다. In this study, we demonstrate the change of optical characteristic by thickness of metal deposition on nano metal grid polarizer film fabrication. Nano metal grid polarizer film consists of aluminium grid polarizer layer on PET (Polyethylene phthalate) substrate. We aim at metal grid layer formation for the large nano wire grid polarizer fabrication. we draw process conditions of the nano metal grid polarizer film fabrication to improve transmittance and extinction ratio and Nano wire grid polarizer film (NWGP) film is fabricated with 140 nm pitch, 70 nm width, and 70 nm depth of metal grid on optimum design conditions. As a result, we get high optical properties of nano wire grid polarizer which is the maximum transmittance of 80% and the extinction ratio of <TEX>$10^6$</TEX> at 600 nm wavelength respectively.

Integrated polarization-dependent sensor for autonomous navigation

Based on the navigation strategy of insects utilizing the polarized skylight, an integrated polarization-dependent sensor for autonomous navigation is presented. The navigation sensor has the features of compact structure, high precision, strong robustness, and a simple manufacture technique. The sensor is composed by integrating a complementary-metal-oxide-semiconductor sensor with a multiorientation nanowire grid polarizer. By nanoimprint lithography, the multiorientation nanowire polarizer is fabricated in one step and the alignment error is eliminated. The statistical theory is added to the interval-division algorithm to calculate the polarization angle of the incident light. The laboratory and outdoor tests for the navigation sensor are implemented and the errors of the measured angle are ±0.02 deg and ±1.3 deg, respectively. The results show that the proposed sensor has potential for application in autonomous navigation.

High-throughput fabrication of compact and flexible bilayer nanowire grid polarizers for deep-ultraviolet to infrared range

The authors present the design and fabrication of a bilayer metallic wire-grid polarizer with a period of 80 nm on a flexible polymeric substrate optimized for broadband operation ranging from the infrared down to the deep-ultraviolet range. Their high-throughput fabrication over large areas is realized by nanoimprint lithography by producing the imprint master stamps using extreme ultraviolet interference lithography. Optical measurements show that the fabricated bilayer polarizer covers a broad spectral range, starting from wavelength of 280 nm. Transverse magnetic transmission of 70% and an extinction ratio of 30 dB were realized.

Design of an integrated polarization band-pass filter

In this study, an integrated polarization band-pass filter was designed; it consists of a bilayer nanowire-grid polarizer and a multilayer dielectric band-pass filter. The grating parameters were optimized by rigorous coupled-wave analysis theory and analyzed by effective medium theory. Transverse magnetic transmission higher than 81% and extinction ratio higher than 1000 were obtained at 400–500 nm, and extremely low transmission in the other spectrum was also realized.

Nanowire Grid Polarizers Integrated into Flexible, Gas Permeable, Biocompatible Materials and Contact Lenses

The integration of optical components directly into contact lens materials permits the realization of advanced display technologies and integrated medical instruments. A process is developed for the fabrication of aluminium nanowire grid polarizers encapsulated in a flexible, gas permeable, and biocompatible material for integration onto rigid, gas‐permeable contact lenses. Gas permeability values an order of magnitude higher than the minimum to prevent eye damage are measured while maintaining strong polarization performance. Further, the methods developed in this work can readily be applied to various optical and electronic technologies, allowing standard fabrication processes on rigid substrates and subsequent transfer to flexible, gas permeable, and biocompatible materials.

Polarized white light emitting diodes with a nano-wire grid polarizer

To achieve a high transmittance and extinction ratio for the polarized white light-emitting diodes (WLEDs), the package structures of polarized WLEDs that are pumped by blue LEDs are studied. A WLED is implemented using a nano-wire grid polarizer (NWGP) and forms a pumping cavity. Combining the reflection and transmission characteristics of a NWGP, the optimized package structure has an air gap between the phosphor resin and the NWGP. Specifically, the angular dependence of the chromaticity coordinates and spatial uniformity of the radiation pattern are investigated and are more uniform than those of conventional LEDs.

Research on the characteristics of tunable structure nanowire-grid polarizer

Nanowire-grid polarizer is of a periodic sub-wave structure of metallic nanowire on the substrate, fabricated by nanoimprint technology. Different from traditional polarization prism and dichroic polarizer, the nanowire-grid polarizer has many advantages such as compact size, easy integration and high polarization performance. However, in the ultraviolet and visible regions, it is infeasible to improve the performance of single layer nanowire structure by reducing the character size of nanowire because of the bottleneck of lithographic process. The double-layer nanowire-grid structure could improve the polarization characteristics at some special wavelengths but not full-wave band of ultraviolet and visible regions. In this paper, we propose a tunable double-layer structure to enhance the extinction ratio and transmission at each wavelength by tuning the distance between two nanowire-grid polarizers through adjusting the voltage applied to PZT. To calculate the transmittance and transmission extinction ratio of tunable structure, software VirtualLab is employed and the Fourier model method is used. The numerical simulation results show that the tunable structure have a higher polarization characteristic in ultraviolet and visible regions than single layer structure and double layers structure.

A Heterodyne Optical Fiber Current Sensor Based on a Nanowire-Grid In-Line Polarizer

A heterodyne optical fiber current sensor based on a nanowire-grid (NWG) in-line polarizer is proposed. The NWG is a one-dimension Au grating fabricated on a fiber tip by focused ion beam machining. Because the grating pitch is far smaller than the wavelength of the incident light, it works like an in-line transflective fiber polarizer with both the transmission and reflection light power being measured simultaneously. Based on this unique feature, an all-fiber optical current sensor is demonstrated. The heterodyne measurement makes it withstand light power variations showing good sensing stability. As an all-fiber sensor, discrete and bulky optical components are saved, making it more reliable in practical applications.