Application of wire-grid polarizers to projection displays

We have measured the optical properties of wire-grid polarizers (WGPs). The implications of these results to the application of WGPs in projectors that use reflective light valves are discussed. In particular, the brightness and the contrast ratio of the projection system are investigated as functions of the angle of incidence of the light beam onto the WGP. It was found that the optimal incident angle is dependent on the physical design of the wire grids. In the sample that we describe, the optimal incident angle was 35 degrees instead of 45 degrees. At the optimal incident angle, both the transmission and the reflection extinction ratios can be quite good. However, WGPs suffer from the drawback of free-carrier absorption by the metal grid.     

Manipulation of extinction spectra of P3HT/PMMA medium arrays on silicon substrate containing self-assembled gold nanoparticles

In this study, we report a simple novel approach to modulate the extinction spectra of P3HT/PMMA by manipulating the medium arrays on a substrate that is coated with self-assembled gold nanoparticles. The 20 nm gold nanoparticles were synthesized and then self-assembled on the APTMS/silicon substrate surface by immersing the substrate into the gold colloid suspension. A high-resolution P3HT/PMMA photoluminescent electron beam resist was used to fabricate various square hole arrays on the substrate containing gold nanoparticles. The P3HT/PMMA medium composition causes the blue shifts in the extinction peaks of up to 40.6 nm by decreasing the period from 500 nm to 200 nm for P3HT/PMMA square hole arrays with a diameter of 100 nm. The magnitude of blue shift is directly proportional to the product of the changes of medium refractive index and the array structure factor. These peak shifts and intensity of extinction spectra for various P3HT/PMMA medium arrays are well described by the finite-difference time-domain (FDTD) simulation results. Since this simple cost-effective technique can tune the extinction spectrum of medium and adding the gold nanoparticles can give more functionalities for sensing applications, such as surface-enhanced Raman scattering (SERS), that provides good opportunities for the design and fabrication of new optoelectronic devices and sensors.     

Binary arrays with perfect odd-periodic autocorrelation

Arrays with good autocorrelation functions are required for coded aperture imaging. A generalized folding procedure is derived that permits the construction of arrays with good correlation properties from well correlating sequences for many array sizes. This synthesis method is applied to the construction of approximately square binary arrays with a single zero element and perfect odd-periodic autocorrelation functions. In addition, new binary arrays with constant sidelobes of their periodic autocorrelation functions (uniformly redundant arrays) can be generated with the generalized folding method.     

High sensitivity plasmonic index sensor using slablike gold nanoring arrays

We investigate the index sensing characteristics of plasmonic arrays based on square lattice slablike gold nanorings (NRs) with different ring widths. The gold NR arrays exhibit two extinction peaks in the visible and near-infrared corresponding to antibonding and bonding modes. Redshift and blueshift in antibonding and bonding modes when broadening the average ring width are observed. We experimentally demonstrate the sensitivity of bonding mode can be tuned by varying the average ring width. High sensitivity of 691 nm per refractive index unit is obtained for NRs with 199 nm average ring width.     

Large‐Scale,Long‐Range‐Ordered Patterning of Nanocrystals via Capillary‐Bridge Manipulation

Deterministic assembly of nanoparticles with programmable patterns is a core opportunity for property‐by‐design fabrication and large‐scale integration of functional materials and devices. The wet‐chemical‐synthesized colloidal nanocrystals are compatible with solution assembly techniques, thus possessing advantages of high efficiency, low cost, and large scale. However, conventional solution process suffers from tradeoffs between spatial precision and long‐range order of nanocrystal assembly arising from the uncontrollable dewetting dynamics and fluid flow. Here, a capillary‐bridge manipulation method is demonstrated for directing the dewetting of nanocrystal inks and deterministically patterning long‐range‐ordered superlattice structures. This is achieved by employing micropillars with programmable size, arrangement, and shape, which permits deterministic manipulation of geometry, position, and dewetting dynamics of capillary bridges. Various superlattice structures, including one‐dimensional (1D), circle, square, pentagon, hexagon, pentagram, cross arrays, are fabricated. Compared to the glassy thin films, long‐range‐ordered superlattice arrays exhibit improved ferroelectric polarization. Coassembly of nanocrystal superlattice and organic functional molecule is further demonstrated. Through introducing azobenzene into superlattice arrays, a switchable ferroelectric polarization is realized, which is triggered by order–disorder transition of nanocrystal stacking in reversible isomerization process of azobenzene. This method offers a platform for patterning nanocrystal superlattices and fabricating microdevices with functionalities for multiferroics, electronics, and photonics.     

Optimizing imaging polarimeters constructed with imperfect optics

Imaging polarimeters are often designed and optimized by assuming that the polarization properties of the optics are nearly ideal. For example, we often assume that the linear polarizers have infinite extinction ratios. It is also usually assumed that the retarding elements have retardances that do not vary either spatially or with the angle of incidence. We consider the case where the polarization optics used to develop an imaging polarimeter are imperfect. Specifically, we examine the expected performance of a system as the extinction ratio of the diattenuators degrades, as the retardance varies spatially, and as the retardance varies with incidence angle. It is found that the penalty in the signal-to-noise ratio for using diattenuators with low extinction ratios is not severe, as an extinction ratio of 5 causes only a 2.0 dB increase in the noise in the reconstructed Stokes parameter images compared with an ideal diattenuator. Likewise, we find that a system can be optimized in the presence of spatially varying retardance, but that angular positioning error is far more important in rotating retarder imaging polarimeters.     

Reconfigurable imaging systems using elliptical nanowires

Materials that have subwavelength structure can add degrees of freedom to optical system design that are not possible with bulk materials. We demonstrate two lenses that are composed out of lithographically patterned arrays of elliptical cross-section silicon nanowires, which can dynamically reconfigure their imaging properties in response to the polarization of the illumination. In each element, two different focusing functions are polarization encoded into a single lens. The first nanowire lens has a different focal length for each linear polarization state, thereby realizing the front end of a nonmechanical zoom imaging system. The second nanowire lens has a different optical axis for each linear polarization state, demonstrating stereoscopic image capture from a single physical aperture.     

Three-dimensional large-screen display with reflection-mode spatial light modulators and a single-projection optical system: analysis of a retardation-modulation method

A stereoscopic projector with polarized glasses is proposed that consists of spatial light modulators (SLM's) that control the retardation of projected light, a polarization beam splitter (PBS), and single-projection optics. This display's features include a three-dimensional (3-D) image display with a single projector and half the size and the power consumption of a conventional 3-D projector. Analysis shows that the cross talk and the extinction ratio of this system depend strongly on the polarized light-separation characteristics of the PBS, the light output, and the extinction ratio of the SLM's. A double-PBS method that drastically improves 3-D image quality is also discussed.     

Wide-viewing integral three-dimensional imaging by use of orthogonal polarization switching

A wide-viewing integral three-dimesional (3D) imaging system that adopts orthogonal polarization switching is proposed and demonstrated. In our scheme,the polarizing sheet attached to the lens array and the orthogonal polarization switching of the elemental image array perform elemental lens switching. The experimental results document that the viewing angle becomes remarkably wider than that of the conventional method. The distinguishing feature of our system is that it requires no mechanical moving part. In addition, because a commercially available polarization shutter screen is used for electrical switching, it is easy to implement this as a practical system. We believe that the proposed method facilitates the practical use of this wide-viewing integral 3D imaging system.     

Thinning and weighting of large planar arrays by simulated annealing

Two-dimensional arrays offer the potential for producing three-dimensional acoustic imaging. The major problem is the complexity arising from the large number of elements in such arrays. In this paper, a synthesis method is proposed that is aimed at designing an aperiodic sparse two-dimensional array to be used with a conventional beam-former. The stochastic algorithm of simulated annealing has been utilized to minimize the number of elements necessary to produce a spatial response that meets given requirements. The proposed method is highly innovative, as it can design very large arrays, optimize both positions and weight coefficients, synthesize asymmetric arrays, and generate array configurations that are valid for every steering direction. Several results are presented, showing notable improvements in the array characteristics and performances over those reported in the literature.     

Three-dimensional imaging analysis of confocal and conventional polarization microscopes by use of Mie scattering theory

We present a three-dimensional imaging analysis of confocal and conventional polarization microscopes by using the extended Mie scattering theory. In the analysis, we calculate the images of a Mie particle whose diameter is comparable with the wavelength of confocal and conventional microscopes. It was found that, when we observe a Mie particle, polarization confocal microscopy is not affected by the polarization distortion that is due to focusing with high-numerical-aperture lenses and does not produce pseudopeaks in the images in comparison with conventional polarization microscopy. The three-dimensional resolution of the polarization microscope and the verification of the proposed analysis method are also discussed.     

Holographic polarization-separation elements

Volume holographic optical elements exhibit a property that we call bidiffringence, in which the diffraction efficiency of the element is strongly dependent on the polarization of the incident beam. Dualelement, volume holographic polarization separators utilizing bidiffringence can provide high extinction ratios, and they can provide greater angular separation of the polarized beams and greater flexibility in the beam-separation parameters than conventional birefringent elements. We designed and constructed holographic polarization separators using dichromated gelatin as the holographic medium. Experimental results are compared with the results predicted by the Kogelnik coupled wave theory.     

Fabrication of thin-film micropolarizer arrays for visible imaging polarimetry

We describe a microfabrication process for fabricating micropolarizer devices with polarization thin film. The polarization film is less than a 0.5 mum thick and can have a polarization extinction ratio of ~330 in the visible wavelength range. A single-state micropolarizer array with polarizing pixels as small as 5 mum x 5 mum has been fabricated. A multilayer spatially multiplexed three-state micropolarizer line array with a 14.4-mum resolution has also been fabricated for visible imaging polarimetry application.     

Terahertz polarization real-time imaging based on balanced electro-optic detection

A terahertz (THz) polarization real-time imaging system that can effectively reduce experimental time consumption for acquiring a sample's polarization information is achieved. An alternative THz polarization measurement method is proposed. In this method, a <110> zinc-blende crystal is used as the sensor, and the probe polarization is adjusted to detect THz electric fields on the two orthogonal polarization components. The relative sensitivity of the imaging system to the THz polarization angle is estimated to be less than 0.5°. To illustrate the ability of the system, two samples are designed and measured by using the system. From their THz polarization real-time images, each region of these samples can be precisely presented. Experimental results clearly show the special influences of different materials on the THz polarization. This work effectively extends the information content obtained by THz real-time imaging and improves the feasibility of the imaging technique.     

Target detection in optically scattering media by polarization-difference imaging

Polarization-difference imaging (PDI) was recently presented by us as a method of imaging through scattering media [Opt. Lett. 20, 608 (1995)]. Here, PDI is compared with conventional, polarizationblind imaging systems under a variety of conditions not previously studied. Through visual and numerical comparison of polarization-difference and polarization-sum images of metallic targets suspended in scattering media, target features initially visible in both types of images are shown to disappear in polarization-sum images as the scatterer concentration is increased, whereas these features remain visible in polarization-difference images. Target features producing an observed degree of linear polarization of less than 1% are visible in polarization-difference images. The ability of PDI to suppress partially polarized background variations selectively is demonstrated, and discrimination of target features on the basis of polarization information is discussed. Our results show that, when compared with conventional imaging, PDI yields a factor of 2-3 increase in the distance at which certain target features can be detected.     

Measurement of light wavelength based on nanostructured ordered pore arrays

A new method of light wavelength measurement is presented based on the nanostructured ordered pore arrays with multi-domains and centimeter square size formed by solution dipping-colloidal monolayer. Because of periodicity of the ordered pore arrays, perpendicular incidence of a parallel beam light on the array will lead to the diffraction spots or ring, depending on relative sizes of the beam and the domain in the arrays. The diffraction angle corresponds to wavelength of the incident light. On this basis, one can measure the wavelength of an incident light in transmission mode using such nanostructured ordered pore arrays, which is different from the conventional one fabricated from Michelson interference principle. Both the resolution and measurement precision can reach < 1 nm in such a simple method. Comparatively, this new measurement setup is simple in structure, low in cost, convenient in measurement, and especially, small in size. It could be used for online demarcation and real-time measurement of light wavelength in such as, mine operation, seabed exploration, and even space exploration due to its miniature.     

太赫兹超表面计算全息

全息术是一种三维成像技术,它已经被应用于多种实际场景。随着计算机科学与技术的迅猛发展,计算全息由于其方便和灵活的特性,已经成为一种广泛应用的全息成像方法。本文回顾了我们近期基于超表面的太赫兹计算全息研究进展。其中,作为全息板的超表面展示出了超越传统光学器件的独特性能。首先,利用超表面实现了对于全息板每个像素的相位振幅同时且独立的调控,进而实现了高质量全息成像。这种新的电磁波操控能力也带来了新的全息成像效果,如利用介质超表面实现了全息像沿传播方向上的连续变化。其次,对超表面在不同偏振态下的响应进行设计,分别实现了线偏振态与频率复用、圆偏振态复用、以及基于表面波的偏振复用超表面全息术。此外,本文提出了依赖于温度变化而主动可控的超表面全息术,为今后计算全息术的设计与实现提供了新的方案,也推动了超表面在实际应用方面的发展。     

Imaging objects hidden in scattering media with fluorescence polarization preservation of contrast agents

A method for fluorescence polarization difference imaging is demonstrated for enhancing the image quality of a luminous object embedded in a random medium. The polarization preservation of light propagating in the scattering medium leads to partially polarized light emission by a contrast-agent dye located inside the object. Subtraction of the images of the luminous object detected at two orthogonal polarization directions improves the image resolution compared with a conventional optical imaging approach.     

Adaptive algorithms for two-channel polarization sensing under various polarization statistics with nonuniform distributions

The polarization of light carries much useful information about the environment. Biological studies have shown that some animal species use polarization information for navigation and other purposes. It has been previously shown that a bioinspired polarization-difference imaging (PDI) technique can facilitate detection and feature extraction of targets in scattering media. It has also been established [J. Opt. Soc. Am. A 15, 359 (1998)] that polarization sum and polarization difference are the optimum pair of linear combinations of images taken through two orthogonally oriented linear polarizers of a scene having a uniform distribution of polarization directions. However, in many real environments the scene has a nonuniform distribution of polarization directions. Using principal component analysis of the polarization statistics of the scene, we develop a method to determine the two optimum information channels with unequal weighting coefficients that can be formed as linear combinations of the images of a scene taken through a pair of linear polarizers not constrained to the horizontal and vertical directions of the scene. We determine the optimal orientations of linear polarization filters that enhance separation of a target from the background, where the target is defined as an area with distinct polarization characteristics as compared to the background. Experimental results confirm that in most situations adaptive PDI outperforms conventional PDI with fixed channels.