Optical Interference Coatings Design Contest 2007: triple bandpass filter and nonpolarizing beam splitter

A triple bandpass filter (28 solutions received) and a nonpolarizing beam splitter (23 solutions received) were the subjects of the design contest held in conjunction with the 2007 Optical Interference Coatings topical meeting of the Optical Society of America. Fifteen designers participated using a wide spectrum of design approaches and optimization strategies to create the submissions. The results differ significantly, but all meet the contest requirements. Fabien Lemarchand wins both contests by submitting the thinnest (6254 nm) triple bandpass design and the widest (61.7 nm) nonpolarizing beam-splitter design. Michael Trubetskov is in second place, followed by Vladimir Pervak in both contests. The submitted designs are described and evaluated.     

Characterizing polarization management in a p-HMPD system

It has been a common challenge to operate optical see-through head-mounted displays in well-lit environments due to the low image brightness and contrast compared with the direct view of a real-world scene. This problem is aggravated in the design of a see-through head-mounted projection display (HMPD) in which the projected light is split twice by a beam splitter and further attenuated greatly by a retroreflective screen. A polarizing head-mounted projection display (p-HMPD) design was recently proposed to enhance the overall flux transfer efficiency and thus increase the brightness and contrast of displayed images. Different from the conventional nonpolarizing HMPD designs, the light polarization states in the p-HMPD system are deliberately manipulated to maximize the flux transfer efficiency, which can potentially result in three times higher efficiency than that of a nonpolarizing HMPD. By measuring the Mueller matrices of the major elements in both a p-HMPD and a nonpolarizing HMPD, we characterize the polarization dependence of each element on incident angles and wavelengths, and also investigate the depolarization effect of the retroreflective screen. Based on these experimental results, we further examine the overall luminance efficiencies of the two types of systems and analyze how various aspects of display performances are affected by the angular and chromatic dependence of the polarization components.     

Diffraction of horizontally polarized ultrasonic plane waves on a periodically corrugated solid-liquid interface for normal incidence and Brewster angle incidence

The theory, and the use at normal incidence, of shear-vertically polarized waves (with polarization vector in the plane containing the incident wave vector and the normal on the interface) using the mode conversion method has been tackled by others. Here we develop the theory for shear-horizontally polarized incident waves (with polarization vector perpendicular to both the normal on the interface and the incoming wave vector). We take into account normal incidence as well as oblique incidence. For normal incidence, we discover the generation of Love waves. If oblique incidence is considered, we discover the existence of a Brewster angle of incidence, comparable with the Brewster angle in optics, in which a diffraction grating can be used as a polarization filter.     

Design and analysis of all-dielectric broadband nonpolarizing parallel-plate beam splitters

Past research on the all-dielectric nonpolarizing beam splitter is reviewed. With the aid of the needle thin-film synthesis method and the conjugate graduate refine method, three different split ratio nonpolarizing parallel-plate beam splitters over a 200 nm spectral range centered at 550 nm with incidence angles of 45 degrees are designed. The chosen materials component and the initial stack are based on the Costich and Thelen theories. The results of design and analysis show that the designs maintain a very low polarization ratio in the working range of the spectrum and has a reasonable angular field.     

Control of polarization for a broadband dichroic filter at 45 degrees incidence

A method for the control of polarization for a broadband dichroic filter was reported and some design examples were elaborated. This method could be applied over a wide range of wavelengths and a wide range of polarizations in the transmission region. A nonpolarizing broadband dichroic filter and a broadband dichroic filter with certain polarization were designed and fabricated by electron beam evaporation with ion beam assisted deposition. The experimental spectral performances showed good agreement with their theoretical curves. In addition, the application of the method was discussed.     

Design and manufacture of all-dielectric nonpolarizing beam splitters

Past research on all-dielectric nonpolarizing beam splitters is reviewed. It is shown that, for a 50-nm spectral region, it is possible to design and manufacture a two-material nonpolarizing plate beam splitter for use at an angle of 45 degrees (with a measured rms reflectance of 0.50 +/- 0.01 for both s- and p-polarized incident light).     

斜入射滤光片的偏振相关损耗抑制技术

多腔窄带薄膜滤光片在倾斜入射时由于偏振光的中心波长会出现分离,会导致其偏振相关损耗迅速增加,严重影响光通信系统的性能.从理论上分析了斜入射时产生偏振相关损耗的原因,并提出了通过优化膜系的方法有效的实现了偏振光中心波长的对准,有效的降低了其通带内的偏振相关损耗.同时还提出了使用偏振分束器的方法,对单偏振光进行调制,在整个透射带内都实现了对偏振相关损耗的抑制.实验结果表明,两种消偏方式都能将窄带滤光片斜入射时的偏振相关损耗减小至0.2dB内,根据实际需要可以应用于不同的场合.     

Normally incident resonant grating reflection filters for efficient narrow-band spectral filtering of finite beams

Resonant grating reflection filters operating at normal incidence are investigated. At normal incidence these structures are shown to have characteristics different from those of structures operated at oblique incidence. We show how higher-order diffraction within the structure laterally confines the incident energy about the point of incidence and results in a broadened angular selectivity. Multimode structures are shown to exhibit broader angular selectivities and narrower spectral linewidths than those of single-mode structures, achieving angular selectivities hundreds of times broader than what could be obtained at oblique incidence. When compared with that for oblique incidence, the increase in angular selectivity is shown to greatly improve the performance of these filters for spectrally filtering finite incident beams.     

Spectral responsivity of various types of silicon photodiode at oblique incidence: comparison of measured and calculated values

The spectral responsivity of several types of silicon photodiode at oblique incidence (approximately 45 degrees) is investigated. Both windowless diodes and diodes that incorporate quartz windows are considered. The spectral responsivities are measured directly for both parallel and perpendicular polarized radiation. For comparison, the responsivity at oblique incidence is also calculated from the normal-incidence measured responsivity in conjunction with the reflectance values at normal and oblique incidence calculated from thin-film theory by use of the measured oxide thicknesses of the diodes and published data on the refractive indices of silicon and fused silica. A technique, believed to be novel, is described for accurately measuring the oxide thicknesses of the diodes. A comparison of calculated and measured responsivity values shows that, when imperfect polarizers are used, it may be more accurate over a certain spectral range to calculate the responsivities at oblique incidence rather than to measure them directly. The additional uncertainty associated with the calculated responsivity values at oblique incidence, with respect to the original source data for normal incidence, is +/-1% over a wide spectral range.     

偏振镜选购经验谈

被摄景物上的反射光形成的眩光往往大部分属于偏振光,可以用偏振镜滤去,从而显著提高画面质量。偏振镜有线偏振镜和圆偏振镜之分,一般的偏振镜为线偏振镜,有可能影响数码相机的AE和AF功能,圆偏振镜的前部起偏振镜作用,通过特定振动方向的偏振光,其后面部分则能使该偏振光的振动方向在一个圆周上旋转,恢复为非偏振光,就不会影响相机的AE和AF功能了。本文介绍如何分辨这两种不同性能和价格的偏振镜。     

Nonpolarizing beam splitter designed by frustrated total internal reflection inside a glass cube

A method for the design of an all-dielectric nonpolarizing prism beam splitter utilizing the principle of frustrated total internal reflection is reported. The nonpolarizing condition for a prism beam splitter is discussed, and some single layer design examples are elaborated. The concept can be applied to a wide range of wavelengths and arbitrary transmittance values, and with the help of a computer design program examples of 400-700 nm, T(p)=T(s)=0.5+/-0.01, with incident angles of 45 degrees and 62 degrees are given. In addition, the sensitivity and application of the design are also discussed.     

Nonpolarizing beam splitter design

A three-step design procedure is developed for dielectric stacks which are required to be nonpolarizing for a given wavelength lambdar and angle of incidence theta 0,r, at which the reflectance Rr is prescribed. The method leads to solutions in which only three layer materials occur and can be applied for a wide range of values of theta0,r and Rr. The media can be chosen from the available coating materials. Furthermore, the procedure offers the possibility of optimizing with respect to the behavior of the reflectance in the neighborhood of lambdar and theta0,r. An example is elaborated, and its results are compared with an actually produced coating.     

Design of 50 G nonpolarizing dense wavelength division multiplexer angle-tuning bandpass filter

Transmission characteristic differences of a narrow bandpass filter between p- and s-polarized light, especially the central wavelength separation, will corrupt the performance of the filter when the incidence is oblique. In this paper, by adding high-index materials asymmetrically to both sides of a low-index spacer, which tunes the equivalent index of the spacer, the central wavelengths of the two polarizations coincide perfectly when in 20° incidence; with different reflected layers on the two sides of the spacers and replacing some reflected layers with equivalent layers, the 0.5 dB normalized passband width is kept at 0.2 nm, which meets the requirement of the 50 G dense wavelength division multiplexer filter.     

Designs of infrared nonpolarizing beam splitters with a Ag layer in a glass cube

A novel design of a nonpolarizing beam splitter with a Ag layer in a cube was proposed and optimized, based on the needle optimization. The digital simulations of the reflectance and reflection-induced retardance were presented. The simulation results showed that both the amplitude and the phase characteristics of the nonpolarizing beam splitter could realize the design targets. The difference between the simulated and the target reflectance of 50% is less than 0.4% and the simulated and the reflection-induced retardance is less than 0.62 degrees in the 1260 -1360 nm range for both p and s components.     

Step method: a new synthesis method for the design of optical filters with intermediate refractive indices

We propose a new synthesis method for the design of multilayer optical filters with intermediate refractive indices, the step method. This method consists in adding infinitesimally small index steps in the index profile at optimal positions and then reoptimizing the thickness and the refractive index of the layers. Application of the method to the design of an antireflective coating, a low-pass edge filter, and an immersed polarizing beam splitter shows that it provides interesting solutions, even in the absence of a proper starting design. The formalism developed for the method also serves to demonstrate that the optimal filter consists of either homogeneous layers that maximize the effective refractive index contrast, or of graded-index layers.     

Optical properties of an isotrophic optically active medium at oblique incidence

The optical properties of an isotropic optically active medium at oblique incidence have been investigated. It was found that the amount of transmitted light converted from p polarization to s polarization and vice versa, through an isotropic optically active medium, is independent of the state of incident polarization. Though the optical rotation through the optically active medium is same for p and s polarization at normal incidence, it becomes different at oblique incidences.     

Effects of the angle of deposition on short-range order in amorphous germanium

A comparison of the atomic arrangements in germanium films deposited at normal and oblique incidence is made. It is shown that the parameters of short-range order are sensitive to the angle ? of deposition. The oblique incidence effects manifest themselves both in the intensity function and in the radial distribution function (RDF). The RDF of a film deposited at oblique incidence has an additional correlation peak at r₀ = 0.174 nm which is not observed for normal incidence. Its location corresponds to the length of the GeO bond. It arises because of the increase in the oxygen content of the filn with increasing obliqueness. The coordination number consistent with the GeO correlations is proportional to the oxygen content of the film as estimated by Auger electron spectroscopy. The incorporated oxygen and the structural anisotropy of obliquely deposited films also influence the shape of the second structural peak of the RDF. The reasons for the different oxygen contents in films prepared under the same vacuum conditions are discussed.     

Nonpolarizing guided-mode resonant grating filter for oblique incidence

A new type of guided-mode resonant grating filter is described. The filter is independent of polarization state for oblique incidence. The filter has a crossed grating structure, and the plane of incidence on the filter contains the symmetric axis of the grating structure. Theoretical considerations and numerical calculations using two-dimensional rigorous coupled-wave analysis show that a rhombic lattice structure is suitable to such filters. In this configuration an incident light wave is diffracted into the waveguide and is divided into two propagation modes whose directions are symmetric with respect to the plane of incidence. In particular, when the propagation directions of the two modes are perpendicular to each other, the fill factor of grating structure can be approximately 50%. The filter was designed for an incident angle of 45 degrees. Tolerances of setting errors and fabrication errors for this filter were estimated by numerical calculations.     

Filter performance of reduced sized defect photonic crystals based on single‐negative materials

Single‐ and multiple‐channeled filters based on single‐negative (SNG) photonic crystals with inversion defects have been demonstrated theoretically. Omnidirectional filters with wide angular apertures and multiple‐channeled filters at normal incidence have been reported. Sharp, high transmission peaks with frequencies lying within the SNG range are obtained. By variation of the structural parameters these structures can also be made to function as tunable or polarizing filters, though the frequencies of the transmission modes in these two cases will lie outside the SNG range. A significant feature of all the filter types discussed is the drastic reduction in size of the proposed structures in comparison to those reported earlier. This implies easier fabrication methods and lower cost. Improved performance of devices has been achieved by proper placement of defects.     

基于偏振分束器的C波段可调谐薄膜滤波器

针对多腔窄带薄膜滤光片在倾斜入射时会产生严重的偏振相关损耗问题,研制了一种基于双折射晶体偏振分束器、信道间隔为100 GHz的角度可调薄膜滤波器.该方法可简化倾斜入射时多腔窄带薄膜滤光片消偏振膜系结构,通过对入射光信号偏振态的控制,仅使用常规窄带滤光片就能实现角度调谐其中心透射波长.该可调谐滤波器件具有结构简单、成本低...