Analysis of the Chirped Super Moiré Gratings Based on Acousto-Optical Superlattices

There are multiple passbands in a chirped Bragg grating based on acousto-optic superlattice. The structure can be regarded as an acousto-induced super Moiré grating (AI-SMG). The analysis shows that the passbands of the AI-SMG are produced by several pairs of neighboring chirped gratings. With suitable structure parameters selected, the passbands can be non-larenzian-shape, narrow flat-top, with ripple less than 0.5dB and steep slope. The devices can be used as tunable narrow-band multichannel transmission filters. This analysis is useful for the designs and applications of the devices.     

亚波长光栅衍射效率特性设计的遗传算法优化

亚波长光栅中的衍射需要使用矢量衍射理论进行分析,其衍射效率与多个因素有关,对任意面形、任意入射条件的亚波长光栅的衍射来说,使用严格的耦合波理论进行分析计算可以得到数值解。通过分析不同参数条件下的衍射特性和衍射效率对各个参数的敏感性,获得了对衍射效率影响最大的光栅参数——槽深。用接近衍射效率曲线的抛物线作为目标函数建立了适应度函数。使用遗传算法进行优化,得到了所期望的衍射效率滤波特性,从而完成了具有防伪功能的亚波长光栅的设计。     

Development and application of patterned conducting polymer thin films as chemoresponsive and electrochemically responsive optical diffraction gratings

We describe the preparation of two-dimensionally patterned polyaniline (PANI) thin films via microtransfer molding and electropolymerization techniques. This procedure yields reproducible conducting polymer patterns with excellent feature periodicity, making them useful as diffraction gratings. The fabricated polymer gratings were characterized via tapping-mode atomic force microscopy. Spectroelectrochemistry was used to characterize the optical properties associated with various intrinsic PANI redox states. In accordance with the Kramers–Kronig relation for change-in-absorptivity and change-in-index-of-refraction, electrochemically induced changes in refractive index (detected via changes in diffraction efficiency) were observed to coincide with electrochemically-induced changes in the PANI electronic absorption spectrum. In addition, the higher oxidation states of PANI and the associated changes in refractive index proved accessible via chemical oxidation. Beyond the novelty of a chemically-switchable transmission grating, the response of this system points to the possibility of developing diffraction-based chemical sensing schemes.     

Precise wavelength tuning of a dye laser using an active diffractive optical element

In this work, an active, reflecting diffraction grating was developed and characterized. A grating was holographically imposed onto the surface of a ceramic which could be deformed via the transverse, inverse piezoelectric effect, thus allowing active fine tuning of the grating constant. The tuning characteristics of this novel optical element were studied and the results compared with the linear theory of the piezoelectric effect. To demonstrate its applicability, the grating was installed in a dye laser and used to effect precise tuning of the output wavelength of the laser within a range of 220 pm. The possibility of quasi-static to high frequency operation of the system will allow this element to find use in a wide variety of applications.     

体光栅耦合波理论中的能量平衡

基于对体光栅衍射效率的计算分析,本文直接地、精细地讨论了体光栅的功率守恒问题.结果指出:弱耦合前提假定下的双波耦合波二阶理论,不能严格地满足能量平衡准则.     

二元矩形软X射线衍射光栅的标量区衍射理论

利用标量区衍射理论分析了正交二元矩形软Ｘ射线衍射光栅的光学特性，给出了理论设计的初步结果。     

Holographic grating formation in dye doped polymer dispersed liquid crystals

We report a detailed investigation on holographic grating formation in dye-doped polymer dispersed liquid crystals. Both optical and scanning electron microscope measurements have been carried out. All the experimental data support the idea that a photorefractive-like effect is the basic mechanism of the optical storage effect, while it is demonstrated that neither droplets' size or shape effects, nor dye or polymer reorientation are involved in the process.     

Polarization dependent loss of arc-induced long-period fibre gratings

We have investigated the polarization properties of long-period fibre gratings fabricated using the electric arc technique. It was found that the choice of the fabrication parameters (electric current, arc duration and pulling tension) affects the polarization dependent loss of the produced gratings. In particular, a non-monotonic dependence on the external pulling tension was obtained.     

Synthesis of tetrazole‐containing azo polymers with properties of photo‐induced birefringence and surface‐relief‐gratings via RAFT polymerization

A novel optically active monomer, 6‐{4‐[4‐(1‐phenyl‐1H‐tetrazol‐5‐yloxy)‐phenylazo] ‐phenoxy}‐hexyl methacrylate (PTPPHMA) bearing tetrazole and azobenzol moieties, was synthesized and polymerized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) as the RAFT agent and 2, 2′‐azobis(isobutyronitrile) (AIBN) as the initiator. Well‐defined optically active photochromic polyPTPPHMA(PPTPPHMA) was obtained. “Living”/controlled characteristics were observed in the polymerization: well‐controlled molecular weights (M_ns), narrow molecular weight distributions (M_w/M_n) of the polymers and successful chain‐extension of PPTPPHMA with styrene (St) as the second monomer. The photochemical interconversion between trans and cis isomers of PPTPPHMA in N,N′‐dimethyl formamide (DMF) solution was explored under irradiation of ultraviolet light. The photoinduced birefringence on the thin films of PPTPPHMA was investigated. A maximum birefringence of 0.1 was obtained, and no significant change of profiles of the birefringence after several cycles of writing/erasing/rewriting sequences was observed. The surface‐relief‐gratings (SRGs) were induced on the polymer films by interference of Kr⁺ laser beams at 413.1 nm with 35 mW/cm² intensity, the diffraction efficiencies from SRGs were measured to be in the range of 2.0–2.5%. The atomic force microscopy (AFM) results showed the gratings produced on the surfaces of the polymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 682–691, 2008     

利用双光栅的多普勒频移测速度

衍射光的多普勒频移是与光栅运动速度有关的量.激光束依次通过动光栅、静光栅衍射,然后使1对光频不同、彼此平行又能部分重叠的衍射光束通过硅光电池进行光电转换,得到的信号电流的频率等于多普勒频移.信号电流经I/V转换、f/V转换和A/D转换后,由单片机测出电压,由此就可以确定动光栅的运动速度.最后对利用双光栅的多普勒频移测气垫导轨上滑块的速度进行分析和讨论.