大尺寸气孔微结构光纤在光纤光栅中的应用

将微结构光纤分为光子晶体光纤和大尺寸气孔微结构光纤两种。详细介绍了大尺寸气孔微结构光纤。其包层的气孔硅结构（或者聚合物硅结构）影响了包层模式的空间分布以及包层模式的有效折射率，使其表现出与传统光纤不同的光学特性。基于这种微结构光纤的光纤光栅对外部折射率的变化显示了很好的稳定性。偏振特性（对长周期光纤光栅）可以大大加强。基于聚合物硅包层的长周期光纤光栅显示了优良的温度调谐性能。     

Bragg gratings in multimode and few-mode optical fibers

Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 μm is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 μm in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed     

A gain-clamped SOA with distributed Bragg reflectors fabricated under both ends of active waveguide with different lengths

We demonstrate a gain-clamped semiconductor optical amplifier (GC-SOA) which has gratings under both end regions of an active waveguide. Two gratings of the new GC-SOA are fabricated in different lengths. Their lasing modes and gain characteristics are measured and analyzed with different combinations of grating lengths. It shows different gain and noise characteristics according to the measurement direction in asymmetric grating combinations.     

Full Strain Tensor Treatment of Fiber Bragg Grating Sensors

Embedded fiber Bragg gratings can be subjected to arbitrary states of strain including shear strain. Such perturbations can cause coupling between polarization modes. Coupled-mode theory in Bragg gratings so far neglected this effect and only considered forward-backward coupling. Polarization mode coupling within a Bragg grating leads to interdependencies between Bragg reflection peaks which have so far been unaddressed. We formulate a full strain tensor treatment of fiber Bragg gratings, considering the coupling of the polarization modes within the grating. We give an approximation for the coupling coefficients affecting the polarization mode coupling and numerically solve the coupled-mode equations for representative states of strain. We show in which way shear strain affects the optical response of a grating and demonstrate how the fiber's beat length influences this characteristic.     

Analysis of multiple wavelength DFB fiber lasers

The behavior of multiwavelength distributed feedback fiber lasers is simulated in a comprehensive numerical model. Multiple fundamental modes can coexist, even though the coupling coefficients of their respective refractive index gratings are not equal, due to induced dynamic gain gratings. We have investigated the effect on the lasing state of variations in coupling strengths, gain parameters, grating Bragg frequency separation, relative phase between the gratings, length of the structure relative to the beat lengths between the gratings, grating center phase-shift errors, and saturation level of the UV-induced refractive index change     

Silicon thin‐film solar cells with rectangular‐shaped grating couplers

As an alternative to randomly textured transparent conductive oxides as front contact for thin‐film silicon solar cells the application of transparent grating couplers was studied. The grating couplers were prepared by sputtering of aluminium‐doped zinc oxide (ZnO) on glass substrate, a photolithography and a lift‐off process and were used as periodically textured substrates. The period size and groove depth of these transparent gratings were tuned independently from each other and varied between 1 and 4 μm and 100–600 nm. The optical properties of rectangular‐shaped gratings and the opto‐electronic behaviour of amorphous and microcrystalline silicon solar cells with integrated grating couplers as a function of the grating parameters (period size P and groove depth h_g) are presented. The optical properties of the gratings are discussed with respect to randomly textured substrates and the achieved solar cell results are compared with the opto‐electronic properties of solar cells deposited on untextured (flat) and randomly textured substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis of fiber Bragg gratings for dispersion compensation inreflective and transmissive geometries

Numerical analysis of the dispersion-compensating properties of fiber Bragg gratings (FBGs) in both reflective and transmissive modes is presented. First, the sensitivity of chirped, reflective gratings to the grating chirp parameter, index modulation, and grating length is examined, showing that apodization provides lower sensitivity to variations in these parameters. Second, we introduce a new transmissive geometry for grating-based dispersion compensation that utilizes the dispersive properties of a uniform Bragg grating in transmission     

从亚波长光栅到超构光栅:原理、设计及应用

随着纳米光子学的发展,光学结构如光学微腔、波导结构、光子晶体、亚波长光栅、超构表面等能够在微纳尺度实现对光的传输与调控,推动了光学集成化的发展。亚波长光栅由于其结构简单、成本低廉等特点得到了科学家们广泛的研究,应用在各种光学器件,逐渐形成了光栅分析模型的成熟理论体系。结合周期性结构耦合行为及超构表面中超构原子的散射调制特性,从亚波长光栅衍生出的超构光栅能够利用周期性布拉格散射提高调控光束的效率,从而避免了超构表面相位离散化带来的效率降低和能量损失。科学家们研究并设计了超构光栅,更多的物理现象及应用被探究和挖掘。文中对亚波长光栅以及超构光栅的基本理论、设计和应用进行了概述。从基本原理出发,论述了亚波长光栅和超构光栅的特性,综述了二者的理论设计及单元设计方法,并介绍了在生物传感、滤光片光谱调控和吸收薄膜等方面的应用。最后,展望了未来的发展方向。     

Mode conversion of ultrafast pulses by grating structures inlayered dielectric waveguides

Various grating configurations are introduced to develop structures for the mode conversion of an ultrafast, ultrawide-bandwidth optical pulse propagating in a layered dielectric waveguide. Introducing a new technique for efficient, real-time mode extraction, we examine these schemes with a full-wave, vector, finite difference time domain (FDTD) Maxwell equation simulator. The resulting FDTD simulator is very flexible and accurate; it is capable of modeling the interaction of few- or many-cycle optical pulsed modes with finite, aperiodic gratings with complex material configurations. The grating structure can be tailored to the pulsed optical modes of interest with this FDTD simulator. It is used to design a composite mode-conversion grating structure that realizes a 29.45% increase in the converted mode energy for an ultrafast six-cycle optical pulse over that achieved with standard uniform grating convertors     

一维4H-碳化硅光栅红外光学特性及红外尺应用

从理论和实验上对极化材料4H-SiC一维光栅的光学特性进行了研究。发现该结构中存在四种光学模式:传播表面声子极化激元、偶极子天线、局域表面声子极化激元和准静态表面声子极化激元。进一步利用传播表面声子极化激元对于光栅结构参数的敏感性和原子层沉积技术生长介质材料,观察到了沉积材料厚度变化和传播表面声子极化激元的峰位偏移量呈现线性关系。该研究有助于新型微纳器件如纳米尺、传感器等的开发。     

Azimuthal mode discrimination in radially chirpedconcentric-circle-grating distributed feedback lasers

We report a theoretical investigation analyzing the threshold modes of a concentric-circle-grating (CCG) distributed feedback laser with a radially chirped first-order Bragg grating. A numerical coupled-mode analysis of a chirped CCG laser shows improved azimuthal mode discrimination for chirped gratings with linear, quadratic, and square-root radial dependence. Negatively chirped gratings, in which the grating period decreases with radius, result in improved threshold discrimination between the circularly symmetric fundamental mode and higher order modes; positively chirped gratings, in which the grating period increases with radius, result in decreased threshold for higher order modes in general. Also, the intensity for the fundamental mode at the grating center can be reduced by an order of magnitude using linearly chirped gratings     

Spectral filtering of gain gratings and spectral evolution ofholographic laser oscillators

We present results of the spectral filtering properties of volume gain gratings and their role as diffractive optical elements in the spectral evolution of holographic laser oscillators. We show that the gain grating acts as a spectral filter with a filter bandwidth that is approximately inversely proportional to the medium length. We investigate holographic laser oscillators and find that, when either the gain grating is written by monochromatic radiation or when it is initiated from broad-band radiation, the output of such oscillators can evolve to single longitudinal mode in correspondence to experimental observations     

亚波长偏振光栅的研究进展

亚波长偏振光栅(PGs)具有衍射效率高,偏振特性好,易于实现偏振、分束、增透、高反、相位延迟等多种功能的优点,且体积小、重量轻、性能稳定可靠,是一种优良的新型光学元件,有着巨大的应用前景.介绍了亚波长偏振光栅的发展概况与最新研究进展,亚波长偏振光栅的特点及衍射理论,并分别对会属亚波长偏振光栅和介质业波长偏振光栅进行了分析.     

A unified treatment of radiation-induced photorefractive, thermal,and neutron transmutation gratings

We have reviewed different types of periodic structures (superlattices) induced by optical, infrared, and neutron irradiation. Both optical and electrical properties of these superlattices are analyzed, starting from the standard photorefractive model. New results on the thermoelectric and pyroelectric dynamic gratings are discussed in connection to the energy conversion and vibration sensing. For the neutron irradiation both real-time and static grating are analyzed, suggesting transmutation doping as a mechanism of recording     

Freestanding GaN Resonant Gratings at Telecommunication Range

We theoretically and experimentally demonstrate a freestanding gallium nitride (GaN) resonant grating at telecommunication range. The optical responses of the freestanding GaN resonant gratings are analyzed by the rigorous coupled-wave analysis method. The freestanding GaN resonant gratings are validated on 850-nm freestanding membrane by a combination of electron beam lithography, fast atom beam, etching, and deep reactive ion etching. The polarization properties of such freestanding GaN resonant gratings are demonstrated in reflectance measurements, and the experimental results correspond well to the theoretical model. The strong resonant peaks show a clear dependence on the duty ratio under transverse magnetic polarization, and a promising resonant peak of the fabricated freestanding GaN resonant grating, in which the grating period $P$ is 1500 nm, the grating height $h$ is 230 nm, and the grating width is 280 nm, is observed at 1516.4 nm with a full-width at half-maximum of 4 nm.      

Fabrication of sidelobe-suppressed InP-InGaAsP vertical coupleroptical filter using pair grating structure

In this letter, we report -19-dB suppression of sidelobes in a grating-assisted codirectional coupler (GACC) optical filter, which is the lowest to the best of our knowledge. Pair grating structures has been employed to control the coupling strength with a raised cosine functional form. A unit pair grating is composed of two unit conventional gratings and the fundamental period of pair gratings is fixed at 2Λ, where Λ is the grating period of conventional GACC filter. The distance between the two gratings inside a pair grating is linearly shifted to control the coupling strength. This structure provides a spatially weighted coupling strength without any change of averaged effective optical index or propagation constant     

Nanoimprint lithography fabrication of waveguide-integrated optical gratings with inexpensive stamps

We demonstrate that a replica grating can be effectively used as an inexpensive stamp for nanoimprint lithography to pattern diffractive optical couplers integrated with planar optical waveguides. Imprinted grating patterns were integrated with silicon oxynitride waveguide films to be used as an evanescent wave sensor in the input grating-coupler configuration. An anti-adhesion layer using an inexpensive, two-step chemical functionalization was developed for the stamps. The stamps were able to withstand imprint temperatures ranging from 140 to 190 °C and high fidelity imprints were obtained. The groove pattern was integrated in waveguide films by etch transfer and light-coupling properties of gratings with 1.2 μm pitch were tested using a λ = 1.55 μm laser. Compared to etched silicon masters, replica optical gratings provide uniform pattern density over their entire surface with no unstructured regions, are inexpensive, and readily available for R&D use.     

Complete Polarization Conversion Characteristics of Dielectric Grating Composed of Left-Handed Materials

The TE/TM polarization conversion characteristics of dielectric grating composed of left-handed materials for the case of plane wave oblique incidence are carefully investigated by a method which combines the multimode network theory with the rigorous mode matching method. It is indicated that complete polarization conversion between TE and TM modes can be realized using left-handed gratings. This can hardly achieve in the conventional right-handed gratings. Comparisons of polarization conversion properties between right-handed gratings and left-handed gratings are given with physical explanations. This unique merit of left-handed periodic structure is of important significance for accurate design of new millimeter wave TE/TM polarization converters.     

POLICRYPS switchable holographic grating: a promising grating electro-optical pixel for high resolution display application

POLICRYPS, an acronym of POlymer LIquid CRYstal Polymer Slices, is a structure made of perfectly aligned liquid crystal films separated by slices of almost pure polymer. Under suitable experimental and geometrical conditions, the structure is obtained by curing a homogeneous syrup of liquid crystal, monomer and curing agent molecules with a spatially modulated pattern of ultraviolet (UV) radiation. From an optical point of view, POLICRYPS is a holographic diffraction grating with a spatial periodicity that can be easily made of sub-micrometric scale, exhibiting diffraction efficiency values as high as 98%. Depending on the used geometry, the POLICRYPS grating can be utilized both in transmission or reflection, with negligible scattering losses, and can be switched ON and OFF by application of an external electric field of the order of few V//spl mu/m. In this paper, we review: 1) the "recipe" to fabricate POLICRYPS holographic gratings, along with their main optical and electro-optical properties; 2) a chemical-diffusive model that, taking into account sample temperature and intensity of the curing radiation, indicates the best conditions to fabricate these gratings; 3) a Kogelnik-like model that accounts for the dependence of the diffraction efficiency on material parameters, sample temperature, and applied electric field. Finally, we discuss the possibility of utilizing a micrometric sized POLICRYPS grating as a Grating Electro-Optical Pixel for high resolution display application.     

高空间频率向列相液晶二进制光栅

研究了向列相液晶在空间变化电场作用下的电光特性。模拟了向列相液晶相位光栅的旨向矢分布。随着光栅空间频率的增加条纹电场变得很重要，而且衍射方式也发生了变化。分析了光栅的光学性能并进行了实际测量。