Surface profile optimization of antireflection gratings for solar cells

The solar cell efficiency can be improved by antireflection gratings. In this paper, the antireflection gratings with different symmetrical surface profiles are investigated by numerical simulations based on the Rigorous Coupled-Wave Analysis. Simulated results show that the antireflection performance of sharp profile such as quadratic profile has a significant improvement compared with triangular and parabolic profiles, while the top cutoff in the grating tip will severely influence the antireflection performance. Meanwhile, proper length of flat region between grating features in the nonclose-packed triangular antireflection grating can have better antireflection performance than the close-packed counterpart for the same grating period and height. Such antireflection gratings with different surface profiles may offer attractive solutions to current commercial silicon solar cell, as well as organic and other semiconductor material based solar cells.     

正弦光栅的制作

介绍了一种制作正弦光栅的方法。与常用的马赫－曾德方法相比，该方法具有使用元件少，逃跑和调节方便，所获得的光栅对比度高等优点。     

用两个正弦光栅实现光学微分

本文通过实验和理论分析,指出用普通正弦光栅实现光学微分的可行性。     

Optimization for sinusoidal profiles in surface relief gratings recorded on photoresist

The formations of sinusoidal surface relief structures recorded in positive photoresist (Allresist AR-P 3120) have been studied and optimized for different recording parameters of gratings with spatial frequency of ～1200 grooves/mm. A stable sinusoidal pattern generated using a two-beam laser interferometric technique was recorded in thin films of positive photoresist deposited on glass substrates. Several gratings were generated by varying the exposure time of interference pattern and time of chemical development of exposed media. Time duration of exposure for 90 s and chemical development for 15 s were observed to be optimum for the translation of the sinusoidal interference pattern into nearly-sinusoidal profiled grooves in the gratings for a developer AR-300-26 of dilution of 2:1 (developer:de-ionized water).     

表面具有光栅结构的sol-gel薄膜制备及衍射效率的研究

介绍了一种在 sol- gel薄膜表面形成光栅结构的方法。用扫描电子显微镜 (SEM)表征了薄膜的表面形貌 ,用原子力显微镜 (AFM)测量了光栅结构的深度。测试了这种结构表面的衍射特性 ,并对结果进行了分析     

Self-processing solgel material for one-step fabrication of micrometer-period sinusoidal phase gratings using the Lloyd's mirror scheme

A novel self-processing silica-zirconia hybrid solgel material has been developed and employed in one-step fabrication of micrometer-period sinusoidal phase gratings. In the process, the gratings with a sinusoidal profile were corrugated on the surface of the solgel film by UV exposure using the Lloyd's mirror setup. No further development or etching step is needed to reveal the sinusoidal profile because the corrugation is formed due to the self-processing property of the solgel material, which is robust enough to be used as an end product. The period, amplitude, diffraction efficiency of the +/-1 order, and surface roughness of one of the fabricated gratings are 0.99 microm, 330 nm, 30.56%, and 1.27 nm, respectively. The new self-processing material is practical and promising for fabrication of micro-optical elements.     

Modelling of strongly nonlinear sinusoidal Bragg gratings by the Method of Single Expression

The one-dimensional problem of plane EM wave interaction with strongly nonlinear sinusoidal Bragg gratings is exactly solved using the new Method of Single Expression (MSE). The basic point of the method is the presentation of the electrical field in the modulated medium (Bragg grating) in the form of a single expression, contrary to the traditional counter-propagating waves approach. The spectral characteristics of linear Bragg gratings of different length are presented. The influence of loss or gain on the spectral characteristics of Bragg gratings is considered. The electrical field amplitude distributions along a grating at the wavelengths corresponding to the minima and maxima of reflectivity in the vicinity of the Bragg resonance are illustrated. Bistable and multistable dependences of reflectivity on the incident electrical field amplitude are obtained for negative and positive nonlinearities.     

profile measurement by projecting two gratings with different pitches

A new method for measuring objects with steps is proposed in which two gratings with different pitches are projected on the object surLace. The method is demonstrated with sinusoidal gratings made of laser interference fringes and also sinusoidal gratings formed by liquid crystal controlled by computer. An object with step height of 20 mm is measured with standard variation below 3%.     

Diffraction from metallic gratings with locally varying profile forms

Measurements of the diffraction characteristics of one-dimensional surface-relief gratings of locally varying profile are compared with rigorous diffraction theory. These gratings result from the superposition of two linear sinusoidal gratings of uniform depth for which the relative phase between the two gratings varies slowly with position. The resultant surface profile exhibits a relatively large-period variation in profile form. The periodic variation in diffraction efficiency that results yields a visual moiré pattern that has interesting asymmetry and polarization properties that alter as the viewing conditions are changed; the gratings can be exploited by diffractive optically variable devices for document security.     

The influence of surface plasma oscillations on the diffraction orders of sinusoidal surface gratings

We have investigated the intensity of p-polarized light diffracted by sinusoidal surface gratings. The structure of resonance anomalies found in the light intensities of the diffraction orders is shown for silver coated gratings with various groove depths.     

Polarization conversion from highly conducting holographic gratings with asymmetric profile

We use a rigorous electromagnetic code to investigate the differences between the zeroth-order cross-polarization reflection coefficients in highly conducting metallic gratings with asymmetric profile. This study results of interest from a practical point of view due to its possible applications as a technique to detect gratings asymmetries. Numerical results in holographic gratings made of gold with asymmetric profiles are presented.     

Flat-top profile of an excimer-laser beam generated using beam-splitter gratings

We present a simple solution to the beam-shaping problem in which a wide, typically rectangular spatial distribution of an excimer-laser beam should be transformed into a flat-top distribution, a few millimeters wide in both directions. The set-up can be made practically lossless and it allows the energy density of the pulse to be increased by a factor of 50. The method finds use, e.g., in pulsed laser deposition, UV lithography and micro machining.     

Microwave verification of a numerical optimization of fourier gratings

A recent holographic technique makes it possible to manufacture a new kind of grating, the “Fourier grating”, whose profile is given by a superposition of a fundamental and a finite number of harmonics. A local theoretical optimization shows that this type of grating can have an efficiency better, than that of the echelette, for a broad wavelength range. In this paper, we show the validity of this theoretical prediction by an experimental verification in the microwave region.     

用粒子群优化算法设计光纤布拉格光栅

用粒子群优化(PSO)算法对二元相位取样光栅进行优化设计.实现了利用二元相位取样光栅对多信道色散和色散斜率的同时补偿.设计得到的二元相位取样光栅的反射谱各信道均匀,时延线性好,带宽、色散量和色散斜率可以根据实际的光纤类型来调整,对折射率调制要求较低.由于只有π相移,因此其制作比多级相位取样光栅相对简单.与其他优化方法相比,粒子群优化算法具有简单、收敛速度快等优点.     

Efficient method for launching in-gap solitons in fiber Bragg gratings using a two-segment apodization profile

We theoretically demonstrate what is a new method for efficient launching of in-gap solitons in fiber Bragg gratings. The method is based on generating a soliton outside the grating bandgap. Then, the soliton is adiabatically coupled into the bandgap by using its particlelike behavior. We compare our method to a previously published launching scheme that is based on generating the soliton directly within the grating bandgap. When using low-intensity incident pulses, the transmission efficiency of our method is three times higher than that of the previously published scheme.     

厄米-高斯光束通过正弦和矩形浮雕光栅传输特性的比较研究

使用严格的傅里叶模式理论和反射-透射系数矩阵递推算法(RTCM)，对不同阶数的厄米-高斯光束通过特征尺寸与波长可比拟的正弦和矩形浮雕光栅中的传输特性做了详细的研究和比较.结果表明，入射光束的初始场分布和浮雕光栅的结构影响浮雕光栅内的光强分布.矩形浮雕光栅对光束匀滑效果优于正弦形浮雕光栅.     

Technique for characterization of dimensional changes in slanted holographic gratings by monitoring the angular selectivity profile

A method has been developed for retrieving the complete angular selectivity profile of transmission holographic gratings in one step. The method is applied to study in real time the shrinkage and changes in the effective optical thickness of a slanted holographic grating recorded in an acrylamide-based photopolymer. It can form the basis of a holographic sensor of analytes that cause a thickness change in the holographic medium. It can also be useful for the study and optimization of holographic recording materials and for quality control during production of holographic optical elements.     

Real-time surface profile measurement using a feedback type of sinusoidal phase modulating interferometer

In this paper, we propose a sinusoidal phase modulating (SPM) interferometer that is insensitive to external disturbances, and its measuring principle is analyzed theoretically. In the SPM interferometer, the interference signal is detected by a high-speed image sensor based on a low-speed CCD and a signal processing circuit is used to obtain the phase of each point on the surface. Therefore, the surface profile can be measured real-time. The experiments measuring the surface profile of a wedge-shaped optical flat show that the measurement time of the SPM interferometer is less than 10 ms, the repetitive measurement accuracy is 4.2 nm. The results show that the impacts of nonlinear distortion of the piezoelectric transducer (PZT) and part external disturbance are removed.     

Synthesis of long-period fiber gratings with a Lagrange multiplier optimization method

Based on the Lagrange multiplier optimization (LMO) method, a new synthesis approach for designing complex long-period fiber grating (LPG) filters is developed and demonstrated. The proposed synthesis method is a simple and direct approach. It was used to efficiently search for optimal solutions and constrain various parameters of the designed LPG filters according to practical requirements. The inverse scattering algorithm is a good tool for designing FBG filters; as well as for designing transmission-type fiber grating filters like LPGs. Compared to the results of the discrete layer-peeling (DLP) inverse scattering algorithm for LPGs, the synthesized LPGs, using the LMO approach, are more flexible and workable for the constraint conditions can be easily set in the user-defined cost functional, such as the limitation on the maximum value of the refractive index modulation and the parameters of the initial guess in LMO algorithm. Linear transmission LPG filters and EDFA gain flattening filters are synthesized and analyzed systematically by using the proposed method with different parameters. Moreover, as a variation-based method, we find that the convergence and the synthesized results of the LMO method are strongly dependent on the initial guess parameters.