Nearly-off-axis transmissivity of Solc birefringent filters

The characteristics of light propagating near the axis of a birefringent filter are studied. A generalized formulation to describe the nearly-off-axis transmissivity of a Solc birefringent filter is derived. On this basis, the polarization conoscopic figures of Solc filters with different numbers of birefringent plates are simulated. Furthermore the variation of spectral transmission with angle of incidence is analyzed, and the field-of-view transmissivity and the spectral transmissivity averaged with respect to the spread of incident light are given. Primary experiments for verification are also demonstrated.     

Precise and versatile formula for birefringent filters

In an investigation of extraordinary- (E-) ray behavior and the index of refraction for E waves in a uniaxial crystal, a precise and versatile formula for birefringent filters, based on the exact construction of the optical path difference, is set up with neither the approximation Δn = n(o) - n(e) ≤ (or n(e)), nor the ambiguity sin(θ)sin(r(ω)) = n(e). The exact construction gives the correct variation of the position and the dimension in each path, yielding the path difference while the filter is tuning. The formula is applicable not only to a filter with its optical axis parallel to the entrance surface (PAPS) but also to a filter with its axis inclined to the surface (PAIS). Also, the formula indicates that a FAIS allows laser wavelengths to be tuned over a wider range than does a FAPS. The origin of the wider range is interpreted to be the greater variation in the index for the FAIS while the filter is tuning. With the help of the formula we design a FAIS for tuning a cw Ti:sapphire laser.     

Synthesis and tuning of high-order Solc-type birefringent filters

Multiple optical wavelength passbands of Solc-type filters can be reselected within each fixed half-period by a scheduled rotation of each birefringent filter element. No additional wave plates are needed, and wavelength channels can be switched on or off while others continue unaffected. Designs for high-order transfer functions suitable for wavelength multiplexing are given along with experimental results for a set of fifth-order filters. This tuning concept is verified and its application in fiber-optic multiplexers is discussed.     

Optical thin-film reflection filters based on the theory of photonic crystals

Based on the theory of photonic crystals and the framework of a single-channel reflection filter that we presented before, structures of reflection filters with multiple channels are proposed. These structures can overcome some drawbacks of conventional multichannel transmission filters and are much easier to fabricate. We have practically fabricated the reflection filters with two and three channels, and the tested results show approximate agreement with theoretical simulation. Moreover, the superprism effect is also simulated in the single-channel reflection filter, the superiorities to transmission filters are discussed, and these analyses may shed some light on new applications of reflection filters in optical communication and other systems.     

Low-loss birefringent spectral filters comprising three identical retarders

Basic fan or folded arrangements comprising three identical retarders in cascade between parallel or crossed polarizers are presented for constructing birefringent spectral filters without an internal polarizer. The retarders' axes are oriented with an angle increment of theta or -theta preferably with /theta/ 相似文献   

Polarization-dependent angle filters based on one-dimensional photonic crystals using mu-negative materials

We study transmission properties of one-dimensional photonic crystals consisting of mu-negative and positive index materials by using transfer matrix methods. The results show that transmission properties of the transverse electric waves depend on permittivity (?), while transmission properties of the transverse magnetic waves depend on permeability (μ); there exists a transmission band inside the single-negative gap in this periodic structure without defects, and the transmission band is insensitive to the incident angle for the transverse electric waves but sensitive for the transverse magnetic waves. This property can be used to make polarization-dependent angle filters.     

Synthetic complex superresolving pupil filter based on double-beam phase modulation

To take advantage of phase-only filters to reduce reflected stray light, two phase plates are used in a synthetic complex superresolving pupil filter to get a small spot for laser direct writing. The amplitude modulation in a conventional complex superresolving pupil filter (CCSPF) is substituted by an equivalent phase modulation. The equivalence between the proposed filter and a CCSPF is established for a general design. The effectiveness of the proposed filter was proven through experiments to obtain a small main lobe width of 0.86 times the size of the airy spot.     

薄膜体声波谐振器的梯形射频滤波器设计

从Mason等效电路模型出发,研究了基于薄膜体声波谐振器的梯形结构射频滤波器的设计。以往的研究中都没有考虑到介质的声损耗,这样得到的滤波器频响中就未计人插入损耗的影响。采用射频网络方法对薄膜体声波谐振器建模,并在模型中加入了介质声损耗的影响,然后就基于薄膜体声波谐振器的梯形射频滤波器的传输响应、带宽、插入损耗、阻带抑制以及带内波纹情况进行了分析和讨论。     

Simple method for accurate characterization of birefringent crystals

We present a simple method to determine the cutting angle and thickness of birefringent crystals. Our method is based on chromatic polarization interferometry and allows for accuracies of typically 0.1 degrees in the cutting angle and 0.5% in the thickness.     

Dual-mode microstrip filters with adjustable transmission zeros

A new type of dual-mode microstrip square-loop resonator that produces asymmetrical frequency responses is proposed. The coupling between degenerate modes of the proposed dual-mode resonator is discussed depending on the perturbation size. The effect of non-orthogonal input/output feed lines located along a straight line on the frequency response is investigated using full-wave electromagnetic simulations. Two second-order bandpass filters using this type of dual-mode microstrip resonator are designed, fabricated and measured to demonstrate the dual-mode microstrip filters exhibiting transmission zero (TZ) shifting property. The one of the second-order filters produces a filter characteristic with two TZs in the upper stopband, whereas the other one has two TZs in the lower and upper stopbands. The shifting property of one of the TZs from one side of the passband to the other side is realised by only changing the perturbation size. The fourth-order filters of this type are also investigated. Both simulated and measured results are presented.     

Efficient temporal shaping of ultrashort pulses with birefringent crystals

We report on a simple and robust technique to temporally shape ultrashort pulses. A number of birefringent crystals with appropriate crystal length and orientation form a crystal set. When a short pulse propagates through the crystal set, the pulse is divided into numerous pulses, producing a desired temporal shape. Flexibility in the final pulse shape is achieved through varying initial pulse duration, divided-pulse number, the polarization-mode delay, and energy distribution of the divided pulses. The energy efficiency of the technique is near 100% for a pulse train of alternating polarizations, and 50% for a linearly polarized pulse train.     

基于MATLAB的专家整定PID控制系统设计与仿真

针对在复杂系统中实现在线整定参数的PID控制问题 ,介绍了一种基于专家系统的自整定PID控制系统设计方案 ,同时利用MATLAB中的SIMULINK和控制系统工具箱进行了仿真研究 ,仿真结果表明 ,专家整定PID控制系统比常规PID控制器(控制参数固定 )控制效果好     

Design considerations of form birefringent microstructures

Diffraction characteristics of high-spatial-frequency (HSF) gratings are evaluated for application to polarization-selective computer-generated holograms by the use of two different approaches: second-order effective-medium theory (EMT) and rigorous coupled-wave analysis (RCWA). The reflectivities and the phase differences for TE- and TM-polarized waves are investigated in terms of various input parameters, and results obtained with second-order EMT and RCWA are compared. It is shown that although the reflection characteristics can be accurately modeled with the second-order EMT, the phase difference created by form birefringence for TE- and TM-polarized waves requires the use of a more rigorous, RCWA approach. The design of HSF gratings in terms of their form birefringence and reflectivity properties is discussed in conjunction with polarization-selective computer-generated holograms. A specific design optimization example furnishes a grating profile that provides a trade-off between the largest form birefrin gence and the lowest reflectivities.     

基于遗传算法的超分辨多元环形滤光片设计

本文研究利用光学超分辨技术提高光盘存储密度.给出了一种可以达到衍射超分辨力的多元环形滤光片的设计结果.介绍了该多元环形滤光片的理论设计方法.之后用遗传算法设计了多组多元环形滤光片的结构参数,模拟结果显示设计的环形滤光片能使横向的半峰全宽半径值减小30%,达到提高信息存储密度的目的.另一方面该环形滤光片能使焦深不变或变长,减小了在记录过程中因为光盘的微小波动而引起的记录信息的错误率.     

Cross-sensitivity effect in temperature-compensated sensors based on highly birefringent fibers

We analyzed the influence of the measurand-temperature cross-sensitivity effect on temperature stability in fiber-optic cross-spliced sensors that employ highly birefringent fibers. We show that the ratio of the measurand-temperature cross-sensitivity coefficient to the measurand first-order sensitivity determines the physical limit for temperature stability in cross-spliced sensors. Employing polarimetric as well as white-light interferometric methods, we experimentally determine a hydrostatic pressure-temperature cross-sensitivity coefficient in York bow-tie 800 fiber. From this we estimate the achievable limit for temperature stability of cross-spliced pressure sensors under environmental temperature changes.     

Real-time polarization state measurement based on a birefringent crystal wedge

Abstract

We present a method of single-shot polarization state measurement based on a birefringent crystal wedge. The phase delay and amplitude angle of detected light are encoded into two groups of fringes through the interference in a crystal wedge and further decoded by fringe position locations. This method has the merit of real-time measurement, a compact set-up and simple calibration. The principle, set-up, calibration and error analysis are presented in details. In the end, a single-shot measurement set-up with 80 kHz temporal resolution is demonstrated to investigate the molecule dynamic behaviour in a TN liquid crystal under a rectangular voltage.     

Wide-bandwidth adjustable Q switch based on rubidium dimers

A new type of Q switching for a flash-lamp-pumped Nd:YAG laser based on the saturable absorption of rudibium dimers is demonstrated. The variation of laser parameters such as output energy, pulse length, and repetition rate by means of temperature-controlled vapor pressure is shown. For a temperature of 320°C, a train of 40-ns pulses separated by 6-μs intervals is generated. When the temperature is 360°C, a single giant pulse with energy of 100 mJ and a pulse length of 10-15 ns is observed. Comparison with a solid-state passive Q switch based on LiF is provided. The new cell construction, consisting of a sealed-off sapphire cell containing rubidium vapor, is proposed for reliable, efficient, adjustable Q switchingthat is applicable to all types of solid-state lasers. The advantages of this mechanism of Q switching, such as thermal insensitivity, frequency locking and line narrowing, and wide spectral bandwidth, covering 0.6-1.3 μm, are discussed.     

Dynamically adjustable annular laser trapping based on axicons

To study the chemotactic response of sperm to an egg and to characterize sperm motility, an annular laser trap based on axicons is designed, simulated with the ray-tracing tool, and implemented. The diameter of the trapping ring can be adjusted dynamically for a range of over 400 microm by simply translating one axicon along the optical axis. Trapping experiments with microspheres and dog sperm demonstrate the feasibility of the system, and the power requirement agrees with theoretical expectation. This new type of laser trapping could provide a prototype of a parallel, objective, and quantitative tool for animal fertility and biotropism study.