Full-range, complex spatial light modulator for real-time holography

We demonstrate a full-range complex and transmissive spatial light modulator (SLM) for simultaneous and independent amplitude and phase modulation of an input wave field. Arbitrary scalar complex optical fields are generated by stacking a pixelated liquid crystal display operating in phase-only (2π) modulation with passive polarization-sensitive components. The principle is based on optical combining the light fields of two neighboring phase-only modulating pixels, which were made orthogonally polarized by a structured half-wave plate, then passing through a birefringent plate to laterally shift one of the beams collinear to the other, and finally bringing to interference by a linear polarizer. Complex modulation by the proposed SLM is experimentally verified in monochrome green operation.     

Simultaneous experimental generation of vacuum squeezing and bright amplitude squeezing from a frequency doubler

Both vacuum-squeezed and bright amplitude-squeezed states of light are experimentally generated from a frequency doubler with a semimonolithic Fabry-Perot configuration consisting of a type II nonlinear crystal and a concave mirror. Vacuum squeezing of 3.2 +/- 0.1 dB and amplitude squeezing of 1.3 +/- 0.2 dB are obtained simultaneously at a pump power of 8 mW. The two quadrature-squeezed optical fields that are generated are of identical frequency at 1080-nm wavelength and orthogonal polarization. Optimizing the input pump power by 19 mW yields as much as 5.0 +/- 0.2 dB of maximum vacuum squeezing. The advantages of the system are its simplicity and multiple utility.     

光轴平行晶体表面时的锥光干涉图

针对光轴平行晶体表面时的锥光干涉图,提出了计算干涉场中振幅和相位分布的方法,据此绘制完整的干涉图,方便地显示出晶体参数改变时锥光干涉图的变化规律．用CCD摄像机拍摄了铌酸锂晶体的锥光干涉图,结果与理论完全一致。     

On the dielectric properties of molecular crystals: II. First-order spatial dispersion and optical activity

The general formal expression for the wavevector- and frequency-dependent dielectric susceptibility tensor of a simple molecular crystal, derived in paper I, is applied to the case of a Bravais lattice with gyrotropic molecules. The dielectric susceptibility tensor is calculated with first-order spatial dispersion and from this an expression for the gyration tensor is derived. As an example the optical rotary power is calculated for light propagating along the optical axis of a gyrotropic tetragonal crystal.     

"Ideal" optical delay lines based on tailored-coupling and reflecting, coupled-resonator optical waveguides

We present a design of "ideal" optical delay lines (i.e., constant amplitude and constant group delay over the desired bandwidth). They are based on reflection from coupled-resonator optical waveguides (CROWs). The inter-resonator coupling coefficients are tailored and decrease monotonically with the distance from the input to realize all-pass Bessel filters. The tailored coupling coefficients result in a frequency-dependent propagating distance which compensates for the group velocity dispersion of CROWs. We present a simple formalism for deriving the time-domain coupling coefficients and convert these coefficients to field coupling coefficients of ring resonators. The reflecting CROWs possess a delay-bandwidth product of 0.5 per resonator, larger than that of any kind of transmitting CROW. In the presence of uniform gain, the gain enhanced by slow light propagation and the constant group delay result in efficient and dispersion-free amplifiers.     

Design of an augmented reality display based on polarization grating

A new optical system for an augmented reality(AR) display is proposed in this paper.The optical system mainly includes a ray deflector, coupling input grating, optical waveguide, and coupling output grating.Both the ray deflector and the coupling input grating are designed based on the diffraction characteristics of the polarization grating, and the coupling output grating is the Bragg reflection grating.Compared with other AR schemes, this AR optical system not only reduces the number of projections from two to one, but also improves the efficiency of light coupling into the optical waveguides.The energy loss is reduced by utilizing the single-order diffraction characteristics of the polarization grating in its coupling input structure.The light deflector uses the polarization selectivity of the polarization grating and the characteristics of the rotating light of the twisted nematic liquid crystal layer to realize beam deflection.The working principle of the optical system is experimentally and theoretically demonstrated.     

Time-division multiplexing of the orbital angular momentum of light

We present an optical setup for generating a sequence of light pulses in which the orbital angular momentum (OAM) degree of freedom is correlated with the temporal one. The setup is based on a single q plate within a ring optical resonator. By this approach, we demonstrate the generation of a train of pulses carrying increasing values of OAM, or, alternatively, of a controlled temporal sequence of pulses having prescribed OAM superposition states. Finally, we exhibit an "OAM-to-time conversion" apparatus that divides different input OAM states into different time bins. The latter application provides a simple approach to digital spiral spectroscopy of pulsed light.     

Defective photonic crystals with greatly enhanced second-harmonic generation

A one-dimensional defective photonic crystal structure is proposed with the aim of studying its nonlinear optical properties. In such a structure, extremely enhanced second-harmonic generation with an efficiency ~5 orders of magnitude higher than that of ordinary films is demonstrated in a numerical simulation. Extraordinary phase conditions of the process in such a structure were explored, and efficient forward and backward second-harmonic generation could be achieved simultaneously. The mechanism of the enhancement is the high field intensity and efficient wave coupling introduced by light localization in defect states, from which many other nonlinear processes can also benefit.     

Experimental generation of optical non-classical states of light with 1.34 <Emphasis Type="Italic">μ</Emphasis>m wavelength

We report the experimental generation of the optical non-classical states with 1.34 μm wavelength which is close to one of the fiber telecommunication windows (1.31 μm). The single-mode amplitude squeezed states with quantum fluctuation of 2.3 ± 0.1 dB below the shot noise limit (SNL) and the entangled states with quantum correlation of 1.1 ± 0.1 dB below the SNL are produced by an optical parametric amplifier with a type-I phase-matched PPKTP crystal and a pair of properly oriented type-II phase-matched KTP crystals, respectively.     

A high-efficient method for generating radially and azimuthally polarized Bessel beams using biaxial crystals

As was shown previously, in propagation of a circularly polarized Bessel light beam along the optical axes of a biaxial crystal, there takes place the conversion of the order of Bessel function. In this paper, a new result is presented which is obtained by varying the polarization state of an input beam. Namely, a linearly polarized beam can be transformed into a beam with the radial or azimuthal polarization state. At that the order-transformation also occurs. The switching between radial and azimuthal polarization states of the output beam is performed by the proper switching between two orthogonal linear polarization states of the input beam. The efficiency of polarization conversion is high and can be practically full at an appropriate choice of the cone angle of the input beam or crystal length.     

基于矩阵理论的螺旋液晶透射光偏振态研究

将螺旋型液品看作是N层双折射材料晶片叠合而成,而每层光轴相对于相邻的晶片有一个小的旋转.本文基于矩阵理论,研究了光在螺旋液晶中传输时偏振态的变化.经过详细的数学推导,理论研究表明.线性偏振光经过螺旋液晶后偏振态会发生改变.当满足一定的条件时,线偏振光的偏振方向旋转90°,左旋圆偏振光经过左旋螺旋液晶后转变为右旋圆偏振光.     

Design and analysis of all-optical 4–2 binary encoder based on photonic crystal

In this paper we theoretically propose combining optical waveguides with nonlinear photonic crystal based ring resonators for realizing an all optical 4–2 encoder. Nonlinear resonant rings are constructed from GaAs as the material used for dielectric rods. By application of optical beam to input ports of the structure the on/off states are realized and the resulting truth table confirms functionality of proposed device. The switching threshold and time delay of the device are about 1 kW/µm² and 1 ps, respectively. The normalized power at the output ports for all the ports in ON states is the same and equal to 60%.     

Near-field probing of photonic crystals

Photonic crystals form an exciting new class of optical materials that can greatly affect optical propagation and light emission. As the relevant length scale is smaller than the wavelength of light, sub-wavelength detection forms an important ingredient to obtain full insight in the physical properties of photonic crystal structures. Spatially resolved near-field measurements allow the observation of phenomena that remain hidden to diffraction-limited far-field investigations. Here, we present near-field investigations in both collection and illumination modes that highlight the power of local studies. We show how propagation losses are unambiguously determined and that light detected in far-field transmission can actually contain contributions from different, sometimes unexpected, local scattering phenomena. Simulations are used to support our findings. Furthermore, it is shown that local coupling of light to a thick three-dimensional photonic crystal is position-dependent and that the spatial distribution of the coupling efficiency itself is frequency-dependent.     

Multitarget Detection Using a Hybrid Optical Joint Transform Correlator with Power Spectrum Subtraction

Multitarget detection using a hybrid optical joint transform correlator with power spectrum subtraction is proposed. This architecture is a programmable single spatial light modulator joint transform correlator. It consists of a liquid crystal display panel, an imaging lens, and a liquid crystal light valve to enhance resolution and space-bandwidth production. In this technique, it has two joint images in the input plane. In the second joint image, the reference image is contrast-reversal. With this technique, the second joint power spectrum is subtracted from the first joint power spectrum and the subtracted joint power spectrum is then taken the inverse Fourier transform. This technique is found to yield better correlation output performance than that of the classical joint transform correlator. Computer simulation results and the optical experimental results for input scene of the multitarget are given.The results have verified the correctness of the system design and performance analysis.     

Multitarget Detection Using a Hybrid Optical Joint Transform Correlator with Power Spectrum Subtraction

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高斯光束在偏硼酸钡单晶和孪晶中的倍频现象

理论探讨了高斯光束在非线性单轴晶体中的倍频效应。基于麦克斯韦方程组并考虑晶体的各向异性推导出负单轴I型晶体相位匹配下的倍频耦合波方程组。建立了具体的关于偏硼酸钡（BBO）单晶以及孪晶的物理模型并做数值求解。对求解所得到的单晶以及孪晶的谐波能流分布、晶体出射面探测点处谐波电场时域分布、总输出能量、输出光束频谱和输入光束角谱分别进行分析讨论,从束腰宽度、晶体结构以及材料性质对倍频的影响等方面做出具体合理的解释。研究结果对于单轴晶体的非线性光学性质的研究以及相应的光学晶体器件的研发等具有一定的参考价值。     

Optical properties of chiral photonic crystals with linear profiles of modulation parameters

The oblique propagation of light through a layer of chiral photonic crystal (PC) with linear profiles of modulation parameters is considered. The problem is solved by the method of Ambartsumyan layer addition. The wavelength dependences of the amplitude characteristics have been studied at different angles of incidence in two cases, i.e., in a chiral PC with a linear profile of modulation period and a chiral PC with a linear profile of modulation depth. It is shown that the photonic band gap is broadened in both cases and that omnidirectional reflection occurs under certain conditions. The nonreciprocity features are investigated for these two cases and it is shown that a chiral PC with a linear profile of modulation period can operate as an ideal optical diode in a certain frequency range. The features of the effect of change in the modulation parameters on the photon density of states, group velocity, and group velocity dispersion are analyzed. It is shown that, when the modulation parameters change in space, the photon density of states at the photonic band gap edges significantly decreases. It is proposed to use PCs with a spatially changing modulation period can be used to compress (expand) light pulses.     

基于扭曲向列液晶空间光调制器的矢量光生成

基于扭曲向列型液晶空间光调制器的旋光特性, 根据空间光调制器所加电压和加载相位与旋光角度的对应关系, 设计了可以生成多种涡旋矢量光的通用光路. 利用该原理和光路系统, 在实验上生成了多种携带轴对称相位的矢量光以及图案般复杂的矢量光, 观察和检测了它们的偏振特性, 获得了较好的实验结果. 并且模拟了具有涡旋相位的矢量光的紧聚焦场, 分析了它们的紧聚焦特性. 由于这种生成矢量光的方法光路装置简单、操作容易, 产生矢量光的过程中几乎不损失能量, 并且不存在聚焦过程, 因此在如强激光矢量光束与物质相互作用、激光加速等方面具有重要的应用潜力.     

Dynamic holography with nonplane waves in sillenites

A three-dimensional model describing two-wave mixing in photorefractive crystals with finite beams of arbitrary shape is presented. The well-known longitudinal and transverse geometries are generalized by allowing an arbitrary orientation of the local grating vector. The coupled equations for the wave amplitudes are solved numerically in the small-angle approximation by introducing the light paths as characteristics. The influence of amplitude distributions and phase-front curvatures as well as the influence of geometrical arrangements and crystal properties (i.e. optical activity, externally applied voltage) on the energy exchange and the evolution of the polarization states is investigated. It is demonstrated that scanning the cross-section of the finite signal beam behind the crystal allows analysis of the coupling process inside the crystal which cannot be studied directly. The results of experiments with finite beams carried out on a BSO crystal are in good agreement with the numerical calculations.