Quantum properties of optical images in coupled nondegenerate parametric processes

Quantum properties of parametric amplification and frequency conversion of an optical image in coupled parametric interactions are analyzed for the case of a remote object. The coupled-wave interaction consists of a traditional process of parametric amplification in the high-frequency pump field accompanied by the frequency mixing of generated and pump waves. The photon number density and signal-to-noise ratio at the interacting frequencies are studied in the image plane at the output of the nonlinear frequency converter in the fixed pump field approximation. The degree of entanglement of optical images at frequencies above and below the pump frequency is investigated.     

Simultaneous parametric generation and up-conversion of entangled optical images

A quantum theory of parametric amplification and frequency conversion of an optical image in coupled nonlinear optical processes that include one parametric amplification process at high-frequency pumping and two up-conversion processes in the same pump field is developed. The field momentum operator that takes into account the diffraction and group velocities of the waves is used to derive the quantum equations related to the spatial dynamics of the images during the interaction. An optical scheme for the amplification and conversion of a close image is considered. The mean photon number density and signal-to-noise ratio are calculated in the fixed-pump-field approximation for images at various frequencies. It has been established that the signal-to-noise ratio decreases with increasing interaction length in the amplified image and increases in the images at the generated frequencies, tending to asymptotic values for all interacting waves. The variance of the difference of the numbers of photons is calculated for various pairs of frequencies. The quantum entanglement of the optical images formed in a high-frequency pump field is shown to be converted to higher frequencies during the generation of sum frequencies. Thus, two pairs of entangled optical images are produced in the process considered.     

Frequency control of surface plasmons with oscillating metal-insulator-metal waveguides

A single frequency of surface plasmon polaritons (SPPs) will be converted to many discrete frequencies as they are transmitted through a metal-insulator-metal waveguide with its core width undergoing a harmonic oscillation. The process of the frequency conversion shares many key properties with the light diffraction in discrete optical systems. By employing the conception of optical diffraction management, we can control the discrete frequencies of SPPs such as the intensity and spectrum width by changing the initial phase of the waveguide oscillation. The study bridges the spatial discrete diffraction and frequency transition of SPP modes. Theoretical analysis based on the effective index method and coupled mode theory is provided in detail.     

Design of Ka-band Monolithic Image Rejection Mixer

In this paper, a 30–40 GHz monolithic image rejection mixer is described. The mixer employs two drain LO injection mixer cells, which can perform well even with zero drain bias voltage. Also it employs Lange Coupler for RF quadrature signal generation. The mixer is fabricated by a commercial 0.18-μm pseudomorphic high electron-mobility transistor (pHEMT) process. It achieves image rejection ratio of more than 20.4 dB and conversion loss of less than 12.6 dB in the frequency range of 30 to 38 GHz.     

基于一代像增强器的高分辨率X射线相机

为了实现在较低剂量下获得较高的分辨率,研制了一款价格低廉的X射线CCD相机。该相机使用硫氧化钆作为转换屏、经一代像增强器增强后的图像通过光锥耦合到CCD相机上;为了提高系统的光传输效率,提出了将像增强器输出直面板或倒像器直接更换成光锥,其小端直接同CCD相机耦合的方案;通过灰度分析计算对比度曲线,拟合得出系统的本征空间分辨率为13 Lp/mm;通过拍摄实际景物,可以清晰地看到其内部的细节,显示出比较好的图像质量。     

Low-frequency magnetoelectric effect in a Galfenol-PZT planar composite structure

The forward and inverse magnetoelectric (ME) effects are experimentally studied in a two-layer planar structure containing mechanically coupled Galfenol and PZT plates. The process of production of polycrystalline Galfenol plates and their magnetic and magnetostriction characteristics are described. For the forward ME conversion, the dependences of the amplitude of the voltage generated by the structure on the magnitude and orientation of a dc magnetic field and the frequency and amplitude of a modulating magnetic field are measured. For the inverse ME conversion, the dependences of the amplitude of the change in the magnetic induction of the structure on the dc magnetic field and the frequency of an ac electric field applied to the structure are measured. The efficiencies of the forward and inverse ME conversion are estimated for the case of low-frequency field modulation and under conditions of the resonance excitation of bending and longitudinal mechanical vibrations in the structure.     

长腔DFB半导体激光器非简并四波混频波长转换效率

本文从理论上计算了长腔DFB-LD中基于非简并四波混频的波长转换效率,由耦合波方程的数值解,得出波长转换效率与腔长、泵浦光功率、增益系数、DFB-LD谐振光与注入光的频率失谐量等的关系.数值计算结果表明,通过提高泵浦光功率、增益和腔长可有效地增大波长转换效率.     

Small-stokes-shift frequency conversion in single-mode birefringent fibers

We report experimental observation of nondegenerate four-photon mixing (FPM) via a new phase-matched process in birefringent fibers. This phase-matching process is characterized by relatively long coherence lengths, and by small pump-to-Stokes frequency shifts (of the order of 100 cm^-1 in high birefringence fibers) that are directly proportional to the fiber birefringence. Pump-to-Stokes energy conversion efficiencies of over 40 percent have been obtained with moderate pump powers (≈1 kW) from a visible cw mode-locked dye laser coupled into single-mode polarization-preserving high-birefringence fibers of a few meters length. In addition, we report the first observation of a totally non-degenerate phase-matched four-photon process in a fiber; this invokes mixing of the original FPM Stokes component with the pump and stimulated Raman radiation.     

Light frequency conversion in photonic crystals

Light frequency conversion when light interacts with a shock wave propagating through a photonic crystal is investigated. Two new phenomena are found, the first is that frequency increases by integral multiple of a certain amount in the process of frequency conversion. The second phenomenon is frequency conversion that still occurs when the shock wave front is replaced by a vacuum area. Through FDTD simulations and analytical theory, photon-phonon interaction and surface decaying mode interpretations for the mechanism of frequency conversion are found.     

Collective dynamics of two-dimensional coupled Brownian motors

The transport properties of coupled Brownian particles in a two-dimensional rocking ratchet are investigated via Langevin simulation. The results show that the average center-of-mass velocity is multi-peaks function of the frequency of the driving force. Furthermore, in the 2D coupled Brownian motor system there are the collective effect and ratchet behavior, which can switch depending on the frequency of driving force. It turns out that the cooperative effect between the interaction of coupled particles and external rocking driving force facilitates collective directional motion and energy conversion.     

基于波导模式变换的圆波导TE62模式激励器的研究

基于不规则波导模式匹配法以及缓变波导中电磁波模式耦合理论,研究了一种W波段圆波导TE₆₂模式激励器. 该波导模式激励器采用矩形波导TE₁₀模式通过侧壁耦合馈入同轴波导,利用同轴波导的选模特性激励TE₆₁模式;随后利用轴向半径周期微扰的圆波导实现TE₆₁–TE₆₂模式变换. 文中推导了矩形-同轴波导模式匹配理论,系统研究了波导结构缓变参数对模式变换效率的影响,完成了模式变换器的优化仿真设计,数值计算结果表明：中心频率处TE₆₂模式的转换效率为94.5%,纯度为98.16%,效率85%以上带宽达到1 GHz,能够满足回旋管冷测的要求. 关键词： 同轴波导 模式变换 耦合模理论 半径微扰     

失谐量子频率转换系统薛定谔方程的显式解析解

根据光和频产生过程的动力学演化总是保持闲置光和信号光的光子数之和守恒这一性质,构建出了光学谐振腔中频率转换系统的含时不变量.并运用此不变量及Lewis-Riesenfeld量子不变量方法,在失谐情形下,对这一双模量子化电磁场耦合系统相应的薛定谔方程进行了求解.得到了系统随时间演化的量子态和演化算符的显示解析表达式.此解对于进一步研究系统各种量子性质是有用的.     

Demonstration of a cavity-enhanced optical parametric chirped-pulse amplification system

The use of a low finesse enhancement cavity resonant with a low average power (<1 W) and a high repetition rate (78 MHz) pump source is shown to achieve 55% conversion efficiency into signal and idler from the coupled pump in an optical parametric process, whereas an equivalent amount of pump power in a single-pass configuration leads to negligible conversion. Careful comparison of the intracavity conversion process to the single-pass case is performed to assess the underlying impedance matching that yields the high conversion results.     

Image fusion algorithm based on redundant-lifting NSWMDA and adaptive PCNN

Pyramid decomposition in the NSCT transformation is a band-pass filtering process in the frequency domain where different scales of images are orthogonal. However, from the perspective of the image content, correlation is likely to exist between the fused images, and this kind of decomposition makes images of different scales contain redundant information, as a result of which the fused image may not capture the subtle information from the original images. In order to overcome the above-mentioned problem, an effective image fusion method based on redundant-lifting non-separable wavelet multi-directional analysis (NSWMDA) and adaptive pulse coupled neural network (PCNN) has been proposed. The original images are firstly decomposed by using the NSWMDA into several sub-bands in order to retain texture detail and contrast information of the images, and then adaptive PCNN algorithm is applied on the high-frequency directional sub-bands to extract the high-frequency information. The low-frequency sub-bands are evaluated by weighted average based on Gaussian kernel with a chosen maximum fusion rule. Results from experiments show that the proposed method can make the fused image maintains more texture details and contrast information.     

Optimization of the idler wavelength tunable cascaded optical parametric oscillator based on chirp-assisted aperiodically poled lithium niobate crystal

We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators(OPO) in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous difference frequency generation(DFG) process by monolithic aperiodically poled, magnesium oxide doped lithium niobate(APMg LN) crystals. The APMg LN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMg LN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal working conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 μJ and 700 μJ are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMg LN crystal is optimized according to this pump condition. To the best of our knowledge,this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMg LN crystals.     

矩形波板法测量光锥与CCD耦合器件的光学传递函数

本文采用直接对矩形波板成像的办法,测得系统的对比传递函数,然后再利用系统对比传递函数与系统的调制传递函数的关系,得到系统的调制传递函数.该方法克服了传统刀口扫描法的缺陷,消除了由于离散型光学元件的离散性产生的空间非平移不变性的影响,减小了测量误差,提高了精确度.     

Nonreciprocal frequency doubling of electromagnetic waves through double resonance and Bragg reflection in photonic crystals

A computational study of the uni-directional second-harmonic generation in a one-dimensional dual photonic crystal structure made of GaAs, AlAs and SiO₂ with quadratic optical nonlinearity and material dispersion is presented. The computational approach uses a shooting method to solve nonlinear wave equations for coupled fundamental and second-harmonic fields and the invariant imbedding method to obtain the linear transmittance and group index spectra. The dual structure consists of two substructures, the conversion structure creating a strongly enhanced second-harmonic signal and the filter structure blocking the fundamental frequency field by Bragg reflection while permitting the passage of the second-harmonic field. The conversion structure is built with an elementary cell consisting of four sublayers whose thicknesses are systematically varied. Doubly resonant second-harmonic generation with very high conversion efficiency is achieved for light incident from the conversion structure side by choosing the geometrical parameters of the elementary cell optimally and controlling the band structure. A new mechanism to enhance second-harmonic generation by controlling the energy flow between the fundamental frequency and second-harmonic fields has also been found.     

力与耦合系统的交互作用和随机能量共振

外界对系统作功的过程就是系统状态发生变化的过程.根据Langevin方程的随机动力学特性,采用微观动力学和宏观热力学方法,建立了基于单一随机轨线的耦合双稳系统的热力学关系.通过力与耦合系统的功交互作用定量地刻画了能量的传递和转换关系,揭示了耦合系统中存在着的随机能量共振现象.从作功与能量的关系进行分析,进一步揭示了随机共振产生的物理本质. 关键词： 耦合双稳系统 随机热力学 随机能量共振 功     

Adiabatic processes in frequency conversion

Adiabatic evolution, an important dynamical process in a variety of classical and quantum systems providing a robust way of steering a system into a desired state 1 - 5 , was introduced only recently to frequency conversion 6 - 9 . Adiabatic frequency conversion allowed the achievement of efficient scalable broadband frequency conversion 8 , 9 and was applied successfully to the conversion of ultrashort pulses, demonstrating near‐100% efficiency for ultrabroadband spectrum 10 - 16 . The underlying analogy between undepleted pump nonlinear processes and coherently excited quantum systems was extended in the past few years to multi‐level quantum systems, demonstrating new concepts in frequency conversion, such as complete frequency conversion through an absorption band 17 - 20 . Additionally, the undepleted pump restriction was removed, enabling the exploration of adiabatic processes in the fully nonlinear dynamics regime of nonlinear optics 21 - 26 . In this article, the basic concept of adiabatic frequency conversion is introduced, and recent advances in ultrashort physics, multi‐process systems, and the fully nonlinear dynamics regime are reviewed.     

Efficient single-photon frequency conversion using a Sagnac interferometer

We propose a scheme for efficient optical frequency conversion at the single-photon power level. The scheme exploits the quantum interference of single-photon states at a three-level quantum emitter coupled to a Sagnac interferometer. We show that this device can achieve single-photon frequency up- or down-conversion with near unity efficiency.