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A quantum analysis of the generalized polarization properties of multimode non-stationary states based on their optical field-strength probability distributions is presented. The quantum generalized polarization is understood as a significant confinement of the probability distribution along certain regions of a multidimensional optical field-strength space. The analysis is addressed to quantum states generated in multimode linear and nonlinear waveguiding (integrated) photonic devices, such as multimode waveguiding directional couplers and waveguiding parametric amplifiers, whose modes fulfill a spatial modal orthogonality. In particular, the generalized polarization degree of coherent, squeezed and Schrödinger’s cat states is analyzed. 相似文献
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Mixture multimode optical field classical states propagating in N?×?N integrated directional couplers are analyzed by using the density matrix formalism in a N-dimensional optical space. These mutimode optical fields present a kind of generalized polarization and accordingly a definition of a multimode polarization degree is proposed. It is based on the distance measure between a mixture state and an unpolarized state in a N-dimensional optical space so that in the case N=2 the standard polarization degree is recovered. It is shown that directional couplers can reduce or increase remarkably the multimode polarization degree of a mixture state. Likewise a simple measurement technique, based on Y junctions, of this multimode polarization degree is proposed. Finally all the results can be formally extended to the special case of multimode single photon quantum states. 相似文献
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In this work a quantum mechanical derivation of the Spin operator in integrated isotropic and anisotropic photonic waveguides is obtained from both first principles of the electromagnetic theory and conservation laws, and moreover, within a phenomenological quantization approach. The Spin operator will be derived by starting from the spin conservation law to obtain the spin flux density and by means of a quantization based on the vector structure and orthonormality property of guided modes; likewise, since anisotropic guides produce polarization changes, and consequently changes of the expected values of spin, we will also present the Momentum operator for anisotropic guides. The expression for the Spin angular momentum operator shows that both the presence of modal longitudinal components and the modal mismatching reduces the spin values, but it comes into the standard expression when it is used in homogeneous media and in particular with uniform and infinite plane modes. Likewise these results have a direct influence on the Stokes's operators which allow one to analyze quantum polarization in integrated photonics. 相似文献
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Two integrated 1 × 2 and 1 × 4 polymer electro-optic switches based on Y-fed directional couplers are designed and optimized in terms of the coupled mode theory, electro-optic modulation theory, conformal transforming method and image method. The principle of the 1 × 2 electro-optic switch is described. Parameters including the core size, buffer layer thickness, electrode thickness, electrode width and electrode gap are optimized. Simulation results show that the length of the designed 1 × 2 switch is about 3.126 mm, the driving voltages of the two branches are as low as 0.891 and ?0.891 V, respectively, the crosstalk and insertion loss are less than ?30 and 1.42 dB, respectively, within the operation wavelength from 1527 to 1574 nm. Under the same driving voltages, the 1 × 4 optical switch with a total length of less than 7 mm can be switched by altering the voltages applied on the electrodes of the three Y-fed directional couplers. Simulation results from the beam propagation method (BPM) indicate that the two designed devices exhibit favorable switching functions. 相似文献
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The presence of multiple bipartite entangled modes in squeezed states generated by four-wave mixing enables ultra-trace sensing, imaging, and metrology applications that are impossible to achieve with single-spatial-mode squeezed states. For Gaussian seed beams, the spatial distribution of these bipartite entangled modes, or coherence areas, across each beam is largely dependent on the spatial modes present in the pump beam, but it has proven difficult to map the distribution of these coherence areas in frequency and space. We demonstrate an accessible method to map the distribution of the coherence areas within these twin beams. We also show that the pump shape can impart different noise properties to each coherence area, and that it is possible to select and detect coherence areas with optimal squeezing with this approach. 相似文献
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We have examined both single and entangled two-mode multiphoton coherent states and shown how the ‘Janus-faced’ properties between two partner states are mirrored in appropriate tomograms. Entropic squeezing, quadrature squeezing and higher-order squeezing properties for a wide range of nonclassical states are estimated directly from tomograms. We have demonstrated how squeezing properties of two-mode entangled states produced at the output port of a quantum beamsplitter are sensitive to the relative phase between the reflected and transmitted fields. This feature allows for the possibility of tuning the relative phase to enhance squeezing properties of the state. Finally, we have examined the manner in which decoherence affects squeezing and the changes in the optical tomogram of the state due to interaction with the environment. 相似文献
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Nonclassical properties exhibited by a chain of cavity modes second harmonic generation in coupled oscillators system, designed by using multichannel optical waveguides, is explored. The solution for the Hamiltonian of the coupled-modes driven by coherent excitation is obtained via an exact formulation of the normal-ordered Fokker-Planck equation. Nonclassical effects, namely the sub-Poissonian photons, squeezing and entanglement are noticed. Multichannel coupling of the coupled oscillators induces new possibilities for correlation between the modes in different channels, henceforth, provides an effective way towards manipulation of quantum light. 相似文献
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光纤探针型近场光镊是近场光学领域中的新型技术,因其可对纳米尺度微粒直接进行捕获和操纵而受到广泛关注,其光纤探针尖端的近场分布特性影响着纳米粒子捕获及操纵的成败探针金属膜外侧电磁场由光波在针尖小孔处衍射而成,根据夫朗和费衍射公式分析了圆形纳米小孔的光波衍射图样,运用时域有限差分法(FDTD)研究了均匀平面波垂直入射于镀膜光纤探针的近场分布,比较了不同锥角、不同出射孔径、不同金属膜厚度及不同入射波长的近场分布情况,并对不同情况下的通光效率进行了分析。通过对各参数的计算与比较,结果表明,当锥角越大、孔径越大、镀合适膜厚并且入射波长越小时,探针尖端的出射光强越大并具有较大的通光效率 相似文献
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A novel optical bean-shaped resonator (BR) biosensor integrated with Mach–Zehnder Interferometer structure based on a silicon-on-isolator platform has been proposed and investigated theoretically and numerically. By characterizing and optimizing the structure, our bean-shaped device exhibits a high extinction ratio over 50?dB and a high Q factor of about 5.46?×?104 in a wide wavelength span. The quasi-free spectral range (FSR) is about 469?nm. The sensitivity of 688.6?nm/refractive index unit (RIU) is achieved for bulk changes of refractive index and the detection range varies from 10?6 to 0.689 RIU. More complex bean-shaped structures can also be cascaded by adding more bending waveguides in BR to obtain wider quasi-FSR range. 相似文献
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Mohammad Taghinejad Zihao Xu Hua Wang Hossein Taghinejad Kyu‐Tae Lee Sean P. Rodrigues Ali Adibi Xiaofeng Qian Tianquan Lian Wenshan Cai 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(5)
Atomically thin transition metal dichalcogenides (TMDs) in their excited states can serve as exceptionally small building blocks for active optical platforms. In this scheme, optical excitation provides a practical approach to control light‐TMD interactions via the photocarrier generation, in an ultrafast manner. Here, it is demonstrated that via a controlled generation of photocarriers the second‐harmonic generation (SHG) from a monolayer MoS2 crystal can be substantially modulated up to ≈55% within a timeframe of ≈250 fs, a set of performance characteristics that showcases the promise of low‐dimensional materials for all‐optical nonlinear data processing. The combined experimental and theoretical study suggests that the large SHG modulation stems from the correlation between the second‐order dielectric susceptibility χ(2) and the density of photoexcited carriers in MoS2. Indeed, the depopulation of the conduction band electrons, at the vicinity of the high‐symmetry K/K′ points of MoS2, suppresses the contribution of interband electronic transitions in the effective χ(2) of the monolayer crystal, enabling the all‐optical modulation of the SHG signal. The strong dependence of the second‐order optical response on the density of photocarriers reveals the promise of time‐resolved nonlinear characterization as an alternative route to monitoring carrier dynamics in excited states of TMDs. 相似文献
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A model based on trapping and releasing of free carriers in band gap states located at the interfaces between electrodes and the ferroelectric film is used to explain the restoration of polarization which is sometimes observed. Experimental data on two kinds of polarization restoration in metal/ferroelectric/metal thin film structures are reported. The increase of polarization, which may be observed at the early stage of fatigue test, is attributed to the release of carriers which are trapped in interfacial states at the virgin state, before fatigue test. On the other hand, the previously reported “self recovery effect” is attributed to a competition between the strength of a trapped carrier-ferroelectric dipole interaction and the applied voltage which acts on the dipole orientation. 相似文献
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A model is presented to calculate the optical force and friction for a three-level atom in a V-type configuration in a weakly driven high-finesse cavity. Analytical expressions for the force and friction are derived using Heisenberg equations. It is demonstrated that the cooling rate can be increased by one order of magnitude over that of a two-level atomic system, which would stimulate further experimental investigations. 相似文献
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如何在低阈值小尺度(毫瓦或皮焦量级、微米以下)情况下激发非线性光学效应是近年来光学领域研究的重要课题。该研究最直接的应用需求就是光子集成芯片,这是未来实现超高速、大容量信息网络体系的基础。光子晶体具有类似于半导体能带的光子禁带(PBG),被誉为“光子半导体”,为人们提供了一种新颖而又实用的操纵光子的物理手段,使低阈值、可集成非线性效应产生成为可能。越来越多的非线性效应在光子晶体中已经被发现,例如光子晶体慢光、带隙孤子、电磁感应透明、二次谐波产生、光学双稳态等,本文将着重对可用于光子集成器件开发的光子晶体非线性效应研究领域的一些主要成果和进展进行总结,介绍其相关应用并对光子晶体非线性效应研究作出展望。
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