原子介质诱导的纠缠

提出了一个利用原子介质在光机械系统中产生纠缠的方案。研究结果表明，当腔场和原子介质间的耦合系数取合适值时，腔场和动镜，镜子与原子，以及腔场和原子之间都是纠缠的。此外，文章考虑了腔场耗散效应，并给出用“logarithmic negativity”去度量系统纠缠的数值解。     

场频率变化对辐射场与原子间耦合系数的影响

对二能级原子与单模辐射场相互作用系统的哈密顿量进行分析,找出光场与原子之间耦合系数与光场频率及谐振腔体积之间的关系。通过利用谐振腔的腔镜振动机制,研究了腔镜振动对光场模式及对腔体积的影响,最终找出辐射场与原子之间耦合系数与场频变化之间的关系。     

Reflection loss of laser mode from tilted end mirror

The reflection of the lowest-order guided TE mode of a slab waveguide from a tilted end mirror is discussed. The problem is applicable to injection lasers if the slab is regarded as an effective refractive index approximation of the channel or ridge waveguide of the laser structure. For a mode width of 3 μm, 5° mirror tilt results in reflection losses in excess of 25 dB; for modes of 6-μm width, 5° mirror tilt causes reflection losses in excess of 45 dB. For small tilt angles the results of this calculation agree with those based on a Gaussian approximation of the guided mode. For larger angles, and hence higher reflection losses, the results depart significantly from the Gaussian approximation     

Radiation loss of grating-assisted directional coupler

The coupling between the guided modes and between guided and radiation modes of two parallel slab waveguides forming a directional coupler in order is computed to determine the radiation losses introduced by the coupling grating. The problem is solved in two stages. First, the guided modes for each waveguide are computed separately and the radiation modes are only determined for the more complicated of the two waveguides, the one that is nearer to the grating. Modifications caused by the presence of the opposite waveguide are then taken into account by computing first-order correction terms. For a practical example of slab waveguides defined in GaInAsP, the authors find that the radiation losses per power exchange length remain below 0.02 dB for a rectangular grating depth of 0.01 μm     

Modal conversion in a gradient-index channel waveguide due to boundary perturbations

The effect of boundary perturbations on channel waveguides has been calculated following the effective-index method. As required by this approach, the index perturbations are assumed separable-a form describing defects expected using planar waveguide fabrication techniques. For sinusoidal perturbations, coupling occurs to, at most, one other guided mode and to a small band of radiation modes. As in the planar case, losses at step-index boundaries are greater than those at graded-index boundaries.     

Effect of transition waveguides on dielectric waveguide directionalcouplers

The coupling of energy between two curved dielectric waveguides is investigated by the staircase approximation method, which combines the building-block approach of multimode network theory with a rigorous mode-matching procedure. Particular attention is directed toward two major effects of transition waveguides on the performance of directional couplers composed of dielectric waveguides: one is the change in the coupling length, the other is the radiation loss. The coupling problem is analyzed in terms of the scattering of an incident guided mode by the coupler structure as a whole. Numerical results are given to illustrate the coupling characteristics of various structures and to establish useful guidelines for the design of directional couplers     

Optimization of coupling between photonic crystal resonator and curved microfiber

The evanescent coupling from a photonic crystal resonator to a micron-thick optical fiber is investigated in detail by using a three-dimensional finite-difference time-domain (3D-FDTD) method. Properly designed photonic crystal cavity and taper structures are proposed, and optimal operating conditions are found to enhance the coupling strength while suppressing other cavity losses including the coupling to the slab propagating mode and to the higher-order fiber mode. In simulation, the coupling into the fundamental fiber mode is discriminated from other cavity losses by spatial and parity filtering of the FDTD results. The coupling efficiency of more than 80% into the fundamental fiber mode together with a total Q factor of 5200 is achieved for the fiber diameter of 1.0 /spl mu/m and the air gap of 200 nm between the fiber and the cavity.     

平板宽波导谐振腔耦合损失理论研究

计算了平板宽波导谐振腔中ＥＨ１１模的耦合损失，结果表明存在两种特定结构使耦合损失最小。     

Modélisation par méthode de propagation de faisceau à partir d’un coupleur à champ évanescent

We present numerical results obtained by 3D-BPM concerning evanescent field coupling in monomode fibres. At first we study the coupling between a monomode fibre and a mode sink. We show the existence or the absence of guided modes. BPM, is also applied to the study of directional couplers consisting of two fibres separated by an index liquid. The transmission coefficient is computed for various geometries and the electric field intensity is visualised by plotting isovalues.     

Design of a Quasi-Optical Mode Converter for a Frequency Step-Tunable Gyrotron

The quasi-optical mode converter for a frequency step-tunable gyrotron which consists of a dimpled-wall antenna (Denisov-type launcher) and a beam-forming mirror system has been optimized for 9 modes from TE_17,6 at 105 GHz to TE_23,8 at 143 GHz. The first mirror is a large quasi-elliptical focusing one; the second and third are phase-correcting mirrors with a non-quadratic shape of the surface. The results of calculations show that for these modes the Denisov-type launcher has a well-focused beam with low diffraction losses, and the radiation pattern presents an almost identical field shape for all modes considered. A multi-mode optimization of the phase-correcting mirrors with two different methods has been tested. The simulations show that the phase-correcting mirrors can be used for broadband operation in the frequency range from 105 GHz up to 143 GHz in the various design modes. This quasi-optical mode converter can achieve efficiencies of 94%-98% for converting the rotating high-order cylindrical cavity modes into the usable fundamental Gaussian mode.     

辐射压力诱导强耦合光机械腔中的简正模式分裂和冷却

在解析边带机制下用量子郞之万方程研究一种由辐射压力与驱动Fabry-Perot光学腔相耦合而产生的光机械动力学行为。随着输入激光功率的增加,振子的涨落光谱呈现简正模式分裂的现象,并且结果和实验相符合。也推导了有效机械阻尼和共振频移。红移边带导致了机械模的冷却,蓝移边带引起了机械模的放大。此外,引入一种近似机制来研究振子的冷却。由于简正模式分裂和基态冷却都要求在解析边带机制下,这就需要考虑简正模式分裂是否会影响到振子的冷却。同时也讨论了操控基态冷却的关键因素。     

Analysis of integrated optical waveguide mirrors

A new method is presented to analyze reflection losses of integrated mirrors, taking into account the exact guided mode profile and assuming that this profile remains unchanged up to the reflecting plane. The fraction of the reflected light coupled to one of the guided modes of the output waveguide is calculated, taking into account the mirror reflection coefficient. The influence of both translation and tilt of the reflecting plane is investigated. The method applies for every guided mode and any reflection angles. Numerical calculations are derived for a 90° optical corner mirror     

Analysis of the coupling of two non-parallel dielectric rod waveguides

In this paper the coupling between two closely spaced single mode dielectric rod waveguides is investigated when the corresponding propagation axes are not in the same plane. An approximate analysis is presented by assuming only first order interaction between the guided waves. For a given incident HE₁₁ mode (in one of the rod waveguides) the coupled wave amplitudes are computed in the other waveguide for both propagation directions. Numerical results are presented for several coupling geometries.     

Theoretical interpretation of the enhanced single-mode stability in extended cavity VCSELs

Paraxial eigenmode analysis demonstrates that the extended cavity stability follows from the geometric scaling of the diffractive cavity losses; the same principle also explains the narrow aperture stability. Because diffraction losses scale as (L/b)/sup 2/ = (L/spl lambda///spl pi/w/sub o//sup 2/)/sup 2/, one can enhance diffraction to differentiate thresholds among modes either by shrinking the mode waist w/sub o/ (smaller aperture) or by extending the cavity length L. The second approach does not limit the vertical cavity semiconductor laser (VCSEL) output power. Our predictions agree with experimental trends, and suggest that diffraction limited modes apply to extended cavity VCSELs, since guided mode theory (effective index or thermal lensing) does not allow strong stability dependence on cavity length. The extended length stabilization holds when factors other than diffraction (such as mode wing clipping or aperture scattering) significantly contribute to cavity losses.     

A high-efficiency quasi-optical mode converter for a 140-GHz 1-MW CW gyrotron

A highly efficient quasi-optical mode converter system with several novel features has been designed and tested at Forschungszentrum Karlsruhe (FZK). The converter consists of a dimpled-wall waveguide launcher, one quasi-elliptical mirror and two toroidal mirrors. The coupled-mode theory has been used to analyze the operation of the prebunching waveguide launcher; the radiated fields from the cut of the launcher have been calculated by the scalar diffraction integral. Simulation results show that the advanced dimpled-wall launcher generates a well-focused Gaussian radiation pattern with low diffraction losses. In this case, toroidal mirrors are sufficient to obtain a desired output beam pattern. An efficiency of more than 98% has been achieved to convert the rotating TE/sub 28,8/ cavity mode at 140 GHz into a fundamental Gaussian beam. Experimental measurements show close agreement with theoretical predictions.     

Experimental study of a quasi-optical cavity with slotted output mirror

This paper describes an experimental study of a quasi-optical cavity to be used in qyrotrons. The cavity configuration was designed so that its output wave could pass into a quasi-optical transmission line. The test cavity was coaxially composed of a pair of annular mirrors, one of which was a curved conical mirror and the other was a plane mirror having a radial slot array for wave output. A mode excited in the cavity at 56.4 GHz was observed by detecting the radiation wave that leaked out through the slotted mirror. It was shown that the present slotted mirror served as a partially and uniformly transparent mirror to radiate the output wave with the same mode as in the cavity.     

Unstable optical resonators for laser applications

A simple geometrical analysis has been developed which describes the lowest-order transverse mode of any large-Fresnel-number optical resonator located in the unstable or high-loss region of the resonator mode chart. Such resonators include, for example, resonators in which one or both of the mirrors are divergent spherical surfaces. The lowest mode in such a resonator is assumed to consist of two oppositely traveling divergent spherical waves which uniformly illuminate the end mirrors. The centers of curvature of these spherical waves do not, in general, coincide with the mirror centers of curvature, but are found by requiring that each center be the image of the other upon reflection from the appropriate mirror. The resonator losses are found from purely geometrical considerations, and are given by simple analytical expressions. These losses turn out to be independent of the mirror sizes, so that hyperbolic universal equiloss contours can be drawn on the resonator mode chart. The losses agree well with more exact results obtained by Fox and Li for a few specific cases. Experimental results in good agreement with the analysis have been obtained using a ruby laser rod having a divergent spherical surface ground directly onto one end of the laser rod. Unstable resonators, particularly the "Cassegrainian" unstable configuration used in the experiments, appear potentially useful for diffraction output coupling applications, and possibly also for transverse mode control, in ruby and other high-gain lasers.     

Unified Approach for Coupling to Cladding and Radiation Modes in Fiber Bragg and Long-Period Gratings

Couplings of core mode to guided cladding and unguided radiation modes in fiber Bragg and long-period gratings are investigated by a unified approach based on complex mode matching method (CMMM). With the combination of the perfectly matched layer (PML) and the perfectly reflecting boundary (PRB), the continuous radiation modes can be well represented by a set of discrete complex modes so that simulation of coupling to radiation modes is greatly simplified and may be treated in the same fashion as guided modes. Numerical results of fiber Bragg and long-period gratings with refractive index of the outer cladding lower, equal, and higher than that of the inner cladding indicate that the unified approach is highly effective in the simulation of couplings to cladding and radiation modes.      

Theory of laser mode coupling produced by cavity-length modulation

Laser mode coupling produced by oscillatory motion of a cavity mirror is analyzed by means of a quasi-normal mode expansion of the cavity field which satisfies the time-dependent boundary conditions. The quasi-normal mode-coupling equations are identical in form to the coupled-mode equations for the phase-modulated fixed length laser.     

Self-consistent calculation of lasing modes in a planar microcavity

The self-consistent calculation of lasing modes in a microcavity with infinite plane mirrors is presented. The semiclassical theory is used, with rigorous boundary conditions included for Maxwell's equations to describe both the emitter distribution and the cavity reflectors. The concept of gain-guided versus index-guided modes in such structures can be removed within the semiclassical model, as rigorous boundary conditions for both the radiation source and passive cavity can be handled exactly. We present calculated curves showing the angular dependence of various lasing modes on mirror reflectivity and the threshold gain susceptibility dependence on mirror reflectivity and active diameter. The linewidth dependence on the transverse lasing mode is also considered. Limitations of the semiclassical approach as compared to a fully quantum mechanical approach is emphasized