Self-mixing interference in distributed feedback laser diode with multiple external cavities

The self-mixing interference in distributed feedback laser diode (DFB-LD) with multiple external cavities is analyzed. Each external cavity is considered to be an optical thin film, and the equivalent reflectivity can be got from the theory of the thin film optics, the general expressions of gain and frequency in compound laser cavity are theoretically deduced. This principle is helpful to build the fiber-coupled self-mixing interference system. Considering that different parameters have influence on self-mixing interference, we make some simulation analysis at different conditions. The output of self-mixing interference is analyzed in numerical analysis, and the amplitude variations of the output gain is discussed along with different parameters, e.g., the coupling coefficient, the linewidth enhancement factor, and the reflection coefficient of external reflector.     

Observation of multi-path interference in broad-area semiconductor lasers with optical feedback

Multi-path interference effects induced by optical feedback in broad-area semiconductor lasers is experimentally studied. An external mirror and an internal laser cavity form a closed composite optical feedback loop. For a very small tilt of the external mirror for the exit facet along the stripe width of the active layer, the light emitted from the laser undergoes multi-path reflections in the composite cavity, and we therefore observe multi-path interference effects of the laser oscillations for a small mirror tilt. The laser output power always shows the fundamental mode of the single feedback loop together with an oscillation of a certain higher multi-path loop. The laser oscillation and the beam profile are strongly dependent on the tilt. We observed up to a nine-fold multi-path interference in the experiment.     

基于飞秒激光加工的马赫-曾德尔干涉氢气传感器

介绍了一种基于光纤微加工的氢气传感技术方案。利用波长为800nm的飞秒激光脉冲在普通单模光纤上加工马赫-曾德尔(M-Z)干涉腔,并采用磁控溅射方法在加工后的M-Z干涉微腔上溅射钯(Pd)膜,制备了一种新型的光纤氢气传感器。分析了加工工艺对微腔干涉效果的影响,选择合适的加工参数以及加工后对微腔进行后续处理,可使微腔的透射光谱的分辨率得到提高。实验研究了腔长为40μm的M-Z干涉传感器分别镀36nm、110nmPd膜后,对氢气的响应。结果表明,在不同的氢气浓度下,镀Pd膜的M-Z干涉传感器都表现出对氢气的敏感特性,随着氢气浓度的增大,透射光谱会向长波长方向偏移,其中Pd膜厚度为110nm比厚度为36nm的传感器对氢气有更好的灵敏度。     

两模腔场谱间的量子干涉

研究了高Q腔中单个二能级原子与两模二项式光场依赖强度耦合相互作用系统的腔场谱,给出了弱初始场条件下的数值结果,讨论了两模光场之间的量子干涉对腔场谱结构的影响. 发现当两模光场的频率差Δ>g（g为原子与腔场间的耦合常数）时,两模光场间的干涉效应对谱结构没有影响,系统的腔肠谱只是两模腔肠谱的简单叠加;当Δ≤g时两模腔场谱间的干涉比较明显. 在强初始场条件下,量子干涉效应可忽略. 关键词： 腔场谱 量子干涉 两模二项式光场     

Possibility of suppressing quantum light fluctuations when excess photon fluctuations occur inside a cavity

Using the optical excitation of a high-Q cavity as an example, it is shown that when light is observed at the output of this cavity, effective suppression of the photocurrent shot noise below the quantum limit is in general independent of the parameters of the stationary state of the field oscillator (in particular, it is independent of the rms photon fluctuations) inside the cavity and can occur not only at any allowed negative value but even at a positive value of the Mandel parameter. It was assumed in solving the problem that the cavity is optically excited by superimposing the radiation of a sub-Poisson laser and a laser with excess photon noise. A formal solution was obtained in terms of the kinetic equation for the density matrix of the actual fields (inside the laser cavities and the empty cavity), which is derived here on the basis of the Heisenberg-Langevin quantum equations, taking into account directed propagation of the field from the laser cavities inside the empty cavity. The resulting kinetic equation can also be used to solve other physical problems, since it is applicable to optical systems that contain, in principle, an arbitrary number of coupled cavities and interference mixers. Zh. éksp. Teor. Fiz. 111, 1579–1600 (May 1997)     

半导体激光Fabry-Perot干涉波长的微位移测量仪

摘要设计了一种基于Fabry-Perot干涉波长测量仪.这种测量仪使用两个Fabry-Perot干涉腔,其中一个作为测量腔、另一个作为参考腔,测量腔的一个反射面与被测对象安装在一起,参考腔的一个反射面与压电陶瓷安装在一起.根据透射光谱中心波长与其干涉腔长之间的关系,当参考腔与测量腔的透射光谱中心波长完全重合时,对纳米级微位移实现实时测量.光源采用半导体激光器,可获得所需要的波长值和波长变化范围.实验结果表明,这种测量仪测量误差不大于1.5 nm,该精度可以满足精密机械加工、光电子和微电子加工以及纳米级测量技术等领域的精度要求.     

Phase stability theory of Bloch eigenstates in active photonic lattices with coupled microlaser arrays

An generic model for the lattice dynamics of coupled microlaser arrays is employed for the lattice stability analysis. Nonlinear cross-cavity gain-coupling effects, characterizing active lattices, are included via the gain dependence on carrier depletion and cross-cavity hole burning. Passive near neighbor interactions (inter-cavity absorption and mirror reflection interference) are also included. The introduction of lattice-orthogonal modes simplifies the derivation of the coupled rate equations. The interaction phase among sites exhibits spontaneous long range “crystallization" into periodic Bloch states whereby the cavity radiation envelopes behave as laser “macro-atoms". The sign of the coupling coefficients as a function of geometry determines in- vs. out-of-phase locking and has practical implications for array design. Emphasis is placed on the stability analysis of Bloch states by including earlier omitted [1] effects of phase perturbations. The importance of the linewidth factor ι is uncovered: unconditional stability results for ι ≤1, otherwise a stability threshold exists for the coupling strength among sites. Choice of low ι gain material permits phase stability with high coupling strength, beneficial in overcoming manufacturing variations among array cavity parameters.     

Supernarrow saturated absorption resonances in weakly coupled two resonant optical cavities

The advantages of the weakly coupled two resonant optical cavities (hereinafter referred to as three-mirror cavity) used for observation of the supernarrow saturated absorption resonances are shown. Among these advantages we can name: (a) the possibility to control the intensity in the cavity with the inside absorbing cell which is important when the gain and absorption saturation parameters differ significantly; (b) the resonances observation from the ‘passive’ side of the three-mirror cavity permits us to decrease drastically the influence of the reflected signal from the detector; (c) if instead of the absorbing cell an active system is put in (gain plus absorption), it is possible by tuning the operating mode of the active interferometer to obtain many-fold gain of the supernarrow resonance amplitude. Received: 11 January 2000 / Revised version: 20 June 2000 / Published online: 9 February 2001     

Kerr效应对二项式腔场谱量子干涉的影响

研究了含Kerr介质高Q腔内单个二能级原子与双模二项式光场发生双光子共振相互作用系统的腔场谱,给出了Kerr效应与量子干涉项ΔS(ω)关系的数值计算结果,讨论了Kerr效应对二项式腔场谱量子干涉的影响.结果表明:若初始时刻原子处于激发态而双模光场处于二项式态,随Kerr效应的增强,致使量子干涉项引起谱线强度的改变量呈现出"不规则的周期性衰减振荡"特性,震荡幅度与两模光场的频差密切相关.在Kerr系数χg(g为光场与原子的耦合常数)时,Kerr效应对干涉项的影响比较强烈;在χg时,趋于平稳.随着Kerr效应的增强,系统腔场谱由对称结构逐渐演化为不对称的多谱线结构.     

随机耦合模型复杂腔体电磁耦合效应统计特性

针对微波脉冲激励下复杂屏蔽腔体内部电路耦合电磁量计算的问题,建立了一个微波混沌腔体,通过测试获取了含内部电路的腔体辐射和辐射散射参数,利用随机耦合模型(RCM),对干扰脉冲能量进行了归一化处理,计算分析了微波脉冲宽度、脉冲间隔、脉冲数目以及腔体损耗因子对目标点感应电磁量统计分布的影响。计算结果表明:脉冲干扰下电路目标点耦合电磁量强于功率源激励;在脉冲能量一定的条件下,目标点耦合电磁量与微波脉冲的宽度、间隔和数目的变化均呈现一定的谐振特性,且单脉冲激励对电路的影响明显强于多脉冲。与此同时,实验还研究了电路易受电磁干扰的目标点的确定方法。     

Opto-electromechanically induced transparency in a hybrid opto-electromechanical system

We study opto-electromechanically induced transparency in a hybrid opto-electromechanical system made up of an optical cavity tunneling-coupled to an opto-mechanical cavity, which is capacitively coupled to a charged mechanical oscillator by a charged and moveable mechanical cavity mirror as an interface. By studying the effects of the different parameters on the output field, we propose a scheme to modulate the opto-electromechanically induced transparency(OEMIT). Our results show that the OEMIT with the transparency windows from single to double to triple can be modulated by changing the tunneling, opto-mechanical and electrical couplings. In addition, the explanation of the OEMIT with multi-windows is given by the energy level diagram based on quantum interference. Our investigation will provide an optimal platform to manipulate the transmission of optical field via microfabricated opto-electromechanical device.     

Forces and spatial ordering of driven atoms in a resonator in the regime of fluorescence suppression

An atom in a high-Q cavity, which is coherently driven at the frequency of a cavity mode, exhibits strong suppression of fluorescence when the atomic decay rate exceeds the cavity linewidth. This effect is due to destructive interference of cavity and pump field, such that at the atomic position the total field intensity has a local minimum. For atomic ensembles the magnitude of the interference effect grows with atom number and depends on the relative atomic positions. It is strongest for a wavelength spaced array of atoms placed at the antinodes of the cavity mode. This suppresses fluorescence and enhanced collective scattering into the cavity mode. We analyze the mechanical forces in the regime where the interference condition is fulfilled. We show that the atomic pattern is mechanically stable whenever the driving frequency is red detuned with respect to the cavity frequency, irrespective of the atomic transition frequency. Hence atomic selforganization, as predicted in [6] can also occur in the parameter regime where superradiant scattering is suppressed by collective interference. PACS 32.80.Pj; 42.50.Pq; 42.50.Fx     

Efficient Scheme for One-Way Quantum Computing with Radiofrequency SQUID Qubits byAdiabatic Passage

We proposed an efficient scheme for constructing a quantum controlled phase-shift gate and generating the cluster states with rf superconducting quantum interference devices (SQUIDs) coupled to a microwave cavity through adiabatic evolution of dark eigenstates. During the operation, the spontaneous emission is suppressed since the rf SQUIDs are always in the three lowest flux states. Considering the influence from the cavity decay with achievable
experimental parameters, we numerically analyze the success probability and the fidelity for generating the two-SQUID maximally entangled state and the controlled phase-shift gate by adiabatic passage.     

Generation of squeezed light upon frequency self-doubling in active nonlinear crystals with regular domain structure

A quantum theory of self-convers of the lasing frequency in active nonlinear crystals placed in a cavity is developed. The generation of nonclassical (quadrature squeezed) light upon self-doubling of the laser radiation frequency is studied in detail, with no limitations on the relations between the relaxation times of the inverse population and the polarization of the medium and the lifetime of a photon in the cavity. The fluctuation spectra of the quadrature components of the fields of the laser radiation and its second harmonic are studied in dependence on the pumping parameters and the parameters of the cavity. Numerical calculations are performed for a Nd:Mg:LiNbO₃ crystal with a regular domain structure.     

超宽带电磁脉冲对典型引信的耦合效应研究

为明晰超宽带电磁脉冲对典型无线电引信的干扰和损伤影响,应用时域有限积分法对典型无线电引信腔体耦合效应进行了数值模拟研究。以典型无线电引信腔体及其低频电路板实际结构为对象进行建模,仿真研究了超宽带电磁脉冲对该引信腔体的耦合特性,分析了引信高低频电路间连线过孔参数和脉冲参数对耦合效应的影响规律,研究了加装印刷电路板对耦合效应的影响。结果表明:与圆形和正方形孔缝相比,矩形孔缝的耦合系数受极化方向的影响显著;脉冲上升时间越小,耦合系数越大;加装印刷电路板后,腔体相同位置处耦合系数下降,谐振频率改变。     

Modelling of diffraction in pillar vertical cavity surface-emitting lasers with embedded Bragg layers

An analytical expression for the reflectivity between the active cavity of a circular symmetric pillar vertical cavity surface-emitting laser (VCSEL) and Bragg mirror, which takes account of diffraction at the interface, is derived. The method (mode-matching in Hankel space) is also used to determine the reflectivity with some of the Bragg layers embedded in the cavity region. The dependence of reflectivity upon various parameters, including number of Bragg pairs, cavity radius and mode number, is discussed. The validity of using the plane wave reflectivity value (which ignores diffraction effects) is seen to depend significantly upon these parameters. As an indicator of the importance of taking these effects into account for pillar diameters of 6 m and less, the variation of threshold gain with cavity radius is given for a commonly used type of VCSEL structure.     

半导体激光自混频干涉速度仪的F-P模型分析

设计了一个半导体激光自混频干涉式测量物体振动速度的实验,利用双镜F_P(法布里_珀罗)等效模型,对半导体激光自混频干涉速度仪中的干涉效应进行了理论分析,推导了干涉信号理论模型的数学表达式,讨论了影响测量信号的因素。结果表明,在半导体激光自混频干涉速度仪的无源腔中空气密度的变化、无源腔长度的变化、激光波长的变化都将会导致信号漂移,从而引起测量误差。而被测物体表面的反射率越高,越有利于测量。     

非简并双光子Jaynes-Cummings模型腔场谱中的量子干涉

研究了两模二项式光场与二能级原子在高Q腔中发生双光子相互作用过程的腔场谱,给出了弱初始场条件下腔场谱的数值计算结果,讨论了两模腔场谱间的量子干涉.结果表明:两模腔场谱间的量子干涉随着频差的增大而呈现出周期性的衰减振荡,其振荡周期约为0·16g(g为原子与光场的相互作用强度系数),频差大于1·6g时干涉效应已经很弱.量子干涉还与初始场强度有关,随着初始场最大光子数的增加,量子干涉效应逐渐增强,但当光子数大于4时,干涉效应迅速减弱,当最大光子数大于6时,量子干涉现象几乎消失.     

Unstable resonator alignment based on the fringe analysis

The existing cavity mirrors alignment method aligns cavities according to the symmetry of the near-field interference fringes of the guided lights by the unstable resonator. Its precision is restricted due to the lack of objective criterion for the fringe symmetry. This article proposes a high-precision cavity mirrors alignment method using the grey projection of fringe patterns as a solution to the problem. First, vertical and horizontal grey projection on the concerned fringe patterns; then an evaluation function for the cavity mirrors alignment is established using the distances between peak/valley values of all the levels in the projection curve as variables; finally, the function value is employed to characterize the fringe symmetry and thus to provide an objective criterion for the alignment effect of the stable resonator cavity mirrors. Experiments show that the proposed method is able to give effective evaluation for the symmetry of the near-field interference fringes of the guided lights and improve the alignment precision greatly.     

Effect of longitudinal pump inhomogeneity on the energy characteristics of steady-state raman lasers

The energy characteristics of externally pumped Raman lasers are calculated taking inhomogeneities in the active medium into account. Equations for the power and steady-state lasing threshold in these systems as function of the parameters of the cavity, pump, and Raman active medium are obtained over the entire ranges of their possible variations. The conditions for applicability of the model of averaged (uniform) fields, which is widely used in the theory of Raman lasers, are determined and interrelations among the cavity parameters favor unidirectional lasing in ring cavity Raman lasers are identified.