Effect of dimension variation for second-harmonic generation in lithium niobate on insulator waveguide[Invited]

We study the effect of dimension variation for second-harmonic generation(SHG) in lithium niobate on insulator(LNOI)waveguides. Non-trivial SHG profiles in both type-0 and type-I quasi-phase matching are observed during the wavelength tuning of the fundamental light. Theoretical modeling shows that the SHG profile and efficiency can be greatly affected by the waveguide cross-section dimension variations, especially the thickness variations. In particular, our analysis shows that a thickness variation of tens of nanometers is in good agreement with the experimental results. Such investigations could be used to evaluate fabrication performance of LNOI-based nonlinear optical devices.     

Ferromagnetic to antiferromagnetic transition of one-dimensional spinor Bose gases with spin-orbit coupling

The effect of the interatomic dipole-dipole interaction on the single-photon transmission spectrum is investigated theoretically in the single-mode optical waveguide containing a pair of dipole interaction two-level atoms and the incident photon, respectively. The results show that the interatomic dipole-dipole interaction can induce a remarkable change in the photon-atom on-resonance frequency in the single-photon transmission spectrum compared with the nonexistence of the interatomic dipole-dipole interaction. As a consequence, the original zero transmission probability at the original photon-atom resonant frequency increases to one directly thanks to the appropriately-chosen dipole-dipole interaction strength. Consequently, this characteristic reveals that the interatomic dipole-dipole interaction treated as an important internal physical mechanism can perform as a functional quantum switching to manipulate the photon’s transmission in the optical waveguide. The corresponding interpretations responsible for this phenomenon are presented.     

硬X射线光子筛波导效应研究

基于快速傅里叶变换光束传播法,研究了硬X射线光子筛中高高宽比金属结构的波导效应,确定了硬X射线光子筛的物理边界条件,采用角谱法计算了硬X射线光子筛的点扩展函数,并分析了吸收体厚度对聚焦性能的影响.研究结果表明波导效应一定程度上有利于抑制光子筛高级衍射的产生,提高聚焦性能.在同样的特征尺寸下,硬X射线光子筛的空间分辨率优于菲涅尔波带片,其缺点是衍射效率的下降.吸收体厚度的提高有利于提高光子筛的聚焦性能和衍射效率,但是相应的纳米加工工艺难度会增加. 关键词： 菲涅尔波带片 硬X射线光子筛 光束传播法 角谱法     

Theoretical Analysis of Spectral Correlations Between Photon Pairs Generated in Nanoscale Silicon Waveguides

Spontaneous four wave mixing in nonlinear waveguide is one of the excellent technique for generating photon pairs in well-defined guided modes. Here we present a comprehensive study of the frequency characteristic of correlated photon pairs generated in telecom C-band from a dispersion-engineered silicon wire waveguide. We have demonstrated that the waveguide configuration,shape of pump pulse,two-photon absorption as well as linear losses have significant influences on the biphoton spectral characteristics and the amount of frequency entanglement generated. The superior performance as well as the structural compactness and CMOS compatibility makes the silicon wire waveguide an ideal integrated platform for the implementation of on-chip quantum technologies.     

Theoretical Analysis of Spectral Correlations Between Photon Pairs Generated in Nanoscale Silicon Waveguides

Spontaneous four wave mixing in nonlinear waveguide is one of the excellent technique for generating photon pairs in well-defined guided modes. Here we present a comprehensive study of the frequency characteristic of correlated photon pairs generated in telecom C-band from a dispersion-engineered silicon wire waveguide. We have demonstrated that the waveguide configuration, shape of pump pulse, two-photon absorption as well as linear losses have significant influences on the biphoton spectral characteristics and the amount of frequency entanglement generated. The superior performance as well as the structural compactness and CMOS compatibility makes the silicon wire waveguide an ideal integrated platform for the implementation of on-chip quantum technologies.     

基于Ⅱ类周期极化铌酸锂波导的通信波段小型化频率纠缠源产生及其量子特性测量

自发参量下转换过程制备的纠缠光源在量子光学及其相关领域有着广泛的应用.本文利用780 nm的分布式布拉格反射镜激光二极管抽运一块长10 mm的Ⅱ类准相位匹配的周期极化铌酸锂波导,产生了偏振正交的频率反关联纠缠光子对.通过实验结果与理论的完美结合得到,当进入波导的抽运光功率为44.9 mW时,下转换双光子对的产生速率为1.87×10~7s~(-1).利用单色仪对下转换光子的频谱进行分析,得到信号和闲置光子的中心波长分别为1561.43 nm和1561.45 nm,频谱宽度为3.62 nm和3.60 nm,双光子符合包络宽度约为3.18 nm,可以得到双光子的频率纠缠度为1.131.00,表征了双光子的频率纠缠特性.利用Hong-Ou-Mandel干涉仪测量双光子的二阶量子干涉特性,测得的干涉可见度为96.1%,干涉图谱的凹陷宽度为1.47 ps.     

Two-photon scattering by a cavity-coupled two-level emitter in a one-dimensional waveguide

We show that two-photon transport can be modulated by a two-level emitter coupled to a cavity in a one-dimensional waveguide. In the ordinary case, the transmitted light has a wider frequency spectrum than the situation without the cavity because it is reflected and scattered many times. But when the two photons are resonant with the cavity resonance reflection frequency, the frequency spectrum of the transmitted light becomes narrower than that without the cavity. This means that properly tuning the cavity resonance frequency can improve the photon–photon interaction. In addition, we show that the two-photon intensity correlation functions are nearly opposite to each other at the two sides of the emitter transition frequency rather than the same, which is exactly the Fano resonance line shape for two photons. Such an effect is important for lowering the power threshold in optical bistable devices and for sensing applications. When the emitter transition frequency equals to the cavity resonance frequency for a high-Q cavity, our results agree with the recent experiments and theories.     

Control of Two-Photon Transport in a One-Dimensional Waveguide

We study the system consisting of a one-dimension waveguide side-coupled to a nonlinear cavity which was doped with a lambda-type atom and investigate the control of photons transport in one-dimension waveguide through manipulating the atom contained in the cavity. Employing the polariton technique, we show that in the single-photon case, the system behaves as a waveguide coupled to a two-level system. By solving the Schr?dinger equation, we show that single photon switch can be achieved by tuning the Rabi frequency of the classical field. In the two-photon case, the system behaves like a waveguide coupled to a cascade three-level system. Two-photon quantum correlation in the position variation can be controlled by adjusting the Rabi frequency.     

Frequency dependence of the photonic noise spectrum in an absorbing or amplifying diffusive medium

A theory is presented for the frequency dependence of the power spectrum of photon current fluctuations originating from a disordered medium. Both the cases of an absorbing medium (“grey body”) and of an amplifying medium (“random laser”) are considered in a waveguide geometry. The semiclassical approach (based on a Boltzmann-Langevin equation) is shown to be in complete agreement with a fully quantum mechanical theory, provided that the effects of wave localization can be neglected. The width of the peak in the power spectrum around zero frequency is much smaller than the inverse coherence time, characteristic for black-body radiation. Simple expressions for the shape of this peak are obtained, in the absorbing case, for waveguide lengths large compared to the absorption length, and, in the amplifying case, close to the laser threshold. Received 8 August 2000     

TE mode photon echo in slab waveguides

A theory of TE mode photon echo in slab waveguides is developed. It is found that the conditions for generation of a photon echo in waveguides can substantially differ from those in bulk material. For the photon echo in waveguides there is an optimum value of the Rabi frequency, and the echo energy does not depend periodically on the Rabi frequency as in the case of bulk material photon echo. Moreover, it is shown that the capability for echo generation is different for different modes. In particular there are several modes in the waveguide which cannot, in principle, generate an echo.     

Fano interference and transparency in a waveguide-nanocavity hybrid system with an auxiliary cavity

We investigate theoretically single photon transport in one-dimensional waveguide coupled to a pair of cavities, which are denoted by the first cavity and the auxiliary cavity. Two cases with no atom and one atom embedded in the first cavity are discussed. The Fano dips in the transmission spectrum and locations of transparency window are calculated. When no atom is embedded in the first cavity, there exists a transparency window under the condition that the first cavity and the auxiliary cavity are not resonant. The locations of the transparency window and Fano line type depend strongly on the eigen frequency of the auxiliary cavity and the coupling strength between the auxiliary cavity and the waveguide. When one atom is embedded in the first cavity, we show that the transparency window exists even though the first cavity, the atom and the auxiliary cavity are resonant. The Fano line type is strongly dependent on the eigen frequency of the auxiliary cavity and the coupling strength. Our results have potential applications in design of quantum devices at the level of single photon,such as single photon switch and single photon routers.     

Tunable wakefield dielectric-filled accelerating structure

The feasibility of the frequency spectrum of Vavilov-Cherenkov radiation being controlled in a wakefield dielectric-filled accelerating structure via an outer ferroelectric layer is studied. The spectrum and amplitude of the field excited in the structure versus the permittivity of the ferroelectric are found. Dielectric losses in the ferroelectric are estimated. It is shown that these losses impose limitations on the ferroelectric layer thickness and the range within which the frequency spectrum of the waveguide can be controlled. The structure under consideration is optimized for the AWA wakefield accelerator. The multilayer construction of the waveguide, in combination with specially shaped ferroelectric-permittivity-controlling electrodes, allows designers to tune the spectrum of the waveguide and suppress electron-bunch-deflecting waveguide modes. Thereby, there appears the possibility of controlling the transverse stability of the beam.     

基于PPKTP波导产生多通道光子对

提出了一种基于PPKTP波导利用自发参量产生多通道纠缠光子对的方案.计算在使用脉冲,连续激光,Ⅰ型、Ⅱ型相位匹配这些不同条件下,同时产生位于通信波段的多通道纠缠光子对的特性.结果显示该方案能够为量子密钥分配网络提供更为高效易行的方案.     

Vacuum Rabi Splitting and Kerr Effect of a Hybrid Spin–Magnon–Photon System

The vacuum Rabi splitting and Kerr effect are investigated theoretically in a hybrid spin–magnon–photon system, where the nitrogen-vacancy center in diamond driven by two light fields is coupled to a spherical micromagnet embedded in a superconducting coplanar waveguide resonator. The results indicate that the phenomenon of the Mollow triplet and vacuum Rabi splitting can appear by controlling the spin–magnon coupling and magnon–photon coupling. It is shown that the probe absorption spectrum can be adjusted effectively via the pump frequency detuning. Moreover, it is demonstrated that the optical Kerr effect can be tuned by changing the Rabi frequency. This work may provide a possibility for the applications in quantum information processing and quantum sensing of magnetic signal.     

基于平面光波导谐振腔的可调谐光电振荡器

提出了一种基于平面光波导谐振腔的可调谐光电振荡器.该振荡器中,相位调制器串联光波导谐振腔,取代了传统系统中的强度调制器、长光纤和滤波器.由于光学谐振腔对光子频率和相位敏感,调节激光器改变输出光的波长,不仅可以调制光的强度,还可以对微波光子进行选频输出.当光子在波导腔中发生谐振时,产生很强的延时特性,可以取代传统系统中的长光纤.整个光电振荡器系统体积为长29.5cm、宽21cm、高7cm.实验中,改变0.1pm的光子波长,能够产生步长为12.535.5 MHz的调谐,调谐范围达2 GHz,且系统能够产生10 GHz的微波信号,在中心频率为10 GHz处其相位噪声为-109.7dBc/Hz@10kHz.该研究为光电振荡器的小型化和实用化提供了一种新的思路.     

Spectrum reshaping of amplified pulse in silicon nanowaveguide

A device consisting of a cascaded semiconductor optical amplifier (SOA) and silicon on insulator (SOI) optical waveguide is presented to amplify and reshape the frequency spectrum of optical pulses in the picoseconds time duration. Numerical simulations show that the output spectrum of the amplified pulse by SOA can be effectively reshaped by utilizing the SOI waveguide. The length of the SOI waveguide may be judiciously adjusted to significantly reduce the frequency chirp of the output pulse from the SOA resulting in reshaping of the output spectrum. We find that the property of pulse spectrum is sensitive to the input pulse power and its temporal width.     

Controllable scattering of a single photon inside a one-dimensional resonator waveguide

We analyze the coherent transport of a single photon, which propagates in a one-dimensional coupled-resonator waveguide and is scattered by a controllable two-level system located inside one of the resonators of this waveguide. Our approach, which uses discrete coordinates, unifies low and high energy effective theories for single-photon scattering. We show that the controllable two-level system can behave as a quantum switch for the coherent transport of a single photon. This study may inspire new electro-optical single-photon quantum devices. We also suggest an experimental setup based on superconducting transmission line resonators and qubits.     

Propagation loss in a two-dimensional triangular photonic crystal waveguide

By means of a plane-wave-based transfer-matrix method, we present an extensive study of propagation loss in two-dimensional (2D) photonic crystal waveguides with limited cladding wall thickness. We examine the dependence of propagation loss on both the propagation direction and the waveguide wall thickness. It is shown that the propagation loss is a function of excitation frequency, wall thickness and waveguide outermost surface morphology. The conclusion that the propagation loss essentially decays exponentially with respect to the cladding wall thickness of a waveguide is valid only to a certain degree. In addition, we find that the propagation loss exhibit very complex behavior with respect to the excitation frequency.     

阶跃波导虚阴极振荡器数值模拟研究

 对一种阶跃波导虚阴极振荡器进行了数值模拟研究。结果表明阶跃波导长度对高功率微波的产生具有较大的影响；阶跃波导的等效圆柱腔谐振频率与阶跃波导长度和半径有关，当其接近二极管的本征振荡频率时，可以获得比较单一的微波频谱和效率较高的微波输出；微波产生效率随阶跃波导长度呈周期性变化。     

NOR and NAND gates using two photon absorption in silicon wire waveguide

Ultrafast all-optical NOR gate based on two photon absorption (2PA) process in SOI waveguide is already established. We have designed NAND gate also based on this process with a novel waveguide coupler structure. Power attenuation due to 2PA process and the working of these gates is developed with FDTD simulation. Dominant 2PA process is incorporated in FDTD update equations and it is shown that the influence of high intensity pump pulses on a different frequency continuous probe beam can be utilized to form NOR as well as NAND gates.