Sagnac gyroscope using a two-dimensional array of coupled optical microresonators

Micron-scale-integrated optical gyroscopes based on the Sagnac effect have a broad array of potential applications in navigation and inertial motion sensing due to the benefit of on-chip integration and potential sensitivities exceeding micro-electromechanical gyroscopes. Here, we analyze the Sagnac effect in a two-dimensional array of evanescently coupled optical microring resonators. We show that the sensitivity to inertial rotations greatly exceeds that of a single resonator with equal enclosed area. Moreover, a comparison between two-dimensional arrays and Sagnac gyroscopes consisting of one-dimensional distributed microresonators arrays of equal footprint shows that the sensitivity to rotations of the two-dimensional array exceeds that of the one-dimensional structures by as much as several orders of magnitude for smaller arrays.     

Temperature induced nonlinearity in coupled microresonators

We present here, our most recent results from theoretical and experimental investigations of optical properties of coupled microresonators. While fused silica spherical microresonators with Q-factors of about 10⁷ to 10⁸ can be quite easily fabricated, the production of a number of equally sized spheres, which appears to be a necessary condition for effective light coupling, has proved challenging. In order to bypass this problem we focus our attention on the investigation of coupled disk microresonators made of fused silica. These may be fabricated in almost arbitrary two-dimensional configuration with nanometer precision. A Q-factor of 10⁵ can be routinely achieved, which relaxes the requirements on uniformity of the microdisks to within the range of fabrication accuracy. The achieved Q-factors are high enough to observe thermal nonlinear effects in the fabricated coupled disks. A detailed experimental analysis of the thermal nonlinear resonance behavior in a system of two coupled microdisks now follows. The results were found to be in good agreement with the respective calculations based on coupled mode theory including temperature induced nonlinear response.     

Modeling of circular integrated optical microresonators by 2-D frequency domain coupled mode theory

Circular integrated optical (ring or disk) microresonators are increasingly employed as compact and versatile wavelength filters. In this paper, we investigate a 2-D frequency domain model for these devices, based on spatial coupled mode theory. The microresonators are functionally represented in terms of two couplers with appropriate connections using bent and straight waveguides. The abstract scattering matrices of the couplers and the propagation constants of the cavity bends allow to compute the spectral responses of the resonators. Capitalizing on the availability of rigorous analytical modal solutions for bent waveguides, the constituent bent-straight waveguide couplers are modeled using a spatial coupled mode formalism derived by means of a variational principle. The resulting scattering matrices show reciprocity properties as expected according to the symmetry of the coupler structures. We present results for the spectral response and field examples for microresonators with mono- and multi-modal cavities for TE and TM polarizations. Comparisons with finite difference time domain simulations show very good overall agreement.     

Mode expansion modeling of rectangular integrated optical microresonators

Two dielectric waveguides that are evanescently coupled to a square or rectangular region of increased refractive index can serve as a very compact integrated optical microresonator. We consider these devices in a spatial two-dimensional setting, where a rigorous mode expansion technique enables accurate and quite efficient numerical simulations of these configurations. The paper is concerned with single resonator units as well as with an add-drop filter constructed by cascading two square cavities. Besides calculating the power transmission spectra, we try to document as far as possible the characteristic electric field patterns that occur at major and minor resonance wavelengths. The influence of the various geometrical parameters on the resonator performance is investigated in detail.     

Mode expansion modeling of rectangular integrated optical microresonators

Two dielectric waveguides that are evanescently coupled to a square or rectangular region of increased refractive index can serve as a very compact integrated optical microresonator. We consider these devices in a spatial two-dimensional setting, where a rigorous mode expansion technique enables accurate and quite efficient numerical simulations of these configurations. The paper is concerned with single resonator units as well as with an add-drop filter constructed by cascading two square cavities. Besides calculating the power transmission spectra, we try to document as far as possible the characteristic electric field patterns that occur at major and minor resonance wavelengths. The influence of the various geometrical parameters on the resonator performance is investigated in detail.     

正三角形及正方形微光学腔模式特性研究

微谐振腔模式特性研究是利用微腔研制新型光电器件的基础．为了研制出能采用平面工艺制作的定向输出的微腔激光器，文章采用解析和数值模拟方法深入研究了正三角形及正方形光学微腔的模式特性，并得到与数值模拟结果符合非常好的解析场分布及模式波长．对正方形光学微腔，把模式组合成满足正方形对称性的场分布，发现其类WG模式只存在品质因子比它小一个数量级以上的偶然简并模式，因此正方形微腔有利于实现真正的单模工作．     

All optical switching in semiconductor microresonators based on pattern selection

We present here a method for selecting optical patterns in a passive semiconductor microresonator, by using a spatial perturbation. A pattern is spontaneously generated in the system, and a switching beam causes this pattern to rotate even if the power in the switching beam is much lower than the power in the pattern. Thus, an all optical switch is realized, that operates at low light levels.     

A computational study of the optical response of strongly coupled metal nanoparticle chains

We study the optical response of strongly coupled metal nanoparticle chains using rigorous multiple scattering calculations. The collective resonant frequency of silver nanosphere chains and the coupling between chains are considered. The coupling between silver nanoparticle chains are understood by the transmission and reflection calculations of 2D periodic arrays of nanospheres. The results are in agreement with recent experiments. The splitting of plasmon resonance modes for different polarizations of the incident light are explored. Our results show that the transverse mode resonant wavelength is very sensitive to the inter-chain distance. Results on the effect of disorder are also presented.     

Hard-molded 51 cm long waveguide array with a 150 GHz bandwidth for board-level optical interconnects

We demonstrated a 51 cm long waveguide array on a poly(methyl methacrylate) sheet fabricated by silicon hard-molding technology. To reduce the silicon sidewall roughness, a wet-oxidation followed by a buffered oxidation etchant etching process is adopted, achieving a surface roughness of 1.2 nm. The waveguide obtained a total insertion loss of -15.1 dB and an adjacent channel cross talk below -31 dB. The 3 dB optical bandwidth is determined to be 150 GHz by the optical autocorrelation method.     

Heat transport in coupled inhomogeneous chains

We first investigate the heat transport in a network model consisting of two coupled dimerized chains. Results indicate that the thermal resistance of each chain increases with the decrease of the mass ratio γ of the two types of atoms. Then, we find, when a light impurity or a heavy one is added in the two coupled homogeneous chains and coupled with a particle of another chain, the interface thermal resistances R_int^l and R_int^r present different dependences on the mass ratio γ'. Finally, a persistent circulation of energy current is observed in coupled inhomogeneous chains with two pairs of interchain coupling.     

Changes in mean square nuclear charge radii from optical isotope shifts of long chains of isotopes

Results of recent measurements on isotope shifts are compiled for 20 chains of isotopes, mostly concerning short-lived radioactives. Unpublished material is also included. The σ <r²> are re-evaluated by using an improved calculation of the electron density at the nucleus. Therefore, in some elements, minor changes occur as compared to results given in the literature.     

Dissipative Kerr solitons in optical microresonators with Raman effect and third-order dispersion

Using the mean-field normalized Lugiato–Lefever equation, we theoretically investigate the dynamics of cavity soliton and comb generation in the presence of Raman effect and the third-order dispersion. Both of them can induce the temporal drift and frequency shift. Based on the moment analysis method, we analytically obtain the temporal and frequency shift,and the results agree with the direct numerical simulation. Finally, the compensation and enhancement of the soliton spectral between the Raman-induced self-frequency shift and soliton recoil are predicted. Our results pave the way for further understanding the soliton dynamics and spectral characteristics, and providing an effective route to manipulate frequency comb.     

Phase compactons in chains of dispersively coupled oscillators

We study the phase dynamics of a chain of autonomous oscillators with a dispersive coupling. In the quasicontinuum limit the basic discrete model reduces to a Korteveg-de Vries-like equation, but with a nonlinear dispersion. The system supports compactons: solitary waves with a compact support and kovatons which are compact formations of glued together kink-antikink pairs that may assume an arbitrary width. These robust objects seem to collide elastically and, together with wave trains, are the building blocks of the dynamics for typical initial conditions. Numerical studies of the complex Ginzburg-Landau and Van der Pol lattices show that the presence of a nondispersive coupling does not affect kovatons, but causes a damping and deceleration or growth and acceleration of compactons.     

Localization in a system of N coupled chains

The behaviour of a quantum particle moving in a system of N coupled chains parallel to each other and packed into a bundle is investigated in the presence of weak disorder. This system may be thought of as a model of an anisotropic thin wire. The dependence of the localization length r_loc on N and t_⊥ is studied (t_⊥ is the interchain exchange integral characterizing the strength of the interchain tunneling). For t_⊥ < t_c ≅ h/τ the localization length r_loc increases proportionally to lt_⊥/(t_τ −t_⊥) attaining a plateau value of the order of Nl (τ is the relaxation time and 1 the mean free path for elastic scattering). Such a behaviour may be called a transition from the Mott localization regime to the Thouless localization regime. It may be considered as a precursor of the insulator-metal transition (r_loc → ∞) occuring for t_⊥ → t_c in the quasi-1d system (N → ∞).     

Hidden symmetry in chains of biological coupled oscillators

We experimentally investigated spatiotemporal patterns in chains of coupled biological oscillators with boundaries and found hidden symmetric patterns that are not straightforwardly derived from explicit geometrical symmetry of the systems. We propose a model of coupled oscillators in chains with a hidden oscillator interconnecting its boundaries. The model can explain all observed patterns including the hidden symmetric ones, while other models such as discrete analogs of Neumann boundary conditions in continuous systems cannot.     

Temperature compensation of optical microresonators using a surface layer with negative thermo-optic coefficient

We theoretically investigate the feasibility of using a surface layer with a negative thermo-optic coefficient to compensate the thermal drift of a resonant frequency in an optical microresonator. Taking a fused-silica microsphere as an example, our analysis has shown that the thermal drift of a whisper-gallery mode can be fully compensated by such a surface layer. We analyze and compare the compensation performances by using different materials as the surface layer.     

Surface adsorption and collapse transition of linear polymer chains

The critical behaviour of surface adsorption and collapse transition of a flexible self-attracting self-avoiding polymer chain is examined. Depending upon the underlying lattice and space dimensionality, phase diagrams that exhibit many different universality domains of critical behavior are found. We discuss these phase diagrams and the values of the critical exponents found from different theoretical methods.     

Investigation of spectral bandwidth of optical parametric amplification

The spectral bandwidth of three-wave-mixing optical parametric amplification has been investigated. A general mathematical model for evaluating the spectral bandwidth of optical parametric amplification is developed with parametric bandwidth and gain bandwidth via three-wave noncollinear interactions. The spectral bandwidth is determined by expanding the wave-vector mismatch in a Taylor series and retaining terms through second order. The model takes into account the effects of crystal length, noncollinear angle, group velocity, group-velocity dispersion and gain coefficient. The relation between parametric bandwidth and gain bandwidth is clearly defined. The model is applied to a BBO OPA, a LBO OPA and a CLBO OPA. PACS 42.65.Yj; 42.65.Lm; 42.65.Ky; 42.60.By     

Excitation and interrogation of whispering-gallery modes in optical microresonators using a single fused-tapered fiber tip

We show that whispering-gallery modes (WGMs) in optical microresonators can be excited and detected using a fused-tapered fiber tip (FTFT). The fabrication of FTFTs is simple and inexpensive; they are robust and allow the excitation and interrogation of the resonances with a single fiber. Excitation of high-Q WGMs in silica microcylinders and microspheres is demonstrated.     

耦合作用下有机铁磁链的临界行为

利用平均场，我们研究了一个具有链间耦合作用的有机铁磁模型，并给出了该模型的全相图。计算表明，链间耦合强烈影响其基态的磁序。当链间耦合达到某临界值时，高自旋基态消失，整个系统由铁磁相转变为近藤单态（Kondo-singlet）相。