Fiber taper coupled high-quality-factor planar microdisk

A fiber taper can evanescently couple to whispering gallery modes (WGMs) in a planar silica microdisk for observing the optical properties of the microdisk cavity. It is revealed that WGMs have very high quality (Q) factors by controlling the air gap between the taper and the microdisk. The best coupling efficiency from the taper to the microdisk is as high as 98%, and can be continuously adjusted from the under-coupling, critical-coupling to over-coupling regimes. The influence of the laboratory circumstance such as surface contamination on the microdisk is also discussed. It is experimentally shown that the high-Q-factor (105) modes can be kept for a long period in a general laboratory circumstance.     

Mode coupling between first- and second-order whispering-gallery modes in coupled microdisks

The mode characteristics for two coupled microdisks are investigated by the finite-difference time-domain technique. In the two coupled micodisks, mode coupling between the same order whispering-gallery modes (WGMs) results in coupled WGMs with split mode wavelengths. The numerical results show that the split mode wavelengths of the coupled first- and second-order WGMs can have a crossing point in some cases, which can induce anticrossing mode coupling between them and greatly reduce the mode Q factor of the coupled first-order WGMs. The time variation of mode field pattern shows the transformation between the coupled first- and second-order WGMs.     

Easily coupled whispering gallery plasmons in dielectric nanospheres embedded in gold films

A new self-aligned robust method for coupling to whispering gallery modes (WGMs) of submicron microspheres utilizes their periodic arrangement without relying on nanopositioned external coupling devices. The microspheres are embedded in a nanostructured gold surface supporting delocalized plasmonic crystal modes that mediate the coupling, and can be tuned by the geometry. Detailed measurements of the angle- and orientation-dependent reflectivity reveal localized plasmonic WGMs whose energies scale with sphere diameter and agree closely with Mie calculations. Coupling between these plasmonic WGMs leads to mode splitting and the formation of plasmonic minibands of a controllable bandwidth.     

Directional escape from a high-Q deformed microsphere induced by short CO2 laser pulses

Nonaxisymmetric fused-silica microspheres were fabricated by using only one microsphere by virtue of short pulses of a CO2 laser. Highly directional emission from whispering-gallery modes (WGMs) was studied through direct free-space evanescent excitation. The observed quality factors of WGMs are high, up to 2x10(7), despite this deformation. We show that WGMs in slightly deformed microspheres possibly play an important role in cavity quantum electrodynamics research.     

Optical manipulation in optofluidic microbubble resonators

An optical manipulation system based on optofluidic microbubble resonators(MBR) is proposed. As the high-Q whispering gallery modes(WGMs) are excited in an MBR, the buildup of the field intensity inside the resonator is large enough to trap nanoscale particles. The optical gradient forces generated by the WGMs with different radial orders are investigated numerically. The negative effect of the resonance detuning induced by the particles is taken into account to investigate the optical gradient forces exerting on the particles. By the stability analysis, the WGMs with high radial orders show a better trapping stability under Brownian motion since most of the optical fields reside within the water core.     

Modification of photon states in photonic molecules with semiconductor nanocrystals

We report on the coherent coupling of whispering gallery modes (WGMs) in a photonic molecule formed from two melamine formaldehyde spherical microcavities coated with a thin shell of CdTe nanocrystals. Utilizing different excitation conditions, the splitting of the WGM resonances originating from bonding and antibonding branches of the photonic states is observed and a fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Observation of optical wavelength switching with controllable spectral position and separation is reported.     

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.     

Anticrossing of Whispering Gallery Modes in microdisk resonators embedded in an anisotropic environment

We numerically investigate the behavior of Whispering Gallery Modes (WGMs) in circularly shaped resonators like microdisks, with diameters in the range of optical vacuum wavelengths. The microdisk is embedded in an uniaxial anisotropic dielectric environment. By changing the optical anisotropy, one obtains spectral tunability of the optical modes. The degree of tunability strongly depends on the radial (azimuthal) mode order M (N). As the modes approach each other spectrally, anticrossing is observed, leading to a rearrangement of the optical states.     

Mode characteristics of silver-coated inverted-wedge silica microdisks

The characteristics of whispering gallery modes(WGM) in silver-coated inverted-wedge silica microdisks are theoretically investigated by using finite element method. Dielectric TE mode always exists in silver-coated inverted-wedge resonators; dielectric TM mode tends to couple with SPP modes; only pure interior surface plasmonic polariton(SPP) mode but not pure exterior SPP mode is observed in contrast to the metal-coated cylindrical and toroidal resonators. The dependence of quality factor of different kinds of WGMs on the radius of the resonator and the thickness of the coated silver layer are systematically analyzed. We find that the quality factors of the hybrid WGMs associated with SPP mode can reach 104. The maximum light intensity enhancement in ambient for a hybrid mode consisting of a dielectric TM mode and an exterior SPP mode can be obtained when a silver film of thickness ~40 nm is deposited. The silver-coated inverted-wedge silica resonators may be widely applied in sensing and surface enhanced Raman scattering.     

消逝场耦合圆柱形微腔中回音壁模式结构的实验研究

采用石英圆柱形微腔与锥形光纤通过消逝场耦合的方式,在实验上观察到了不同半径的柱形微腔中清晰的回音壁模式,耦合效率接近10%. 利用柱形微腔回音壁模式位置和间隔的解析近似公式,对实验所得的透射光谱做了模式的精确标定,共振波长的实验值和标定值间的误差小于0.05nm. 引入回音壁模式的“模场半径”概念,由“模场半径”计算出的模式间隔和实验测量值之间符合很好. 利用透射光谱中的共振波长和理论标定波长间的差值,得到了实验光谱范围内(1295—1320nm)石英光纤的色散曲线,折射率精度达10^-5. 关键词： 圆柱形微腔 回音壁模式 模式标定 模场半径     

Simultaneous measurement of refractive index and temperature using a microring resonator

An approach to the simultaneous measurement of refractive-index(RI) and temperature changes using optical ring resonators is proposed and theoretically demonstrated.With a liquid-core silica ring resonator as an example,two different-order whispering gallery modes(WGMs) might differ in not only RI but also temperature sensitivities.Thus,a second-order sensing matrix should be defined based on these WGMs to determine RI and temperature changes simultaneously.The analysis shows that the RI and temperature detection limits can be achieved on the order of 10 7 RI unit and 10 3 K at a wavelength of approximately 780 nm.     

Resonance splitting in gyrotropic ring resonators

We present the theoretical concept of an optical isolator based on resonance splitting in a silicon ring resonator covered with a magneto-optical polymer cladding. For this task, a perturbation method is derived for the modes in the cylindrical coordinate system. A polymer magneto-optical cladding causing a 0.01 amplitude of the off-diagonal element of the dielectric tensor is assumed. It is shown that the derived resonance splitting of the clockwise and counterclockwise modes increases for smaller ring radii. For the ring with a radius of approximately 1.5μm, a 29GHz splitting is demonstrated. An integrated optical isolator with a 10μm geometrical footprint is proposed based on a critically coupled ring resonator.     

光学微盘腔与三能级量子点系统中的模耦合研究

用一种全量子理论方法研究了波导、光学微盘腔与三能级量子点耦合系统的动力学过程,求出其耦合后的透射模和反射模的解析解. 由于微腔表面粗糙引起反向散射,在微腔内形成两简并回音壁耦合共振模,其耦合率为β;量子点的两激发态分别以耦合率g₁,g₂与回音壁耦合共振模产生耦合. 在实数空间里,得出透射光谱和反射光谱的数值解,这些三能级模型结果比二能级模型结果更接近真实光学微盘腔系统,能更好地显示耦合系统的动力学特性. 关键词： 模耦合 光学微盘腔 三能级量子点 全量子理论     

Controlled observation of nondegenerate cavity modes in a microdroplet on a superhydrophobic surface

We demonstrate controlled lifting of the azimuthal degeneracy of the whispering gallery modes (WGMs) of single glycerol-water microdroplets standing on a superhydrophobic surface by using a uniform electric field. A good agreement is observed between the measured spectral positions of the nondegenerate WGMs and predictions made for a prolate spheroid. Our results reveal fewer azimuthal modes than expected from an ideal spherical microdroplet due to the truncation by the surface. We use this difference to estimate the contact angles of the microdroplets.     

Sensor based on an integrated optical microcavity

A novel integrated optical sensor based on a cylindrical microcavity (MC) is proposed. A MC sustains so-called whispering-gallery modes (WGMs), in which the energy of the optical field can be efficiently stored. By monitoring the scattering intensity from the MC, one can detect minute changes in the refractive index of the WGM, for instance, as a result of analyte adsorption. Measurement of a change in refractive index of as little as 10(-4) is demonstrated experimentally. The MC-based integrated optical sensor may have a size of approximately 8mum , and it is rugged and inexpensive.     

Dispersive medium’s normal coupled modes and low threshold optical bistability in a symmetric one-dimensional photonic crystal

We present a detailed study of the dispersive medium’s normal coupled modes in a symmetric one-dimensional photonic crystals (1D PCs). The splitting, homogeneous broadening effect, and the detuning effect of the normal coupled modes can be well controlled by adjusting the parameters of the dispersive medium. The bistable behavior of the PCs with Kerr medium is also investigated and it is found that the threshold intensity of nonlinear optical bistability (OB) of 1D PCs with dispersive medium is much lower than that of structure without dispersive medium. The threshold intensity is strikingly sensitive to the coupling strength of the dispersive medium.     

Whispering-gallery modes in glass microspheres: optimization of pumping in a modified confocal microscope

Whispering-gallery modes (WGMs) on Nd3+-doped glass microspheres with a radius of ～15?μm were measured in a modified confocal microscope, where a dual spatial resolution in both excitation and detection zones was possible. As an alternative to the standard excitation mechanism by an evanescent wave, we used an efficient pumping/detecting scheme, focusing a laser in the microsphere and exciting the Nd3+ ions, whose fluorescent emission produces the WGMs. We have also measured the generated WGMs by changing the detection zone, where higher amplitude resonances were found when exciting in the center and detecting at the edge of the microsphere.     

Waveguide modulated non-local optical interaction of semiconductor microdisks

The non-local optical interaction of two semiconductor microdisks with a waveguide bridged at radial direction is proposed and studied by three dimensional finite-difference time-domain （FDTD） electromagnetic simulations. The strong and weak optical interactions between two microdisks are observed and ascribed to the internal coupled modes with different coupling ratios. The vertical radiation losses and the related mode quality factors are modulated by waveguide length and present oscillation characteristics for the resonant modes. In addition, the optical leakage of coupling system is affected by the etching depth of disks due to tile emission of minor components of electric field.