Self-localization of whispering-gallery modes in a spherical microcavity filled with a cold electron plasma

We have studied the mechanisms and conditions for self-localization of laser radiation in a cold collisionless electron plasma for a spherical microcavity in the quasistatic approximation, taking into account the appearance of striction nonlinearity and also relativistic effects connected with forced oscillatory motion of the electrons. We have shown that when whispering-gallery modes interact nonlinearly with the electron plasma, a spherical plasmon is excited which is localized within the finite volume of the microsphere. We have established that realization of self-localized spherical structures, in the form of an electromagnetic field and spherical plasmons within a microcavity filled with a cold electron plasma, is primarily due to appearance of relativistic nonlinearity of the medium. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 59–64, January–February, 2006.     

Prescribed nondegenerate high-order modes in an axial-asymmetric high-finesse Fabry-Perot microcavity

We report an axial-asymmetric high-Q Fabry-Perot cavity supporting nondegenerate Hermite-Gaussian modes of the same mode order. Axial asymmetry of mirror surface was introduced by mechanically grinding off one side of a cylindrical mirror substrate without degrading the original mirror quality. The bases of the resulting Hermite-Gaussian modes were aligned with respect to the direction of grinding, making it possible to prescribe the mirror principal axes.     

Mathematical study of the two-dimensional lasing problem for the whispering-gallery modes in a circular dielectric microcavity

Microdisk lasers are investigated for their thresholds characteristics. We present a novel approach for studying the threshold gains of the whispering-gallery (WG) and other modes based on solving the boundary value problem for the Maxwell's equations. The novelty is that we consider the real-value pairs of frequencies and material gains as eigenvalues. In the two-dimensional (2D) approximation this problem is reduced to the set of independent transcendental equations. A Newton's method is further used to calculate the thresholds and natural frequencies numerically.     

Experimental investigation of a gyrotron with whispering-gallery modes

Radiophysics and Quantum Electronics -     

Control of light pulse propagation with only a few cold atoms in a high-finesse microcavity

Propagation of a light pulse through a high-Q optical microcavity containing a few cold atoms (N<10) in its cavity mode is investigated experimentally. With less than ten cold rubidium atoms launched into an optical microcavity, up to 170 ns propagation lead time ("superluminal"), and 440 ns propagation delay time (subluminal) are observed. Comparison of the experimental data with numerical simulations as well as future experiments are discussed.     

Nonlinear whispering-gallery modes in a microellipse cavity

We study theoretically the effect of deformed microelliptical cavities on lasing characteristics. We show that the transition of stationary lasing states from unidirectional rotational waves to a mixture of clockwise and anticlockwise rotational waves occurs when the shape of a disk is deformed to that of an ellipse.     

High-Q exterior whispering-gallery modes in a metal-coated microresonator

We propose a kind of plasmonic whispering-gallery mode highly localized on the exterior surface of a metal-coated microresonator. This exterior (EX) surface mode possesses high quality factors at room temperature, and can be efficiently excited by a tapered fiber. The EX mode can couple to an interior (IN) mode and this coupling produces a strong anticrossing behavior, which not only allows conversion of IN to EX modes, but also forms a long-lived antisymmetric mode. As a potential application, the EX mode could be used for a biosensor with a sensitivity high of up to 500 nm per refraction index unit, a large figure of merit, and a wide detection range.     

Lasing modes in a spiral-shaped dielectric microcavity

The resonance patterns and lasing modes in a spiral-shaped dielectric microcavity are investigated through passive and active medium calculations. We find that the high-Q resonance modes are whispering-gallery-like modes, and these resonance modes can be easily excited as lasing modes. We also find that the quasi-scarred resonance mode, which shows strong directional emission beams from the cavity boundary, can be excited with selectively applied external pumping. Through a spectral analysis of the time evolution of the light field, the competition between these lasing modes is discussed.     

Longitudinal whispering-gallery modes in metal microcavities

Longitudinal waves in microcavities emerging because of spatial dispersion are investigated. It is shown that longitudinal modes similar to whispering-gallery modes exist in microcavities of this kind. These longitudinal modes should exist in metal microcavities in the vicinity of the plasma frequency.     

Optomechanical dynamics in detuned whispering-gallery modes cavity

The dynamics of a microresonator in detuned whispering-gallery modes (WGM) cavity opto-mechanical system are investigated by the quantum Langevin equation. A WGM cavity coupling to two parallel waveguides is devised to study the transmission and reflection of this system. In single mode WGM cavity, without optomechanical coupling, both the transmission and reflection of the cavity present a Lorentzian dip and peak. When the coupling between the cavity mode and mechanical mode is considered, the transmission and reflection of the optomechanical cavity show “W” and “M” shape mode splitting. Moreover, under the action of a controlling and a probe laser, the output field at the probe frequency presents electromagnetically induced transparency (EIT)-like spectrum in the system. We give the physical origin of EIT-like and the pump-probe response for the WGM shares all the features of the Λ system in atoms. Further, due to backscattering, the two traveling waves in WGM are coupled with a rate γ. The transmission and reflection of the optomechanical cavity display three modes splitting in the spectra with optomechanical coupling between the two cavity modes and the mechanical mode.     

Oscillatory light loss within the cladding of a straight optical fiber: comparison with whispering-gallery modes

Light propagating within the cladding of a straight optical fiber exhibits wavelength-dependent oscillatory loss that resembles the whispering-gallery modes of a bent fiber. This novel observation can be explained by interference of light only within the cladding and the buffer without any influence of the fiber core. The technique promises applications similar to those that are due to whispering-gallery modes but without the additional requirement of having a bent fiber.     

Pigtailing the high-Q microsphere cavity: a simple fiber coupler for optical whispering-gallery modes

We demonstrate a simple method for efficient coupling of standard single-mode optical fibers to a high- Q optical microsphere cavity. Phase-matched excitation of whispering-gallery modes is provided by an angle-polished fiber tip in which the core-guided wave undergoes total internal reflection. In the experimental setup, which included a microsphere with both an input and an output coupler, the total fiber-to-fiber transmission at resonance reached 23% (total insertion loss, 6.3 dB), with loaded quality factor Q>/=3x10(7) and unloaded Q approximately 1.2x10(8) at 1550 nm. A simple pigtailing method for microspheres permits their wider use in fiber optics and photonics devices.     

Shift of whispering-gallery modes in microspheres by protein adsorption

Biosensors based on the shift of whispering-gallery modes in microspheres accompanying protein adsorption are described by use of a perturbation theory. For random spatial adsorption, theory predicts that the shift should be inversely proportional to microsphere radius R and proportional to protein surface density and excess polarizability. Measurements are found to be consistent with the theory, and the correspondence enables the average surface area occupied by a single protein to be estimated. These results are consistent with crystallographic data for bovine serum albumin. The theoretical shift for adsorption of a single protein is found to be extremely sensitive to the target region, with adsorption in the most sensitive region varying as 1/R(5/2). Specific parameters for single protein or virus particle detection are predicted.     

Coupling of whispering-gallery modes in size-mismatched microdisk photonic molecules

Mechanisms of whispering-gallery (WG)-mode coupling in microdisk photonic molecules (PMs) with slight and significant size mismatches are numerically investigated. The results reveal two different scenarios of modes interaction depending on the degree of this mismatch and offer new insight into how PM parameters can be tuned to control and modify WG-mode wavelengths and Q factors. From a practical point of view, these findings offer a way to fabricate PM microlaser structures that exhibit low thresholds and directional emission and at the same time are more tolerant to fabrication errors than previously explored coupled-cavity structures composed of identical microresonators.     

Directional emission from whispering-gallery modes in deformed fused-silica microspheres

Highly directional emissions from whispering-gallery modes are demonstrated in deformed nonaxisymmetric fused-silica microspheres. Ray trajectory analysis indicates that ray dynamics in a three-dimensional reso-nator differs qualitatively from that of a two-dimensional system, with Arnol'd diffusion playing an essential role in the three-dimensional system.     

Threshold reduction in a cyclic photonic molecule laser composed of identical microdisks with whispering-gallery modes

Lasing modes in cyclic photonic molecules (CPMs) composed of several identical thin semiconductor microdisks in free space are studied in a linear approximation. Maxwell's equations with exact boundary conditions and the radiation condition at infinity are considered as a specific eigenvalue problem that enables one to find natural frequencies and threshold gains. It is demonstrated that careful tuning of the distance between the disks in CPMs is able to drastically reduce the lasing thresholds of the whispering-gallery modes having small azimuth indices.     

Visualizing the whispering gallery modes in a cylindrical optical microcavity

Whispering gallery modes in cylindrical integrated optics microcavities have, for what is to our knowledge the first time, been mapped with a photon scanning tunneling microscope. Optical images were obtained with a spatial resolution of 50 nm. By combination of information on the spatial optical distributions with wavelength-dependent measurements, an unexpectedly rich variety of intracavity phenomena, such as polarization conversion and interference of copropagating and counterpropagating modes, could be directly observed. A quantitative comparison of the experimental data with computer simulations results in a comprehensive understanding of the various whispering gallery modes inside the microcavity.     

All-optical switch based on photonic crystal microcavity with multi-resonant modes

We present a design of all-optical switches based on one-dimensional photonic crystals (1D PhC) doped with nonlinear optical materials. The 1D PhC switch structure is composed of a PhC cavity sandwiched by two accessional PhC microcavities. The center PhC cavity has two resonant frequencies with nearly the same quality factors (Q), while the accessional PhC cavities have the same resonant frequency, which is equal to one of the resonant frequencies of the center cavity. The two accessional PhC cavities cause reduction of Q value in this resonant frequency and result in different Q values of two modes. We realize all-optical switch effect by selecting pump light wavelength at the low Q mode and probe light wavelength at the other mode. The theoretical simulations by using the finite difference time domain method show that the pump light intensity required to realize optical switch effect in the designed switch is 50 times smaller than that in one-dimensional photonic crystals cavity with only one resonant mode.     

Optical modes in wavelength-sized organic microcavity structures

We show the impact of lateral structuring on the optical properties of organic thin films in microcavities. The active material tris-(8-hydroxy quinoline) aluminium (Alq₃) was deposited using shadow mask evaporation, resulting in various micron sized shapes. A simplified box model is employed to describe the steady state electric field distribution in these mesa cavities. The complex mode structure measured in transmission and photoluminescence is confirmed by a transfer matrix calculation and a Fourier transform of the internal electric field distribution.     

Optical manipulation of microparticles using whispering-gallery modes in a silicon nitride microdisk resonator

We demonstrate optical manipulation of 1?μm sized polystyrene microparticles on silicon nitride microdisk resonator devices using whispering-gallery modes in an integrated optofluidic chip. We demonstrate multiple trapping tracks and extended trapping ranges within single wavelengths through exciting high-order modes. We observe various sets of trapping tracks and ranges through exciting various resonance modes. We switch particle traveling tracks by tuning the laser wavelength to various wavelengths. We also observe microparticles assembling along the trapping tracks.