Photonic band mixing in linear chains of optically coupled microspheres

Roslyak, Oleksiy

doi:10.1103/physreve.73.036606

Cited by 31 publications

(15 citation statements)

References 21 publications

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“…Initial studies have concentrated on the optical coupling effects between whispering gallery modes (WGMs) in microspheres [18–24]. The notable advance in this area has been the identification of two distinct mechanisms of optical transport by using the generalized multiparticle Mie theory: evanescent WGM-based coupling and nanojet coupling [25].…”

Section: Introductionmentioning

confidence: 99%

Contact focusing multimodal microprobes for ultraprecise laser tissue surgery

et al. 2011

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Focusing of multimodal beams by chains of dielectric microspheres assembled directly inside the cores of hollow waveguides is studied by using numerical ray tracing. The device designs are optimized for laser surgery in contact mode with strongly absorbing tissue. By analyzing a broad range of parameters it is demonstrated that chains formed by three or five spheres with a refractive index of 1.65-1.75 provide a two-fold improvement in spatial resolution over single spheres at the cost of 0.2-0.4 attenuation in peak intensity of the central focused beam. Potential applications include ultra precise laser ablation or coagulation in the eye and brain, cellular surgery, and the coupling of light into photonic nanostructures.

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Section: Introductionmentioning

confidence: 99%

Contact focusing multimodal microprobes for ultraprecise laser tissue surgery

et al. 2011

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“…4b describes coupling of the FM to other WGMs, most important of which are terms with l < L. There are two reasons for this. First, modes with lower l and higher radial numbers can spectrally overlap with the l = L, s = 1 mode [16] and thus have a large effect on the field distribution. Second, these modes usually have lower Q-factors and contribute more significantly to the radiation losses of the system.…”

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confidence: 99%

Rayleigh scattering of whispering gallery modes of microspheres due to a single dipole scatterer

Rubin

2009

Phys. Rev. A

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The interaction of whispering gallery modes (WGM) of optical microresonators with subwavelength imperfections has been studied both experimentally and theoretically. This interaction is responsible for the formation of spectral doublets in place of single resonance peaks, and for degrading of Q-factors of the resonances. Within the currently accepted framework the spectral doublets are explained as a result of degeneracy removal of clockwise and counterclockwise WGMs due to their coupling caused by defect-induced backscattering, while the degrading of the Q-factor is described phenomenologically as an additional contribution to the overall decay rate of WGM due to coupling between WGM and radiative modes. Here we show that the existing understanding of this phenomenon is conceptually wrong and develop an exact theory of WGM interaction with a single defect, which provides a unified treatment for both aspects of this interaction explaining existing experiments and predicting new phenomena.Elastic (with no change in frequency) scattering of light due to small (compared to wavelength) particles is one of the most fundamental and intensively studied optical phenomena. Its modern history began almost one hundred fifty years ago with the explanation of the blue color of sky in a series of papers by Lord Rayleigh[1], where the now famous 1/λ 4 cross section law, where λ is the wavelength of light in vacuum, was derived. Since then it has been customary to refer to processes of elastic interaction of light with subwavelength particles as Rayleigh scattering. Besides providing us with beautiful blue skies and red sunsets, Rayleigh scattering is important for a large number of fundamental optical phenomena as well as for numerous applications. Recent developments in optics and photonics have created new situations in which the manifestations of Rayleigh scattering are significantly modified. Particularly drastic modification of this process is expected when light is confined in all three dimensions inside optical microresonators in the form of whispering gallery modes (WGM) [2]. Given the fundamental nature of this process it is not surprising that it has attracted a significant amount of attention in recent years [3,4,5,6,7].While whispering gallery modes can occur in various types of geometries [8] we will focus on spherical microresonators. WGMs in this case correspond to Mie resonances [9] with ultra narrow widths, γ ls ≪ ω ls , where ω ls is the frequency of the mode, and respectively high (up to 10 9 for silica microspheres [8]) Q-factors defined as Q ls = ω ls /γ ls . WGMs are characterized by polar and azimuthal indexes, l and m, and a radial number s determining, respectively, the angular and radial dependence of the fields in a spherical coordinate system centered at the sphere. The resonance frequency ω ls does not depend on the azimuthal number, which reflects the degeneracy of the resonances due to full spherical symmetry of the problem. WGMs are also characterized by their the mode volume, which can be very d...

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“…This limits the application of the dipolar dispersion diagrams to realistic waveguides assembled of dielectric nanoparticles. As an alternative to the dipole approximation a "semiclassical" approach based on the coupling of the whispering gallery modes of individual spheres could be employed to recover the array band structure [69,70] if the wavelength is much smaller than the diameter of the spheres. The general case, however, requires a full-wave Mie scattering approach to account for all possible multipole resonances [19] involving a very complicated multiscattering picture which mathematically manifests itself in infinite multipole sums.…”

Section: Light Guiding Above the Light Linementioning

confidence: 99%

Light Trapping above the Light Cone in One-Dimensional Arrays of Dielectric Spheres

2017

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Abstract:We demonstrate bound states in the radiation continuum (BSC) in a linear periodic array of dielectric spheres in air above the light cone. We classify the BSCs by orbital angular momentum m = 0, ±1, ±2 according to the rotational symmetry of the array, Bloch wave vector β directed along the array according to the translational symmetry, and polarization. The most simple symmetry protected BSCs have m = 0, β = 0 and occur in a wide range of the radius of the spheres and dielectric constant. More sophisticated BSCs with m = 0, β = 0 exist only for a selected radius of spheres at fixed dielectric constant. We also find robust Bloch BSCs with β = 0, m = 0. All BSCs reside within the first but below the other diffraction continua. We show that the BSCs can be easily detected by bright features in scattering of different plane waves by the array as dependent on type of the BSC. The symmetry protected TE/TM BSCs can be traced by collapsing Fano resonance in cross-sections of normally incident TE/TM plane waves. When plane wave with circular polarization with frequency tuned to the bound states with OAM illuminates the array the spin angular momentum of the incident wave transfers into the orbital angular momentum of the BSC. This, in turn, gives rise to giant vortical power currents rotating around the array. Incident wave with linear polarization with frequency tuned to the Bloch bound state in the continuum induces giant laminar power currents. At last, the plane wave with linear polarization incident under tilt relative to the axis of array excites Poynting currents spiralling around the array. It is demonstrated numerically that quasi-bound leaky modes of the array can propagate both stationary waves and light pulses to a distance of 60 wavelengths at the frequencies close to the bound states in the radiation continuum. A semi-analytical estimate for decay rates of the guided waves is found to match the numerical data to a good accuracy.

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Photonic band mixing in linear chains of optically coupled microspheres

Cited by 31 publications

References 21 publications

Contact focusing multimodal microprobes for ultraprecise laser tissue surgery

Contact focusing multimodal microprobes for ultraprecise laser tissue surgery

Rayleigh scattering of whispering gallery modes of microspheres due to a single dipole scatterer

Light Trapping above the Light Cone in One-Dimensional Arrays of Dielectric Spheres

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