Abstract
In this paper, we give a general model for analysis of multimode Whispering Gallery Mode (WGM) resonators coupled to multimode tapered fibers based on the coupled-mode theory. Such formulation takes into account the asymmetry of the taper-resonator coupling. Simulations for a microsphere show that the tapered fiber coupling mechanism induces cross-coupling between coherent orthonormal WGMs. We show that the degree of such cross-coupling depends basically on the fiber diameter, air-gap between the taper and resonator, intrinsic losses and eccentricity. The WGM cross-coupling affects the total transmission and spectral line-shape of the internal powers resulting in a controllable transformation of the line-shape to non-Lorentzian spectra. This analysis can be utilized to precisely determine the output and intra-cavity intensity of multimode microresonators, which is important in lasers, nonlinear optical signal generation and realization of optical delays.
Highlights
The transmission spectrum of a Waveguide-coupled optical Whispering Gallery Mode (WGM) microresonator is a result of interference between the incoming waveguide-mode and the outcoupled excited resonator-modes
The model is applied to a silica microsphere exhibiting degenerate WGMs resembling a coherent multimode cavity, and it is demonstrated that depending on the tapered fiber loading, WGMs contribute to the distortion of the total transmission spectra of the resonator to a non-Lorentzian line-shape
Transition between perfect and deformed microspheres with various levels of deformations can be dynamically achieved by applying mechanical strain [29,30,31] to realize non-permanent deformations. In this Paper, a general model based on Coupled-Mode Theory (CMT) is developed to model multimode waveguides coupled to multimode cavities
Summary
The transmission spectrum of a Waveguide-coupled optical Whispering Gallery Mode (WGM) microresonator is a result of interference between the incoming waveguide-mode and the outcoupled excited resonator-modes. Coherent interference of a specific WGM with another resonant mode with different bandwidth results in alteration of the transmission spectrum to a non-Lorentzian line-shape by virtue of Fano interference. Such interference is a result of interaction of fields with different pathways which can be experimentally realized in coupled [7] or single cavities [8, 9]. The model is applied to a silica microsphere exhibiting degenerate WGMs resembling a coherent multimode cavity, and it is demonstrated that depending on the tapered fiber loading, WGMs contribute to the distortion of the total transmission spectra of the resonator to a non-Lorentzian line-shape
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