Abstract
We report on theoretical and experimental investigation of azimuthal and longitudinal modes in rolled-up microtubes at telecom wavelengths. These microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs bilayer. We apply planar waveguide method and a quasi-potential model to analyze the azimuthal and longitudinal modes in the microtubes near 1550 nm. Then we demonstrate these modes in transmission spectrum by evanescent light coupling. The experimental observations agree well with the calculated results. Surface-scattering-induced mode splitting is also observed in both transmission and reflection spectra at ~1600 nm. The mode splitting is in essence the non-degeneracy of clockwise and counter-clockwise whispering-gallery modes of the microtubes. This study is significant for understanding the physics of modes in microtubes and other microcavities with three-dimensional optical confinement, as well as for potential applications such as microtube-based photonic integrated devices and sensing purposes.
Highlights
The rapid development of chip-level information transmission using photonic integrated circuits (PICs) calls for novel components to meet the requirements of size, cost, performance, and ease of operation
We present theoretical and experimental characterization of the azimuthal and longitudinal modes in rolled-up InGaAs/GaAs microtubes at telecom wavelengths
Mode resonant wavelengths near telecom wavelengths have been calculated and quasiHermite-Gaussian longitudinal mode profiles have been simulated. These modes have been demonstrated in the microtube transmission spectrum by using an adiabatic fiber taper for evanescent light coupling
Summary
The rapid development of chip-level information transmission using photonic integrated circuits (PICs) calls for novel components to meet the requirements of size, cost, performance, and ease of operation. Similar to conventional circle-shaped optical cavities (e.g., rings, disks, toroids, and spheres), light in microtubes is confined by total internal reflection and resonates as whispering-gallery modes (WGMs) [21] These modes are confined in three dimensions (radial, azimuthal and longitudinal directions) and behave differently from modes in twodimensional (2-D) cavities (e.g., microrings). Planar waveguide method and a quasi-potential model are utilized to investigate the azimuthal and longitudinal modes We demonstrate these modes in the microtube transmission spectrum by evanescent light coupling using an adiabatic fiber taper. The splitting is in essence the non-degeneracy of clockwise and counter-clockwise WGMs induced by localized scattering centers on the microtube surfaces These results are useful for explaining the mode behaviors of microtube and other 3-D microcavities, as well as for potential applications such as microtube-based photonic integrated devices and sensing purposes [31,32]
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