Acoustooptic-Mode-Coupling-Based Whispering Gallery Mode Excitation in Silica-Capillary Microresonator

An acoustooptic-mode-coupling-based scheme is proposed for excitation of whispering gallery modes (WGMs) in a silica-capillary microresonator. By exploiting acoustooptic mode coupling in a cladding-etched optical fiber, the evanescent field is strengthened by the cladding modes coupled from the core mode through axial flexural wave modulation, leading to the significant enhancement of the mode coupling between evanescent field and WGMs in a silica-capillary microresonator. WGM resonance peaks have been experimentally acquired by employing a cladding-reduced optical fiber with a diameter of 20.68 μm, which is more robust than the coupling fibers of a few microns in diameter used in conventional WGM excitation schemes. Our proposed WGM coupling approach has desirable merits such as compactness, ease of fabrication, improved WGM coupling efficiency, and robustness, which is anticipated to find potential applications in optical filtering, microresonator laser, fiber sensor, as well as signal processing. Additionally, by controlling the electric driving signals to apply acoustic modulation, it would be convenient to achieve flexible tuning of WGMs based on acoustooptic coupling approach.