Abstract
Thermo-optic tuning of whispering gallery modes (WGMs) in a nematic liquid crystal-filled thin-walled capillary tube resonator is reported. WGMs were excited by the evanescent field from a tapered optical fiber. Tapered optical fiber fabrication and reduction of wall thickness of the capillary tube was carried out by a ceramic micro-heater brushing technique. A simple and robust packaging technique is demonstrated to ensure stable and repeatable operation of the device. Tunability of WGMs with temperature was demonstrated with a sensitivity of 267.5 ± 2.5 pm/°C. The demonstrated thermo-optic method for WGMs tuning is potentially useful for many tunable photonic devices and sensors.
Highlights
Optical whispering gallery modes (WGMs) are the electromagnetic resonances supported by open dielectric resonators with the dimensions in the order of few millimeters or smaller and a circular shape, e.g., spherical, cylindrical, disk, ring, toroidal etc
WGMs were excited by the evanescent field from a tapered optical fiber
Tunability of WGMs with temperature was demonstrated with a sensitivity of 267.5 ± 2.5 pm/°C
Summary
Optical whispering gallery modes (WGMs) are the electromagnetic resonances supported by open dielectric resonators with the dimensions in the order of few millimeters or smaller and a circular shape, e.g., spherical, cylindrical, disk, ring, toroidal etc. Silica has relatively low thermo-optic and thermal expansion coefficients, so if a silica resonator device is used for sensing of environmental parameters or utilizes thermo-optic tuning, a means to enhance its temperature sensitivity is required. Such an enhancement is often achieved by coating of the resonator surface with suitable functional materials. LCORRs have been used in various sensing applications including the detection of DNA, viruses, proteins and cancer biomarkers [32] In this manuscript, we propose to enhance the temperature sensitivity of a silica capillary tube resonator with a submicron wall thickness by filling it with a nematic liquid crystal (LC) for thermo-optic tuning applications. The simplicity, mechanical stability, and the direct interaction of the coupling region with the surroundings (the coupling region is not embedded in a polymer) are the advantages of the proposed packaging technique
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