Autler-Townes splitting and induced transparency windows in a multimode microfiber knot.

In this Letter, Autler-Townes splitting and induced transparency windows are observed in a multimode microfiber knot. The microfiber knot is fabricated using tapered single-mode fiber, with the knot position located at the transition area of the tapered fiber. The spectrum, in analogy to Autler-Townes splitting, derives from the mode splitting of two high-order excited modes, which is theoretically explained by the multimode transfer matrix method. Moreover, without adding resonators, two induced transparency windows are realized with the tunable coupling coefficients and phase difference of excited knot modes. The tunable, easily fabricated, compact, and robust microfiber knot has potential applications in optical sensing, filters, slow light, and optical switching.

High-temperature sensor based on suspended-core microstructured optical fiber.

We propose a high-temperature sensor based on a suspended-core microstructured optical fiber (SCMF). The sensor is constructed by fusion splicing a piece of SCMF between two sections of multimode fibers (MMFs) which act as light beam couplers. The multimode interference is formed by the air cladding modes and the silica core modes in the SCMF. Fast Fourier transform is adapted to filtering the raw transmission spectra of the MMF-SCMF-MMF structure. The wavelength shift of the dominant spatial frequency is monitored as the temperature varies from 50 °C to 800 °C. The sensitivities of 31.6 pm/°C and 51.6 pm/°C in the temperature range of 50 °C-450 °C and 450 °C-800 °C are respectively achieved. Taking advantage of the compact size, good stability and repeatability, easy fabrication, and low cost, this proposed high-temperature sensor has an applicable value.

Magnetic-field tuning whispering gallery mode based on hollow microbubble resonator with Terfenol-D-fixed.

We propose a method of magnetic-field tuning whispering gallery modes (WGMs) based on a hollow microbubble resonator (HMBR) with Terfenol-D-fixed. WGMs are excited by the evanescent field from a tapered fiber coupling with an HMBR. Both ends of the HMBR are fixed with Terfenol-D and vary with different lengths of the Terfenol-D. The length of the Terfenol-D varies with the external magnetic field for the high magnetostriction coefficient of Terfenol-D. The magnetic field sensitivity of 0.081 pm/mT in the magnetic field range of 0.14 mT-21.8 mT is achieved. The $Q$Q-factor of the HMBR can be regulated up to ${2.07} \times {{10}^4}$2.07×104 with physical stretching HMBR. This work provides a novel tuning whispering gallery mode scheme and a broad application prospect in the fields of optical measurement and precise optical clocks in the future.