Haimei Luo

Temperature-Insensitive Microdisplacement Sensor Based on Locally Bent Microfiber Taper Modal Interferometer

We report a temperature-insensitive microdisplacement sensor with a locally bent microfiber taper interferometer. The microfiber taper waist diameter can be optimized to minimize the spectral shift of the sensor owing to the environmental temperature change. With a ~ 1.92-μm-diameter microfiber taper, a bimodal fiber interferometer is proposed and experimentally fabricated. The transmission spectrum shows substantially small temperature dependence matching well with the theoretical estimation. The transmission spectrum is red-shifted in response to microdisplacement with a high sensitivity of 102 pm/μm but without requirement for temperature compensation.

Modal Interferometer Based on a C-Shaped Ultrathin Fiber Taper for High-Sensitivity Refractive Index Measurement

The ultrathin fiber taper fabricated by adiabatically stretching a heated single-mode optical fiber (SMF) is made in a C-shape bent to form a modal interferometer. The interference fringes due to the mode beating in the multimode taper waist are dependent on the bending radius. Under an optimized bending radius, a maximum 18 dB interference depth can be obtained. The influence of the fiber taper geometry on the interference fringes is discussed. The proposed modal interferometer has a high refractive index (RI) sensitivity of ~658 nm/RIU (refractive index unit) for RI= 1.333–1.353, which is expected to be useful for precision bio/chemical sensing applications.

Analysis of temperature-dependent mode transition in nanosized liquid crystal layer-coated long period gratings

The cladding mode reorganization in high refractive-index (HRI)-coated long period gratings (LPGs) is theoretically analyzed and experimentally observed with the aim of exploring the sensitivity of the resonance wavelength to the change of the refractive index in a nanoscale overlay. Experimental results show that the transition between cladding modes and overlay modes occurs when the refractive index of the liquid crystal (LC) overlay is changed from 1.477 to 1.515 by increasing its temperature from 20 degrees C to 65 degrees C. The spectral tuning ability of LPGs coated with a HRI LC layer by electro-optic modulation on a LC layer is also demonstrated, and the maximum tuning range can reach approximately 10 nm by choosing a highly sensitive operating point in the transition region.

Design and analysis of a highly efficient coupler between a micro/nano optical fiber and an SOI waveguide.

A compact coupling structure is proposed for highly efficient coupling between a micro/nano fiber and a silicon-on-insulator waveguide. The proposed structure is characterized by high coupling efficiency, wavelength insensitivity, large misalignment tolerance, and easy fabrication. Theoretical analysis and numerical simulation results show that coupling efficiency of >90% can be achieved with a taper length of ∼4.5  μm.

On polarization characteristic in fiber Mach-Zehnder interferometer with short different length of two arms

Polarization dependent of fiber Mach-Zehnder interferometer is one of the factors which restrict the precision and stability of interferometer based on Mach-Zehnder structure. Making use of Jones Matrix, a propagation equation of polarization dependent fiber Mach-Zehnder interferometer was given, and then the output spectrum was shown by the propagation equation. Then an experimentally result is demonstrated to verify analysis result. It shows the calculating result is consistent with experiment. This result provides a theory guidance to analyze the influence of polarization characteristic in interferometers based on Mach-Zehnder structure. The method also can be adapted in other fiber interferometers such as fiber Michelson interferometer and so on.