Xiaoling Tan

Compact and Ultrasensitive Temperature Sensor With a Fully Liquid-Filled Photonic Crystal Fiber Mach–Zehnder Interferometer

We propose a compact and ultrasensitive all-fiber temperature sensor based on an in-line fully liquid-filled photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI). It consists of a small piece of index-guiding PCF fully infiltrated by fluid and two standard single-mode fibers offset spliced with PCF. Two core modes LP01 and LP11 are conveniently used as optical arms to form the in-line MZI-type interferometer. Experimental and theoretical investigations of its response to temperature confirm that high temperature sensitivity up to -1.83 nm/°C could be realized with such a compact interferometeric PCF temperature sensor.

Polymer Microbubble-Based Fabry–Perot Fiber Interferometer and Sensing Applications

A polymer microbubble-based Fabry-Perot fiber interferometer (FPI) for pressure and temperature measurement is proposed and demonstrated. By splicing a small segment of photonic bandgap fiber to a single-mode fiber and immersing such a fiber tip into an optical adhesive, a micro air bubble could be buried into the formed polymer diaphragm. Size of air bubble and polymer diaphragm thickness can be controlled by adjusting arc discharge intensity at the fiber splice point. In order to achieve the wide dynamic range and high-resolution measurement, a demodulation algorithm based on absolute phase analysis is adopted and present high sensitivity for simultaneous pressure and temperature sensing. This simple and reproducible fabrication method of such a sensor gives an alternative way to construct FPI-based biomedical and microfluidic sensors.

V-groove all-fiber core-cladding intermodal interferometer for high-temperature sensing

Novel V-groove all-fiber core-cladding intermodal interferometers fabricated by CO2 laser irradiation on a standard single-mode fiber are described. The high-order cladding modes are excited due to the special V-groove structure. The interferometers are classified as Mach-Zehnder and Michelson type based on the way they are structured. Benefiting from the large difference of thermal coefficients of the core and high-order cladding modes, both types receive high temperature sensitivity by monitoring the wavelength shift of the interference spectrum, and their responses to temperature are similar. Compared with the Mach-Zehnder interferometer, the Michelson interferometer is more compact and more flexible in application.

UV-Curable Polymer Microhemisphere-Based Fiber-Optic Fabry-Perot Interferometer for Simultaneous Measurement of Refractive Index and Temperature

A fiber-optic Fabry-Perot interferometer based on UV-curable polymer microhemisphere is proposed and demonstrated. The polymer microhemisphere is formed by adhering and solidifying a liquid microdroplet of UV-curable adhesive to the end face of a cleaved single-mode fiber. The height of polymer microhemisphere could be flexibly controlled by adjusting the diameter of a single-mode fiber. The theoretical and experimental results demonstrate that the refractive index (RI) and the temperature of external environment can be simultaneously measured by the fringe contrast variation and the wavelength shift of reflection spectra separately, alleviating the cross sensitivity effectively. The obtained temperature and RI sensitivities are about 0.19 nm/°C and 260 dB/RIU in the RI range of 1.38-1.42.

Core Mode-Cladding Supermode Modal Interferometer and High-Temperature Sensing Application Based on All-Solid Photonic Bandgap Fiber

A core-mode-cladding-supermode modal interferometer with all-solid photonic bandgap fiber (AS-PBF) is constructed, and a reflective Michelson-type high-temperature sensor is fabricated. Such a fiber sensor is constituted by a small segment of AS-PBF and a leading single-mode fiber. The splice region of the two fibers is weakly tapered to excite the cladding supermode. Both the interference spectra and the near-field infrared CCD images verify that the LP01 cladding supermode is effectively excited and interferes with the LP01 core mode, which agrees well with theoretical results. Benefiting from a large effective thermooptic coefficient between the two modes, temperature sensitivity up to 0.111 nm/°C at 500 °C is obtained in experiment. The proposed sensor is compact and easy to fabricate, which makes it very attractive for high-temperature sensing applications.

In-line flat-top comb filter based on a cascaded all-solid photonic bandgap fiber intermodal interferometer.

In this paper, an in-line comb filter with flat-top spectral response is proposed and constructed based on a cascaded all-solid photonic bandgap fiber modal interferometer. It consists of two short pieces of all-solid photonic bandgap fiber and two standard single-mode fibers as lead fibers with core-offset splices between them. The theoretical and experimental results demonstrated that by employing a cut and resplice process on the central position of all-solid photonic bandgap fiber, the interference spectra are well tailored and flat-top spectral profiles could be realized by the controllable offset amount of the resplice. The channel position also could be tuned by applying longitudinal torsion with up to 4 nm tuning range. Such a flat-top fiber comb filter is easy-to-fabricate and with a designable passband width and flat-top profile.

Realization of All-in-Fiber Liquid-Core Microstructured Optical Fiber

We present an approach for manufacturing liquid-core microstructured optical fiber (MOF) with an all-in-fiber configuration. The MOF is first fusion-spliced with conventional fiber pigtails, with channels left open at the spliced interfaces to allow filling. After liquid filling, the channels are sealed by adhesives to prevent evaporation of the liquid. To verify the efficacy of this method, we filled a simplified hollow-core MOF (SHC-MOF) with a solution of aqueous quantum dots, and the temperature characteristics of the filled SHC-MOF were measured. The fluorescent peak wavelength and intensity changed reversibly over 48 h of repeated temperature cycling, indicating that the all-in-fiber configuration of the integrated liquid-core SHC-MOF has long-term stability and that the evaporation of the filling solution is minimal.

High-birefringence photonic crystal fiber Michelson interferometer with cascaded fiber Bragg grating for pressure and temperature discrimination

A simple and compact interferometer for temperature and pressure discrimination is proposed and demonstrated experimentally. It consists of a short section of high-birefringence photonic crystal fiber (Hi-Bi PCF) and a cascaded fiber Bragg grating (FBG). In the Hi-Bi PCF, two orthogonal polarized modes are employed as optical arms to construct, such as a Michelson interferometer. Combined with a cascaded FBG, pressure and temperature measurements are discriminated by a matrix method, and the pressure sensitivity of Hi-Bi PCF is determined to be around 3.65  nm/MPa. The proposed Michelson interferometer is easy-to-fabricate, flexible, and low-cost, which shows great potential in future applications of remote sensing.

Quantum Dots-Based Multiplexed Fiber-Optic Temperature Sensors

Quantum dots (QDs)-based multiplexed fiber-optic temperature sensors are proposed for multi-point sensing, which are composed of hollow-core microstructured optical fibers filled with aqueous QDs solutions of different fluorescent wavelengths. A parallel reflective configuration is adopted to avoid the crosstalk of fluorescent emissions, and to construct practical probes. Temperature experiments show that the fluorescent peak wavelength and the self-referenced intensity of two sensors both change with temperature linearly in the range from -10 °C to 120 °C with favorable reversibility. At last, the crosstalk of both the fluorescent peak wavelength and the self-referenced intensity of two sensors is tested for in the range of the temperature measurements.

Sensitivity-Enhanced U-Shaped Fiber SERS Probe With Photoreduced Silver Nanoparticles

This paper presents a novel U-shaped fiber surface-enhanced Raman scattering (SERS) spectra probe with high-performance remote sensing based on femtosecond laser ablation and deposition of photoreduced silver nanoparticles. As the width of the U-shaped structure is around 12 μm, the sensitivity is enhanced about four times more than that of a single-endface-based fiber SERS probe. The experiment results show that there is a nonlinear relationship between the SERS signal and the width of the U-shaped structure, whereas the SERS signal is sharply decreased with the increasing width of the U-shape. Our U-shaped fiber SERS probe shows a feasible method for high-performance, real-time, and remote measurement of the SERS signal in biochemical analysis.