Kai Ni

An Optical Fiber Curvature Sensor Based on Two Peanut-Shape Structures Modal Interferometer

A novel curvature sensor based on optical fiber modal interferometer is demonstrated. It consists of two peanut-shape structures that are formed only by single mode fibers. The two peanut-shape structures can split and recombine the core and cladding modes, consequently, it produces modal interference. The experimental results show that the shift of the peak wavelength is almost linearly proportional to the change of curvature, and the sensitivities of the sensors with the lengths of 21, 26, and 30 mm are -18.46, -21.87, and 13.68 nm/m-1, respectively. The proposed curvature sensor is simple, high sensitive, and inexpensive.

Humidity Sensor With a PVA-Coated Photonic Crystal Fiber Interferometer

A photonic crystal fiber (PCF)-model interferometer (MI)-based relative humidity (RH) sensor is proposed and experimentally demonstrated. The PCF-MI is formed by fusion splicing a short length of PCF between two single-mode fibers with the air holes of the PCF in the splicing regions being fully collapsed. It was then coated with a layer of polyvinyl alcohol by using a dip-coating process. Experimental results show that a high humidity sensitivity of 40.9 pm/%RH is achieved within a measurement range of 20–95%RH. The sensor also shows good repeatability and low temperature independence.

Hot-Wire Anemometer Based on Silver-Coated Fiber Bragg Grating Assisted by No-Core Fiber

A novel hot-wire anemometer based on a silver-coated optical fiber Bragg grating (FBG) is proposed and experimentally demonstrated with the assistance of a short length of no-core fiber (NCF). The silver coating deposited on the surface of the FBG absorbs light of a pump laser, which is coupled into the fiber cladding by the NCF, to generate the heat, whereas air flow cools down the FBG by taking the heat away. A dynamic thermal equilibrium with a temperature codetermined by the pump laser power and airflow velocity can be reached. Bragg wavelength of the FBG changes with temperature thus is used to measure airflow velocity. Experimental results reveal that the highest resolution of ~ 0.0017 m/s is achieved and the measurement range covers 0-13.7 m/s.

Miniature pH sensor based on optical fiber Fabry-Perot interferometer

An optical fiber Fabry-Perot interferometer (FPI) coated with polyvinyl alcohol/poly-acrylic acid (PVA/PAA) hydrogel is proposed for pH value measurement. The FPI is formed by splicing a section of hollow-core photonic crystal fiber (HCPCF) between two standard single mode fibers. Its optical path different is modulated by the coated PVA/PAA hydrogel sensing film through swelling effect which depends on pH value of the tested solution. High sensitivity up to 11nm/pH is achieved within the pH value range between pH 4.1 and pH 6.9.

Fiber optic anemometer based on metal-coated fiber Bragg grating

A novel hot-wire anemometer based on a silver-coated optical fiber Bragg grating (FBG) is proposed and experimentally demonstrated with the assistance of a short length of no-core fiber (NCF). Experimental results reveal that highest resolution of ~0.0017 m/s is achieved and the measurement range covers 0-13.7 m/s.

A high sensitivity refractometer based on a partial liquid-filled hollow-core photonic bandgap fiber

A novel and high sensitivity refractometer is realized by using a short partial liquid-filled hollow-core photonic bandgap fiber (HC-PBGF). Since the liquid filled into partial air-holes of HC-PBGF forms an asymmetric waveguide structure, the confinement loss of the partial filled HC-PBGF is high sensitive to the refractive index of the filled liquid when the wavelength of the input light on Y polarization mode is fixed at the band gap edge. The proposed refractometer can realize a trace measurement by filling the tested liquid into HC-PBGF partially with 1 mm length and the refractive index sensitivity in theory is as high as 1.5×10−8 at approximately 1.333.