Limin Hu

Temperature-Insensitive Magnetic Field Sensor Based on Nanoparticle Magnetic Fluid and Photonic Crystal Fiber

A novel magnetic field sensor based on the magnetic fluid and Mach-Zehnder interferometer is proposed. The sensor takes advantage of the tunable refractive index property of the magnetic fluid and the modal interference property of the collapsed photonic crystal fiber. The achieved sensitivity and resolution of the sensor are 2.367 pm/Oe and 4.22 Oe, respectively. The magnetic field sensor is insensitive to the temperature variation with a temperature coefficient of 3.2 pm/°C.

Photonic Crystal Fiber Strain Sensor Based on Modified Mach–Zehnder Interferometer

In this paper, a novel strain sensor is proposed and demonstrated by employing a modified photonic crystal fiber (PCF)-based Mach-Zehnder interferometer, in which a collapsed region is introduced at the middle point of the PCF to improve the extinction ratio. Experimental results show that this proposed structure has a high sensitivity of 11.22 over a range of 1.28 and high-temperature stability.

Temperature Sensing Based on Ethanol-Filled Photonic Crystal Fiber Modal Interferometer

A modal interferometer made of a short ethanol-filled photonic crystal fiber (PCF) combined with a fully collapsed splicing with single-mode fibers (SMFs) is proposed for temperature measurement. Two fully collapsed splicing regions between the ethanol-filled PCF and SMFs excite and recombine two interfering modes in the ethanol-filled PCF. The interference spectrum of the ethanol-filled PCF is more sensitive to temperature than that of original PCF. By monitoring one peak wavelength shift of the ethanol-filled PCF modal interference spectrum, the temperature sensitivity reaches up to -0.35 nm/°C for a 3.25-cm long ethanol-filled PCF.

A tilt sensor with a compact dimension based on a long-period fiber grating

A tilt sensor with a compact dimension based on a long-period fiber grating (LPG) is proposed and experimentally demonstrated. The LPG is fixed in a rigid Plexi-glass tubular with a slant orientation and half of the LPG is immersed into the NaCl aqueous solutions, whereas the other half is exposed in air. The tilt angle is obtained by monitoring the dip wavelength shift of the LPG, which changes gradually when the immersed length of the LPG varies with the tilt angle. Experimental results show that the average sensitivity 0.077 nm/° is achieved within the measurement range from -30° to 30° at the static measurement.

A Hollow Core Fiber-Based Intermodal Interferometer for Measurement of Strain and Temperature

A hollow core fiber-based all-fiber intermodal interferometer is proposed for measurement of strain and temperature. The sensing structure is simply a short segment of hollow core silica fiber being sandwiched between two normal single mode fibers. The fabrication process only involves a conventional fusion splicer and a mechanical fiber cleaver. Experimental results show that sensitivities of 1.21 pm/με and 21.30 pm/°C are achieved for strain and temperature measurements, respectively.

Temperature-insensitive load sensor with a single fiber Bragg grating

A simple novel load sensor has been demonstrated by embedding a uniform fiber Bragg grating (FBG) along the axis of a tapered cylindrical polymer rod. Due to the load-induced nonuniform strain field applied along the length of the FBG, the bandwidth of its reflection spectrum varies linearly with the applied load. By measuring the reflected optical power of the chirped FBG illuminated by a flattened broadband light source, temperature-insensitive measurement of load is realized. It is intensity-modulated so that complex wavelength interrogation system is avoided in the sensor system. In the experiment, the achieved sensitivity is 0.99 nW/N over a range from 0 to 43.12 N. Since the FBG is well protected by embedding in the tapered elastic polymer rod, excellent reliability is expected.

A novel tilt sensor with a large measurement range based on long-period fiber grating

A novel one-dimensional tilt sensor with a large measurement range is demonstrated by gluing one long-period fiber grating (LPG) at a slanted orientation in a plexi-glass tubular with sucrose solution filled. Experimental results show that resolution of 0.13° has been achieved in the range of −30° to 30°.

Temperature-insensitive 2D tilt sensor with two chirped fiber Bragg gratings

A novel temperature-insensitive tilt sensor is proposed by embedding two chirped fiber Bragg gratings (CFBGs) into a cylindrical cantilever-based pendulum in two orthogonal planes. Due to the tilt-induced nonuniform strain field applied along the length of the CFBGs, their bandwidths of reflection spectra vary with the applied tilt angle. By measuring the reflected optical powers of the two CFBGs illuminated by a flattened broadband light source, temperature-insensitive measurement of both inclination angle and direction in two dimensions can be realized. Theoretical calculations and preliminary experimental results verified the feasibility of the proposed sensor design. The measurement is in real-time manner and the sensor is cost-efficient because it is an intensity-modulated sensor.

A Compact High Sensitivity Micro-Displacement Sensor Based on a Long-Period Fiber Grating with an Air-Cavity

a compact high sensitivity micro-displacement sensor based on a long-period fiber grating (LPG) with an air-cavity is proposed and experimentally demonstrated. The sensor head is obtained by composing an air-cavity with a LPG and a single mode fiber (SMF). The shift of the wavelength of the LPG is depended on the length of the air gap. The experimental results show that the sensitivity 0.2155nm/μm is achieved within the measurement range of 0 to 140μm at the initial air gap length of about 216μm.