Quandong Huang

Ambient refractive index-independent bending vector sensor based on seven-core photonic crystal fiber using lateral offset splicing

A novel, simple, and compact optical fiber directional bending vector sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The device consists of a piece of seven-core photonic crystal fiber (PCF) sandwiched between two single mode fibers (SMFs) with a lateral offset splicing joint that covering two cores of PCF. Bending sensitivity of the seven-core PCF based MZI is changed by an axial rotation angle, which shows its capacity for recognizing positive and negative directions. Within a curvature range of -7.05 m-1 to 7.05 m-1, the calculated bending sensitivities of two resonant central wavelengths with opposite fiber orientations are 1.232 nm/m-1 and 1.174 nm/m-1, respectively. This novel MZI is formed by invoking interference between the LP01-like supermode and other higher order supermodes in the core, which leads to insensitive to ambient refractive index (ARI). We have also investigated the transmission characteristics of the sensor with the temperature change.

Micro-bending vector sensor based on six-air-hole grapefruit microstructure fiber using lateral offset splicing

A one-dimensional micro-bending vector sensor based on two-mode interference has been introduced. This device was fabricated by lateral offset splicing a piece of six-air-hole grapefruit microstructure fiber (GMF) with single mode fiber (SMF). Variation of effective mode index occurred by micro-bending was investigated in simulation and experiment. This device exhibits micro-bending sensitivities of 0.441 nm/m(-1) and -0.754 nm/m(-1) at 0° and 180° bending orientations, respectively. Moreover, this sensor is immune to surrounding refractive index (SRI) and presents a low crosstalk of temperature.

High-Temperature Sensor Based on 45° Tilted Fiber End Fabricated by Femtosecond Laser

In this letter, we proposed and experimentally demonstrated a novel fiber sensing head based on 45° tilted fiber end for high-temperature measurement. The sensing head was fabricated by femtosecond laser using a line-scanning method. The light is mainly split into two beams at the 45° tilted fiber end, which forms a Michelson interference with a fringe visibility of ~20 dB. The experimental consequences show that the sensing head can withstand high temperature up to 800 °C and the temperature sensitivity is 19.7 pm/°C at 600 °C and 1605 nm. The merits of the sensing head are extremely compact, low cost, simple in configuration, easy for batch fabrication, and available to detect the temperature at precise location in microsize space.

In-Fiber Grating Fabricated by Femtosecond Laser Direct Writing for Strain Sensing

In this letter, we reported long period fiber gratings (LPFGs) fabricated by femtosecond laser pulses direct writing in grapefruit microstructured fiber. The mode field distribution and dispersion property of this fiber was analyzed by finite-element method. Two LPFGs were fabricated with different periods of 230 and 250 μm, the resonant dips appeared at the wavelengths of 1325.8 and 1449.4 nm, respectively. In addition, sensing characteristics of the LPFG with the period of 250 μm were investigated in theory and experiment. The experimental results show that the strain and temperature sensitivities are 1.88 pm/με and 0.267 pm/°C, respectively. It indicates that the temperature cross sensitivity is as low as 0.142 με/°C.

Pressure sensing of Fabry-Perot interferometer with a microchannel demodulated by a FBG

A novel and compact fiber-probe pressure sensor was demonstrated based on micro Fabry-Perot interferometer (FPI). The device was fabricated by splicing both ends of a short section simplified hollow-core photonic crystal fiber (SHCPCF) with single mode fibers (SMFs), and then a micro channel was drilled by femtosecond laser micromachining in the SHC-PCF to significantly enhance the pressure sensitivity. The pressure sensing characteristics based on micro-FPI have been investigated by measuring the signals through the demodulation of phase since the external signal imposing on the interferometer will induce the phase change of interference signal. Then a FBG was cascaded to demodulate the signal. A micro FPI demonstrates a maximum pressure sensitivity of 32 dB/MPa, while a low temperature cross-sensitivity of 0.27 KPa/°C. Hence it may have potential for pressure applications in harsh environment.

Long-Period Fiber Gratings Fabricated in All-Solid Photonic Bandgap Fibers by Femtosecond Laser

LPFGs in all-solid photonic bandgap fiber are inscribed by femtosecond laser pulses. The resonance peaks appear in the forbidden band of AS-PBGF, which LP01-like supermode can be guided. Mode coupling between the guided LP01-like supermodes can be obtained.

Twist characteristic of long period fiber grating in all-solid photonic crystal fiber

A long period fiber grating (LPFG) with resonance wavelength of 1335.76 nm was investigated, a twist sensitivity of 43.33 pm/(rad/m) against wavelength was obtained and its twist direction can be detected as well.