Huaping Gong

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.

Polarization-dependent curvature sensor based on an in-fiber Mach-Zehnder interferometer with a difference arithmetic demodulation method.

A curvature sensor based on a polarization-dependent in-fiber Mach-Zehnder interferometer (MZI) is proposed. The MZI is fabricated by core-offset fusion splicing one section of polarization maintaining fiber (PMF) between two single mode fibers (SMFs). Two independent interference patterns corresponding to the two orthogonal polarization modes for the PMF are obtained. The couple efficiency between the core mode and the cladding mode decreased with the increasing of the bending on the MZI part. The curvature variation on the MZI part can be obtained by detecting the fringe visibility of the interference patterns. A difference arithmetic demodulation method is used to reduce the effects of the light source power fluctuations and temperature cross-sensitivity. Experimental results show that maximal sensitivity of -0.882 dB/m(-1) is obtained under a measurement range of 0.1 to 0.35 m(-1) for the curvature sensor. With the use of difference arithmetic demodulation method, the temperature-curvature cross-sensitivity and light source power fluctuations effects on the proposed sensor are decreased by 94% and 91%, respectively.

Strain Sensor Realized by Using Low-Birefringence Photonic-Crystal-Fiber-Based Sagnac Loop

An optical fiber strain sensor by using a low-birefringence photonic crystal fiber (PCF)-based Sagnac loop is demonstrated. A fiber Sagnac loop is formed by the low-birefringence PCF of about 40 cm, and a section of about 140-mm PCF is used as the strain sensing element. The output spectra of Sagnac loop under different strain levels are measured and analyzed. The sensitivity of the strain measurement of -0.457 pm/με is achieved within the range of 0-2520 με. The temperature effect is also analyzed.

Mach–Zehnder Photonic Crystal Interferometer in Cavity Ring-Down Loop for Curvature Measurement

Abstract-An all-fiber Mach-Zehnder interferometer curvature sensor fabricated by collapsing both ends of a photonic crystal fiber connected to a single-mode fiber is described. The interferometer is inscribed into the cavity ring-down loop and shows high sensitivity of 0.7311(μs)^-1 · m and high repeatability when a curvature of 0.4135 to 0.8122 m^-1 is applied. High correlation value of 0.997 is obtained with low standard error of 1.05%. This corresponds to a minimum detectable curvature of 4.849 × 10^-3 m^-1. The proposed sensor also displays low sensitivity to temperature with a value of 0.0008(μs ·° C)^-1.

Miniature refractometer based on modal interference in a hollow-core photonic crystal fiber with collapsed splicing

A miniature modal interferometer based on a hollow-core photonic crystal fiber (HC-PCF) for refractive index measurement is demonstrated. The modal interferometer is fabricated by splicing the two ends of a 1.2-mm-long HC-PCF to a single-mode fiber (SMF). The air holes of the HC-PCF are fully collapsed by the discharge arc during the splicing procedure, and the length of each collapsed region is about 300 μm. The transmission spectra with different refractive indices outside the HC-PCF are measured. Measurement resolutions of an 8.1×10(-4) refractive index unit (RIU) in the range of 1.35 to 1.39, and 4.3×10(-4) RIU in the range of 1.39 to 1.43 are achieved, respectively. The temperature effect of the proposed refractometer is also analyzed.

Curvature Sensor Based on Hollow-Core Photonic Crystal Fiber Sagnac Interferometer

A fiber-optic curvature sensor based on hollow-core photonic crystal fiber (HC-PCF) Sagnac interferometer is demonstrated. The two ends of the 36 cm HC-PCF are spliced to the two arms of a 3 dB single-mode fiber coupler to form a Sagnac interferometer. The output spectra of the Sagnac interferometer under different curvatures are measured and analyzed. The results show that the wavelength shift has a linear relationship with the curvature, and the sensitivity of 0.232 nm·m is achieved in the curvature range of 0-9.9 m-1. The temperature sensitivity is only 3.7 pm/°C, and the cross sensitivity to the curvature measurement is ~ 0.016 m-1/°C. This merit of low sensitivity to temperature is very useful for the curvature measurement.

Simultaneous Measurement of Curvature and Temperature Based on Mach–Zehnder Interferometer Comprising Core-Offset and Spherical-Shape Structures

A novel sensor for simultaneous measurement of curvature and temperature based on the Mach-Zehnder interferometer (MZI) is presented. The sensor consists of slight core-offset and spherical-shape structures. The core offset excites cladding modes, and the spherical shape couples the cladding modes back into the core and interferes with the core mode. Two dips of the interference fringe shift with the variation of curvature or temperature, and simultaneous measurement of curvature and temperature can be realized by means of a sensitivity coefficient matrix. Two MZIs with different lengths are fabricated. For sensor 1 with the length of 20 mm, the curvature sensitivity is as high as -22.227 nm/m -1 in the range of 4.66-5.50 m -1, and the temperature sensitivity is 0.0847 nm/°C in the range of 60 °C-100 °C. For sensor 2 with the length of 16 mm, the curvature sensitivity is -20.128 nm/m -1 in the range from 5.66 to 6.53 m -1, and the temperature sensitivity is 0.0737 nm/°C in the range from 40 °C to 100 °C.

Temperature Sensor Based on Modal Interference in Hollow-Core Photonic Bandgap Fiber With Collapse Splicing

A temperature sensor based on modal interference in a hollow-core photonic bandgap fiber (HC-PBGF) is presented. The modal interferometer is fabricated by splicing the two ends of a 12-mm HC-PBGF to the standard single-mode fibers. The airholes in the core and cladding of the HC-PBGF are completely collapsed during the fusion splicing, and the length of the collapsed area of about 300 μm is observed. The transmission spectra under different temperatures are measured. The sensitivity of 31.8 pm/°C is achieved in the range of 25 °C-60 °C. The influence of the length of HC-PBGF on the sensitivity is also investigated.

Miniature and robust optical fiber in-line Mach–Zehnder interferometer based on a hollow ellipsoid

An optical fiber in-line Mach-Zehnder interferometer based on a hollow ellipsoid fabricated by femtosecond laser micromachining and fusion-splicing technique is demonstrated. The surface of the hollow ellipsoid acts as an internal mirror that can be utilized for the construction of an interferometer. Such an interferometer device is miniature and robust and can perform external refractive index, curvature, and high-temperature sensing in a mutually independent way, and hence a simultaneous multiple parameter measurement capability can be readily achieved.

Simultaneous Refractive Index and Temperature Measurement Based on Mach–Zehnder Interferometer Concatenating Two Bi-Tapers and a Long-Period Grating

An all-fiber sensor for simultaneous refractive index (RI) and temperature measurement based on Mach-Zehnder interferometer (MZI) is proposed and demonstrated experimentally. The MZI consists of two bi-tapers and a long-period grating. Two dips in the interference spectrum exhibit different responses to the variations of RI and temperature, and simultaneous measurement of RI and temperature can be realized by means of sensitivity coefficient matrix. Experimental results show that the RI and temperature sensitivity for the proposed sensor are -108.16 nm/RI and 0.12 nm/°C, respectively.