Guangwei Fu

Refractive index insensitive temperature sensor based on specialty triple-clad fiber

A refractive index (RI) insensitive temperature sensor based on specialty triple-clad fiber (STCF) is proposed. Based on coupling mode theory, the STCF can be equivalent to a rod waveguide and two tube waveguides. Then the cladding mode resonance characteristic of STCF is analyzed by calculating different mode dispersion curves, which indicates that it works only on the mode resonance from core to the fluorine-doped silica cladding, and finally a resonance wavelength can be obtained. Two straightforward experiments are performed to prove its sensing properties. Experimental results show that it has sensitivities of 72.17 pm/°C at temperature range from 35°C~95°C with characteristics of insensitive to external RI in the range from 1.3450 to 1.4607. Thus, this proposed sensor can be used for solution temperature monitoring in real time.

Air-Holes Collapse Properties of Photonic Crystal Fiber in Heating Process by

For the fusion splicing of photonic crystal fiber (PCF), the air-hole collapse in heating process is important for minimizing the splicing loss. To analyze the air-hole collapse properties in heating process by CO2 laser, a theoretical model of PCF has been proposed. The variation relationships among the splicing loss, air-hole collapse, and heating time are analyzed, respectively. The results show that the theoretical simulation is basically in accordance with the experimental data. Thus, the air-hole collapse can be controlled by adjusting the splicing power and heating time. Errors are also given.

\hbox{CO}_{2}

Based on the intermittent cooling method, a fused tapered Photonic Crystal Fiber (PCF) interferometer is proposed. In the process of tapering, stop heating and wait for cooling at different taper length. Repeat heating and cooling, until taper goes to the expected length. Compared with the ordinary fused tapered method, the fringe contrast of the transmission spectra of this sensor is 15.06 dB. The transmission spectra in different concentrations of glycerol solution are obtained, and the temperature cross-sensitivity of the sensor is studied. The experimental results show that as the external refractive index increases, the transmission spectra of the sensor shift to longer wavelength. In the measuring glycerol solution, the refractive index sensitivity of the sensor can achieve 797.674 nm/RIU, and the temperature sensitivity is only 0.00125 nm/°C.

Laser

The connection technology between specialty solid coupled optical taper and large core multi-mode fiber was investigated in FSO receiving systems. We mainly analyzed the loss of central axis deviation, connection gap, two central axis tilt, and end face tilt, respectively. The results showed that the simulation experimental results can be properly used to improve the coupling efficiency between specialty optical taper and multi-mode fiber.

Research on Fused Tapered Photonic Crystal Fiber Sensor Based on the Method of Intermittent Cooling

A high sensitivity strain sensor based on cascaded cladding mode resonant double-clad fiber (DCF) and simple mode fiber is proposed. The basic principle of the sensor is analyzed, and the preparation of the sensor is performed. In different length of double-clad fiber, the strain sensing characteristics are analyzed detailedly. Experimental results show that, as the length of the connected double-clad fiber increases, the trough of the resonant spectrum will gradually increase. That is, the length of the access DCF is inversely proportional to the free spectral range. With the increase of tensile force, the resonance spectrum is blue shift, and the tension sensitivity can be up to -1.87nm/mε.

Connection Loss between Specialty Optical Taper and Large Core Multi-Mode Fiber in FSO Receiving Systems

An asymmetric spherical-shape structure strain sensor based on few mode fiber is proposed and demonstrated. It is fabricated by waist enlarge two splicing spots between a section of few mode fiber and two single-mode fibers. Fiber core mode interfere with cladding mode due to the excite and couple function of spherical-shape structure, respectively. Based on the double beam interference principle, the environmental strain will change the optical path difference and then change the output light intensity. Experimental results show that transmission spectrum will become close when FMF length increasing, and the optical power at certain wavelength is increasing with the strain increasing. When the length of the FMF is 5.9cm, the diameter of two asymmetric spherical-shapes are 171.36μm and 194.60μm, the strain sensitivity can be up to 0.00748dB/με. Therefore, this sensor has the advantages of simple structure, easy fabrication, high sensitivity and so on, it has potential applications in structure detecting field.

High sensitivity strain sensor based on cascaded cladding mode resonant double-clad fiber and simple mode fiber

We report the first fabrication of a polarization converter in a highly birefringent elliptical microfiber, which is made by periodically twisting a microfiber with an ellipticity of ∼0.7 and a diameter of ∼2.8 along its major axis. Strong input polarization suppression of ∼20 dB is achieved at a resonant wavelength of ∼1556.4 nm with a device length of ∼3.12 mm, one or even more two orders of magnitude shorter than that fabricated in the conventional Hi-Bi fiber. This device demonstrates temperature stability, which is of 15pm/O.

An asymmetric spherical-shape structure strain sensor based on few mode fiber

In this paper, a corroded photonic crystal fiber (PCF) sensor is presented on the basis of core-offset splicing and waist-enlarged fiber taper corroded by hydrofluoric acid (HF). The Mach-Zehnder interference theory is used to analyze the relationship between transmission spectrum and strain. The final results obtained from experiments show that the strain sensor’s sensitivity is about −6.57 pm/μe and the linearity is 0.99962 within the range of 0~1000 μe, while the sensor is corroded by HF for 35 minutes at room temperature. In the temperature range of 20°C~80°C, the sensor’s sensitivity to temperature is only 1.63 pm/°C, which is insensitive to temperature. Because of its advantage compared to traditional optical fiber sensors, this sensor can avert the cross-sensitive problem when temperature and strain are measured together and has some other advantages including easily fabricated, simple structure and accurate sensitivity. It can be used in many fields, such as industrial production, monitoring, and aerospace.

Temperature insensitive structural polarization converters in highly birefringent microfibers

We report the fabrication of long-period gratings (LPGs) in elliptical microfibers with femtosecond laser. Based on the numerical analysis of the modes and the mode coupling condition of elliptical microfibers, an LPG is fabricated with a very short pitch of by periodically modifying the fiber surface, which demonstrates very strong polarization-dependent resonances, a very low temperature sensitivity of a few picometers in air, and high temperature sensitivity of −1.62 nm/°C in refractive index oil.

Temperature Insensitive Strain Sensor with Asymmetrical Cascading Structure Based on Photonic Crystal Fiber in Chemical Corrosion

A curvature sensor based on tapered triple cladding quartz specialty fiber (TTCQSF) is proposed. It is formed by a section of triple cladding quartz specialty fiber which is tapered after splicing both ends of it with single-mode fibers (SMFs). Then a SMF-TTCQSF-SMF structure is fabricated. The experimental results show that the curvature sensitivity is -6.52nm/m-1 in the range of 0~1.293m-1, and is -17.48dB/m-1 in the range of 0.473~1.293m-1. The sensor is small in size, simple in structure and easy to fabricate. So it will have a good application prospect in the fields of curvature measurement.