D. N. Wang

Asymmetric long period fiber gratings fabricated by use of CO2 laser to carve periodic grooves on the optical fiber

An asymmetric long period fiber grating (LPFG) with a large attenuation of −47.39dB and a low insertion loss of 0.34dB is fabricated by use of focused CO2 laser beam to carve periodic grooves on one side of the optical fiber. Such periodic grooves and the stretch-induced periodic microbends can effectively enhance the refractive index modulation and increase the average strain sensitivity of the resonant wavelength of the LPFG to −102.89nm∕me. The resonant wavelength and the peak attenuation of the LPFG can be tuned by ∼12nm and ∼20dB, respectively, by the application of a stretching force.

High-Temperature Sensing Using Miniaturized Fiber In-Line Mach–Zehnder Interferometer

A miniaturized single fiber in-line Mach-Zehnder interferometer is proposed for high-temperature sensing. The interferometer has a microcavity in one of its arms, formed by removing part of the fiber core and cladding, while the other arm remains in the fiber core. Because the fiber core exhibits a temperature coefficient of refractive index which is different from that of air, the interferometer is sensitive to temperature variation. The microcavity structured interferometer also has excellent sustainability to high temperatures up to 1100°C . The system is compact, reliable and can detect the temperature at precise location.

Fiber In-Line Mach–Zehnder Interferometer Embedded in FBG for Simultaneous Refractive Index and Temperature Measurement

An ultracompact optical fiber sensor based on a Mach-Zehnder interferometer (MZI) embedded in fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous refractive index (RI) and temperature measurement. By use of the resonant wavelength of the FBG and the interference dip of the MZI, the RI and temperature of the surrounding medium can be unambiguously determined. The interesting properties of the sensor include good operation linearity, extremely high RI sensitivity up to ~ -9148 nm/RI unit in the RI range between 1.30 and 1.325, and precise sensing location, determined by the MZI cavity created.

Selectively Infiltrated Photonic Crystal Fiber With Ultrahigh Temperature Sensitivity

By selective filling of one of the air holes in the photonic crystal fiber, the fundamental core mode can be effectively coupled to the fundamental mode of the adjacent liquid rod waveguide at the resonant wavelength with extremely high temperature sensitivity. The spectral power of the rod mode can be filtered out by fusion splicing the selectively infiltrated photonic crystal fiber with conventional single-mode fiber, resulting in a sharp dip in the transmission spectrum. Such a device is demonstrated in our experiment by filling standard 1.46 refractive index liquid into one of the air holes of the commercially available photonic crystal fiber by use of femtosecond laser-assisted selective infiltration technique. The average temperature sensitivity achieved is ~54.3 nm/°C.

Sub-micron silica diaphragm-based fiber-tip Fabry–Perot interferometer for pressure measurement

We demonstrate a sub-micron silica diaphragm-based fiber-tip Fabry-Perot interferometer for pressure sensing applications. The thinnest silica diaphragm, with a thickness of ∼320u2009u2009nm, has been achieved by use of an improved electrical arc discharge technique. Such a sub-micron silica diaphragm breaks the sensitivity limitation imposed by traditional all-silica Fabry-Perot interferometric pressure sensors and, as a result, a high pressure sensitivity of ∼1036u2009u2009pm/MPa at 1550xa0nm and a low temperature cross-sensitivity of ∼960u2009u2009Pa/°C are achieved when a silica diaphragm of ∼500u2009u2009nm in thickness is used. Moreover, the all-silica spherical structure enhanced the mechanical strength of the micro-cavity sensor, making it suitable for high sensitivity pressure sensing in harsh environments.

Measurement of gas diffusion coefficient using photonic crystal fiber

We report the use of photonic crystal fiber (PCF) for the measurement of gas diffusion constant. PCF has uniform airhole columns along the fiber length that provide the basis for the study of gas diffusion based on the capillary method. The gas concentration within the airhole columns is monitored by measuring the attenuation of light through the PCF caused by the evanescent wave absorption of light by the gas sample.

Femtosecond Laser Inscribed Long-Period Gratings in All-Solid Photonic Bandgap Fibers

Long-period fiber gratings are inscribed in all-solid photonic bandgap fibers by use of a femtosecond laser with the line-scanning method. The coupling from the fundamental core mode to LP11 core mode can be readily obtained and the resonant wavelength of the grating is found to be highly sensitive to tensile strain while being nearly insensitive or only slightly sensitive to temperature, curvature, and external refractive index. Such gratings can be effectively used in stable spectral filters and optical fiber sensors with largely reduced cross-sensitivity.

Tunable dual-wavelength picosecond pulse generation by the use of two Fabry-Pe/spl acute/rot laser diodes in an external injection seeding scheme

An attractive alternative to generate tunable dual wavelength pulses by external injection seeding of a gain-switched Fabry-Pe/spl acute/rot laser diode (FP-LD) is demonstrated. The external injection-seeding branch consists of only a FP-LD, a 3-dB coupler and two fiber Bragg gratings (FBGs). The two wavelengths can be selected and their spacing can be tuned by adjusting two FBGs. The output sidemode-suppression- ratio is better than 17 dB over a 10 nm wavelength tuning range. The whole system is simple and of low cost.

CO 2 laser-grooved long period fiber grating temperature sensor system based on intensity modulation

A long period fiber grating (LPFG) temperature sensor system based on intensity modulation is developed. The LPFG employed is fabricated by the use of a focused CO2 laser beam to carve periodic grooves on the fiber. The temperature measurement resolution of up to 0.1 degrees C has been obtained within the temperature range between 20 degrees C and 100 degrees C. The system uses a simple intensity measurement method and exhibits the advantages of convenient intensity measurement, double temperature sensitivity, high resolution, simple configuration, and low cost.

Improving the wavelength detection accuracy of FBG sensors using an ADALINE network

We report the use of an adaptive linear network for enhancing the wavelength detection accuracy in fiber Bragg grating sensors. A wavelength detection accuracy of /spl sim/10 pm is experimentally achieved when the unwanted interferometric signals are presented.