A.P. Zhang

Low-cost high-performance fiber-optic pH sensor based on thin-core fiber modal interferometer

A new fiber-optic pH sensor based on a thin-core fiber modal interferometer with electrostatic self-assembled nanocoating is presented. After inserting a segment of thin-core fiber into a standard single-mode fiber, high-order cladding modes are excited and interfere with the core mode to form an in-fiber modal interferometer. The side surface of the sensor is then deposited with poly(allylamine hydrochloride) and poly(acrylic acid) nanocoating by electrostatic self-assembly technique. A fast and linear response is obtained in either acid or alkali solution (in the pH range 2.5 to 10) with resolution of 0.013 pH unit.

Sandwiched long-period gratings for simultaneous measurement of refractive index and temperature

A simultaneous measurement of external refractive-index (RI) and temperature is presented by using a sandwiched structure of long-period gratings (LPGs). An LPG pair with codirectional coupling between the guided mode and a low-order cladding mode acts as a temperature sensor with low RI sensitivity, whereas another in-between LPG which couples the guided mode with a higher order cladding mode performs as an RI sensing element. The experimental results show such an all-LPG structure is not only suitable for use as a compact temperature-compensated RI sensor, but also convenient for fabrication.

Fiber-Optic High-Temperature Sensor Based on Thin-Core Fiber Modal Interferometer

We present a new fiber-optic high-temperature sensor based on a thin-core fiber (TCF) modal interferometer. A thin-core fiber, whose core radius is about half of the radius of a standard single-mode fiber (SMF), is inserted between standard SMFs to form an extremely simple in-fiber modal interferometer. The wavelength of the transmission dip increases linearly with the temperature. Experimental demonstration shows that it can be used to sense temperature up to 850 °C with a sensitivity of about 18.3 pm/ °C.

High-Resolution Strain and Temperature Sensor Based on Distributed Bragg Reflector Fiber Laser

We present a high-resolution strain and temperature sensor by using a polarimetric distributed Bragg reflector fiber laser. The mean wavelength and polarization beat frequency of the laser output are utilized to determine the strain and temperature of the sensor. Experimental results show that the sensor has a capability of sensing strain and temperature simultaneously, with root mean square deviations of 9.3 mu epsiv and 0.05degC, respectively.

Optical Refractive-Index Sensor Based on Dual Fiber-Bragg Gratings Interposed With a Multimode-Fiber Taper

A new type of optical refractive-index (RI) sensor is proposed and experimentally demonstrated by using a structure of two single-mode fiber (SMF) Bragg gratings with a multimode fiber (MMF) taper in-between. The loss induced by a mismatch of waveguide structure between SMFs and MMFs is amplified by a tapering process, and is utilized for RI sensing through evanescent field. Experimental results show that the sensor possesses a tailorable sensitivity to the change of external RI and has a good linear response in the simultaneous measurement of external RI and temperature

Implementation and Characterization of Liquid-Level Sensor Based on a Long-Period Fiber Grating Mach–Zehnder Interferometer

An optical liquid-level sensor (LLS) based on a long-period fiber grating (LPG) interferometer is proposed and experimentally demonstrated. Two identical 3-dB LPGs are fabricated to form an in-fiber Mach-Zehnder interferometer, and the fiber portion between two LPGs is exposed to the liquid as the sensing element. The sensitivity and measurement range of the sensors employing different orders of cladding modes are investigated both theoretically and experimentally. The experimental results show good linearity and large measurement range. One of the significant advantages of such a sensing structure is that the measurement level is not limited to the length of the LPG itself. Also, the measurement range and sensitivity of the proposed LLS can be readily tailored for a particular applications.

Simultaneous Measurement of Refractive Index and Temperature by Using Dual Long-Period Gratings With an Etching Process

A new structure of long-period grating (LPG) sensor is introduced for simultaneous measurement of the refractive index (RI) and temperature. This type of grating device consists of two LPG sections, one of which is post etched by hydrofluoric acid (HF) solution and, therefore, has an improved RI sensitivity (the demonstrated improvement of sensitivity is 3.6 times). The experimental results show that this LPG sensor has a good performance in terms of linearity and sensitivity.

Fiber-Optic Acetylene Gas Sensor Based on Microstructured Optical Fiber Bragg Gratings

A fiber-optic acetylene gas sensor based on a microstructured optical fiber Bragg grating (MOFBG) is presented. The microstructured optical fiber (MOF) is specially designed to have a photosensitive core and holey cladding for grating fabrication and gas detection. The micro-holes of the MOF serve as gas cells, in which the acetylene molecules interact with light through the evanescent-waves of guided modes. The MOFBG with a specific period is utilized to not only make the sensor work in reflection mode, but also selectively determine the wavelength and the order of the acting fiber mode for gas sensing. The MOF is prepared by using the well-known stack-and-draw method, and the Bragg gratings are fabricated by using 193-nm laser pulses. Experiments for the use of the MOFBG for acetylene gas detection have been successfully demonstrated.

High-Frequency Ultrasonic Hydrophone Based on a Cladding-Etched DBR Fiber Laser

Distributed-Bragg-reflector (DBR) fiber-laser-based ultrasonic hydrophone has been found to possess increased detectable frequency range due to the improved sensitivity in the high-frequency region when the fiber cladding thickness was reduced. A wet etching technique is utilized to reduce the fiber diameter of the DBR laser. The peak response frequency moves from 21 to 40 MHz when the fiber diameter was reduced from 125 to 68 m.

A novel fast response fiber-optic pH sensor based on nanoporous self-assembled multilayer films

Three-component multilayer films were prepared by consecutively depositing a polycation blend of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC) and poly(diallyldimethylammonium) (PDDA) with poly(acrylic acid) (PAA). The self-assembly and disintegration behavior of the multilayer films were investigated in details by UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that nanoporous PDDA/PAA multilayer films can be obtained conveniently by partly disintegrating (PVPMC + PDDA)/PAA multilayer films in a 0.15 M NaCl solution. A novel fast response fiber-optic pH sensor was successfully prepared by constructing nanoporous self-assembly multilayer films on the thin-core fiber interferometer (TCFMI) surface. The response time of a fiber-optic pH sensor deposited with nanoporous PDDA/PAA multilayer film (20 s rise time (tr) and 15 s fall time (tf)) was only one-tenth of that with the nonporous PDDA/PAA multilayer film (240 s and 160 s for tr and tf).