Jinxing Liang

Fiber-Optic Temperature Sensor Based on Difference of Thermal Expansion Coefficient Between Fused Silica and Metallic Materials

In this paper, we report a novel fiber-optic Fabry-Perot interferometric (FFPI) temperature sensor based on the difference of thermal expansion coefficient between fused silica and metallic materials. The sensor head is made by a single-mode fiber (SMF). A gold film and a nickel film are sputtered and electroplated on the surface of the SMF. Then, a microcavity is micromachined by focused ion beam (FIB) milling. Because the thermal expansion coefficient of nickel is about 20 times of fused silica, the different thermal expansions force the sensor head to bend when the temperature is high or low. Its temperature sensitivity is over 14 pm/°C in a wide range from -79°C to +70°C. And the coefficient of determination R2 is excellent (over 0.995). Moreover, the metallic cylinder can reinforce the cavity spot of the fiber sensor, so that this kind of sensor can work in harsh environments. For the first time to the best of our knowledge, we report this type of FFPI temperature sensor based on difference of thermal expansion coefficient between fused silica and metallic materials.

NIR Spectrum Analysis of Natural Gas Based on Hollow-Core Photonic Bandgap Fiber

In this paper, we present a quantitative near-infrared spectroscopy measurement of the chemical compositions of gas mixtures, such as natural gas, based on a photonic bandgap fiber gas cell. The absorption spectra of the methane and ethane gases were investigated in the near-infrared region. The absorption lines of the ethane gas were observed in the 1600-1616-nm region, and were totally different from those of the methane gas. To our knowledge, this is the first study to measure the individual absorption lines of ethane in this range of wavelengths, and our finding has a great potential for sensing highly sensitive gases.

An experimental study on fabricating an inverted mesa-type quartz crystal resonator using a cheap wet etching process.

In this study, a miniaturized high fundamental frequency quartz crystal microbalance (QCM) is fabricated for sensor applications using a wet etching technique. The vibration area is reduced in the fabrication of the high frequency QCM with an inverted mesa structure. To reduce the complexity of the side wall profile that results from anisotropic quartz etching, a rectangular vibration area is used instead of the conventional circular structure. QCMs with high Q values exceeding 25,000 at 47 MHz, 27,000 at 60 MHz, 24,000 at 73 MHz and 25,000 at 84 MHz are fabricated on 4 × 4 mm2 chips with small vibration areas of 1.2 × 1.4 mm2. A PMMA-based flow cell is designed and manufactured to characterize the behavior of the fabricated QCM chip in a liquid. Q values as high as 1,006 at 47 MHz, 904 at 62 MHz, 867 at 71 MHz and 747 at 84 MHz are obtained when one side of the chip is exposed to pure water. These results show that fabricated QCM chips can be used for bio- and chemical sensor applications in liquids.

High-sensitivity fiber-optic Fabry-Perot interferometer temperature sensor

A novel structure of a fiber-optic Fabry–Perot interferometric (FFPI) temperature sensor is presented in this paper. The design of the sensor is analyzed and evaluated by the finite-difference time-domain (FDTD) method. Then, the proposed sensor is fabricated using a conventional single-mode fiber (SMF). A gold (Au) layer and a nickel (Ni) layer are sputtered and electroplated on the surface of the SMF, respectively. As a Fabry–Perot (FP) cavity, a micro-punch-hole is machined by focused ion beam (FIB) milling. Here, the structure of the FP cavity can be considered a pair of bimetallic strips. On the basis of the sharp difference in thermal expansion coefficient between the fused silica and the metallic materials, the temperature sensitivity of the proposed sensor was determined to be over 70 pm/°C in the 0 to +60 °C range. The standard deviation of temperature is less than 0.15 °C in 1 h.

Doubled Optical Path Length for Photonic Bandgap Fiber Gas Cell Using Micromirror

In this paper, we presented the double optical path length of a photonic bandgap fiber (PBGF) gas cell. The gas sensor sensitivity can be improved by a two fold lengthening of the optical length without changing the gas fluid. Furthermore, a high-reflection micromirror was included in the proposed double optical path length gas cell. A Cr/Au sputtering process was applied to fabricate the vertical micromirror using a single-mode fiber (SMF). A measurement system for low gas concentrations based on the micromirror has been implemented, and sensitivity was improved without increasing the response time.

Flip Chip Bonding of a Quartz MEMS-Based Vibrating Beam Accelerometer.

In this study, a novel method to assemble a micro-accelerometer by a flip chip bonding technique is proposed and demonstrated. Both the main two parts of the accelerometer, a double-ended tuning fork and a base-proof mass structure, are fabricated using a quartz wet etching process on Z cut quartz wafers with a thickness of 100 μm and 300 μm, respectively. The finite element method is used to simulate the vibration mode and optimize the sensing element structure. Taking advantage of self-alignment function of the flip chip bonding process, the two parts were precisely bonded at the desired joint position via AuSn solder. Experimental demonstrations were performed on a maximum scale of 4 × 8 mm2 chip, and high sensitivity up to 9.55 Hz/g with a DETF resonator and a Q value of 5000 in air was achieved.

Design and fabrication of quartz micro-electro-mechanical system-based double-ended tuning fork with variable sections

In this paper, we report a novel double-ended tuning fork (DETF) with variable sections. The DETF is fabricated using a quartz micro-electro-mechanical system (MEMS) technique and packaged using the flip chip technique. The central part of the vibration beam is thinned to enhance the force-frequency sensitivity but not decrease the vibration frequency. The mechanical quality factor (Q value) can also be maintained, which determines the mechanical noise performance. Three types of DETF are designed and fabricated with a fixed beam length of 4 mm. The vibration characteristics (vibration frequency, Q value, and equivalent circuit parameters) are evaluated using an impedance analyzer 4294A. The finite element method (FEM) is used to simulate the natural frequency and force-frequency sensitivity. For the natural frequencies, the experimental results agreed well with the simulation results. High Q values are achieved for all the DETFs, which are 9924, 7083, and 6335. By multiplying the force-frequency sensitivity (ΔF) by the measured Q values, the performance of the new DETF structure can be improved by 1.9 times.

U-Band Wavelength References Based on Photonic Bandgap Fiber Technology

In this paper, we surveyed potential wavelength references in U-band wavelength region. The hollow-core photonic bandgap fiber (PBGF) filled with methane (CH4) gas is used as a gas cell. The experimental results clearly indicate that the weak absorption lines of methane can be used as U-band wavelength division multiplexing (WDM) channel references due to the long interaction path length provided by PBGF. The absorption lines of CH4 are useful as wavelength references in the 1625-1700 nm region. In addition, we have measured the pressure broadening and the wavelength stability of absorption lines, and find that absorption lines are particularly insensitive to external perturbation. This technique is useful for wavelength calibration of components of communication system, or as monitor the wavelength of the channels. It may be implemented in next-generation WDM communication systems.