Hiroshi Oigawa

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.

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.

Electrode Optimization of 100 MHz High-Frequency Quartz Resonator Based on Equivalent Mass Method

Electrode optimization based on the equivalent mass method was carried out for a 100 MHz high-frequency fundamental thickness-shear AT-cut (quartz cut with a cutting angle of about 35.25° to the optic axis of the crystal) quartz resonator. Firstly, the electrode dimensions were optimized through three-dimensional finite-element modeling by the equivalent mass method. Secondly, on the basis of simulation results, 100 MHz fundamental frequency resonators were fabricated and quality factors were measured. The experimental and calculated results are highly consistent with the simulation results. The equivalent mass method combined with the finite-element method is confirmed to be applicable in the development of high-frequency quartz resonators.

Vibration Analysis of Original Shape Quartz Resonator for High Quality Factor Realization

AT-cut quartz resonators are widely used as timing devices in computers, mobile information, and communication tools, etc. Recently, quartz resonators have been applied to highly sensitive devices. To improve frequency stability, AT-cut quartz resonators must have an excellent temperature characteristic and high quality (Q) factor. Energy trapping and spurious mode coupling strongly affect the performance of resonators, and both parameters are determined by the shape of the resonator. As for achieving a higher Q, the most effective technique is to process the quartz cross-sectional shape into a plano-convex or bi-convex shape. However, it is difficult to manufacture a convex shape on the surface of a quartz wafer. For this reason, we propose an equivalent plano-convex shape, which was realized by arranging fine protrusions on the surface of quartz. In addition, the optimization of the original resonator shape has been discussed.

Size optimization for high frequency quartz resonator using finite element vibration analysis

In this study, size optimization for a high frequency AT-cut quartz resonator using finite element vibration analysis is presented. The objective resonator is a high frequency fundamental resonator with one-sided electrodes structure, which has high Q value and low resistance compared to the widely used overtone resonators. The one-sided electrodes structure was designed to obtain effective energy trapping and suppress inharmonic overtone (IO) mode. A convenient 2-D model using rectangular element was established to well reconcile calculation time with accuracy. A frequency mode chart describing the relationship between vibration coupling and size of quart plate was achieved. Vibration coupling and energy trapping effect were examined for different sizes of electrodes. COMSOL MULTIPHYSICS™ was adopted as a FEM analysis tool and the simulation results confirmed the effectiveness of this work.

Development of optimal electroplated platinum-black catalyst for quartz hydrogen sensors

A catalytic combustion type hydrogen sensor using quartz resonator with electroplated platinum-black catalysts was developed to provide high sensitivity and high reliability. In the previous work, because of catalysts pasted on the electrodes, Q-factor of the quartz resonator was decreased seriously. This paper is discussed about the fabrication method of platinum-black catalysts, which is able to realized excellent hydrogen sensitivity, and high Q-factor of resonator. As an experimental result, the highest Q-factor and the highest sensitivity were obtained by the platinum-black catalyst with thickness of around 100 nm.

Use of a new anisotropic etching simulator on quartz crystal

This paper describes features of a new anisotropic etching simulator and its applications on predicting etching shape of quartz crystal. The simulator is suitable to predict etching profiles of two-dimensional initial shape which has a profile formed by straight lines. In this simulator, a program flow with uneven time step was used to furthest reduced the probability of improper shape prediction. We present here two examples of its application on both Z-plate and AT-plate quartz crystal to show its good performance.

Application of a 2-D anisotropic etching simulator on perforated etching of quartz wafer

This paper describes features of a new anisotropic etching simulator and its applications on predicting perforated etching shape of quartz wafer. Specialized flow chart and relative process was designed to deal with etching after perforation. We present here two examples of its application on Z-plate and one example on AT-plate quartz crystal to show its good performance.