Zengshou Peng

A high precision metrology method and system for thin film's parameters based on reflectance spectrum

How to determine the parameters of thin film precisely and rapidly becomes more and more important. In this paper, a new method based on reflectance spectrum combining complex-shape method to determine multi parameters of thin film simultaneously by dwindling the polyhedron is first presented. On the one hand, this new method fix out the problem of multiple solutions well. On the other hand, for there is no dependence on interferential spectrum and transparent area, the method can be applied to diverse sorts of reflectance spectrum with a fast speed, nice convergence, and high precision. In the meantime, the metrology system based on this method is built up and measured experiment for standard thin film sample is implemented also. Comparing the measured results to the standard values of the standard thin film sample, the results show that the error degree is about ± 3%. The experimental results prove this method has a nice application value.

Distributed Fiber Optic Stress Sensor System Based on P-OFDR

We first proposed and demonstrated a distributed fiber sensor with high spatial resolution for detecting and locating distributed stress. The sensor system consists of a section polarization-maintaining fiber (PMF) and an optical frequency domain reflectometry (OFDR). The PMF used as sensing element and the polarization mode coupling loss in PM fiber resulting from the external stress would produce. Through monitoring the backscattered light with the distributed polarization mode coupling loss along the PMF under test, the distributed fiber optic stress sensor based on polarizationsensitive OFDR (P-OFDR) was obtained. In our experiment, a tunable single frequency fiber ring laser with narrow linewidth was developed to act as scanning frequency light source, and then the P-OFDR system was structured. The fiber laser and the distributed fiber sensor system have been investigated experimentally in detail. The experimental results show that its spatial resolution is about 5cm, the sensitivity is less than -80dBm and the maximum dynamic range are about 70dB. With advantages of high spatial resolution, high sensitivity and large dynamic range due to extremely narrow linewidth and heterodyne detection, this distributed fiber optic stress sensor has a number of potential applications for smart structure, structural health monitoring, defense and security monitoring.

Stable Narrow Linewidth Ring Fiber Laser with a Passive Fiber Bragg Grating Fabry-Perot Etalon and a Fiber Saturable Absorber

Narrow linewidth fiber lasers have become more and more necessary in field of coherent communication, fiber optic sensor, and high resolutions optical spectrum analysis, especially long-range distributed fiber sensing system. In this paper, a simple and stable narrow linewidth Er3+ -doped ring fiber laser is first proposed and experimentally demonstrated. In the cavity, a passive fiber Bragg grating Fabry-Perot (FBG F-P) etalon acts as mode-selecting device to greatly reduce the longitudinal-mode density, while a section un-pumped Er3+ -doped fiber serves as a saturable absorber to ensure the single longitudinal-mode (SLM) operation. Meanwhile the stability of lasing frequency is further improved by controlling the temperature of the FBG F-P, and then through varying the temperature the lasing wavelength tuning is achieved also. Finally stable SLM laser at 1550nm with linewidth about 7.5 kHz, maximum output power 39 mW and the corresponding slope efficiency 30% is acquired.

Research of Narrow Line-width Er3+-doped Fiber Ring Laser with FBG F-P Etalon and FBG Sagnac Loop

A novel method of narrow line-width Er3+-doped fiber ring laser based on FBG F-P etalon and FBG Sagnac loop is presented in this paper. The all-fiber single frequency and narrow line-width Er3+-doped fiber ring laser has been designed in which two 976 nm laser diodes are used as the pump sources, the high concentration Er3+-doped fiber as the gain medium, the fiber Faraday rotator is adopted to eliminate the spatial hole burning effect, the FBG F-P etalon and FBG Sagnac loop filter can discriminate and select laser longitudinal modes efficiently. The experiment system using 3m long Er3+-doped fibers is presented, when the maximum pump power of two 976nm laser diodes is 146mW, the fiber laser exhibits 16mW threshold and stable single frequency 1550nm laser with the output powers of 45mW is acquired, and the slope efficiency is about 34.6%. The 3dB line-width is less than 9.3 kHz, measured by the delayed selfheterodyne method with 15km single-mode fiber, and no mode hopping is observed. The fiber laser has the advantages of simple structure, high efficiency and high reliability and it has great potential applications in the fields of optical fiber sensing system.

Research of surface plasma resonance optical fiber hydrogen sensor

An optical fiber hydrogen sensor based on the measuring principle of surface plasma resonance is introduced. The structure of the hydrogen-sensitive head which is coated with Pd-Ag alloy film on the surface of the etched optical fiber is investigated theoretically. When hydrogen gas is absorbed into the Pd thin layer of the sensing head, the Pd hydride is formed and then the refraction index of the etched optical fiber surface will be changed with different hydrogen gas concentration. The surface plasma wave is stimulated by the light wave in optical fiber and the surface plasma resonance occurs between the thin metal layer and the medium surface of hydrogen gas. The Pd-Ag alloy film thickness versus the sensitivity of hydrogen sensing head is analyzed and optimized via the numerical method. The sensing head which is based on surface plasma resonance is manufactured and used in the experiment system of hydrogen gas detecting, and the experiment results demonstrate that the detecting system has high sensitivity with the hydrogen concentration in the range of 0%-4%, the accuracy, resolution and response time are respectively 5%, 0.1% and 30s. This sensor structure can be applied to detecting the low concentration of hydrogen gas.