利用自發性布里淵散射量測不同光纖的超音波傳輸特性

Abstract

在本篇論文當中，我們利用光纖的自發性布里淵散射效應，來量測超音波在不同光纖介質的傳輸行為，因為超音波和探測光波訊號同時在光纖中互相作用，所以可藉量測分佈式的布里淵頻譜的偏移量及能量準位而得到超音波的傳輸距離及衰減量。在我們的研究當中，BOTDR（Brillouin optical-time-domain reflectometer）可以量測分佈式的布里淵散射頻譜，所以藉由分析光纖的分佈式布里淵散射頻譜，可以得到不同的超音波的頻率及振幅在光纖中傳導之超音波傳輸特性。 對於超音波振盪器部分，其是利用射頻訊號來調變壓電薄膜材料（PZT）。而射頻產生器的頻率範圍約在1至2MHz，並透過圓錐形的預型體結構來將聲波能量耦合到不同光纖當中。 對於不同光纖的傳導超音波特性，我們分別對四種傳輸媒介作了研究，包含有單模光纖、色散位移單模光纖、大有效面積非零色散光纖、及真波光纖等光纖。並利用BOTDR量測技術，可以精確的量測及分析傳導超音波在四種光纖的傳輸特性。

In this thesis, we use the spontaneous Brillouin scattering effect in optical fibers to measure the propagation behavior of guided ultrasonic wave for different fibers. Due to the interaction between guided ultrasonic wave and the probe optical signal, the transmitted distance and attenuation of ultrasonic waves in optic-fibers can be observed by measuring the distributed Brillouin frequency-shift and power levels. Brillouin optical-time-domain reflectometer (BOTDR) is used to measure the distributed Brillouin-spectra in our study. By analyzing the distributed Brillouin-spectra along the optic-fibers, the transmission characteristics of guided ultrasonic waves in optic-fibers can be retrieved for different ultrasonic frequencies and amplitudes. In the part of the ultrasonic oscillator, it uses the RF signal to modulate piezo-electricity thin film material (PZT). The RF signal frequency ranging from 1 to 2MHz is utilized as the RF source. The silica horn with cone structure is used to guide ultrasonic energy into optic-fibers. To study the propagation behaviors of guided ultrasonic waves in different fibers, the optic-fibers including single mode fiber (SMF), dispersion shift fiber (DSF), large-effective area non-zero dispersion shift fiber (LEAF), and True-wave fiber (TWF) have been used as the transmission media. Using BOTDR measurement technology, the propagation characteristics of guided ultrasonic waves in these four fibers were measured and analyzed detailedly.