光纖傳輸飛秒脈衝光源及其在工程與生醫光電上 的應用

Abstract

在本論文中，吾人展示了數種不同的光纖傳輸超短脈衝雷射光源以及其相關的光電系統，這些展示的成果使得光纖傳輸的脈衝光源在生醫光電以及工程中之種種應用更為實際。本論文的目標主要分為幾個部分：首先是建造在非線性光學顯微術以及在非線性內視鏡系統中所需要用的光纖傳輸脈衝光源；其次是建立光纖輸出極寬頻可調雷射；最後是基於此種光纖輸出極寬頻可調雷射提出並且展示一種在射頻/微波時間延遲上的新穎應用。 在非線性光學顯微術應用方面，吾人首先建立了一套微小化、高輸出功率並且自啟動的鉻貴橄欖石飛秒固態鎖模雷射，此鉻貴橄欖石雷射所輸出的飛秒脈衝係經由大模態面積光子晶體光纖來傳遞並且壓縮到時間上之轉換極限。藉由此光纖輸出之超短脈衝雷射光源，吾人隨後建立了一套微小以及可靠的雙光子螢光顯微鏡系統。其後，為了實際臨床上的應用，我們嘗試利用光纖集束建立了一套光束掃瞄非線性光學內視鏡。由於光纖集束在此鉻貴橄欖石飛秒雷射輸出波長的色散值很小，吾人不需經由使用任何額外的光學元件來補償超短脈衝光源在光纖中之傳遞變形。最後我們分析了系統的空間解析度並且以數張生物影像展示了此系統的可行性。 在另一方面，除了傳輸的功能，光纖還可以被用來當作寬頻的頻率轉換元件。利用高能量脈衝在非線性光纖中的光孤子自我頻率位移效應，吾人建立一可調範圍破世界紀錄之光纖輸出極寬頻可調雷射（波長輸出範圍從1.2微米到2.2微米），其可調範圍可達910奈米之多。此外，對於此種光纖輸出極寬頻可調雷射，吾人也提出並且建立一套全光纖化之連續可調射頻時間延遲系統。這個射頻/微波的超大時間延遲系統在實驗上最大延遲時間為730柰秒。與其它現有技術比較，這個延遲系統的架構比較簡單，並且具有容易操作與具有極大範圍可調延遲，深具在民用通訊以及衛星雷達上的應用潛力。

In this thesis, for different applications, various fiber-delivered femtosecond light sources and systems were built up to make the fiber-optics pulsed sources more promising and more practical in biophotonic and industrial applications. Subsequently, the purpose of this thesis is threefold. First, it is to develop different fiber-delivered femtoscond sources for nonlinear microscopy and nonlinear endoscopy. Secondly, it is to develop a widely wavelength tunable fiber-delivered femtosecond source, which is highly desirable for many different applications. Finally, the third objective is to present a new application of the demonstrated fiber-delivered wavelength tunable source on the photonic true time delays. In the regard of practical nonlinear light microscopy, a compact, self-starting high-power femtosecond Cr:Forsterite laser was set up. Delivered by a large-mode-area photonic crystal fiber, the generated chirped laser pulses can be compressed down to be with a nearly transform limited pulsewidth. Based on this fiber-delivered and fiber-enhanced Cr:Forsterite laser source, a compact and reliable two-photon fluorescence microscopy system can thus be realized. In regard to practical clinical applications, following the previous demonstration of nonlinear light microscopy, a beam-scanning nonlinear light endoscope based on a flexible fiber bundle was setup. Excited with a femtosecond Cr:Forsterite laser, the degradation in multi-photon multi-harmonic excitation efficiency due to the pulse broadening effect was significantly reduced without utilizing any external pulse-compression or spectral-compression devices. The system’s spatial resolution has been characterized and several image examples will be given. Moreover, except the delivery function, optical fibers can be utilized as broadband wavelength shifters. A widely tunable femtosecond light source, based on the soliton-self-frequency-shift effect of high power Cr:Forsterite laser pulses propagating inside a highly nonlinear photonic crystal fiber, was successfully set up. A record 910nm wavelength tuning range from 1.2