飛秒高功率光固子壓縮自啟式加波鎖模掺鉺光纖雷射

Abstract

本論文，是利用非線性光學中的光固子效應壓縮飛秒光纖雷射產生一個壓縮脈衝光。然而，利用光固子壓縮會造成脈衝品質的劣化，劣化的程度與光固子階數成正比；為了去改善光固子壓縮的缺點，我們提出了利用大模面積的高濃度掺鉺光纖來製作掺鉺光纖放大器，除了進一步縮短掺鉺光纖的長度之外，更使得脈衝在被放大過程中，所產生的非線性效應能夠達到最小化。而在脈衝被放大之前，我們利用單模光纖事先引入適當的負啾頻量，目的是要預先補償在放大的過程中所引入的正啾頻量，使脈衝在放大的過程中能夠連續地窄化。這樣的架構能夠降低光固子壓縮的階數與抑制底座的產生。另外，在放大之後，我們選擇一段最佳的單模光纖長度，擷取出在光固子效應下最窄的脈衝。利用這種設計可以獲得一個波形完整乾淨的壓縮脈衝，脈衝寬度為56飛秒，放大壓縮後的峰值功率為46千瓦。最後，為了更進一步縮短脈衝寬度，獲得更大的壓縮率，我們將單模光纖與大有效面積光纖結合成二階式的光固子壓縮，其脈衝寬度可由原始的300飛秒壓縮到30飛秒，而脈衝的峰值功率也得以有700倍以上的放大。

Femtosecond soliton effect compression is investigated to obtain pulses from passively mode-locked fiber lasers. Due to the inherent drawback of soliton-effect compression that the pulse quality Qc (defined as the energy ratio of the central pulse to total pulse) is decreasing monotonically from its ideal value of 1 as the soliton order N increases, we propose a new concept of using a simplified Erbium-doped fiber Amplifier (EDFA) based all-fiber compressor. A very short but highly-doped large-mode-field-area (LMFA) Er-doped fiber is employed to minimize the nonlinear process occurred during the high-power amplification of Erbium-doped fiber laser (EDFL) pulses. By using a pre-chirped single-mode fiber (SMF) segment for controlling the chirp of fiber laser pulse before launching into the Er-doped fiber and the last compression stage. Optimized pre-chirping, amplification and compression of the fiber laser pulse can be achieved under the fine adjustment on both the lengths of the SMF segments before and after the LMFA-EDFA. We primarily report that a 100% energy confinement within the central portion of the compressed soliton pulse is obtained, which exists a peak power of 46 kW and a pulsewidth of 56 fs. A additional compression stage is employed to further shorten the amplified EDFL pulsewidth and to achieve largest compression ratio, which combines the SMF and large-effective-area fiber (LEAF) to perform a dual-stage soliton compression link. As a result the pulsewidth shrinks from 300 fs to 30 fs associated with a maximum peak-power amplification ratio of >700.