本文主要研究目標為降低被動式Q-開關1030-nm全光纖雷射之腔內功耗以提升系統效率。雷射共振腔採用多模雷射二極體來作為泵浦光源，並使用雙披覆層光纖來達成高雷射輸出功率。系統中的增益介質與可飽和吸收體皆為摻鐿光纖，因此結合設置第二共振腔的增益開關機制與模態場面積不匹配技術來增加Q開關的切換速度。雙雷射共振腔的設計將可達成自平衡的Q與增益開關雙脈衝序列輸出。共振腔內基於光纖之間模態場不匹配所造成的損耗，將透過熱擴張纖核法與光纖拉錐法來降低。經過最佳化實驗參數之後，整個共振腔內初始損耗最大的熔接點，其穿透損耗可以從4.1 dB降至0.7 dB。最後將製作完成的模態場匹配器接上雷射架構中，Q-開關脈衝雷射之輸出斜率效率達到25.5%。在輸入泵浦功率8.3 W下，成功獲得脈衝重複率為126 kHz、脈衝寬度為310 ns、脈衝峰值功率為42.5 W之1030- nm Q-開關脈衝雷射輸出。

In this study, the main goal is to improve the slope efficiency of 1030-nm passively Q-switched all-fiber laser. The laser was saturable absorber Q-switched at 1030 nm and gain-switched at 1070 nm, using the method of mode-field-area mismatch. Although the use of mode-field-area mismatching technique has successfully activated the Q-switching mechanism, it also led to a higher intracavity loss. A low-loss mode-field adaption for dissimilar fibers had been demonstrated using a combination of thermally expanded core and physically fiber tapering methods. By optimizing the experimental parameters, the transmission loss at the splice joint between the mode-field mismatching fibers in the resonant cavity can be reduced from 4.1 dB to 0.7 dB. After the fabricated MFA was added into the laser system, the slope efficiency of the Q-switched laser reached 25.5%. At last, with a pump power of 8.3 W, sequentially Q-switched pulses with a repetition rate of 126 kHz, a width of 310 ns, and a peak power of 42.5 W were achieved.

參考文獻與資料
[1] Einstein, A. (1917). On the quantum theory of radiation. Phys. Z., 18, 121-128.
[2] Alan Chodos, Jennifer Ouellette, Ernie Tretkoff. (2005). Einstein Predicts Stimulated Emission. APS NEWS, Aug/Sep(Vol.14,number 8)
[3] Steen, W. M. (1998). Laser Materials Processing, 2nd Ed. P.5
[4] Schawlow, A. L., & Townes, C. H. (1958). Infrared and optical masers. Physical Review, 112(6), 1940.
[5] Maiman, T. H. (1960). Stimulated optical radiation in ruby masers. Nature, 187:493.
[6] Gloge, D. (1971). Weakly guiding fibers. Applied Optics, 10(10), 2252-2258.
[7] Koester, C. J., & Snitzer, E. (1964). Amplification in a fiber laser. Applied optics, 3(10), 1182-1186.
[8] Stone, J., & Burrus, C. (1973). Neodymium‐doped silica lasers in end‐pumped fiber geometry. Applied Physics Letters, 23(7), 388-389.
[9] Poole, S. B., Payne, D. N., Mears, R. J., Fermann, M. E., & Laming, R. I. (1986). Fabrication and characterization of low-loss optical fibers containing rare-earth ions. J. Lightwave Technol, 4(7), 870-876.
[10] Snitzer, E., Po, H., Hakimi, F., Tumminelli, R., & McCollum, B. C. (1988, January). Double clad, offset core Nd fiber laser. In Optical fiber sensors (p. PD5). Optical Society of America.
[11] Furusawa, K., Malinowski, A., Price, J. H., Monro, T. M., Sahu, J. K., Nilsson, J., & Richardson, D. J. (2001). Cladding pumped Ytterbium-doped fiber laser with holey inner and outer cladding. Optics Express, 9(13), 714-720.
[12] Norman, Stephen, et al. (2004). "Latest development of high-power fiber lasers in SPI." Fiber Lasers: Technology, Systems, and Applications. Vol. 5335. International Society for Optics and Photonics.
[13] Kao, K. C., & Hockham, G. A. (1966, July). Dielectric-fiber surface waveguides for optical frequencies. In Proceedings of the Institution of Electrical Engineers (Vol. 113, No. 7, pp. 1151-1158). IET Digital Library.
[14] Brown, D. C., & Hoffman, H. J. (2001). Thermal, stress, and thermo-optic effects in high average power double-clad silica fiber lasers. IEEE Journal of quantum electronics, 37(2), 207-217.
[15] Li, Zhihong, et al. (2001). "Theoretical and experimental study of pulse-amplitude-equalization in a rational harmonic mode-locked fiber ring laser." IEEE journal of quantum electronics 37.1 : 33-37.
[16] Hellwarth, R. W. (1961). Control of fluorescent pulsations. In Advances in Quantum Electronics (p. 334).
[17] McClung, F. J., & Hellwarth, R. W. (1962). Giant optical pulsations from ruby. Journal of Applied Physics, 33(3), 828-829.
[18] Wagner, W. G., & Lengyel, B. A. (1963). Evolution of the giant pulse in a laser. Journal of Applied Physics, 34(7), 2040-2046.
[19] Wang, C. C. (1963). Optical giant pulses from a Q-switched laser. Proceedings of the IEEE, 51(12), 1767-1767.
[20] El-Sherif, A. F., & King, T. A. (2003). High-energy, high-brightness Q-switched Tm3+-doped fiber laser using an electro-optic modulator. Optics communications, 218(4-6), 337-344.
[21] Delgado-Pinar, M., Zalvidea, D., Diez, A., Pérez-Millán, P., & Andrés, M. V. (2006). Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating. Optics express, 14(3), 1106-1112.
[22] Paschotta, R., Häring, R., Gini, E., Melchior, H., Keller, U., Offerhaus, H. L., & Richardson, D. J. (1999). Passively Q-switched 0.1-mJ fiber laser system at 1.53μ m. Optics letters, 24(6), 388-390.
[23] Ridderbusch, H., & Graf, T. (2007). Saturation of 1047- and 1064-nm absorption in Cr4+:YAG Crystals. IEEE journal of quantum electronics,
43(2), 168-173.
[24] Dvoyrin, V. V., Mashinsky, V. M., & Dianov, E. M. (2007). Yb-Bi pulsed fiber lasers. Optics letters, 32(5), 451-453.
[25] Fotiadi, A. A., Kurkov, A. S., & Razdobreev, I. M. (2005, June). All-fiber passively Q-switched Ytterbium laser. In Lasers and Electro-Optics Europe, 2005. CLEO/Europe. 2005 Conference on (p. 515). IEEE.
[26] Tsai, T. Y., Fang, Y. C., Huang, H. M., Tsao, H. X., & Lin, S. T. (2010). Saturable absorber Q-and gain-switched all-Yb3+ all-fiber laser at 976 and 1064 nm. Optics express, 18(23), 23523-23528.
[27] Tsai, T. Y., Fang, Y. C., Lee, Z. C., & Tsao, H. X. (2009). All-fiber passively Q-switched erbium laser using mismatch of mode field areas and a saturable-amplifier pump switch. Optics letters, 34(19), 2891-2893.
[28] Tsai, T. Y., & Fang, Y. C. (2009). A self-Q-switched all-fiber erbium laser at 1530 nm using an auxiliary 1570-nm erbium laser. Optics express, 17(24), 21628-21633.
[29] Mears, R. J., Reekie, L., Jauncey, I. M., & Payne, D. N. (1987). Low-noise erbium-doped fibre amplifier operating at 1.54 μm. Electronics Letters, 23(19), 1026-1028.
[30] Lu, K., & Dutta, N. K. (2002). Spectroscopic properties of Yb-doped silica glass. Journal of applied physics, 91(2), 576-581.
[31] Paschotta, R., Nilsson, J., Tropper, A. C., & Hanna, D. C. (1997). Ytterbium-doped fiber amplifiers. IEEE Journal of quantum electronics, 33(7), 1049-1056.
[32] A., Siegman, (1986). Passive Saturable Absorber Q-switching, in Chap. 26.3, Lasers (University Science Books), pp. 1024-1033.
[33] Tsai, T. Y., Fang, Y. C., & Hung, S. H. (2010). Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers. Optics express, 18(10), 10049-10054.
[34] Adel, P., Auerbach, M., Fallnich, C., Unger, S., Müller, H. R., & Kirchhof, J. (2003). Passive Q-switching by Tm 3+ co-doping of a Yb 3+-fiber laser. Optics Express, 11(21), 2730-2735.
[35] Kurkov, A. S., Sholokhov, E. M., & Medvedkov, O. I. (2009). All fiber Yb‐Ho pulsed laser. Laser Physics Letters, 6(2), 135-138.
[36] Keshavarz, A., & Kazempour, M. (2012). Numerical calculation of coupling efficiency for an elegant Hermite-Cosh-Gaussian beams. Int. J. Opt. Photonics, 6(2), 75-82.
[37] Wang, B. S., & Mies, E. W. (2007, November). Advanced topics on fusion splicing of specialty fibers and devices. Passive Components and Fiber-based Devices IV (Vol. 6781, p. 678130). International Society for Optics and Photonics.
[38] Zhou, X., Chen, Z., Zhou, H., & Hou, J. (2014). Mode-field adaptor between large-mode-area fiber and single-mode fiber based on fiber tapering and thermally expanded core technique. Applied optics, 53(22), 5053-5057.
[39] Zhou, X., Chen, Z., Chen, H., Li, J., & Hou, J. (2013). Mode field adaptation between single-mode fiber and large mode area fiber by thermally expanded core technique. Optics & Laser Technology, 47, 72-75.
[40] Faucher, M., & Lize, Y. K. (2007, May). Mode field adaptation for high power fiber lasers. In Conference on Lasers and Electro-Optics (p. CFI7). Optical Society of America.
[41] Kerttula, J., Filippov, V., Ustimchik, V., Chamorovskiy, Y., & Okhotnikov, O. G. (2012). Mode evolution in long tapered fibers with high tapering ratio. Optics Express, 20(23), 25461-25470.
[42] McLandrich, M. N. (1988). Core dopant profiles in weakly fused single-mode fibres. Electronics Letters, 24(1), 8-10.
[43] 周旋风. 光纤模场适配器的制作研究, 湖南：国防科学技术大学, 2012 : 12-19.
Zhou, X., Studies on manufacture of fiber mode field adaptor. Hunan, National University of Defense Technology, 2012 : 12-19.
[44] Chen, H., Qiu, Y., Li, G., Zhang, H., & Chen, Q. (2012). Improving fiber to waveguide coupling efficiency by use of a highly germanium-doped thermally expanded core fiber. Optics & Laser Technology, 44(3), 679-682.
[45] Wang, B., & Mies, E. (2009, February). Review of fabrication techniques for fused fiber components for fiber lasers. Fiber Lasers VI: Technology, Systems, and Applications (Vol. 7195, p. 71950A). International Society for Optics and Photonics.
[46] 李坤,薛竣文,苏秉华,东苗,张韦,吕海娟. 光纤熔接机加热扩芯制作模场适配器的研究. 光学技术, 2016, 42(5): 450-452
LI K., XUE J.W., SU B.H., DONG M., ZHANG W., LV H.J. Study on the fabrication of fiber mode field adaptors by thermally expanded core technique with an optical fiber fusion splicer. Optical Technique, 2016, 42(5): 450-452