本文選題：超短脈沖　切入點：鎖模激光器　出處：《北京交通大學》2017年碩士論文

【摘要】：超短激光脈沖由于具有功率高、脈沖窄、光譜寬等一系列的優(yōu)點,在高容量通信,微觀探測,受控熱核聚變,生物醫(yī)學等領(lǐng)域有重要的應用價值。當前,被動鎖模光纖激光器被認為是產(chǎn)生超短脈沖最好的光源�？娠柡臀阵w是被動鎖模激光器實現(xiàn)鎖模的關(guān)鍵器件,其作用是實現(xiàn)對光脈沖的可飽和吸收。常見的鎖模器件包括:半導體可飽和吸收鏡、碳納米管、石墨烯、克爾透鏡以及非線性偏轉(zhuǎn)鎖模。本文主要工作是對一種新的可飽和吸收體—多芯光纖可飽和吸收體的研究,分別對纖芯數(shù)、耦合系數(shù)、非線性系數(shù)進行討論,研究這些因素對于可飽和吸收特性的影響。具體內(nèi)容為:首先,分別對雙芯、三芯、五芯和七芯光纖進行仿真,通過計算光纖耦合系數(shù)和非線性系數(shù),然后數(shù)值求解非線性耦合模方程組后發(fā)現(xiàn),對于不同的光纖結(jié)構(gòu),多芯光纖總是表現(xiàn)為對低功率密度光脈沖吸收和高功率密度光脈沖透過的飽和吸收特性,且不同纖芯數(shù)對于這種特性的影響相差不大。因此,在后面的討論中,均是采用的雙芯光纖結(jié)構(gòu)。其次,光纖結(jié)構(gòu)和入射波長均會影響其耦合系數(shù),從而影響到可飽和吸收特性。研究發(fā)現(xiàn),雙芯光纖作為可飽和吸收體所需的飽和功率隨耦合系數(shù)的減小而降低。此外,當選取合適的長度時雙芯光纖有較好的濾波特性。對于文中所選雙芯光纖結(jié)構(gòu),當光纖長度為81倍半拍長度時,在波長范圍1530nm～1570nm可以實現(xiàn)帶通濾波特性。通過向光纖纖芯中注入高非線性液體能夠有效的提高光纖的非線性。研究表明,光纖非線性的提高能有效地降低其作為可飽和吸收體的飽和功率。針對雙芯光纖研究了由于芯徑和折射率差導致的不對稱性對可飽和吸收特性的影響,結(jié)果表明不對稱性不僅會降低耦合效率,而且增大了飽和功率。最后,將所研究的雙芯光纖可飽和吸收體置于全正常色散的超短脈沖鎖模光纖激光器中進行數(shù)值仿真,通過對激光器輸出脈沖在時域和頻域的分析,驗證了這類雙芯光纖可飽和吸收體可以被用于鎖模光纖激光器中。
[Abstract]:The ultrashort laser pulse has a series of advantages such as high power, narrow pulse and broad spectrum, so it has important application value in the fields of high capacity communication, micro detection, controlled thermonuclear fusion, biomedicine and so on. Passive mode-locked fiber laser is considered to be the best light source to produce ultrashort pulse, and saturable absorber is the key device to realize mode-locking in passive mode-locked laser. Common mode-locked devices include semiconductor saturable absorbers, carbon nanotubes, graphene, Kerr lens and nonlinear deflection mode-locking. The main work of this paper is to study a new saturable absorber, multi-core fiber saturable absorber, and discuss the core number, coupling coefficient and nonlinear coefficient, respectively. The effects of these factors on the saturable absorption characteristics are studied. Firstly, the fiber coupling coefficient and nonlinear coefficient are calculated by simulating the fiber with two cores, three cores, five cores and seven cores, respectively. After solving the nonlinear coupled mode equations numerically, it is found that for different fiber structures, the multi-core fiber always exhibits the characteristics of saturation absorption of low power density optical pulse and high power density optical pulse transmission. And the influence of different core number on this characteristic is not different. Therefore, in the later discussion, the two-core fiber structure is adopted. Secondly, the coupling coefficient is affected by the fiber structure and the incident wavelength. It is found that the saturation power required by the dual-core fiber as a saturable absorber decreases with the decrease of the coupling coefficient. The dual-core fiber has better filtering characteristics when the appropriate length is chosen. For the two-core fiber structure, when the length of the fiber is 81 times the length of half-beat, In the wavelength range, 1530nm~1570nm can realize the band-pass filtering characteristics. The nonlinear properties of the fiber can be effectively improved by injecting high nonlinear liquid into the fiber core. The enhancement of fiber nonlinearity can effectively reduce the saturation power of the fiber as a saturable absorber. The effect of asymmetry caused by the difference of core diameter and refractive index on the saturable absorption characteristics of dual-core fiber is studied. The results show that asymmetry not only reduces the coupling efficiency, but also increases the saturation power. Finally, the saturable absorber of the dual-core fiber is numerically simulated in a fully normal dispersion ultrashort pulse mode-locked fiber laser. By analyzing the laser output pulse in time and frequency domain, it is proved that this kind of saturable absorber can be used in mode-locked fiber laser.
【學位授予單位】：北京交通大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN248;TN253

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本文編號：1658607