【摘要】：當(dāng)前高功率光纖激光放大系統(tǒng)中,基于振蕩器的常規(guī)種子源存在時(shí)域不穩(wěn)定的現(xiàn)象,進(jìn)而導(dǎo)致激光的高峰值功率并降低非線性效應(yīng)閾值,限制系統(tǒng)功率的進(jìn)一步提升。隨機(jī)光纖激光器作為一種結(jié)構(gòu)簡(jiǎn)單、時(shí)域穩(wěn)定的新型光纖激光器,有望成為種子源時(shí)域不穩(wěn)的解決方案。本文以隨機(jī)光纖激光器為研究對(duì)象,分析其在功率提升和光場(chǎng)調(diào)控上的實(shí)現(xiàn)方式與應(yīng)用潛力。隨機(jī)光纖激光器利用長(zhǎng)距離被動(dòng)光纖中的拉曼增益和隨機(jī)分布式反饋,具有結(jié)構(gòu)簡(jiǎn)單、轉(zhuǎn)換效率高、光譜平滑、時(shí)域穩(wěn)定等顯著特點(diǎn)。本文基于激光速率方程,確定合適的邊界條件并考慮瑞利散射的影響,構(gòu)建隨機(jī)光纖激光器的理論模型。首先,基于構(gòu)建的理論模型,通過數(shù)值模擬計(jì)算隨機(jī)光纖激光器受光纖長(zhǎng)度、端面反饋等因素影響的激光閾值特性;同時(shí)考慮二階拉曼斯托克斯光的閾值,計(jì)算不同光纖長(zhǎng)度下隨機(jī)光纖激光器前、后向輸出的最高功率與光學(xué)轉(zhuǎn)換效率。其次,修改邊界條件建立半腔結(jié)構(gòu)的隨機(jī)光纖激光器理論模型,研究半腔結(jié)構(gòu)設(shè)計(jì)對(duì)激光閾值和沿光纖功率分布的影響。計(jì)算結(jié)果表明,半腔結(jié)構(gòu)的隨機(jī)光纖激光器可以有效降低出光閾值,并且將前、后向傳輸?shù)碾S機(jī)激光集合起來實(shí)現(xiàn)單端的高功率、高效率輸出。最后,著重對(duì)短腔的隨機(jī)光纖激光器進(jìn)行數(shù)值模擬,發(fā)現(xiàn)減小光纖長(zhǎng)度是繼續(xù)提升隨機(jī)激光器最高輸出功率的直接方案,并且短腔模型的閾值對(duì)寄生反饋尤其敏感。以上的理論分析與數(shù)值計(jì)算結(jié)果表明,構(gòu)成半腔結(jié)構(gòu)的短腔隨機(jī)光纖激光器是獲得高功率、高效率隨機(jī)光纖激光輸出的理想方案。對(duì)實(shí)現(xiàn)隨機(jī)光纖激光功率提升的方案進(jìn)行了實(shí)驗(yàn)研究。首先基于數(shù)值計(jì)算結(jié)果設(shè)計(jì)短腔隨機(jī)光纖激光器系統(tǒng),采用120 m被動(dòng)光纖與半腔結(jié)構(gòu),獲得近200 W1173 nm的隨機(jī)光纖激光輸出,光學(xué)轉(zhuǎn)換效率約89%,功率和效率均為已公開報(bào)道的國(guó)際最高水平。其次,構(gòu)建1070 nm波段的隨機(jī)光纖激光器實(shí)驗(yàn)系統(tǒng),通過對(duì)比時(shí)域和頻域特征分析其噪聲濾波特性,驗(yàn)證泵浦噪聲被有效濾除的隨機(jī)激光發(fā)射過程并獲得時(shí)域穩(wěn)定的激光輸出,首次實(shí)現(xiàn)隨機(jī)光纖激光工作波長(zhǎng)與摻鐿光纖放大器的增益譜相匹配。最后,利用構(gòu)建的1070 nm隨機(jī)光纖激光器作為時(shí)域穩(wěn)定的種子源,基于MOPA結(jié)構(gòu)的摻鐿光纖放大器進(jìn)行千瓦級(jí)的功率放大,功率放大的過程中未觀察到光譜展寬現(xiàn)象,最終實(shí)現(xiàn)1030 W半高全寬約1 nm的激光輸出,放大過程中斜率效率約為79.7%。該高功率放大過程中的光譜不展寬(spectral-broadening-free)現(xiàn)象為高功率窄線寬激光以及光譜合成等方面的研究提供了重要參考。對(duì)隨機(jī)光纖激光器光譜、模式的調(diào)控技術(shù)進(jìn)行了實(shí)驗(yàn)探索。基于可調(diào)諧濾波器和保偏光纖環(huán)形鏡,設(shè)計(jì)實(shí)現(xiàn)分別具有可調(diào)諧和多波長(zhǎng)光譜特性的隨機(jī)光纖激光器系統(tǒng),獲得的可調(diào)諧和多波長(zhǎng)光譜均具有數(shù)十納米的寬光譜范圍和較高的信噪比。基于少模光纖布拉格光柵和隨機(jī)分布式反饋,并利用錯(cuò)芯熔接方式激發(fā)高階模,獲得空間模式可調(diào)的隨機(jī)分布式反饋光纖激光輸出;另外通過全保偏的隨機(jī)光纖激光器結(jié)構(gòu)設(shè)計(jì)和光纖彎曲纏繞的偏振模選擇技術(shù),國(guó)際上首次實(shí)現(xiàn)線偏振的隨機(jī)光纖激光輸出。
[Abstract]:In the current high-power optical fiber laser amplification system, the time-domain instability phenomenon exists in the conventional seed source based on the oscillator, so that the peak value power of the laser is reduced and the non-linear effect threshold is reduced, and further improvement of the system power is limited. As a new type of fiber laser with simple structure and stable time-domain, the random-fiber laser is expected to be a solution to the time-domain instability of the seed source. In this paper, a random fiber laser is used as a research object to analyze its implementation and application potential in power and light field control. The random fiber laser uses the Raman gain and the random distributed feedback in the long-distance passive optical fiber, and has the characteristics of simple structure, high conversion efficiency, smooth spectrum, stable time domain and the like. In this paper, based on the laser rate equation, the appropriate boundary conditions are determined and the influence of Rayleigh scattering is taken into account, and the theoretical model of the random fiber laser is constructed. Firstly, based on the constructed theoretical model, the laser threshold characteristic affected by the factors such as the optical fiber length and the end surface feedback of the random optical fiber laser is simulated by numerical simulation; meanwhile, the threshold value of the second-order Raman Stokes light is taken into account, and the random optical fiber laser is calculated before the different optical fiber lengths are calculated, The highest power and the optical conversion efficiency of the backward output. Secondly, the effect of the half-cavity structure design on the laser threshold and the power distribution along the fiber is studied. The results show that the random-fiber laser of the half-cavity structure can effectively reduce the light-emitting threshold and set up the random laser at the front and back to realize the high-power and high-efficiency output of the single-end. In the end, the numerical simulation of the short-cavity random-fiber laser is focused on, and it is found that the reduction of the length of the fiber is a direct solution to the increase of the maximum output power of the random laser, and the threshold of the short-cavity model is particularly sensitive to the parasitic feedback. The above theoretical analysis and numerical calculation results show that the short-cavity random-fiber laser making up the half-cavity structure is an ideal solution for obtaining high-power and high-efficiency random-fiber laser output. The experimental research of the scheme for realizing the laser power of the random optical fiber is carried out. First, based on the numerical results, a short-cavity random-fiber laser system is designed, and a 120m passive optical fiber and a half-cavity structure are adopted to obtain a random optical fiber laser output of nearly 200 W1173 nm, the optical conversion efficiency is about 89%, and the power and the efficiency are the highest levels of the published report. secondly, constructing a random fiber laser experiment system of 1070 nm wave band, analyzing the noise filtering characteristic of the frequency domain and the frequency domain characteristic, verifying that the pump noise is effectively filtered out by a random laser emission process and obtaining a time-domain stable laser output, And the wavelength of the random optical fiber laser is matched with the gain spectrum of the doped fiber amplifier for the first time. and finally, using the constructed 1070 nm random fiber laser as a seed source with stable time domain, the doped fiber amplifier based on the MOPA structure is used for carrying out the power amplification of the kilowatt level, the spectrum broadening phenomenon is not observed in the process of power amplification, and the laser output of the 1030W semi-high full width of about 1 nm is finally realized, The slope efficiency in the amplification process is about 79.7%. The spectrum-free-free phenomenon in the high power amplification process provides an important reference for the research of high-power narrow line-width laser and spectral synthesis. The control technology of the spectrum and mode of the random optical fiber laser has been explored. Based on the tunable filter and the polarization-maintaining fiber ring-shaped mirror, a random optical fiber laser system with tunable and multi-wavelength spectral characteristics is designed, and the obtained tunable and multi-wavelength spectrum both have a wide spectral range of tens of nanometers and a higher signal-to-noise ratio. a random distributed feedback optical fiber laser output with adjustable spatial mode is obtained based on the small-mode fiber Bragg grating and the random distributed feedback, and the high-order mode is excited by the cross-core welding mode; In addition, the optical fiber laser output of the linear polarization is realized for the first time on the basis of the design of the whole polarization-maintaining random fiber laser and the polarization mode selection technique of the fiber bending and winding.
【學(xué)位授予單位】：國(guó)防科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TN248

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