軸對稱矢量光束光纖激光器脈沖產(chǎn)生及效率增強
發(fā)布時間：2018-07-17 06:58
【摘要】：軸對稱矢量光束是指光束電場分布在光束橫截面上關(guān)于中心點對稱,是全矢量電磁波方程的軸對稱解,常見的兩種軸對稱矢量光束有徑向和角向偏振光束兩種分布。此類光束可以通過主動或被動方法得到,在保證軸對稱特性的同時對其進行操控的技術(shù)也被逐漸開發(fā)出來。此類光束奇異的偏振特性導(dǎo)致了特殊的大數(shù)值孔徑聚焦特性,在高精度成像、金屬加工以及粒子操控領(lǐng)域內(nèi)有很重要的應(yīng)用。少模光纖中的LP11模式由四種簡并模式(TM01,TE01,HE21even,HE21odd)組成,這四種模式均表現(xiàn)出軸對稱偏振特性,其中TM01和TE01分別對應(yīng)徑向和角向偏振光束。利用錯位耦合或者長周期布拉格光柵可以實現(xiàn)少模光纖內(nèi)LP11模式的激發(fā),但是很難在保證耦合效率的同時得到高純度的模式輸出,因此基于少模光纖光柵的模式選擇方案被提出用于高純度的軸對稱矢量光束產(chǎn)生。在本文中,我們介紹了軸對稱矢量光束的數(shù)學(xué)特性及各類產(chǎn)生方法,并基于光纖模式理論詳細闡述了少模光纖光柵的反射及模式選擇理論。本研究課題得到國家自然科學(xué)基金的支持,實現(xiàn)了軸對稱矢量光束的鎖模脈沖產(chǎn)生及諧振效率增強。本文主要的研究工作及成果如下:1.通過在光纖激光器內(nèi)加入電光調(diào)制器結(jié)合錯位耦合級聯(lián)少模光纖光柵的方式實現(xiàn)了軸對稱矢量光束的鎖模脈沖輸出。實驗得到的脈沖軸對稱矢量光束重頻12.059MHz,脈寬2ns,并且激光器工作在極窄線寬的單波長范圍內(nèi),30dB光譜寬度0.2nm,極大的保證了輸出軸對稱矢量光束的模式純度。2.基于碳納米管的可飽和吸收特性,實現(xiàn)了軸對稱矢量光束的超短脈沖被動鎖模輸出。選擇損傷閾值高、工作波長寬且偏振無關(guān)的碳納米管作為腔內(nèi)可飽和吸收體實現(xiàn)了自啟動的被動鎖模,通過調(diào)節(jié)腔內(nèi)PC實現(xiàn)了徑向偏振光束的超短脈沖輸出,得到的鎖模脈沖重頻10.61MHz,脈寬22.73ps。鎖模狀態(tài)下激光器輸出光譜被很好的限制在了少模光纖光柵的基模反射峰內(nèi),30dB輸出譜寬0.3nm。通過模式積分方法計算得到的徑向偏振光束的模式純度為98.03%。3.在全少模雙布拉格反射光纖激光器中利用雙包層摻鐿光纖中增益飽和以及橫�？v向拍頻引起的橫場空間燒孔長周期光柵,實現(xiàn)了諧振效率極大增強的軸對稱矢量光束輸出。當泵浦達到某閾值時,激光器輸出效率從13.36%突變?yōu)?2.48%,同時我們利用此類光致長周期光柵機制結(jié)合速率方程通過數(shù)值模擬驗證了其對于激光器諧振的影響。模擬結(jié)果得到了與實驗結(jié)果一致的結(jié)論,并得到了 LP01及LP11模式不同泵浦狀態(tài)下在激光器內(nèi)的運轉(zhuǎn)情況。4.為擺脫少模光纖光柵反射譜寬的限制,設(shè)計了兩款寬譜的模式響應(yīng)器件�；谀Ｊ今詈侠碚撎岢隽四Ｊ竭x擇耦合器的方案,并利用光纖熔融拉錐的方式初步驗證了理論的合理性,此外還設(shè)計了基于PLC波導(dǎo)耦合的方案并提出了一種基于模式傳輸相干疊加的耦合理論解釋。此外設(shè)計通過光纖拉錐鍍膜形成的包層金屬化光纖實現(xiàn)了寬譜的角向偏振選擇輸出,并通過數(shù)值模擬詳細研究了錐區(qū)粗細、金屬膜厚以及工作波長對不同模式損耗的影響。本論文的主要創(chuàng)新點有:1.利用電光調(diào)制器結(jié)合錯位耦合級聯(lián)少模光纖光柵的方式,在保證激光器的窄譜運轉(zhuǎn)同時實現(xiàn)了軸對稱矢量光束的主動鎖模輸出。2.選擇損傷閾值高、工作波長寬且偏振無關(guān)的碳納米管作為腔內(nèi)可飽和吸收體,實現(xiàn)了光纖激光器的自啟動窄譜鎖模,并利用少模光纖光柵實現(xiàn)了軸對稱矢量光束的超短脈沖輸出。3.在全少模雙布拉格反射光纖激光器中利用雙包層摻鐿光纖中增益飽和以及橫模縱向拍頻引起的橫場空間燒孔長周期光柵,實現(xiàn)了諧振效率極大增強的軸對稱矢量光束輸出。并結(jié)合速率方程和光致長周期通過數(shù)值模擬驗證了此模式畸變對于激光器諧振的影響,得到了與實驗結(jié)果一致的結(jié)論。
[Abstract]:Axisymmetric vector beam is an axisymmetric solution of the distribution of electric field on the center point on the cross section of the beam. It is an axisymmetric solution of the full vector electromagnetic wave equation. The common two axisymmetric vector beams have two kinds of distribution of radial and angular polarization beams. This kind of beam can be obtained by active or passive methods. The technology of its manipulation has also been developed. The singular polarization characteristics of such beams lead to special large numerical aperture focusing characteristics, which are very important in the field of high-precision imaging, metal processing and particle manipulation. The LP11 mode in the less mode fiber consists of four degenerate modes (TM01, TE01, HE21even, HE21odd), which are four. The model shows axisymmetric polarization, in which TM01 and TE01 correspond to radial and angular polarization respectively. Using dislocation coupling or long period Prague grating can realize the excitation of LP11 mode in the less mode fiber, but it is difficult to obtain the mode output of high purity while ensuring the coupling efficiency. Therefore, the optical fiber grating is based on the less mode fiber Bragg grating. The mode selection scheme is proposed for high-purity axisymmetric vector beam generation. In this paper, we introduce the mathematical characteristics and various generation methods of axisymmetric vector beams. Based on the optical fiber mode theory, the reflection and mode selection theory of the small mode fiber Bragg gratings are elaborated in detail. The research subject gets the National Natural Science Foundation. The main research work and results are as follows: 1. the pulse output of the axisymmetric vector beam is realized by adding an electro-optic modulator in a fiber laser with a staggered coupling cascaded less mode fiber Bragg grating. The experimental pulse is obtained. The impulse axisymmetric vector beam has a heavy frequency 12.059MHz and a pulse width of 2ns, and the laser is working in the single wavelength range of the very narrow line width and the 30dB spectrum width 0.2nm, which greatly guarantees the mode purity of the output axisymmetric vector beam,.2. is based on the saturated absorption characteristic of the carbon nanotube, and the ultra short pulse passive mode locking output of the axisymmetric vector beam is realized. The carbon nanotube with high damage threshold, wide working wavelength and independent polarization can realize self starting passive mode locking as an intracavity saturable absorber. The ultrashort pulse output of the radial polarization beam is realized by adjusting the PC of the cavity, and the mode locked pulse heavy frequency 10.61MHz is obtained, and the output spectrum of the laser is very good under the pulse width 22.73ps. mode. Limited to the base mode reflection peak of the less mode fiber Bragg grating, the mode purity of the radial polarization beam calculated by the 30dB output spectrum width 0.3nm. through the mode integration method is 98.03%.3. in the full mode double Prague reflective fiber laser using the gain saturation in the double cladding Ytterbium fiber and the transverse field space burning caused by the transverse mode longitudinal beat frequency. The output efficiency of the axisymmetric vector beam is greatly enhanced by the long period grating. When the pump reaches a threshold, the output efficiency of the laser is changed from 13.36% to 32.48%. At the same time, we use this kind of photoinduced long period grating mechanism and the rate equation to verify the effect of its effect on the laser resonance. According to the conclusion that is consistent with the experimental results, and the operation of the laser in the LP01 and LP11 modes is obtained in the laser, two wide spectrum pattern response devices are designed to get rid of the width of the reflection spectrum of the small mode fiber Bragg grating. Based on the mode coupling theory, the scheme of mode selection coupler is proposed and the fiber melting is used. The mode of the taper has preliminarily verified the rationality of the theory. In addition, a coupling theory based on the PLC waveguide coupling is designed and a coupling theory based on the coherent superposition of mode transmission is proposed. In addition, the wide spectrum angular polarization selection output is realized by the cladding metallized fiber formed by the optical fiber taper coating, and the numerical simulation is carried out by numerical simulation. The effects of cone thickness, metal film thickness and working wavelength on different modes loss are studied in detail. The main innovations of this paper are as follows: 1. using an electro-optical modulator to combine the dislocation coupled cascaded small mode fiber Bragg grating, the active mode locked output.2. selection loss of the axis to the vector beam is realized at the same time in the narrow spectrum operation of the laser. The carbon nanotube with high injury threshold and wide working wavelength and independent polarization is used as an intracavity saturable absorber, realizing the self starting narrow spectrum lock mode of the fiber laser, and using the small mode fiber Bragg grating to realize the ultra short pulse output.3. of the axisymmetric vector beam in the double cladding Ytterbium doped fiber laser with the full mode double Prague reflective fiber laser. The long period grating in the transverse field caused by the gain saturation and the transverse mode longitudinal beat frequency has realized the output of the axisymmetric vector beam with greatly enhanced resonant efficiency. The effect of the pattern distortion to the laser resonance is verified by the rate equation and the long period of light induced by the numerical simulation. The conclusion is consistent with the experimental results.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TN248
[Abstract]:Axisymmetric vector beam is an axisymmetric solution of the distribution of electric field on the center point on the cross section of the beam. It is an axisymmetric solution of the full vector electromagnetic wave equation. The common two axisymmetric vector beams have two kinds of distribution of radial and angular polarization beams. This kind of beam can be obtained by active or passive methods. The technology of its manipulation has also been developed. The singular polarization characteristics of such beams lead to special large numerical aperture focusing characteristics, which are very important in the field of high-precision imaging, metal processing and particle manipulation. The LP11 mode in the less mode fiber consists of four degenerate modes (TM01, TE01, HE21even, HE21odd), which are four. The model shows axisymmetric polarization, in which TM01 and TE01 correspond to radial and angular polarization respectively. Using dislocation coupling or long period Prague grating can realize the excitation of LP11 mode in the less mode fiber, but it is difficult to obtain the mode output of high purity while ensuring the coupling efficiency. Therefore, the optical fiber grating is based on the less mode fiber Bragg grating. The mode selection scheme is proposed for high-purity axisymmetric vector beam generation. In this paper, we introduce the mathematical characteristics and various generation methods of axisymmetric vector beams. Based on the optical fiber mode theory, the reflection and mode selection theory of the small mode fiber Bragg gratings are elaborated in detail. The research subject gets the National Natural Science Foundation. The main research work and results are as follows: 1. the pulse output of the axisymmetric vector beam is realized by adding an electro-optic modulator in a fiber laser with a staggered coupling cascaded less mode fiber Bragg grating. The experimental pulse is obtained. The impulse axisymmetric vector beam has a heavy frequency 12.059MHz and a pulse width of 2ns, and the laser is working in the single wavelength range of the very narrow line width and the 30dB spectrum width 0.2nm, which greatly guarantees the mode purity of the output axisymmetric vector beam,.2. is based on the saturated absorption characteristic of the carbon nanotube, and the ultra short pulse passive mode locking output of the axisymmetric vector beam is realized. The carbon nanotube with high damage threshold, wide working wavelength and independent polarization can realize self starting passive mode locking as an intracavity saturable absorber. The ultrashort pulse output of the radial polarization beam is realized by adjusting the PC of the cavity, and the mode locked pulse heavy frequency 10.61MHz is obtained, and the output spectrum of the laser is very good under the pulse width 22.73ps. mode. Limited to the base mode reflection peak of the less mode fiber Bragg grating, the mode purity of the radial polarization beam calculated by the 30dB output spectrum width 0.3nm. through the mode integration method is 98.03%.3. in the full mode double Prague reflective fiber laser using the gain saturation in the double cladding Ytterbium fiber and the transverse field space burning caused by the transverse mode longitudinal beat frequency. The output efficiency of the axisymmetric vector beam is greatly enhanced by the long period grating. When the pump reaches a threshold, the output efficiency of the laser is changed from 13.36% to 32.48%. At the same time, we use this kind of photoinduced long period grating mechanism and the rate equation to verify the effect of its effect on the laser resonance. According to the conclusion that is consistent with the experimental results, and the operation of the laser in the LP01 and LP11 modes is obtained in the laser, two wide spectrum pattern response devices are designed to get rid of the width of the reflection spectrum of the small mode fiber Bragg grating. Based on the mode coupling theory, the scheme of mode selection coupler is proposed and the fiber melting is used. The mode of the taper has preliminarily verified the rationality of the theory. In addition, a coupling theory based on the PLC waveguide coupling is designed and a coupling theory based on the coherent superposition of mode transmission is proposed. In addition, the wide spectrum angular polarization selection output is realized by the cladding metallized fiber formed by the optical fiber taper coating, and the numerical simulation is carried out by numerical simulation. The effects of cone thickness, metal film thickness and working wavelength on different modes loss are studied in detail. The main innovations of this paper are as follows: 1. using an electro-optical modulator to combine the dislocation coupled cascaded small mode fiber Bragg grating, the active mode locked output.2. selection loss of the axis to the vector beam is realized at the same time in the narrow spectrum operation of the laser. The carbon nanotube with high injury threshold and wide working wavelength and independent polarization is used as an intracavity saturable absorber, realizing the self starting narrow spectrum lock mode of the fiber laser, and using the small mode fiber Bragg grating to realize the ultra short pulse output.3. of the axisymmetric vector beam in the double cladding Ytterbium doped fiber laser with the full mode double Prague reflective fiber laser. The long period grating in the transverse field caused by the gain saturation and the transverse mode longitudinal beat frequency has realized the output of the axisymmetric vector beam with greatly enhanced resonant efficiency. The effect of the pattern distortion to the laser resonance is verified by the rate equation and the long period of light induced by the numerical simulation. The conclusion is consistent with the experimental results.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TN248
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