激光二极管阵列外腔锁相技术研究
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摘要
大功率激光二极管阵列(DLA)由于具有体积小、光电转换效率高的特点而越来越受到人们的重视，并在激光加工、激光手术等领域得到了广泛的应用。
锁相DLA在80年代曾经历了一个快速发展时期。当时，人们通过倏逝波、漏波、Y结耦合、衍射耦合等手段实现了DLA的锁相。由于这些手段只是对于传统的小尺寸发光区的DLA可行，所以没有获得理想的输出功率。
根据耦合模理论以及TALBOT腔理论，我们对DLA外腔锁相进行了深入的理论分析。外腔锁相技术可以有效改进DLA的发光特性，使它有良好的发散度、高的相干性及定标放大性。这种方法可以实现宽发光区的标准DLA的相位锁定。研究表明，长度为TALBOT距离Z_T的整数倍的外腔结构不能有效区分最高和最低阶模式，而改用1／4 TALBOT腔进行DLA外腔锁相，可以抑制最低阶模式，优选最高阶模式振荡，但是远场会出现两个光斑。于是，提出采用选频相位共轭反馈系统实现DLA的外腔锁相，该方法可以克服1／4TALBOT腔远场两个光斑的缺点，有利于能量的集中利用。
在外腔(EC)中二极管激光阵列(DLA)的一个激光单元既可以接收来自其相邻单元发出的辐射(C_1)，也可以接收自身发出的经激光器前端面反射回来的辐射(S)和在外腔中反射后回到激光器中的辐射(C_0)。实现外腔锁相运转意味着|C_0/S|、|C_1/S|均应大于1。在此基础上，我们分析了实现DLA外腔相位锁定时所允许的端面反射系数、以及该系数与外腔腔长和外腔反射
四川，悦理卜祠眨d卜理卜七立今仑文
系数等的关系。
推导了外腔中二极管激光阵列各发光单元之间的藕合系数，结果表明:
增加外腔长度有利于减小各阶祸合系数的差别和实现“并联祸合”，但是外腔
的作用效果下降;降低阵列前端面的反射系数，有利于实现外腔锁相;外腔
锁相中并联祸合的单元数越多，激光二极管阵列前端面的反射系数的允许值
越小。
通过分析输出腔镜、快轴准直透镜、芯片焊接、冷却器设计等关键的环
节，对外腔锁相需要考虑的问题进行了深入的探讨。采用三维有限元方法分
析了DLA背冷式封装结构的散热效率，对冷却器结构参数进行了优化设计。
High power diode laser arrays (LDA) have considerable attention in the industrialzed economies for the small volume and high efficiency, and have been widely used in materials processing, laser medicine etc.
Phase locking DLA had been developed remarkedly in 1980s. At that time, people had gotten the phase locking DLA through evanescent wave, leaky wave, Y-jont coupling and diffraction coupling. Usually the above mentioned measures are applicable to the traditional DLA with small emitters, and people had not gotten the ideal output power.
According to the coupling mode theory and TALBOT cavity theory, we have made an in-depth theoretical analyses on the DLA phase locked in an external cavity (EC) . The phase locking may efficiently improve the radiating properties of the DLA and have good diverging degree, high coherence and scalability. The methods may result in the phase locking on the standard DLA with wide emitters. The integral TALBOT cavity length may not be able to provide sufficient discrimination between the highest and fundamental mode. We may suppress the fundamental mode and choose the highest mode by selecting an external cavity length of a quarter TALBOT distance. The drawback of the 1/4 Talbot cavity is that the LDA generates a double peak far field pattern. The frequency-selective phase-conjugate feedback (FSPCF) system may be used to phase lock the DLA in an EC to overcome the drawback of the double peak far
field in the 1/4 TALBOT cavity and to make full use of the pump sources.
An emitter of a DLA positioned in an EC can receive the light emitted from its neighboring elements and that of itself after being reflected at the DLA facet. Expressions describing the received radiations from neighboring elements (C1) and that from itself(S)as soon as from the external cavity(C0)have been deduced. Considering the fact that | C0/S| should be larger than unify if the EC is of effective and | C1/S | should be larger than unify if the phase locking may be established in the EC, requirements on the reflection at the DLA facet have been specified in terms of the cavity length and reflection coefficient of the external mirror.
Expressions describing couplings between different emitters of a diode laser array (DLA) , positioned in an external cavity (EC) , have been deduced. The results show that: the increase of the length of the EC reduce the differences between these coupling coefficients, which is favorable to achieving the so called "parallel coupling" at the expense of the effectiveness of the EC; decreasing the reflection coefficient at the front facet of the DLA is favorable to achieving phase locking in EC; the more the parallelly coupled emitters are, the lower the allowed reflection coefficient at the front facet of the DLA is.
Through considering the output cavity mirror, fast axis collimation lens, chips welding, cooler designing and so on, we have widely understood the necessary consideration for the phase locking DLA in an EC.The thermal resistance of the DLA with back cooling packaged structure was calculated by three-dimension finite element method. The calculated results indicated that the cooling water channel depth and fin width have optimum values.
锁相DLA在80年代曾经历了一个快速发展时期。当时，人们通过倏逝波、漏波、Y结耦合、衍射耦合等手段实现了DLA的锁相。由于这些手段只是对于传统的小尺寸发光区的DLA可行，所以没有获得理想的输出功率。
根据耦合模理论以及TALBOT腔理论，我们对DLA外腔锁相进行了深入的理论分析。外腔锁相技术可以有效改进DLA的发光特性，使它有良好的发散度、高的相干性及定标放大性。这种方法可以实现宽发光区的标准DLA的相位锁定。研究表明，长度为TALBOT距离Z_T的整数倍的外腔结构不能有效区分最高和最低阶模式，而改用1／4 TALBOT腔进行DLA外腔锁相，可以抑制最低阶模式，优选最高阶模式振荡，但是远场会出现两个光斑。于是，提出采用选频相位共轭反馈系统实现DLA的外腔锁相，该方法可以克服1／4TALBOT腔远场两个光斑的缺点，有利于能量的集中利用。
在外腔(EC)中二极管激光阵列(DLA)的一个激光单元既可以接收来自其相邻单元发出的辐射(C_1)，也可以接收自身发出的经激光器前端面反射回来的辐射(S)和在外腔中反射后回到激光器中的辐射(C_0)。实现外腔锁相运转意味着|C_0/S|、|C_1/S|均应大于1。在此基础上，我们分析了实现DLA外腔相位锁定时所允许的端面反射系数、以及该系数与外腔腔长和外腔反射
四川，悦理卜祠眨d卜理卜七立今仑文
系数等的关系。
推导了外腔中二极管激光阵列各发光单元之间的藕合系数，结果表明:
增加外腔长度有利于减小各阶祸合系数的差别和实现“并联祸合”，但是外腔
的作用效果下降;降低阵列前端面的反射系数，有利于实现外腔锁相;外腔
锁相中并联祸合的单元数越多，激光二极管阵列前端面的反射系数的允许值
越小。
通过分析输出腔镜、快轴准直透镜、芯片焊接、冷却器设计等关键的环
节，对外腔锁相需要考虑的问题进行了深入的探讨。采用三维有限元方法分
析了DLA背冷式封装结构的散热效率，对冷却器结构参数进行了优化设计。
High power diode laser arrays (LDA) have considerable attention in the industrialzed economies for the small volume and high efficiency, and have been widely used in materials processing, laser medicine etc.
Phase locking DLA had been developed remarkedly in 1980s. At that time, people had gotten the phase locking DLA through evanescent wave, leaky wave, Y-jont coupling and diffraction coupling. Usually the above mentioned measures are applicable to the traditional DLA with small emitters, and people had not gotten the ideal output power.
According to the coupling mode theory and TALBOT cavity theory, we have made an in-depth theoretical analyses on the DLA phase locked in an external cavity (EC) . The phase locking may efficiently improve the radiating properties of the DLA and have good diverging degree, high coherence and scalability. The methods may result in the phase locking on the standard DLA with wide emitters. The integral TALBOT cavity length may not be able to provide sufficient discrimination between the highest and fundamental mode. We may suppress the fundamental mode and choose the highest mode by selecting an external cavity length of a quarter TALBOT distance. The drawback of the 1/4 Talbot cavity is that the LDA generates a double peak far field pattern. The frequency-selective phase-conjugate feedback (FSPCF) system may be used to phase lock the DLA in an EC to overcome the drawback of the double peak far
field in the 1/4 TALBOT cavity and to make full use of the pump sources.
An emitter of a DLA positioned in an EC can receive the light emitted from its neighboring elements and that of itself after being reflected at the DLA facet. Expressions describing the received radiations from neighboring elements (C1) and that from itself(S)as soon as from the external cavity(C0)have been deduced. Considering the fact that | C0/S| should be larger than unify if the EC is of effective and | C1/S | should be larger than unify if the phase locking may be established in the EC, requirements on the reflection at the DLA facet have been specified in terms of the cavity length and reflection coefficient of the external mirror.
Expressions describing couplings between different emitters of a diode laser array (DLA) , positioned in an external cavity (EC) , have been deduced. The results show that: the increase of the length of the EC reduce the differences between these coupling coefficients, which is favorable to achieving the so called "parallel coupling" at the expense of the effectiveness of the EC; decreasing the reflection coefficient at the front facet of the DLA is favorable to achieving phase locking in EC; the more the parallelly coupled emitters are, the lower the allowed reflection coefficient at the front facet of the DLA is.
Through considering the output cavity mirror, fast axis collimation lens, chips welding, cooler designing and so on, we have widely understood the necessary consideration for the phase locking DLA in an EC.The thermal resistance of the DLA with back cooling packaged structure was calculated by three-dimension finite element method. The calculated results indicated that the cooling water channel depth and fin width have optimum values.
引文
[1] J.K.Wade, L.J.Mawst,D.Botez. High continuous wave, 0.8μm-band, At-free active region diode laser, Appl.phys.Lett., 1997, 70(2), 149～151
[2] C.Hanke, L.Korte, B.Acklin et al.,High reliable 40 W-CW-InGaAIAs/GaAs808 nm laser bars, SPIE, 1999, 3462, 47～53
[3] J.Jandeleit,N.Wiedmann,A.Ostlender et al., Packaging and characterization of high power diode lasers, SPIE, 2000, 3945, 270～277
[4] D.Botez, L.J.Mawst, A.Bhattacharya, et. al., 6% CW wallplug efficiency from Al-free 0.98μm emitting diode lasers, Electron. Lett., 1996, 32, 2012～2013
[5] A.A.Karpinski,Simple thermal management of long pulse-large multi-bar laser diode arrays, SPIE, 2148, 339～350
[6] W.Koechner,Solid State Laser Engineering, 4th edn., Springer Ser. Opt. Sci. 1 (Springer, Berlin, Heidelberg 1996) , 302
[7] 武德勇，高松信，严地勇等，高功率线阵半导体激光器光纤耦合设计，激光杂志，2002，23(5)，19～20
[8] B.J.Comaskey, High averge power diode pumped slab laser, IEEE Journal of quantum electronics, 1992, 28(4),992～996
[9] S. Fujikawa, High-power high-efficient diode-side-pumped Nd:YAG laser, OSA TOPS Vol.10,Advanced solid state lasers,1997,296～299
[10] J.Randall, Diode array pumped kilowatt laser, SPIE, 1998, Vol. 3264, 2～8
[11] H.Weber, diode pumped solid state lasers: from low to 10-kW, SPIE, 1999, 3862, 2
[12] W.F.krupke, Advanced diode pumped solid state lasers ( DPSLLS ): new term trends and future prospects, SPIE, 2000, 3889, 21
[13] 有清，固体激光二极管泵浦阵列的现代化制造，激光与光电子学进展，1996，9，17～19
[14] J.Haden, J.Endriz, M.Salzmann, et al., Advances in high-averge power long life laser-diode pump array architectures, SPIE, 1995, 2382, 2～21
[15] L.Rogers, S.Macomb, Diode laser target manufacturing, Laser solutions for manufacturing,1999, 14(60), 25～28
[16] E.K.Mc, Diode laser solve soldering problems,Industrial Laser Rev., 1998, 13(2),16～18
[17] 有清，高功率激光二极管将投入工业使用，激光与光电子学进展，1998，2，36～37
[18] 颜严，从征，以光纤传输2kW二极管激光，激光与光电子学进展，2000，1，42～42
[19] S.Heinemann, L.Leininger, Fiber coupled diode lasers and beam-shaped high-power stacks, SPIE, 3267, 116～124
[20] U.Brauch,P.Loosen,and H.Opower, High power diode laser for direct applications, Topics Appl.Phys., 2000, 8,303～367
[21] 吕百达，关于激光光束质量若干问题的分析，激光技术，1998，22(1)，14～17
[22] 杨成龙，光束质量概念谈，激光杂志，1996，17(1)，1～5
[23] 冯国英，吕百达，孔繁龙等，用二维CCD系统测量光束质量的实验研究，强激光与粒子束，1997，9(4)，491～495
[24] 白光，罗山，激光二极管线阵和列阵的极限输出参数，激光与光电子学进展，1998，4, 19～22
[25] D.Botez and L.J.Mawst,Phase-locked laser arrays revisited, IEEE Circuits & Devices, 1996, 25～32
[26] R.Lang, Injection locking properties of a semiconductor laser, IEEE J. of Quantum electronics, 1982, 18(6), 976～983
[27] J.R.Leger, Lateral mode control of an AIGaAs laser array in a Talbot cavity, Appl.phys.lett., 1989, 55(4), 334～336
[28] R.G.Waarts, W.Cassarly, J.M.Finlan, etc., Semiconductor laser array in an extemal Talbot cavity, SPIE,1992,1634, 288～298
[29] V.V.Apollonov, S.I.Derzhavin, V.A.Filonenko etc., High power laser diode array phase-locking, SPIE, 2000, 3889, 134～146
[2] C.Hanke, L.Korte, B.Acklin et al.,High reliable 40 W-CW-InGaAIAs/GaAs808 nm laser bars, SPIE, 1999, 3462, 47～53
[3] J.Jandeleit,N.Wiedmann,A.Ostlender et al., Packaging and characterization of high power diode lasers, SPIE, 2000, 3945, 270～277
[4] D.Botez, L.J.Mawst, A.Bhattacharya, et. al., 6% CW wallplug efficiency from Al-free 0.98μm emitting diode lasers, Electron. Lett., 1996, 32, 2012～2013
[5] A.A.Karpinski,Simple thermal management of long pulse-large multi-bar laser diode arrays, SPIE, 2148, 339～350
[6] W.Koechner,Solid State Laser Engineering, 4th edn., Springer Ser. Opt. Sci. 1 (Springer, Berlin, Heidelberg 1996) , 302
[7] 武德勇，高松信，严地勇等，高功率线阵半导体激光器光纤耦合设计，激光杂志，2002，23(5)，19～20
[8] B.J.Comaskey, High averge power diode pumped slab laser, IEEE Journal of quantum electronics, 1992, 28(4),992～996
[9] S. Fujikawa, High-power high-efficient diode-side-pumped Nd:YAG laser, OSA TOPS Vol.10,Advanced solid state lasers,1997,296～299
[10] J.Randall, Diode array pumped kilowatt laser, SPIE, 1998, Vol. 3264, 2～8
[11] H.Weber, diode pumped solid state lasers: from low to 10-kW, SPIE, 1999, 3862, 2
[12] W.F.krupke, Advanced diode pumped solid state lasers ( DPSLLS ): new term trends and future prospects, SPIE, 2000, 3889, 21
[13] 有清，固体激光二极管泵浦阵列的现代化制造，激光与光电子学进展，1996，9，17～19
[14] J.Haden, J.Endriz, M.Salzmann, et al., Advances in high-averge power long life laser-diode pump array architectures, SPIE, 1995, 2382, 2～21
[15] L.Rogers, S.Macomb, Diode laser target manufacturing, Laser solutions for manufacturing,1999, 14(60), 25～28
[16] E.K.Mc, Diode laser solve soldering problems,Industrial Laser Rev., 1998, 13(2),16～18
[17] 有清，高功率激光二极管将投入工业使用，激光与光电子学进展，1998，2，36～37
[18] 颜严，从征，以光纤传输2kW二极管激光，激光与光电子学进展，2000，1，42～42
[19] S.Heinemann, L.Leininger, Fiber coupled diode lasers and beam-shaped high-power stacks, SPIE, 3267, 116～124
[20] U.Brauch,P.Loosen,and H.Opower, High power diode laser for direct applications, Topics Appl.Phys., 2000, 8,303～367
[21] 吕百达，关于激光光束质量若干问题的分析，激光技术，1998，22(1)，14～17
[22] 杨成龙，光束质量概念谈，激光杂志，1996，17(1)，1～5
[23] 冯国英，吕百达，孔繁龙等，用二维CCD系统测量光束质量的实验研究，强激光与粒子束，1997，9(4)，491～495
[24] 白光，罗山，激光二极管线阵和列阵的极限输出参数，激光与光电子学进展，1998，4, 19～22
[25] D.Botez and L.J.Mawst,Phase-locked laser arrays revisited, IEEE Circuits & Devices, 1996, 25～32
[26] R.Lang, Injection locking properties of a semiconductor laser, IEEE J. of Quantum electronics, 1982, 18(6), 976～983
[27] J.R.Leger, Lateral mode control of an AIGaAs laser array in a Talbot cavity, Appl.phys.lett., 1989, 55(4), 334～336
[28] R.G.Waarts, W.Cassarly, J.M.Finlan, etc., Semiconductor laser array in an extemal Talbot cavity, SPIE,1992,1634, 288～298
[29] V.V.Apollonov, S.I.Derzhavin, V.A.Filonenko etc., High power laser diode array phase-locking, SPIE, 2000, 3889, 134～146