Coupling characteristics of laterally coupled gratings with slots

Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm-4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.     

石墨片作辅助热沉的高功率半导体激光器热传导特性

为使边发射高功率单管半导体激光器有源区温度降低,增加封装结构的散热性能,降低器件封装成本,提出一种采用高热导率的石墨片作为辅助热沉的高功率半导体激光器封装结构。利用有限元分析研究了采用石墨片作辅助热沉后,封装器件的工作热阻更低,散热效果更好。研究分析过渡热沉铜钨合金与辅助热沉石墨的宽度尺寸变化对半导体激光器有源区温度的影响。新型封装结构与使用铜钨合金作为过渡热沉的传统结构相比,有源区结温降低4.5 K,热阻降低0.45 K/W。通过计算可知,激光器的最大输出功率为20.6 W。在研究结果的指导下,确定铜钨合金与石墨的结构尺寸,以达到最好的散热效果。     

试验优化设计Er3+/Yb3+共掺BaGd2ZnO5荧光粉及其上转换发光性质

为得到绿光和红光最大发光强度的Er³⁺/Yb³⁺共掺BaGd₂ZnO₅上转换材料荧光粉, 首先采用试验优化设计中的均匀设计初步寻找Er³⁺/Yb³⁺合理的掺杂浓度; 其次通过二次通用旋转组合设计进一步优化实验, 建立起Er³⁺/Yb³⁺掺杂浓度与绿光和红光发光强度的回归方程; 最后通过遗传算法计算出方程的最优解, 即绿光和红光最大发光强度时对应的Er³⁺/Yb³⁺掺杂浓度. 利用传统的高温固相法分别制备出最优样品. 采用X 射线衍射对得到荧光粉的晶体结构进行了分析, 证明了所有产物均为纯相BaGd₂ZnO₅. 采用980 nm抽运激光作为激发源, 在同样的条件下测量了样品的上转换荧光发射光谱, 从中可见样品有较强的红光发射和绿光发射, 发光中心位于662, 551和527 nm, 分别对应于⁴F_9/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 及²H_11/2→⁴I_15/2能级跃迁. 研究了绿光和红光最优样品的上转换发光强度与激光器工作电流之间的关系, 通过分析发现红色和绿色上转换发光均为双光子过程. 由归一化的绿色上转换发射光谱可以看出, 激光器工作电流导致的样品温度变化可以忽略不计. 由于能级²H_11/2和⁴S_3/2之间存在热平衡, 并满足玻尔兹曼分布, 由此探讨了绿光最优样品上转换发射光谱中的绿色发射与温度的关系, 计算出²H_11/2和⁴S_3/2之间的能级差为ΔE=926.11 cm^-1. 研究了绿光最优样品的温度效应, 随着温度的升高, 发射强度逐渐变小, 出现了温度猝灭现象. 并计算了样品的激活能, 分别为总体激活能ΔE_总=0.45 eV, 绿光激活能ΔE_绿=0.45 eV, 红光激活能ΔE_红=0.46 eV.     

组合优化设计制备Y~(3+)/Dy~(3+)共掺Bi_2ZnB_2O_7新型荧光粉的发光性质

为获得Bi2ZnB2O7:Y3+/Dy3+新型荧光粉材料的最强黄光发光强度,运用均匀设计和二次通用旋转组合设计相结合法对Y3+/Dy3+最佳离子掺杂浓度进行优化研究,得到Y3+和Dy3+离子的最佳掺杂浓度分别为4.498mol%和6.001mol%.采用高温固相法合成最优样品,对样品结构进行表征,测定其激发光谱和发射光谱对Dy3+离子在Bi2ZnB2O7基质中的发光性质,研究发现:样品在452nm激发下,发射光谱主要由(460~500nm)蓝光发射、(550~610nm)黄光发射、(650~700nm)红光发射组成,分别对应于Dy3+的4F9/2→6H15/2、4F9/2→6H13/2及4F9/2→6H11/2跃迁;Bi2ZnB2O7基质为Dy3+提供了非中心对称的晶格格位;最优样品中Dy3+的荧光寿命为0.427ms,与相同浓度Dy3+单掺杂样品相比较可知引入Y3+在一定程度上提高了发光强度.     

Experimental optimum design and luminescence properties of NaY(Gd)(MoO_4)_2:Er~(3+)phosphors

Three-factor orthogonal design(OD) of Er~(3+)/Gd~(3+)/T(calcination temperature) is used to optimize the luminescent intensity of Na Y(Gd)(MoO_4)_2:Er~(3+)phosphor.Firstly,the uniform design(UD) is introduced to explore the doping concentration range of Er~(3+)/Gd~(3+).Then OD and range analysis are performed based on the results of UD to obtain the primary and secondary sequence and the best combination of Er~(3+),Gd~(3+),and T within the experimental range.The optimum sample is prepared by the high temperature solid state method.Photoluminescence excitation and emission spectra of the optimum sample are detected.The intense green emissions(530 nm and 550 nm) are observed which originate from Er~(3+)~2H_(11/2)→~4I_(15/2)and~4S_(3/2)→~4I_(15/2),respectively.Thermal effect is investigated in the optimum NaY(Gd~(3+))(MoO_4)_2:Er~(3+)phosphors,and the green emission intensity decreases as temperature increases.     

宽范围可调谐内腔液晶垂直腔面发射激光器设计与研究

为增加可调谐激光器的波长调谐范围,提高系统的可靠性和稳定性,基于液晶的电控双折射特性,设计了一种中心波长为852 nm的内腔液晶可调谐垂直腔面发射激光器结构。分析了该结构获得宽范围波长调谐和单偏振稳定输出的物理原理,利用传输矩阵法进一步计算整个器件下不同液晶层厚度所对应的反射谱,得出不同液晶厚度和折射率下激光器的激射波长。结果表明,液晶可调谐激光器单偏振波长调谐范围达到31 nm,调谐效率大于10 nm/V。     

All-fiber erbium-doped dissipative soliton laser with multimode interference based on saturable-reserve saturable hybrid optical switch

Reverse saturable absorption is essential for the realization of dissipative solitons. In this paper, we introduce reverse saturable absorption by using nonlinear multimode interference (NL-MMI), for the first time, to the best of our knowledge, and obtain a stable dissipative soliton operation. By adjusting the coupling efficiency from multimode fiber to single mode fiber, the absorption properties of NL-MMI can be switched between saturation and reverse saturation. The dissipative soliton can be obtained with pulse width of 975 fs in the experiment, the 3-dB bandwidth at 1555 nm is 16 nm, and the maximum output power is 11.48 mW. The nonlinear absorption optical modulation and high damage threshold characteristics of the NL-MMI based ultrafast optical switch provide a new idea for realizing dissipative solitons.     

组合优化设计制备Y^(3+)/Dy^(3+)共掺Bi_2ZnB_2O_7新型荧光粉的发光性质EI北大核心CSCD

为获得Bi2ZnB2O7:Y3+/Dy3+新型荧光粉材料的最强黄光发光强度,运用均匀设计和二次通用旋转组合设计相结合法对Y3+/Dy3+最佳离子掺杂浓度进行优化研究,得到Y3+和Dy3+离子的最佳掺杂浓度分别为4.498mol%和6.001mol%.采用高温固相法合成最优样品,对样品结构进行表征,测定其激发光谱和发射光谱对Dy3+离子在Bi2ZnB2O7基质中的发光性质,研究发现:样品在452nm激发下,发射光谱主要由(460~500nm)蓝光发射、(550~610nm)黄光发射、(650~700nm)红光发射组成,分别对应于Dy3+的4F9/2→6H15/2、4F9/2→6H13/2及4F9/2→6H11/2跃迁;Bi2ZnB2O7基质为Dy3+提供了非中心对称的晶格格位;最优样品中Dy3+的荧光寿命为0.427ms,与相同浓度Dy3+单掺杂样品相比较可知引入Y3+在一定程度上提高了发光强度.     

BaY_2ZnO_5:Tm~(3+)/Yb~(3+)荧光粉的试验优化设计合成及发光性质研究

为了获得BaY_2ZnO_5:Tm~(3+)/Yb~(3+)荧光粉材料的最大蓝色上转换发光强度,采用正交试验设计与二次通用旋转组合设计相结合的两步连续优化法对Tm~(3+)和Yb~(3+)掺杂浓度进行全局优化,得到该体系最强蓝光发射下的离子掺杂最佳浓度.采用高温固相反应法合成出蓝色上转换发光强度最强的BaY_2ZnO_5:Tm~(3+)/Yb~(3+)荧光粉材料,并对样品的晶体结构和上转换发光性质进行了研究.980nm红外光激发下,测量了最优样品在不同激发电流下的上转换发射光谱,由强度制约关系确定样品的蓝色上转换发光为三光子过程.测量了最优样品温度相关的上转换发射光谱,发现样品的蓝色上转换发光强度随着样品温度的升高而持续减弱,即发生了温度猝灭现象,计算得激活能约为0.602eV.