【作者】 董雷；

【导师】 赵圣之； 刘水华；

【作者基本信息】 山东大学 ， 光学工程， 2010， 博士

【摘要】 宽可调谐半导体激光器是一类非常重要的半导体光电器件,由于能大幅减少备用激光器的数量,被认为是光纤通信密集波分复用系统中的理想光源,并在未来智能光网络中也将发挥越来越重要的作用。除此之外,在测量和传感领域,宽可调谐半导体激光器也有很广泛的应用前景。这其中取样光栅分布布拉格反射(Sampled Grating Distributed Bragg Reflector, SGDBR)半导体激光器由于调谐范围宽、光谱质量好、波长调谐速度快、功能扩展性强等特点广为关注。本论文围绕宽可调谐SGDBR半导体激光器的研制开展了以下几方面的工作：1.设计并优化激光器中取样光栅的结构。详细讨论了取样光栅的取样长度、取样周期数、占空比和端面反射等结构参数对光栅反射谱特性以及激光器性能,包括调谐范围、输出功率和边模抑制比的影响,给出了优化后的结果。2.对激光器的有源区和无源区材料进行模拟设计,计算有源区中多量子阱的能带结构和增益谱线,对不同带隙材料的折射率变化范围和相应的吸收损耗进行计算。并对两个不同区段的光场分布、折射率匹配以及重叠积分等进行模拟研究。3.建立新型动态分析模型,模型中根据激光器有源区和无源区的不同特点而采用不同的处理方法：在激光器有源区中仍然使用传统的时域行波法；而对结构复杂的无源区则首先采用频域分析方法,然后通过数字滤波器把两种方法有效地结合起来；利用该模型对SGDBR半导体激光器的静态和动态特性,尤其是波长切换性能进行分析,并进一步将该模型推广到集成器件的动态特性研究中。4.采用Cl2／H2做为刻蚀气体,通过测量多量子阱的光荧光强度,详细分析ICP等离子体刻蚀设备中各个参数对材料表面损伤的影响,包括压强、ICP功率、RF功率以及刻蚀气体组分等,从中总结出高密度等离子体低损伤刻蚀规律。根据所得结果,在低损伤刻蚀条件下取得了良好的刻蚀形貌。将这一工艺应用到实际激光器制程中,所制作的DFB激光器的输出特性和老化测试结果证明了该工艺的可靠性,并进一步用于改进取样光栅的制作工艺中。5.对MOCVD对接工艺进行研究,将对接界面腐蚀方案由原来的纯湿法腐蚀改进为干法刻蚀与湿法腐蚀相结合,提高了腐蚀界面的可控制性和重复率；同时改进MOCVD的生长工艺,显著提高了材料生长质量,实现了波导间高质量的对接生长。6.在理论设计和相关配套工艺的支持下,实际制作了宽可调谐SGDBR半导体激光器；利用精密反射计测量对接界面的残余反射在10-4量级；同时为克服SGDBR半导体激光器结构上的固有缺陷对激光器性能带来的不利影响,开展SGDBR半导体激光器集成SOA器件的研制工作。7.利用LabVIEW软件编写激光器自动化测试系统,测试结果表明研制的器件准连续调谐范围大于35nm,在整个调谐范围内的边模抑制比大于30dB。此外对集成器件的测试结果表明通过引入SOA有效地改善了各个输出通道间的输出功率均匀度,并对器件的波长切换特性进行测量。测试结果表明SGDBR半导体激光器激射波长从1541.92nm切换至1546.76 nm仅需6.2 ns左右的时间。本论文中的主要创新工作包括：Ⅰ系统分析了取样光栅中各个结构参数与光栅反射谱特性之间的联系,以及对激光器性能,包括调谐范围、输出功率和边模抑制比的影响；并根据上述结果得出一组SGDBR半导体激光器前、后取样光栅的优化参数。Ⅱ建立了新型动态分析模型。该模型根据激光器有源区和无源区的不同特点而采用不同的处理方法：在激光器有源区中仍然使用传统的时域行波法；而对结构复杂的无源区则首先采用频域分析方法,然后通过数字滤波器把时域行波法和频域方法有效地结合起来；利用该模型对SGDBR半导体激光器的静态和动态特性,尤其是激光器的波长切换性能进行分析,并进一步将该模型推广到更为复杂的集成器件的动态特性研究中。Ⅲ对高密度等离子体的刻蚀损伤展开研究。系统研究了采用Cl2／H2时ICP刻蚀系统中各个参数对材料表面损伤的影响,总结了刻蚀损伤规律；将这一结果引入到DFB半导体激光器的制程中,激光器的出光性能和老化测试结果表明工艺的可靠性,并进一步用于取样光栅制作工艺的改进。Ⅳ研究MOCVD对接生长工艺,先后采用两套方案,将对接界面的腐蚀工艺从最初的纯湿法腐蚀改为干、湿法相结合,并在MOCVD生长程序上做进一步改进,提高了对接工艺的可靠性和重复性。集合上述研究成果,包括MOCVD对接工艺、取样光栅制作工艺和理论模型优化得到的结果,实际制作了SGDBR半导体激光器器件。并针对激光器结构上固有缺陷,制作了SGDBR半导体激光器集成SOA器件,有效改善了各个通道输出功率的均匀度以及提升输出功率。更多还原

【Abstract】 Widely tunable laser diodes, which can set output wavelength according to the requirements, are one of the most important semiconductor optoelectronic devices. They are now playing an important role in the dense wavelength division multiplexing (DWDM) systems for reducing the required number of inventory lasers, and also expected to have wide applications in the further intelligent optical network. Furthermore, they also have widespread application prospects in the measurement and sensing field. Sampled-grating distributed Bragg reflector (SGDBR) lasers are the most promising candidates since they have wide tuning range, high side-mode suppression ratio (SMSR), small linewidth, fast switching speed and strong expanding characteristic of function.In this dissertation, the research work focus on the theoretical analysis and experimental research on widely tunable SGDBR laser diode. Specifically, the main work contains the followings:1. Design and optimize the sampled-grating structure for the tunable laser diode. The impact of the sampled grating in a distributed Bragg reflector laser on the tuning range, output power, and side-mode suppression ratio were investigated in detail. The optimization parameters consisted of the sampled length, the number of the sampled period, duty cycle and facet reflectivity.2. Numerically simulated the semiconductor materials of the active and passive regions of the laser diode. The band structure and gain spectrum of the multi-quantum wells were provided. The tuning range and the corresponding absorbing losses of semiconductor materials with different band-gap were calculated. Furthermore, by utilizing OlympIOs simulator software, optical field distribution in the active and passive regions, the refractive index mismatch and optical overlap were also studied.3. A new dynamical theoretical model for simulating widely tunable SGDBR lasers has been developed. The model integrates both time-domain traveling-wave method and frequency-domain transfer-matrix method into a single procedure. The active region of the device is still operated in the conventional time domain, while the passive parts are firstly performed by the transfer-matrix method and then transformed to the time domain via digital filters approach. Both the static and dynamic characteristics of SGDBR lasers, such as L-I curve, output spectrum, tuning characteristics, large-signal modulation, and dynamic wavelength switching, can be clearly visible in our model and in qualitative agreement with the published experimental results. Furthermore, this new model is also applied in the investigation of the dynamical properties of the complex Photonic Integrated Circuits (PICs).4. Using C12/H2 as etching etchants, the surface damage of the InP/InGaAsP material in ICP etching system was investigated. By measuring the changes of photoluminescence (PL) intensity from a specially designed InP/InGaAsP multi-quantum well (MQW) in both exposed and protected regions, and utilizing a Gaussian Depth Distribution model, the extent of damage was quantitatively analyzed. The influences of pressure, ICP power, RF power and Cl2/H2 mixing ratio of ICP system on the surface damage extent were revealed. Based on these results, a set of optimized low damage etching parameters with a less than 16 nm damage-depth was finally obtained. This technique has been successfully applied into the fabrication of DFB laser and the sampled grating. Both laser performance and accelerated aging test verified the reliability of our ICP etching processing in Bragg grating fabrication.5. The systematic study has been made to investigate the Butt-Joint techniques. The total wet-etching process for butt coupling was replaced by dry-etching followed by a small amount of selective wet etching to improve the reproducibility and the uniformity of the process. Meanwhile, the growth procedure of MOCVD was also adjusted to obtain a more reliable butt coupling.6. Based on the optimized parameters and related processing technology, the widely tunable SGDBR laser diode has been made. The residual reflection at the butt-joint interface is as low as 10-4 tested by precision reflectmeter. Furthermore, in order to overcome many defects existing in the nature structure of SGDBR laser diode, the SGDBR laser diode integrated with SOA is also fabricated.7. An automatic wavelength measurement and control system for SGDBR laser diode was developed by using LabVIEW virtual instrument software. The fabricated device features that quasi-continuous wavelength tuning range is more than 35 nm and the side mode suppression ratio (SMSR) is higher than 30 dB within the whole tuning range. The uniformity of different channel can be improved by integrating SOA in the SGDBR device. The wavelength-switching test indicated that the time delay can be less than 6.2 ns when the output wavelength switched from 1542.92 nm to 1546.76 nm.The main innovations of this dissertation are as follows:Ⅰ. The relationship between the structure parameters of sampling grating and the reflection spectrum has been analyzed systematically. The impacts of the sampling grating in a distributed Bragg reflector laser on the tuning range, output power, and side-mode suppression ratio (SMSR) were analyzed. Finally, optimized grating parameters were obtained.Ⅱ. A new dynamical model was established. This model integrates both time-domain method and frequency-domain method into a single procedure. The active region of the device is still operated in the conventional time domain, while the passive parts are firstly performed by the frequency method and then transformed to the time domain via digital filters. Both the static and dynamic characteristics of SGDBR lasers, especially the wavelength switching performance, can be clearly visible in our model. And it indicates that this new model can be furthre extended to the dynamical simulation of the complex Photonic Integrated Circuits (PICs).Ⅲ. The dry-etch damage of high-density plasma was studied. The effects of various etching parameters of Inductively Coupled Plasma (ICP) system on the etching damage using Cl2 and H2 mixing gases were investigated systematically, and the law of low-damage etching conditions were summed up. These conclusions have been applied to the fabrication of DFB lasers. The performance and aging experiment of lasers confirmed the validity of our conclusions and techniques. And it was used for improving the fabrication of sampling grating.Ⅳ. The Butt-Joint techniques were studied. The total wet-etching process for butt coupling was replaced by dry-etching followed by a small amount of selective wet etching to improve the reproducibility and the uniformity of the process. Meanwhile, the growth procedure of MOCVD was also adjusted to obtain a more reliable result. Based on the optimized parameters and related processing technology, the widely tunable SGDBR laser diode has been made. Furthermore, in order to overcome many defects existing in the nature structure of SGDBR laser diode, the SGDBR laser diode integrated with SOA is also fabricated.更多还原