【作者】 陈敏；

【导师】 施跃春；

【作者基本信息】 南京大学 ， 材料工程（专业学位）， 2020， 硕士

【摘要】 随着光通信的不断发展,更大规模、更快速度、更高容量的信息传输系统,正潜移默化地改变大众的生活。传统的分立的光子器件存在体积大、功耗高等缺点,不再适应光通信网络的需求。因此出现了能同时集成多种光子器件,且体积小的光子集成（Photonic Integrated Circuits,PIC）芯片。DFB半导体激光器单模特性好,是光通信系统和PIC芯片中常用的光源。目前PIC芯片多在硅基平台上制备,但光在硅波导中散射损耗较大,因此研究者考虑提高DFB半导体激光器的出光功率来补偿波导损耗。此外,DFB半导体激光器也是光谱吸收型气体检测系统常用的光源。由于气体吸收光谱很窄,因此对波长准确性的要求很高。例如在甲烷气体检测中,泛频带2ν₃的宽度小于3.0 nm。所以在追求提高激光器出光功率的同时,还应保证激射波长的准确性。重构等效啁啾（Reconstruction Equivalent Chirp,REC）技术提出,采用取样光栅结构来代替真实结构,可以将激射波长的控制精度提高两个数量级。本文致力于提高激光器的出光功率和波长准确性,首先通过耦合模方程和修正的传输矩阵法,分析得到在波导取样莫尔光栅（Sampled MoiréGrating,SMG）的+1子光栅中可以等效实现莫尔光栅效应。即通过对取样周期、SMG长度、取样初相位差等参数的设计,可以同时引入π相移和切趾效应。随后我们制作了SMG-DFB半导体激光器,在两端面镀AR/HR膜来提高出光功率。封装后在25.0℃、700.0 m A下测试得到,激光器的出光功率都超过了170.0 m W。阈值电流平均为40.0 m A,斜效率在0.26～0.28 m W/m A之间。另外论文测试了不同温度下的P-I曲线,结果显示阈值电流与温度呈正比,斜效率与温度呈反比。基于SMG的优势,本文首次提出了在激光器中采用SMG-GR波导光栅结构,即在SMG一端集成光栅反射器（Grating Reflector,GR）来提高光反馈。在设计的SMG-GR-DFB半导体激光器中,SMG段为有源区,产生激射;而GR段仅以光栅反射器存在,为激射波长提供光反馈,本身不产生激射。激光器的两端面镀AR/AR膜,避免了HR膜引入端面随机相位。论文将SMG-GR-DFB激光器分别与SMG-DFB、π-EPS（Equivalent Phase Shift,EPS）-GR-DFB激光器进行了对比计算。仿真结果说明SMG-GR-DFB激光器具有更高的出光功率、良好的单模特性以及可以有效避免空间烧孔（Spatial Hole Burning,SHB）效应等优势。此外,SMG-GR的制备只需要全息曝光技术和微米级光刻,工艺成熟,成本低廉,便于规模化制备。具有这些优势的SMG-GR-DFB半导体激光器,有望在未来光通信系统、气体检测系统中得到实际应用。更多还原

【Abstract】 With the continuous development of optical communication networks,larger-scale,faster-speed,and higher-capacity information transmission systems are subtly changing people’s lives.Traditional discrete photonic devices have some disadvantages like large volume and high power consumption,and no longer meet the needs of optical communication networks.Therefore,the small-sized photonic integrated circuit（PIC）chips appear,and multiple photonic devices can be integrated at the same time.Among a variety of optoelectronic devices,the DFB semiconductor laser has good single longitudinal mode（SLM）characteristics,and is a commonly used light source for optical communication systems and PIC chips.PIC chips are mostly prepared on a silicon-based platform,but the light has a large scattering loss in the silicon waveguide,so the researchers consider increasing the output power of the DFB semiconductor lasers to compensate for the waveguide loss.In addition,DFB semiconductor lasers are also commonly used as light sources for spectral absorption gas detection systems.Because the gas absorption spectrum is very narrow,the requirement for wavelength accuracy is very high.For example,in methane gas detection,the width of the pan band 2ν₃ is less than 3.0 nm.Therefore,while pursuing the improvement of the laser output power,the accuracy of the lasing wavelength should also be ensured.In addition,reconstruction equivalent chirp（REC）technology proposes that using sampling grating structure instead of real grating structure,can improve the control accuracy of lasing wavelength by two orders of magnitude.In this paper,from the perspective of improving the output power and wavelength accuracy,we have done some experimental and theoretical research.Firstly,the coupled mode equation and the modified transfer matrix method are combined to analyze the+1sub-grating in the waveguide sampling moirégrating（SMG）,and find that the moiréeffect can be equivalently achieved in the+1 sub-grating.That is to say,through the design of the sampling period,length of SMG,sampling initial phase difference and other parameters of SMG,πphase shift and apodization effect can be introduced simultaneously.Subsequently,we fabricate SMG-DFB semiconductor lasers,which are coated with anti-reflection/high reflection（AR/HR）coatings on both facet to increase the optical power.After encapsulation,the SMG-DFB semiconductor lasers are tested at25.0℃and 700.0 m A.Test results show that the output power of the lasers exceed 170.0m W.The average threshold current is 40.0 m A,and the slope efficiency is between 0.26～0.28 m W/m A.In addition,I test the P-I curves at different temperature,the test results show that the threshold current is directly proportional to the temperature,and the slope efficiency is inversely proportional to the temperature.Based on the advantages of SMG,this paper first proposed the use of SMG-GR waveguide grating structure in DFB semiconductor laser.That is,integrating a grating reflector（GR）at one end of SMG to improve the optical feedback for the lasing mode.In the designed SMG-GR-DFB semiconductor laser,the SMG segment is the active region and generates lasing mode.While the GR segment only exists as a reflector,which provides optical feedback for the lasing mode,and does not generate lasing mode itself.AR/AR coatings are used on both facets of the SMG-GR-DFB semiconductor laser,which avoids the introduction of random phases on the facet by HR coating.This paper compares the SMG-GR-DFB semiconductor laser with the SMG-DFB semiconductor laser,andπ-EPS（equivalent phase shift,EPS）-GR-DFB semiconductor laser.The simulation results show that the SMG-GR-DFB semiconductor laser has some advantages,such as higher light output power,good SLM characteristics and can be effective avoid the spatial hole burning（SHB）effect.In addition,the preparation of SMG-GR only requires holographic exposure technology and micrometer scale photolithography.The process is mature and the cost is low,which is convenient for large-scale promotion.With so many advangtages,SMG-GR-DFB semiconductor lasers are expected to be widely used in the future optical communication systems and gas detection systems.更多还原