【作者】 王强；

【导师】 关宝璐；

【作者基本信息】 北京工业大学 ， 微电子学与固体电子学， 2014， 硕士

【摘要】 垂直腔面发射激光器（Vertical Cavity Surface Emitting Laser, VCSEL）是半导体激光器的一种，是由日本东京工业大学的Iga教授于1977年提出的一种新型的半导体激光器结构。VCSEL的独特之处在于其激射光的方向垂直于谐振腔表面，且其结构通常由上反射镜、有源区和下反射镜三个部分组成。由于VCSEL特殊的结构，使其具有诸如阈值电流低、易与光纤耦合、单纵模发射、波长稳定性好、调制带宽大和使用寿命高等优点，并且广泛应用于光谱学、光互联、气体探测和光通信等领域。随着信息技术的快速发展，人们对于光通信的速度和质量的要求越来越高。为了解决密集波分复用通信技术（Dense Wavelength Division Multiplexing，DWDM）中光信号源的问题，人们提出了制备波长可调谐的VCSEL的想法并很快受到相关科研人员的关注和研究。经过二十多年的发展，关于VCSEL波长调谐方式的研究主要集中于电热调谐，静电调谐，压电调谐和液晶调谐四类。前三种调谐方式需要使用悬臂梁或者MEMS （Micro-Electro-Mechanical System）可移动薄膜结构，这种结构在调谐过程中易受到外界机械振动的影响，降低了器件调谐的稳定性。而且由于可移动调谐结构的存在，使得器件封装工艺的难度增加，不利于进行大规模地商业化生产。但是，利用向列相型液晶的双折射特性，通过改变液晶的折射率来实现波长调谐的方法则不需要使用悬臂梁或MEMS可移动薄膜结构，从而很好地避免了上述问题。针对液晶波长可调谐VCSEL的研究，本文主要做了以下工作：1.提出一种新型的内腔液晶波长可调谐VCSEL结构。该结构由上反射镜、“半结构”的VCSEL （Half-VCSEL）和液晶盒三部分组成。液晶盒主要由铟锡氧化物（Indium Tin Oxides, ITO）调谐电极、取向膜、衬垫和液晶组成。Half-VCSEL是“半结构”的VCSEL，主要由GaAs衬底，下反射镜和有源区三个部分组成。从模拟计算结果可知，该结构能够实现波长的调谐范围大于20nm，并且可以实现单偏振输出。2.基于传输矩阵法，模拟了内腔液晶层的厚度和液晶分子的转动角度对VCSEL调谐特性、阈值特性和偏振特性的影响。与通过改变空气隙厚度实现调谐的三种调谐方式一样，如果内腔液晶层的厚度改变也会极大地影响VCSEL的特性。因此本文研究了内腔液晶层的厚度对VCSEL特性的影响，得到了内腔液晶层的最优厚度为2025nm。另外，本文研究了液晶分子从0rad旋转到π/2rad的过程中，液晶材料的折射率会随着液晶分子转动的关系，并得出了VCSEL输出光特性的变化规律。3.结合上下反射镜的反射率及量子阱增益随温度变化的关系，研究了温度对定波长VCSEL偏振跳变特性的影响。测试并分析了850nm VCSEL在不同温度下的偏振跳变特性。在此基础上，模拟了不同温度下激光器的反射率和增益变化，并给出了二者对偏振跳变特性的影响。4.从双折射角度出发，研究了不同氧化孔径，不同温度下，液晶对VCSEL偏振特性的影响。将液晶涂覆于VCSEL表面，制备了表面液晶-VCSEL，并进行了测试和分析。给出了涂覆液晶后VCSEL偏振第一跳变点和第二跳变点之间电流值增大的原因，并分析了液晶层对VCSEL峰值光功率及阈值电流的影响。5.开展了液晶盒等关键工艺技术的研究。采用摩擦取向法制备了液晶盒，使用光刻和腐蚀等工艺，制备了内腔液晶波长可调谐VCSEL的Half-VCSEL结构，为内腔液晶波长可调谐VCSEL的制备提供了较多的技术经验。更多还原

【Abstract】 Vertical cavity surface emitting laser (VCSEL) is a semiconductor laser which isoriginated from Iga, the doctor of Tokyo University of Technology in1977. The laserlight direction is perpendicular to the cavity surface of VCSEL. The up reflector,active area and down reflector constitute the VCSEL. The effective cavity length ofVCSEL is shorter than edge-emitting laser. There are many advantages of VCSELbecause of its special structure, like low threshold current, easy to link fiber, singlelongitudinal mode, large modulation bandwidth and long life etc. There are a lot ofapplication of VCSEL, like spectroscopy, optical link, gas detection and opticalcommunication etc.People’s requirement to quality and velocity of optical communication becomesmore and more rigorous. For solving the optical source of Dense WavelengthDivision Multiplexing (DWDM), the wavelength tunable VCSEL is proposed andstudied. More than twenty years later, there are four wavelength tunable methods,electro-thermal, electrostatic, piezoelectricity tuning and tuning with liquid crystal.The former three ways are all based on the Micro-Electro-Mechanical System(MEMS) which is a removable structure and easily influenced by the mechanicalvibration. On the other hand, it is difficult to finish the package for VCSEL with thisstructure. And VCSEL with this structure could not be fabricated as large scalecommercially. However, the liquid crystal which has birefringence solves the questionabove. The liquid crystal is embedded in the intracavity of VCSEL. The wavelengthchanges as refractive index of liquid crystal changes. For the study of wavelengthtunable VCSEL with intracavity liquid crystal, this dissertation shows a lot work asfollowed.1. A new structure of wavelength tunable VCSEL with intracavity liquid crystal isproposed. This structure consists three parts, up reflector, Half-VCSEL and liquidcrystal cell. The liquid crystal cell is used to bloom liquid crystal. It consists ofITO (Indium Tin Oxides) tuning electrode, alignment film, spacer and liquidcrystal. Half-VCSEL consists of GaAs substrate, down reflector and active area.The wavelength tunable range is more than20nm. And the output polarization issingle and stable.2. The thickness of liquid crystal and turning angle of liquid crystal moleculeinfluence the tunable, threshold and polarization characteristics. Based on transfermatrix method, we get the optimal thickness is2025nm. The change of VCSELperformance is showed as the liquid crystal molecule turns from0rad to π/2rad. 3. The850-nm VCSEL with different apertures is fabricated. The polarization switchis measured at different temperatures and analyzed by simulating the influencefrom reflectivity of reflector and quantum well gain.4. The850-nm VCSEL with liquid crystal overlay is presented utilizing thebirefringence of nematic liquid crystal. The threshold current, peak of opticalpower and I-P characteristics at different temperatures were measured andanalyzed. And the current between the first polarization hope and the second oneincreases because of the birefringence of liquid crystal.5. The liquid crystal cell part is made by friction alignment. The Half-VCSEL part isfabricated by lithography and etching. These crafts provide useful guideline forthe fabrication of complete wavelength tunable VCSEL with intracavity liquidcrystal.更多还原