长波红外QCL芯片三维光学结构设计与优化

Design and optimization of three-dimensional optical structures for long-wave infrared QCL chip

摘要:

针对长波红外量子级联激光器(quantum cascade laser,QCL)波导损耗较大和光限制因子较低等问题,本文详细研究了8.3 μm长波红外QCL芯片三维光学结构对光波导及电学性能的影响。在外延生长方向,研究和对比了“InP+InGaAs”和“全InP”两种波导结构的材料厚度、掺杂浓度等因素对光波导性能的影响,结果证实“全InP”波导结构可实现更低的波导损耗和模式重叠系数。在脊波导两侧方向,考察了脊宽对光波导性能的影响,发现采用将脊两侧包覆的InP∶Fe掩埋异质结构(buried heterostructure,BH) 能使脊宽小于10 μm的芯片的模式重叠系数更低。在腔面膜方向,通过研究涂层厚度与反射率的关系实现对腔面损耗的优化。结果表明,当增透(antireflection,AR) 膜Y₂O₃的厚度为990 nm时,增透膜反射率和腔面损耗分别为3.43%和3.37 cm-1,此时电光转换效率(wall plug efficiency,WPE) 可以达到极大值12.91%。

Abstract:

Aiming at the problems of large waveguide loss and low optical confinement factor of long-wavelength infrared quantum cascade laser (QCL),this paper studies in detail the effects of the three-dimensional optical structure of 8.3 μm long-wavelength infrared QCL chip on the optical waveguide and the electrical performance.In the direction of epitaxial growth,the effects of material thickness,doping concentration and other factors on the optical waveguide performance of "InP+InGaAs" and "All-InP" waveguide structures are investigated and compared.The results confirm that the "All-InP" waveguide structure can achieve lower waveguide loss and mode overlap coefficient.In the direction of ridge waveguide sides,the effect of ridge width on the optical waveguide performance is investigated.It is found that the mode overlap coefficient of the chip with ridge width less than 10 μm can be reduced by using InP∶Fe buried heterostructure (BH) on both sides of the ridge.In the direction of the cavity surface film,the optimization of the mirror loss is accomplished by studying the relationship between the film thickness and reflectivity.The results show that when the thickness of the Y₂O₃ antireflection (AR) coating is 990 nm,the reflectivity of the antireflection and the mirror loss are 3.43% and 3.37 cm-1,respectively,and which then lead to the maximum wall plug efficiency (WPE) of 12.91%.