基于共振波导光栅结构准连续域束缚态的低阈值纳米激光器的数值研究

Numerical study of the low-threshold nanolaser based on quasi-bound states in the continuum supported by resonant waveguide grating structures

纳米激光作为一种纳米级相干光源,是光电集成芯片的关键器件.激光器进一步小型化的阻碍在于随着激光器谐振腔体积的减小,其损耗迅速增大.连续域束缚态(bound states in the continuum,BICs)能有效降低全介质结构的辐射损耗.本文提出一种基于全介质共振波导光栅(resonant waveguide grating structures,RWGs)准BIC的纳米激光器,可有效降低纳米激光器的阈值.将传统两部分光栅转换为四部分光栅,可激发波导结构的准BIC模式.本文数值研究了该模式的受激辐射放大特性.结果表明:TE偏振光照射下,基于四部分光栅的RWG结构的纳米激光阈值比基于传统RWG结构的阈值低20.86%.TM偏振光照射时,阈值比传统RWG结构降低了3.3倍.而且TE偏振光照射时纳米激光的阈值比TM偏振光照射时阈值大约低一个数量级,这是因为TE偏振光照射时,结构的电场局域在波导层内,增强了光与增益材料的相互作用,从而降低了纳米激光的阈值.

As a nanoscale coherent light source,semiconductor nanolaser is a key device for future optoelectronic integrated chips.The obstacle of further miniaturization of the nanolaser is that the loss increases rapidly with the decrease of cavity volume.The bound states in the continuum(BICs) can overcome the high radiative loss.Here,we propose a nanolaser based on quasi-BIC mode supported by all-dielectric resonant waveguide grating(RWG),which can effectively reduce the threshold of nanolaser.The quasi-BIC mode of the waveguide can be excited when the traditional two-part grating becomes a four-part grating.The laser behavior of the quasi-BIC is studied by finite difference-time-domain(FDTD) numerical simulation.The results show that the threshold of the naolaser based on four part-grating RWG is 20.86% lower than that of nanolaser based on two part-grating RWG when subjected to TE-polarized light irradiation.For the TM-polarized light irradiation,the threshold is3.3 times lower than the threshold for the nanolaser based on four part-grating RWG.We also find that the threshold of the nanolaser under TE-polarized light irradiation is about one order of magnitude lower than that under TM-polarized light irradiation.Because the electric field of the structure is well confined inside the waveguide layer under TE-polarized light,which can enhance the interaction between light and gain materials and reduce the threshold of nanolasers.