一维增透亚波长光栅的研究

Research of 1D Sub-wavelength Grating Anti-reflection

将具有高透射性的亚波长光栅置于微机械波长可调谐垂直腔面发射激光器(VCSEL)的内腔当中可以提高波长的调谐范围,为了使波长调谐范围达到最优则必须优化高透射性的亚波长光栅使其透射率达到最大。利用严格耦合波法分析了亚波长光栅的占空比、周期、厚度和入射角对其透射率的影响并找出最优的光栅参数。通过计算分析可得,对于TE和TM偏振存在最佳的占空比使其透射率达到99.5%。在文中条件下,它们对应的占空比分别为0.23和0.80。而光栅厚度对于TE和TM偏振透射率的影响是周期性的,在一个周期内存在一个最佳值使其透射率达到最高。在文中条件下,TE偏振的厚度周期是150 nm,TM偏振的厚度周期是300 nm。当光栅参数不变时,无论是TE还是TM偏振光,它们的透射率只有在垂直入射光栅时(入射角为0°)才能达到最大。而通过等效介质原理可以得出,周期对透射率没有影响。最后计算了透射率在光栅厚度和占空比同时变化时的变化趋势,并从中得出最优的光栅参数。

High transmission sub-wavelength gratings placed in the micro-electro-mechanical system（ MEMS） wavelength tunable vertical cavity surface emitting laser（ VCSEL） inner cavity can improve the wavelength tuning range. In order to make the wavelength tuning range of the tunable VCSEL be largest,the transmittance of the anti-reflection sub-wavelength must be the maximum. By using rigorous coupled wave analysis（ RCWA）,the effects of the sub-wavelength parameters（ e. g.,duty cycle,period,thickness） and angle of incidence on the transmission were analyzed,and the optimum parameters and angle of incidence were gotten. Either TE or TM polarization has the optimum duty cycle to make its transmittance get 99. 5%. The duty cycles of TE and TM polarization are 0. 23 and 0. 8 under the conditions of this paper. The effect of the grating thickness on the transmittance is periodic variation. The period of TE and TM polarization are 150 nm and 300 nm,respectively. For fixed grating parameters,the transmittance can be maximum only when the incidence angle of the light source is 0°,no matter TE or TM polarization. From equivalent medium theory（ EMT）,it is found that the grating period has no influence on the grating transmittance. At last,the transmittance was calculated when the grating thickness and duty cycle changed together,and the optimum grating parameters were gotten.