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为了实现在一种稳定的材料上制作简单的光栅耦合器,提出了在钛扩散铌酸锂波导上制作光折变长周期光栅耦合器的方案。利用有效折射率法和耦合模理论,确定了耦合器的结构参数,包括光栅周期为74.28μm,两波导的分开距离为8μm以及100%耦合情况下光栅的最小长度为2.42 cm。分析了传输光谱,得到3 d B带宽为5.20 nm。模拟结果表明,当光栅长度和偏移距离的容差分别为0.37 cm和0.21 cm时,耦合效率可以达到90%以上。该耦合器有望应用于粗波分复用系统。
In order to fabricate a simple grating coupler on a stable material, a scheme of fabricating a photorefractive long-period grating coupler on a titanium-diffused lithium niobate waveguide has been proposed. The structure parameters of the coupler were determined by effective refractive index method and coupled mode theory. The grating period was 74.28μm, the separation distance of two waveguides was 8μm, and the minimum length of the grating was 2.42 cm with 100% coupling. The transmission spectrum was analyzed and the 3 d B bandwidth was found to be 5.20 nm. Simulation results show that the coupling efficiency can reach more than 90% when the tolerance of grating length and offset distance are 0.37 cm and 0.21 cm, respectively. The coupler is expected to be applied to the CWDM system.