光纤端面耦合周期极化铌酸锂(PPLN)薄膜波导器件的研究

Study on Fiber End-Face Coupled Periodically Poled Lithium Niobate (PPLN) Thin Film Waveguide Device

通过有限元模拟器从理论上分析了在理想光学系统中实现光纤与周期性极化铌酸锂(PPLN)波导之间高效耦合的可行性。仿真模拟了单模保偏光纤和透镜光纤在空间中的发散情况。针对截面尺寸为10μm×10μm、长度为20 mm的PPLN脊形波导,进行了与两种不同光纤的直接端面耦合模拟分析。分析发现,尽管透镜光纤的耦合效率高达95%,但其基模占比却不足5%。鉴于PPLN倍频器件主要依赖于激光的基模进行工作,这使透镜光纤的耦合效率在实际应用中显得相对较低。相比之下,单模保偏光纤的基模占比高达93.8%,显示出更为优越的性能。因此,本文选择了单模保偏光纤与PPLN脊形波导进行封装测试。实验结果表明:当温度为24.8℃,从光纤放大器输出的泵浦功率最大为1.6 W时,计算扣除输入端光纤与波导的耦合损耗后的输入泵浦功率为1.2 W,光纤到波导的耦合效率为75%,略高于当前已知的最高效率72%。1 560 nm基频光的输入功率为1.2 W时,最大输出653 mW的倍频光,光光转换效率达到了54.4%,归一化转换效率为20.2%/(W·cm^(2))。

The feasibility of achieving efficient coupling between an optical fiber and a periodically poled lithium niobate(PPLN) waveguide in an ideal optical system was theoretically analyzed using a finite element simulator.Divergence of single-mode polarization-maintaining fiber and lensed fiber in space was simulated.Direct end-face coupling simulations were conducted for a PPLN ridge waveguide with a cross-sectional size of 10 μm×10 μm and a length of 20 mm,involving two different types of fibers.It is found that despite the lensed fiber achieving a coupling efficiency of up to 95%,its fundamental mode contribution is less than 5%.Given that PPLN frequency-doubling devices primarily rely on the laser's fundamental mode for operation,this renders the coupling efficiency of the lensed fiber relatively low in practical applications.In contrast,ordinary single-mode fiber exhibits a significantly higher fundamental mode contribution of 93.8%,demonstrating its superior performance.Therefore,this study selects ordinary single-mode fiber for encapsulation testing with PPLN ridge waveguides.The experimental results show that when the maximum pump power output from the fiber amplifier reaches 1.6 W,the calculated input pump power,after deducting the coupling losses between the input fiber and the waveguide,stands at 1.2 W.The fiber-to-waveguide coupling efficiency is 75%,slightly exceeding the currently known advanced value of 72%.At a temperature of 24.8 ℃,with an input power of 1.2 W at the fundamental wavelength of 1 560 nm,the maximum output of frequency-doubled light is 653 mW.The optical-to-optical conversion efficiency reaches 54.4%,with a normalized conversion efficiency of 20.2%/(W·cm^(2)).