Yang Jinye, Dong Yue, Xu Yin, Zhang Bo, Ni Yi
Appl Opt. 2020 Sep 1;59(25):7705-7711. doi: 10.1364/AO.397476.
A compact asymmetrical directional coupler (ADC), which is composed of a strip and a tilted subwavelength gratings (TSWG) waveguide, is proposed to realize a broadband and high-extinction-ratio polarization beam splitter (PBS). In addition to conventional SWG structural parameters, such as its period and duty cycle, a TSWG waveguide provides an extra degree of freedom to solely adjust the TE modal effective index for more accurate phase matching. Hence the TE polarization state is coupled more efficiently in the ADC system, and then the extinction ratio (ER) is consequently improved. The simulation of our proposed device demonstrated a higher coupling efficiency and an ultrahigh ER of 34.2 dB for the TM polarization state at the center wavelength around 1550 nm. The operating bandwidth of the TM polarization state defined as the spectral range, with ER higher than 20 dB, is determined to be as broad as 75 nm. And, with an assisted hybrid plasmonic waveguide at the end of the cross port, the achieved bandwidth of the TE polarization state is as broad as 133 nm. They are much broader than those of other DC/ADC implemented PBS devices. Moreover, further analysis shows that the tilting angle of the TSWG waveguide has much higher fabrication tolerance than changing SWG duty cycle.
本文提出了一种由条形波导和倾斜亚波长光栅（TSWG）波导组成的紧凑型非对称定向耦合器（ADC），用于实现宽带、高消光比的偏振光束分离器（PBS）。除了传统亚波长光栅（SWG）的结构参数，如周期和占空比外，TSWG波导还提供了一个额外的自由度，可单独调节TE模式的有效折射率，以实现更精确的相位匹配。因此，TE偏振态在ADC系统中耦合效率更高，从而提高了消光比（ER）。对我们所提出器件的仿真表明，在中心波长约为1550 nm时，对于TM偏振态，耦合效率更高，消光比高达34.2 dB。定义为ER高于20 dB的光谱范围的TM偏振态的工作带宽确定为宽达75 nm。并且，在交叉端口末端采用辅助混合等离子体波导，TE偏振态实现的带宽宽达133 nm。它们比其他采用DC/ADC的PBS器件的带宽要宽得多。此外，进一步分析表明，TSWG波导的倾斜角比改变SWG占空比具有更高的制造容差。
