Surface grating couplers are diffractive periodic structures that enable efficient coupling of light between optical fibers and planar waveguides. Conventional grating couplers have polarization specific and limited wavelength operation, because of the intrinsic radiation angle dependency on both wavelength and polarization. In this Letter, we propose, to the best of our knowledge, the first polarization-independent surface fiber-chip grating coupler, behaving as a wavelength splitter for the O and C communication bands. Polarization insensitivity is achieved by subwavelength segmentation of the silicon gratings, together with a novel design to allow the dual wavelengths to propagate along two opposite directions in the chip. For the TE and TM polarizations, coupling efficiencies around −4.5 dB are achieved at both 1310 nm and 1550 nm, with an average 1-dB bandwidth of ~45 nm and ~60 nm, respectively. This grating coupler concept can be used as a part of transceivers to increase the data rate of wavelength-division-multiplexing (WDM) systems for fiber-to-the-home (FTTH) network services.

中文翻译：

---

用于波长解复用的双波段偏振无关子波长光栅耦合器

表面光栅耦合器是衍射周期结构，可在光纤和平面波导之间实现光的有效耦合。由于固有的辐射角依赖于波长和偏振，传统的光栅耦合器具有偏振特定和有限的波长操作。在这封信中，据我们所知，我们提出了第一个与偏振无关的表面光纤芯片光栅耦合器，用作 O 和 C 通信波段的分光器。通过硅光栅的亚波长分段，以及允许双波长在芯片中沿两个相反方向传播的新颖设计，实现了偏振不敏感性。对于 TE 和 TM 极化，在 1310 nm 和 1550 nm 处都实现了 -4.5 dB 左右的耦合效率，平均 1-dB 带宽分别为 ~45 nm 和 ~60 nm。这种光栅耦合器概念可用作收发器的一部分，以提高光纤到户 (FTTH) 网络服务的波分复用 (WDM) 系统的数据速率。