Hu Changran, Pan An, Li Tingan, Wang Xuanhao, Liu Yuheng, Tao Shiqi, Zeng Cheng, Xia Jinsong
Opt Express. 2021 Feb 15;29(4):5397-5406. doi: 10.1364/OE.416492.
Lithium niobate (LN) devices have been widely used in optical communication and nonlinear optics due to its attractive optical properties. The emergence of the thin-film lithium niobate on insulator (LNOI) improves performances of LN-based devices greatly. However, a high-efficient fiber-chip optical coupler is still necessary for the LNOI-based devices for practical applications. In this paper, we demonstrate a highly efficient and polarization-independent edge coupler based on LNOI. The coupler, fabricated by a standard semiconductor process, shows a low fiber-chip coupling loss of 0.54 dB/0.59 dB per facet at 1550 nm for TE/TM light, respectively, when coupled with an ultra-high numerical aperture fiber (UHNAF) of which the mode field diameter is about 3.2 μm. The coupling loss is lower than 1dB/facet for both TE and TM light in the wavelength range of 1527 nm to 1630 nm. A relatively large tolerance for optical misalignment is also proved, due to the coupler's large mode spot size up to 3.2 μm. The coupler shows a promising stability in high optical power and temperature variation.
铌酸锂（LN）器件因其具有吸引人的光学特性而在光通信和非线性光学中得到广泛应用。绝缘体上的薄膜铌酸锂（LNOI）的出现极大地提高了基于LN的器件的性能。然而，对于基于LNOI的器件在实际应用中，高效的光纤 - 芯片光耦合器仍然是必要的。在本文中，我们展示了一种基于LNOI的高效且偏振无关的边缘耦合器。该耦合器通过标准半导体工艺制造，当与模式场直径约为3.2μm的超高数值孔径光纤（UHNAF）耦合时，在1550nm处，对于TE/TM光，每个面的光纤 - 芯片耦合损耗分别低至0.54dB/0.59dB。在1527nm至1630nm的波长范围内，TE和TM光的耦合损耗均低于1dB/面。由于耦合器的模式光斑尺寸高达3.2μm，还证明了其对光学对准具有相对较大的容差。该耦合器在高光功率和温度变化方面显示出有前景的稳定性。
