Kohmu Naohiro, Ishii Maho, Hatai Ryosuke, Ishigure Takaaki
Opt Express. 2022 Jan 31;30(3):4351-4364. doi: 10.1364/OE.446899.
In this paper, we present a low-loss optical assembly utilizing a 90°-bent graded-index (GI) core polymer optical waveguide on vertical cavity surface emitting laser (VCSEL) based optical transceivers. The proposed assembly can replace conventional components such as mirrors and lenses for realizing subminiature optical engines applicable to on-board integration. To minimize the total insertion loss of the waveguide when connected to a high-speed VCSEL and a GI-core multimode fiber (MMF) at each end, the characteristics of the beam emitted from VCSELs are measured and taken into consideration for the waveguide design. In order to confirm the effect of insertion loss reduction by the waveguide numerical aperture control, 90°-bent GI-core polymer waveguides are fabricated applying the Mosquito method. The fabricated waveguide exhibits a total insertion loss as low as about 2 dB at 850-nm wavelength, which includes the coupling losses at both ends, bending, and propagation losses. We also investigate a way to reduce the insertion loss when a gap exists between the waveguide and VCSEL chip. We theoretically and experimentally confirm that filling the gap with a high index resin can reduce the coupling loss by 5 dB.
在本文中，我们展示了一种低损耗光学组件，该组件在基于垂直腔面发射激光器（VCSEL）的光收发器中采用了一个90°弯曲的渐变折射率（GI）芯聚合物光波导。所提出的组件可以替代诸如镜子和透镜等传统组件，以实现适用于板载集成的超小型光学引擎。为了在波导两端分别连接高速VCSEL和GI芯多模光纤（MMF）时将波导的总插入损耗降至最低，对从VCSEL发射的光束特性进行了测量，并在波导设计中予以考虑。为了通过波导数值孔径控制来确认降低插入损耗的效果，采用Mosquito方法制作了90°弯曲的GI芯聚合物光波导。所制作的波导在850 nm波长处呈现出低至约2 dB的总插入损耗，其中包括两端的耦合损耗、弯曲损耗和传播损耗。我们还研究了在波导与VCSEL芯片之间存在间隙时降低插入损耗的方法。我们从理论和实验上证实，用高折射率树脂填充该间隙可将耦合损耗降低5 dB。
