For further advancement of next-generation high-performance computers, low-power consumption, high-density, and
low-cost optical interconnection technologies should be adopted, and thus, optical printed circuit boards (O-PCBs)
integrating polymer optical waveguides would be a key device. In particular, for low-power consumption, the link power
budget should be low enough. In the optical link that consists of two waveguides on PCBs and a graded-index (GI)
multimode fiber (MMF) connecting the two PCBs, such a low power budget is expected when GI-core waveguides are
utilized. Essentially low coupling loss between the GI-core waveguide and a GI-MMF is one of the reasons of the low
power budget, since the mode power profile mismatch between MMFs and GI-core waveguides is smaller than that
between MMFs and SI-core waveguides.
In this paper, we compose an optical link of vertical cavity surface emitting laser (VCSEL)-waveguide: SI or
GI-MMF-waveguide: SI or GI-PD, and quantitatively evaluate the coupling loss at each connection point. When all the
components are perfectly aligned, the total coupling loss is 1.9 dB in the link with GI-core waveguide. On the other
hand, the SI-core waveguide link shows 0.8 dB higher coupling loss (2.72dB) than the GI-core waveguide link. When a
misalignment of ±10 μm is added at each connection and 50-μm gaps are added at both VCSEL-waveguide and
waveguide-PD connections, the GI-waveguide link demonstrate approximately 2-dB advantage in the power budget over
the SI-waveguide link. Given limited power budget consideration for high bit rate optical links (~25 Gb/s), GI-core
waveguide enabling low link power budget would be a promising component for O-PCBs.