3 / 2018-08-17 16:24:27

Application of graded-index multimode polymer optical waveguide to a coupling device between multimode fiber and VCSEL chip

restricted mode launch,optical coupling device,graded-index polymer waveguide

These days, wide deployment of cloud computing services leads the growth of IP traffic in the large scale data centers. In order to realize high-speed transmission at low cost, optical fiber links have already been installed in many datacenters, which are mainly composed of graded-index multimode fibers (GI-MMFs: OM3/OM4) and surface emitting lasers (VCSELs). For higher throughputs, the network topology is shifted from tree-type to fabric-type. While this shift realizes larger scale network, longer-reach connection (up to 1 – 2 km) is required. However, due to modal dispersion, current MMF links can support just a few hundred meter long over 25 Gbps. To reduce the modal dispersion, restricted mode launch (RML) approaches have been focused on, by which mode power distribution in a GI-MMF is controlled. We already found that the spot size (S.S.) and the numerical aperture (NA) of the MMF launch beam should be small. Both of them could not be satisfied with a simple lens system. Thus in this paper, we propose the RML exciter using GI polymer tapered waveguides. The waveguides are experimentally fabricated applying an imprint method, by which the refractive index profile is easily controlled. At first, the profile of the fabricated GI straight (not tapered) waveguides are measured. Then using the measured profile, beam propagation simulation (BPM) is performed. It is revealed that a tapered waveguide with an appropriate shape can minimize the S.S. and NA at the same time. Finally, GI tapered waveguide is actually fabricated and the S.S. and NA are evaluated.