Graded-index core polymer optical waveguide circuit fabricated using a microdispenser for high-density on-board optical interconnects

Abstract

We introduce a simple photo-mask-free fabrication method of multimode polymer optical waveguides (PPOWs): “the Mosquito method” that utilizes a micro-dispenser. In the Mosquito method, a viscous monomer for cores is directly dispensed from a thin needle into a cladding monomer that is coated on a substrate. Because of the monomer diffusion, graded-index (GI) circular core is formed. By adjusting several parameters to control the core shape and diameter, 15-cm long, 40-m core diameter, with 125-m pitch GI-circular core PPOWs (12 channels) are successfully fabricated by the Mosquito method. We experimentally demonstrate superior optical properties of the GI- circular core polymer waveguides: connection loss with GI multimode fibers, inter-channel crosstalk, etc. to SI-square core polymer waveguides composed of the same silicone polymer materials. Furthermore, we fabricate GI-core PPOW circuits in which perpendicularly curved waveguides are involved by applying the Mosquito method. The curved PPOWs with a 250-m pitch are obtained successfully and the curve-radius is varied from 3 mm to 20 mm by adjusting the scanning program of the needle. The insertion loss of the curved waveguides is measured for evaluating the bending losses. The waveguide with lager curve-radius shows lower insertion loss, namely low bending loss. Additionally, it is experimentally confirmed that the curved waveguides with higher numerical aperture (NA = 0.30) fabricated utilizing a different silicone resin for the cladding exhibit a bending loss as low as 0.5 dB even under 3-mm curve radius. The Mosquito-method would be a promising method for realizing highspeed and high-density on-board optical interconnects.