Densely-aligned graded-index multiple-core polymer optical waveguide: Fabrication and inter-channel crosstalk property

We present two methods for fabricating densely-aligned graded-index (GI) multiple-core polymer optical waveguides utilizing soft-lithography and dispensers. For on-board optical interconnects with polymer waveguides, much higher data rate and channel density have been required in the past few years. However, because of the high scattering loss of polymer waveguides, their inter-channel crosstalk is of great concern, when narrower pitch is required. Meanwhile, we have demonstrated low propagation loss and low inter-channel crosstalk of polymer optical waveguides with GI cores due to the optical confinement effect of the GI-core. Hence, the channel density could be increased for GI multiple-core waveguides. In this paper, we successfully fabricate a polymer waveguide with GI cores directly on a substrate utilizing the soft-lithography method or a dispenser. We experimentally confirm that near parabolic refractive index profiles are formed in the parallel cores with 50 μm × 30 μm size at 125-μm pitch in a length of 20 cm. We also use a copolymer for forming the GI profile, and then, confirm the high-temperature stability of the parabolic index profile compared to the one formed with a doped polymer. Finally, we discuss the crosstalk properties of the fabricated waveguides.