To meet the increasing demand for board level high speed data transmission in the area of high performance computing, much attention has been paid to employ high performance polymer optical waveguide. So far, optical interconnects have been considered to have advantages over electronic solutions in various aspects, such as lower power consumption, larger information carrying capacity and immunity to crosstalk. It is one of the advantages that waveguides are possible to be curved and crossed light paths in the same circuit plane. GI-core polymer waveguides are capable of confining the signal light around the core center more tightly, by which the GI-core waveguides exhibit low propagation loss, low crosstalk, and low modal dispersion. Therefore, GI-core reduces the loss in meshed waveguide compared to SI-core meshed waveguides. The material of our GI-core polymer waveguide is Polynorbornene. The varnish for both core and cladding is prepared and coated onto a substrate then the coated layers are exposed to a UV light through a photomask and heated at a certain temperature. After heating, index profile changes and GI-core waveguide is formed. This is our original photo-addressing method. We confirm that extremely low crossings loss is observed in both 90-degree (0.53 dB/500 crosses) and 45-degree (1.55 dB/500 crosses). Also, we succeed high-speed data transmission. We expect that this ultra low crossing loss GI-core waveguide will be one of the promising components giving a strong impact on high performance computing systems in near future.
We successfully fabricate multi-channel GI circular-core polymer waveguides with precisely controlled pitches utilizing the Mosquito method. The Mosquito method is a very simple method for fabricating GI-core polymer optical waveguides that utilizes a micro dispenser. In this method, a viscous core monomer is directly dispensed into a cladding monomer layer before UV cured, and circular cores are formed by curing both the core and cladding under a UV exposure. Here, it is a concern that a needle position accuracy influences on the interchannel pitch when parallel cores are fabricated by parallel repetitive scan of a single needle. However, we succeeded in controlling the pitch with the Mosquito method and then, GI-core waveguides with 250.7±5.2 μm, 126.7±2.6 μm and 61.7±3.4 μm are successfully fabricated for the pre-set values of 250 μm, 125 μm and 62.5 μm, respectively. Then, we demonstrate a 4 × 10 Gbps transmission over the fabricated GI-core waveguide by connecting the waveguide to an MMF ribbon with a 250-μm pitch, which is realized because the pitch of the fabricated waveguide is accurately controlled to 250 μm.