Experimental assessment of SU-8 optical waveguides buried in plastic substrate for optical interconnections

Multimode polymer waveguides have been developed to create low-cost, high-speed on-board optical interconnects. Buried optical waveguides made from SU-8 in a polymethyl methacrylate polymer (PMMA) substrate covered with a thin PMMA sheet are a low-cost option for electro-optical interconnects. The propagation losses for a 600  μm×600  μm straight waveguide were 1.96, 1.32, and 1.39  dB/cm, respectively, at three different wavelengths (850, 1310, and 1550 nm). The bending loss for a 15 mm bending radius is as high as 6  dB/cm. Transition and radiation losses dominate overall loss when the bending radius is less than 30 mm. The waveguide was excited using a multimode 850 nm VCSEL transmitter and detected using butt-coupled and lens-coupled receivers. The coupling loss was about 1 dB for the butt-coupling technique and 2 dB for lens coupling. The response bandwidth and the group delay of direct modulated (IF) signal were independent of the channel waveguide for communication speeds up to more than 3 GHz. This technique is viable for low-cost, short-length buried optical waveguides.