RESUMO
Electro-optical circuit boards should provide simple and cost-effective coupling techniques and crosstalk levels of less than -30 dB. A dicing saw was used to create waveguide grooves with a surface roughness of less than 183 nm in a 1.6-mm-thick polymethyl methacrylate polymer (PMMA) substrate. The buried optical waveguides were made from SU-8 in a PMMA substrate covered with a 1-mm PMMA sheet. The propagation loss for a 500 µm×570 µm straight waveguide was 0.9 dB/cm at 1310 nm. The coupling between parallel waveguides was measured at separation distances from 45 to 595 µm. The crosstalk was less than -40 dB for 65-mm-long waveguides. This fabrication method shows potential for dense optical interconnects with very low crosstalk.
RESUMO
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.
