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.