Versatile SOG/SU-8/fluorinated SU-8 rib optical waveguides as microsystems: single-mode TE 00 -TM 00 straight waveguides, S-Bends, Y-Junctions, Mach-Zehnder interferometers

Abstract

The authors present a successful design, realisation and characterisation of single-mode TE₀₀-TM₀₀ rib optical waveguides composed of SU-8/SOG polymers subjected (or not) to an apt fluorine-plasma treatment. Such techniques based on radiofrequency fluorine plasma treatment (CF₄) proved to strongly modify the properties regarding optical losses due to propagation (selectivity on the polarisation modes, and so on). After realisation of sundry single mode optical waveguides (straight, S-bends, Y-junctions, Mach-Zehnder (MZ) interferometers), the linear absorption coefficient of energy α^TE-TM of such rib waveguides have been measured for both optical modes TE₀₀ and TM₀₀ on Si/SiO₂/SU-8 structures that yield optical losses of 1.36 dB/cm and 2.01 dB/cm respectively. Optical losses ascribed to Si/SiO₂/SOG/SU-8 microstructures have been evaluated to 2.33 dB/cm and 2.95 dB/cm for both polarisations. Concerning the fluorine plasma treatment on SU-8 polymer waveguides, the optical losses regarding Si/SiO₂/Fluorinated SU-8 microstructures have been evaluated to 1.25 dB/cm for TE₀₀ polarisation, having then been reduced by 0.11 dB/cm, compared to propagation in pure SU-8. Moreover, such a specific plasma treatment leads to a substantial selectivity on optical polarisation states regarding the TM₀₀ optical mode which has been advantageously used. Thereby, integrated optical polarizers have been achieved on fluorinated SU-8. Hence, as a crucial step for designing polymer components devoted to microsensors applications, the SU-8 (fluorinated or not) polymer appears as a promising candidate for integrated optics with low optical losses.