Versatile SOG/SU-8/fluorinated SU-8 rib optical waveguides as microsystems: single-mode TE00-TM00 straight waveguides, S-bends, Y-junctions, Mach-Zehnder interferometers
Résumé
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 αTE-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.