An approach to UV written integrated optical waveguides using novel acrylate based polymers
Optical polymer waveguides using copolymer, poly(methylmethacrylate/2- methacryloylethylmethacrylate), P(MMA/MAOEMA) were fabricated using a UV direct writing technique and were characterised for integrated optical applications. Copolymers of methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) were prepared and methacryloylated to give thermal crosslinking functionality as well as photocrosslinking for UV writing. The polymer structures, thermal properties and crosslinking properties involving double bond disappearance were confirmed using spectroscopy. In order to reduce scattering loss it has been necessary to develop uniform film fabrication processes and develop ways of polishing samples. The photosensitivity of polymer materials were measured prior to UV writing to establish optimal energy fluence conditions. Refractive index changes of 4 x 10-3 were achieved by UV lamp bulk exposure which is sufficient for waveguide definition. The optimal energy fluence was also investigated by considering waveguide profile. The intrinsic loss of P(MMA/MAOEMA) is estimated theoretically and compared to the actual waveguide propagation losses that were measured to be -1 dB/cm at 633 nm, 1054 nm and 1310 nm by the cut-back method. The loss at 800 nm was relatively lower than at 1310 nm and 1550 nm by taking white light absorption spectra. Thermally crosslinked polymer waveguide gave NA<0.05 which leads to single mode operation at 633 nm. Photosensitivity enhanced prebaked polymer waveguide using improved fabrication method gave NA ~0.10 which lead to multi-mode operation at 633 nm but single mode operation at 1310 nm. These polymers show no polarisation dependent loss within the experimental error. Y-splitters with bend radius of 200 mm give ~50% splitting ratios with branch loss less than 0.3 dB/cm.