Proceedings Article | 15 April 2003
Proc. SPIE. 4941, Laser Micromachining for Optoelectronic Device Fabrication
KEYWORDS: Optical filters, Optical design, Waveguides, Polarization, Fiber Bragg gratings, Cladding, Hydrogen, Plasma enhanced chemical vapor deposition, Photonic integrated circuits, Multiplexers
Silica-on-Silicon is a well established technology for the fabrication of low insertion loss planar lightwave circuits. The Ge-doped waveguide core material, deposited with low temperature plasma enhanced chemical vapor deposition and not subjected to high temperature annealing, is highly UV light photosensitive, due to residual Ge/Si-OH groups in the material that, similarly to hydrogen loading, can contribute to the formation of those defect centers responsible for the photosensitivity. Gratings have been fabricated using a pulsed 193 nm ArF excimer laser and a phase mask. 25 mm long gratings, written on standard straight waveguides, show a record 47 dB extinction ratio and 0.2 nm rejection bandwidth for TE polarization, without hydrogen loading. Such narrow linewidth filters could find application in dense WDM systems. We designed and fabricated a compact Add/Drop multiplexer based on a high bandwidth, 2x2 multimode interference device, having a Bragg grating written in the multi-mode region. The characterization for the TE polarization prove the proposed Add/Drop principle, showing, in correspondence of the dropped channel, a 30dB dip at the transmitted output and a reflection peak at the drop output, this last having a larger bandwidth, and around 3dB excess loss respect to the transmitted channels.
