Optical path length trimming technique using thinfilm heaters for silica-based waveguides on Si

The authors propose a practical optical path length trimming technique and demonstrate this using thin film heaters for silica based planar lightwave circuits (PLCs). Irreversible refractive index changes up to 1.5 × 10-4 can be obtained to trim the PLC response by simply controlling the heating power and time. This technique is applied successfully to thermo-optic switches to maximise their extinction ratios.