Measurement of very low-loss silica on silicon waveguides with a ring resonator

The loss in phosphorus-doped silica on silicon waveguides was accurately measured using a 6-cm-diam ring resonator, by recording the transmission of a narrow linewidth external-cavity laser through the resonator as a function of temperature. A finesse of 45 and resonance width of 24.2 MHz were obtained, indicating guide loss of 2.6 dB per meter, which is the best result thus far measured for these waveguides. The shift in the modes with temperature was measured in the temperature range 30–120 °C and found to be close to 1/8 Å/deg.