Figure 3

Characterization of the novel single-mode microresonator.

(a) Cold cavity transmission of the designed single-mode microresonator, measured with the high resolution coherent swept wavelength interferometer. Higher order modes are not observed in the microresonator, but the weak TE and TM coupling around 1558 nm results in a 10% reduction in the cavity loading (green lines and inset on the right). Inset on the left: resonance at 1556 nm is undercoupled with a loaded Q of 1,000,000. (b) Wavelength dependence of the free spectral range (FSR), measuring a non-equidistance of the modes, , of 196 ± 10 kHz. The extracted group velocity dispersion is anomalous at −50 ± 2.6 fs²/mm. The slight dispersion disruption around 1558 nm is negligible in the Kerr frequency comb formation, evidenced by the smooth spectral shapes shown in Fig. 4. (c) At a different temperature (ΔT = 7 °C) where the TE and the TM resonances become closer to degeneracy, stronger polarization coupling results in further reduction in the cavity loading. The input is TE polarized and the output is analyzed by either a TE or a TM polarizer, showing the hybridized modes are superposition of both polarization states.