Abstract
High-Q microresonator is perceived as a promising platform for optical frequency comb generation, via dissipative soliton formation. In order to achieve a higher quality factor and obtain the necessary anomalous dispersion, multi-mode waveguides were previously implemented in Si3N4 microresonators. However, coupling between different transverse mode families in multi-mode waveguides results in periodic disruption of dispersion and quality factor, and consequently causes perturbation to dissipative soliton formation and amplitude modulation to the corresponding spectrum. Careful choice of pump wavelength to avoid the mode crossing region is thus critical in conventional Si3N4 microresonators. Here, we report a novel design of Si3N4 microresonator in which single-mode operation, high quality factor, and anomalous dispersion are attained simultaneously. The novel microresonator is consisted of uniform single-mode waveguides in the semi-circle region, to eliminate bending induced mode coupling, and adiabatically tapered waveguides in the straight region, to avoid excitation of higher order modes. The intrinsic quality factor of the microresonator reaches 1.36 × 106 while the group velocity dispersion remains to be anomalous at −50 fs2/mm. With this novel microresonator, we demonstrate that broadband phase-locked Kerr frequency combs with flat and smooth spectra can be generated by pumping at any resonances in the optical C-band.
Highlights
Microresonator type Single-mode waveguide with a uniform width of 1 μm Multi-mode waveguide with a uniform width of 2 μm Single-mode waveguide with varying widths from 1 to 2 μm loaded Q 0.6 M 1.1 M 1.0 M intrinsic Q 0.83 M 1.56 M 1.36 M mode crossing region and increase of cavity’s free spectral range (FSR) are necessary for dissipative soliton formation in conventional Si3N4 microresonators
We report a novel design of Si3N4 microresonator in which single-mode operation, high quality factor, and anomalous dispersion are attained simultaneously
The spectra spanning more than 20 THz are smooth without periodic amplitude modulations
Summary
Microresonator type Single-mode waveguide with a uniform width of 1 μm Multi-mode waveguide with a uniform width of 2 μm Single-mode waveguide with varying widths from 1 to 2 μm loaded Q 0.6 M 1.1 M 1.0 M intrinsic Q 0.83 M 1.56 M 1.36 M mode crossing region and increase of cavity’s free spectral range (FSR) are necessary for dissipative soliton formation in conventional Si3N4 microresonators. We report a novel design of Si3N4 microresonator in which single-mode operation, high quality factor, and anomalous dispersion are attained simultaneously. A high resolution coherent swept wavelength interferometer is implemented to determine the intrinsic quality factor and the group velocity dispersion (GVD, β2) of the microresonator.
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