Abstract
We propose and demonstrate a dispersion control technique by combination of different waveguide cross sections in an aluminum nitride micro-ring resonator. Narrow and wide waveguides with normal and anomalous dispersion, respectively, are linked with tapering waveguides and enclosed in a ring resonator to produce a total dispersion near zero. The mode-coupling in multimoded waveguides is also effectively suppressed. This technique provides new degrees of freedom and enhanced flexibility in engineering the dispersion of microcomb resonators.
Highlights
Optical frequency combs [1,2] are of considerable interests for applications including optical clocks, frequency metrology and molecular spectroscopy [3,4,5]
The large enhancement of circulating optical power in these high Q resonators has led to dramatic reduction of threshold of comb generation
We propose that the dispersion can be compensated by combining two waveguides of different cross sections with opposite signs of dispersion within a single ring resonator
Summary
Optical frequency combs [1,2] are of considerable interests for applications including optical clocks, frequency metrology and molecular spectroscopy [3,4,5]. Other methods have been studied, for example, by changing the sidewall angle of silica toroids [14], oxidation of silicon micro-disks [15], atomic layer deposition on SiN [16], microstructuring of MgF2 resonators [17], etc These dispersion engineering techniques, only uniformly adjust the waveguide cross section of the whole resonator that does not have many degree of freedoms for complete dispersion engineering. We propose that the dispersion can be compensated by combining two waveguides of different cross sections with opposite signs of dispersion within a single ring resonator This method can eliminate the mode crossing in multimode waveguide, which is inevitable for anomalous dispersion within the current design. We apply this design concept to AlN micro-resonators and experimentally realized a near-zero dispersion without mode crossing
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