Physics Department News and Events

Global climate is influenced by the Arctic hydrologic cycle, which is, in part, regulated by sea ice through its control on evaporation and precipitation. However, the quantitative link between precipitation and sea ice extent is poorly constrained. This talk presents observational evidence for the response of precipitation to sea ice reduction and assesses the sensitivity of the response. Changes in the proportion of moisture sourced from the Arctic with sea ice change in the Canadian Arctic and Greenland Sea regions over the past two decades are inferred from annually averaged deuterium excess (d-excess) measurements from six sites. Other influences on the Arctic hydrologic cycle, such as the strength of meridional transport, are assessed using the North Atlantic Oscillation index. We find that the independent, direct effect of sea ice on the increase of the percentage of Arctic sourced moisture (or Arctic moisture proportion, AMP) is 18.2 ± 4.6% and 10.8 ± 3.6%/100,000 km2 sea ice lost for each region, respectively, corresponding to increases of 10.9 ± 2.8% and 2.7 ± 1.1%/1 °C of warming in the vapor source regions. The moisture source changes likely result in increases of precipitation and changes in energy balance, creating significant uncertainty for climate predictions.

Institut für Theoretische Physik, Universitat Bremen

Nonlinear-wave mixing in optical microresonators offers a promising avenue for compact optical-frequency microcomb generation [1]. These microcombs have rapidly found applications across diverse fields, including optical frequency synthesis and high-capacity data communication systems. A fundamental characteristic of microcombs is their spectral profile, which is principally determined by the resonator’s dispersion. An illustrative example is the sech2 spectrum of dissipative Kerr solitons that emerges under anomalous group-velocity dispersion.

Concurrently, photonic crystal ring resonators (PhCR) have emerged as a flexible way of tailoring of optical microcavities [2]. These ring resonators introduce a corrugation to the inner wall of the waveguide, enabling precise and independent control of cavity mode resonance frequencies while preserving a high quality factor (Q). This innovative approach offers mode-by-mode frequency splitting capabilities, vastly expanding the design space for managing the nonlinear dynamics of optical states, such as Kerr solitons.

This presentation explores the advantages of this enhanced control, initially focusing on the control and generation of microcombs in the normal dispersion regime. I also demonstrate the creation of a ‘meta-dispersion’ resonator by selectively manipulating the resonance of multiple modes with a PhCR. The nonlinear modeling of these structures unveils new comb states and instabilities.
Furthermore, by embedding the governing equation of the system into a genetic algorithm, we efficiently pinpoint a dispersion profile that yields a microcomb closely aligned with a user-defined target spectrum [3].