Octave-spanning Kerr soliton frequency combs in dispersion-and dissipation-engineered lithium niobate microresonators

Dissipative Kerr solitons from optical microresonators,commonly referred to as soliton microcombs,have been developed for a broad range of applications,including precision measurement,optical frequency synthesis,and ultrastable microwave and millimeter wave generation,all on a chip.An important goal for microcombs is self-referencing,which requires octave-spanning bandwidths to detect and stabilize the comb carrier envelope offset frequency.Further,detection and locking of the comb spacings are often achieved using frequency division by electro-optic modulation.The thin-film lithium niobate photonic platform,with its low loss,strong second-and third-order nonlinearities,as well as large Pockels effect,is ideally suited for these tasks.However,octave-spanning soliton microcombs are challenging to demonstrate on this platform,largely complicated by strong Raman effects hindering reliable fabrication of soliton devices.Here,we demonstrate entirely connected and octave-spanning soliton microcombs on thin-film lithium niobate.With appropriate control over microresonator free spectral range and dissipation spectrum,we show that soliton-inhibiting Raman effects are suppressed,and soliton devices are fabricated with near-unity yield.Our work offers an unambiguous method for soliton generation on strongly Raman-active materials.Further,it anticipates monolithically integrated,self-referenced frequency standards in conjunction with established technologies,such as periodically poled waveguides and electro-optic modulators,on thin-film lithium niobate.

Observation evidence for the entropy switch model of substorm onset

The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms(THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.

Twenty-nine million intrinsic Q-factor monolithic microresonators on thin-film lithium niobate

The recent emergence of thin-film lithium niobate(TFLN)has extended the landscape of integrated photonics.This has been enabled by the commercialization of TFLN wafers and advanced nanofabrication of TFLN such as high-quality dry etching.However,fabrication imperfections still limit the propagation loss to a few dB/m,restricting the impact of this platform.Here,we demonstrate TFLN microresonators with a record-high intrinsic quality(Q)factor of twenty-nine million,corresponding to an ultra-low propagation loss of 1.3 dB/m.We present spectral analysis and the statistical distribution of Q factors across different resonator geometries.Our work pushes the fabrication limits of TFLN photonics to achieve a Q factor within 1 order of magnitude of the material limit.