Generation of Kerr soliton microcomb in a normally dispersed lithium niobate microdisk resonator by mode trimming

Anomalous microresonator dispersion is mandatory for Kerr soliton microcomb formation, which depends critically on the geometry of the microresonator and can hardly be tuned after the structure is made. To date, cavity-based microcombs have only been generated with fundamental whispering gallery modes (WGMs) of anomalous dispersion in microresonators. Moreover, microcomb generation in highly Raman-active platforms such as lithium niobate (LN) microresonators frequently suffers from stimulated Raman scattering and mode crossing due to the existence of multiple families of high-order WGMs. Here, we reveal a unique Kerr soliton microcomb generation mechanism through mode trimming in a weakly perturbed LN microdisk resonator. Remarkably, the soliton comb is generated with fundamental WGMs of normal dispersion and free from the mode crossing and Raman scattering effects. A robust soliton with a spectrum spanning from 1450 nm to 1620 nm at an on-chip pump power of 35 mW. Our discovery offers a powerful solution to circumvent the stringent requirements on high-precision dispersion engineering and termination of Raman excitation for soliton generation in the high-Q microdisk.Comment: 16 pages,and 5 figure

Electro-optically tunable low phase-noise microwave synthesizer in an active lithium niobate microdisk

Photonic-based low-phase-noise microwave generation with real-time frequency tuning is crucial for a broad spectrum of subjects, including next-generation wireless communications, radar, metrology, and modern instrumentation. Here, for the first time to the best of our knowledge, narrow-bandwidth dual-wavelength microlasers are generated from nearly degenerate polygon modes in a high-Q active lithium niobate microdisk. The high-Q polygon modes formation with independently controllable resonant wavelengths and free spectral ranges is enabled by the weak perturbation of the whispering gallery microdisk resonators using a tapered fiber. The stable beating signal confirms the low phase-noise achieved in the tunable laser. Owing to the high spatial overlap factors between the two nearly degenerate lasing modes as well as that between the two lasing modes and the pump mode, gain competition between the two modes is suppressed, leading to stable dual-wavelength laser generation and in turn the low noise microwave source. The measured microwave signal shows a linewidth of ~6.87 kHz, a phase noise of ~-123 dBc/Hz, and an electro-optic tuning efficiency of -1.66 MHz/V.Comment: 13 pages, 5 figure

Erbium-ytterbium co-doped lithium niobate single-mode microdisk laser with an ultralow threshold of 1 uW

We demonstrate single-mode microdisk lasers in the telecom band with ultra-low thresholds on erbium-ytterbium co-doped thin-film lithium niobate (TFLN). The active microdisk were fabricated with high-Q factors by photo-lithography assisted chemo-mechanical etching. Thanks to the erbium-ytterbium co-doping providing high optical gain, the ultra-low loss nanostructuring, and the excitation of high-Q coherent polygon modes which suppresses multi-mode lasing and allows high spatial mode overlap factor between pump and lasing modes, single-mode laser emission operating at 1530 nm wavelength was observed with an ultra-low threshold, under 980-nm-band optical pump. The threshold was measured as low as 1 uW, which is one order of magnitude smaller than the best results previously reported in single-mode active TFLN microlasers. And the conversion efficiency reaches 0.406%, which is also the highest value reported in single-mode active TFLN microlasers.Comment: 5 pages,3 figure

How Does Sustainable Rural Tourism Cause Rural Community Development?

Rural tourism has been developing vigorously, and rural community functions are becoming diversified in China. Therefore, this paper takes China as an example to explore how sustainable rural tourism affects rural community development in the long and short run over the period 1994–2020. Sustainable rural tourism can be measured using two indicators: total rural tourism revenue and number of rural tourists. Rural community development is measured by the number of rural community service institutions. Then, by incorporating other variables and using the autoregressive distributed lag bounds co-integration technique to perform an empirical analysis, we found that, whether in the long or short run, sustainable rural tourism always plays a positive and significant role in promoting rural community development. In particular, in the long run, rural infrastructure construction, rural ecological environment, agricultural fiscal expenditure, agricultural technological progress, and rural human capital are identified as the major forces behind rural community development. Meanwhile, in the short run, rural infrastructure construction, rural ecological environment, agricultural fiscal expenditure, agricultural technological progress, and rural human capital are also major drivers of rural community development. This paper contributes to the current literature by filling in the existing gaps in several aspects

Low-Threshold Anti-Stokes Raman Microlaser on Thin-Film Lithium Niobate Chip

Raman microlasers form on-chip versatile light sources by optical pumping, enabling numerical applications ranging from telecommunications to biological detection. Stimulated Raman scattering (SRS) lasing has been demonstrated in optical microresonators, leveraging high Q factors and small mode volume to generate downconverted photons based on the interaction of light with the Stokes vibrational mode. Unlike redshifted SRS, stimulated anti-Stokes Raman scattering (SARS) further involves the interplay between the pump photon and the SRS photon to generate an upconverted photon, depending on a highly efficient SRS signal as an essential prerequisite. Therefore, achieving SARS in microresonators is challenging due to the low lasing efficiencies of integrated Raman lasers caused by intrinsically low Raman gain. In this work, high-Q whispering gallery microresonators were fabricated by femtosecond laser photolithography assisted chemo-mechanical etching on thin-film lithium niobate (TFLN), which is a strong Raman-gain photonic platform. The high Q factor reached 4.42 × 106, which dramatically increased the circulating light intensity within a small volume. And a strong Stokes vibrational frequency of 264 cm−1 of lithium niobate was selectively excited, leading to a highly efficient SRS lasing signal with a conversion efficiency of 40.6%. And the threshold for SRS was only 0.33 mW, which is about half the best record previously reported on a TFLN platform. The combination of high Q factors, a small cavity size of 120 μm, and the excitation of a strong Raman mode allowed the formation of SARS lasing with only a 0.46 mW pump threshold