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Integrated Raman microlasers, particularly discrete multi‐color lasers which are crucial for extending the emission wavelength range of chip‐scale laser sources to much shorter wavelengths, are highly in demand for various spectroscopy, microscopy analysis, and biological detection applications. However, integrated multi‐color Raman microlasers have yet to be demonstrated because of the requirement of high‐Q microresonators possessing large χ(2) nonlinearity, strong Raman phonon branches, and the challenge in the cavity‐enhanced multi‐photon hyper‐Raman scattering parametric process. In this work, integrated multi‐color Raman lasers have been demonstrated for the first time at weak pump levels, via the excitation of high‐Q (> 6 × 106) phase‐matched modes in single thin‐film lithium niobate (TFLN) microresonators by dispersion engineering. Raman lasing is observed at 1712 nm for a 1547‐nm pump threshold power of only 620 µW, representing the state of the art in the TFLN platform. Furthermore, multi‐color Raman lasers are realized at discrete wavelengths of 1712, 813, 533, and 406 nm with pump levels as low as 1.60 mW, which is more than two orders of magnitude lower than the current records (i.e., 200 mW) in bulk resonators, allowed by the fulfillment of the requisite conditions consisting of broadband natural phase match, multiple‐resonance, and high‐Q factors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Monolithically integrated single-frequency microlasers were demonstrated with high output powers in single un-suspended microdisks coupled with bus-waveguides on active lithium niobate (LN) platform. • Owing to the long cavity lengths (1 mm) for high optical gain and mode regulation for suppressing multimode lasing, a microdisk laser with a linewidth of 0.11 MHz and a maximum output power of 62.1 μW has been achieved at room temperature, which are one order of magnitude narrower and higher than the best results previously reported on monolithically integrated LN microlasers, respectively. Integrated on-chip microdisk lasers have attracted great attention as a light source of compact size, low lasing threshold and narrow bandwidth. However, challenges remain unresolved in terms of single mode operation at high output power while maintaining the ultra-narrow bandwidth. In this work, we demonstrate monolithically integrated on-chip single-frequency disk lasers coupled with bus-waveguides fabricated by photolithography assisted chemo-mechanical etching. Owing to the long cavity lengths (e.g., 409 μm and 1 mm) for high optical gain and high-Q mode regulation for suppressing multimode lasing, a disk laser with a narrow linewidth of 0.11 MHz and a maximum output power of 62.1 μW has been achieved at room temperature. These two values are about one order of magnitude better than the best results previously reported on monolithically integrated LN microlasers. [ABSTRACT FROM AUTHOR]