We report the observation of stimulated Brillouin scattering and lasing at 1550 nm in barium fluoride (BaF 2 ) crystal. Brillouin lasing was achieved with ultra-high quality (Q) factor monolithic whispering gallery mode (WGM) mm-size disk resonators. Overmoded resonators were specifically used to provide cavity resonances for both the pump and all Brillouin Stokes waves. Single and multiple Brillouin Stokes radiations with frequency shift ranging from 8.2 GHz up to 49 GHz have been generated through cascaded Brillouin lasing. BaF 2 resonator-based Brillouin lasing can find potential applications for high-coherence lasers and microwave photonics.Stimulated Brillouin scattering (SBS) is a nonlinear optical process resulting from the coherent interaction of light and acoustic waves. It is usually related to the effect of electrostriction and gives rise to inelastic light backscattering with a Doppler downshift related to the acoustic phonon frequency. Over the past years, SBS has been extensively studied in numerous optical waveguides such as optical fibers 1-3 , photonics crystal fibers 4,5 , and on-chip photonic integrated circuits [6][7][8] . A variety of nonlinear materials including silica, chalcogenide or silicon have been investigated. Enhanced SBS has been recently predicted and demonstrated in nanoscale silicon photonic waveguides 9,10 , where the radiation pressure combines with electrostriction to greatly improve the Brillouin gain, thus bridging the gap between SBS and optomechanics. Enhanced and cascaded SBS can also be easily achieved in nonlinear optical cavities, leading to narrow-linewidth and efficient SBS lasing 11,12 . Among optical resonators, whispering gallery mode (WGM) resonators have a number of qualities that make them very attractive for investigating SBS. Their advantages include a strong light confinement due to small mode volumes and ultra-high Q factors 13 . Moreover, crystalline WGM resonators are very interesting because of their broad transparency window ranging from the ultraviolet to the mid-infrared region [14][15][16] . These photonic platforms thus appear as alternative and promising solutions for nonlinear applications, and thus opens an approach to harness and enhance the interaction between photons and acoustic phonons. For instance, Brillouin lasing with microwatt threshold power has recently been observed in ultra-high Q-factor CaF 2 WGM resonators 17 . A narrow-linewidth Brillouin microcavity laser and an ultra-low-phase-noise microwave synthetizer have also been demonstrated using chemically etched ultrahigh-Q silica-on-silicon wedge resonators 18,19 . Brillouin scattering from surface acoustic waves has also been reported in MgF 2 WGM resonators and in silica microspheres [20][21][22] .
We demonstrate a monolithic optical whispering gallery mode resonator fabricated with barium fluoride (BaF 2 ) with an ultra-high quality (Q) factor above 10 9 at 1550 nm, and measured with both the linewidth and cavity-ring-down methods. Vertical scanning optical profilometry shows that the root mean square surface roughness of 2 nm is achieved for our mm-size disk. To the best of our knowledge, we show for the first time that one billion Q-factor is achievable by precision polishing in relatively soft crystals with mohs hardness of 3. We show that complex thermo-optical dynamics can take place in these resonators. Beside usual applications in nonlinear optics and microwave photonics, high energy particle scintillation detection utilizing monolithic BaF 2 resonators potentially becomes feasible. c 2018 Optical Society of America OCIS codes: 140.4780; 350.3950; 140.6810; 260.1180; 290.5930 Monolithic whispering gallery mode (WGM) resonators are idoneous platforms to study various properties of optical materials. These resonators have attracted large interest, as they can feature ultra-high Q factors and small mode volumes [1]. Light in such resonators is trapped by a process of successive total internal reflections at the inner side of the disk circumference. Therefore, they do not require additional precision optical coating and are able to reach Q factors close to the material absorption limit.Beside
We report on a wide-range efficient method for optical second harmonic generation based on a whispering gallery mode resonator made from crystalline beta barium borate. In this single resonator, we were able to generate second harmonic fields for four different pump wavelengths ranging from the infrared (1557 nm) to the visible (634 nm) regime. The highest conversion efficiencies achieved in this whispering gallery mode resonator are as high as 4.6% (mW)−1. This conversion process is based on type-I phase matching with continuously varying optical axis orientation in an xy-cut configuration of the resonator. In such a geometry, the second harmonic whispering gallery mode experiences an oscillatory modulation of the refractive index. This enables wide-range cyclic phase matching along the circumference of the disk resonator.
Universal nonlinear scattering processes such as Brillouin, Raman, and Kerr effects are fundamental light-matter interactions of particular theoretical and experimental importance. They originate from the interaction of a laser field with an optical medium at the lattice, molecular, and electronic scale, respectively. These nonlinear effects are generally observed and analyzed separately, because they do not often occur concomitantly. In this article, we report the simultaneous excitation of these three fundamental interactions in mm-size ultra-high Q whispering gallery mode resonators under continuous wave pumping. Universal nonlinear scattering is demonstrated in barium fluoride and strontium fluoride, separately. We further propose a unified theory based on a spatiotemporal formalism for the understanding of this phenomenology.
We investigate the mechanisms leading to phase locking in Raman optical frequency combs generated with ultrahigh Q crystalline whispering gallery mode disk resonators. We show that several regimes can be triggered depending on the pumping conditions, such as single-frequency Raman lasing, multimode operation involving more than one family of cavity eigenmodes, and Kerr-assisted Raman frequency comb generation. The phase locking and coherence of the combs are experimentally monitored through the measurement of beat signal spectra. These phase-locked combs, which feature high coherence and wide spectral spans, are obtained with pump powers in the range of a few tens of mW. In particular, Raman frequency combs with multiple free-spectral range spacings are reported, and the measured beat signal in the microwave domain features a 3 dB linewidth smaller than 50 Hz, thereby indicating phase locking.
We report the fabrication for the first time of a strontium fluoride (SrF(2)) whispering-gallery mode resonator with quality factor in excess of 1 billion. The millimeter-size disk-resonator is polished until the surface roughness decreases down to a root-mean square value of 1.2 nm, as measured with a vertical scanning profilometer. We also demonstrate that this ultrahigh Q resonator allows for the generation of a normal-dispersion Kerr optical frequency comb at 1550 nm.
In this Letter, we show that giant thermo-optical oscillations can be triggered in millimeter (mm)-size whispering gallery mode (WGM) disk resonators when they are pumped by a resonant continuous-wave laser. Our resonator is an ultrahigh-Q barium fluoride cavity that features a positive thermo-optic coefficient and a negative thermo-elastic coefficient. We demonstrate for the first time, to our knowledge, that the complex interplay between these two thermic coefficients and the intrinsic Kerr nonlinearity yields very sharp slow-fast relaxation oscillations with a slow timescale that can be exceptionally large, typically of the order of 1 s. We use a time-domain model to gain understanding into this instability, and we find that both the experimental and theoretical results are in excellent agreement. The understanding of these thermal effects is an essential requirement for every WGM-related application and our study demonstrates that even in the case of mm-size resonators, such effects can still be accurately analyzed using nonlinear time-domain models.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.