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The coherent interaction between optical and acoustic waves via stimulated Brillouin scattering (SBS) is a fundamental tool for manipulating light at GHz frequencies. Its narrowband and noise-suppressing characteristics have recently enabled microwave-photonic functionality in integrated devices based on chalcogenide glasses, silica and silicon. Diamond possesses much higher acoustic and bandgap frequencies and superior thermal properties, promising increased frequency, bandwidth and power; however, fabrication of low-loss optical and acoustic guidance structures with the resonances matched to the Brillouin shift is currently challenging. Here we use intense cavity-enhanced Raman generation to drive a diamond Brillouin laser without acoustic guidance. Our versatile configuration - the first demonstration of a free-space Brillouin laser - provides tens-of-watts of continuous Brillouin laser output on a 71 GHz Stokes shift with user switching between single Stokes and Brillouin frequency comb output. These results open the door to high-power, high-coherence lasers and Brillouin frequency combs, and are a major step towards on-chip diamond SBS devices.
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High-power lasers have numerous scientific and industrial applications. Some key areas include laser cutting and welding in manufacturing, directed energy in fusion reactors or defense applications, laser surgery in medicine, and advanced photolithography in the semiconductor industry. These applications require optical components, in particular mirrors, that withstand high optical powers for directing light from the laser to the target. Ordinarily, mirrors are comprised of multilayer coatings of different refractive index and thickness. At high powers, imperfections in these layers lead to absorption of light, resulting in thermal stress and permanent damage to the mirror. Here we design, simulate, fabricate, and demonstrate monolithic and highly reflective dielectric mirrors which operate under high laser powers without damage. The mirrors are realized by etching nanostructures into the surface of single-crystal diamond, a material with exceptional optical and thermal properties. We measure reflectivities of greater than 98% and demonstrate damage-free operation using 10 kW of continuous-wave laser light at 1070 nm, with intensities up to 4.6 MW/cm2. In contrast, at these laser powers, we observe damage to a standard dielectric mirror based on optical coatings. Our results initiate a new category of broadband optics that operate in extreme conditions.
We use theoretical analysis and numerical simulation to investigate the operation of a laser oscillating from gain supplied by stimulated Brillouin scattering (SBS) in a microresonator. The interaction of the forward, backward, and density waves within the microresonator results in a set of coupled-mode equations describing both the lasers phase and amplitude evolution over time. Using this coupled-mode formalism, we investigate the performance of the SBS laser under noise perturbation and identify the fundamental parameters and their optimization to enable low-noise SBS operation. The intrinsic laser linewidth, which is primarily limited by incoherent thermal occupation of the density wave, can be of order hertz or below. Our analysis also determines the SBS lasers relaxation oscillation, which results from the coupling between the optical and density waves, and appears as a resonance in both the phase and amplitude quadratures. We further explore contributions of the pump noise to the SBS lasers performance, which we find under most circumstances to increase the SBS laser noise beyond its fundamental limits. By tightly stabilizing the pump laser onto the microcavity resonance, the transfer of pump noise is significantly reduced. Our analysis is both supported and extended through numerical simulations of the SBS laser.
Ultrastable lasers serve as the backbone for some of the most advanced scientific experiments today and enable the ability to perform atomic spectroscopy and laser interferometry at the highest levels of precision possible. With the recent and increasing interest in applying these systems outside of the laboratory, it remains an open question as how to realize a laser source that can reach the extraordinary levels of narrow linewidth required and yet still remain sufficiently compact and portable for field use. Critical to the development of this ideal laser source is the necessity for the laser to be insensitive to both short- and long-term fluctuations in temperature, which ultimately broaden the laser linewidth and cause drift in the lasers center frequency. We show here that the use of a large mode-volume optical resonator, which acts to suppress the resonators fast thermal fluctuations, together with the stimulated Brillouin scattering (SBS) optical nonlinearity presents a powerful combination that enables the ability to lase with an ultra-narrow linewidth of 20 Hz. To address the lasers long-term temperature drift, we apply the narrow Brillouin line as a metrological tool that precisely senses a minute change in the resonators temperature at the level of 85 nK. The precision afforded by this temperature measurement enables new possibilities for the stabilization of resonators against environmental perturbation.
The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result proper material and structure engineering allows one to control each contribution individually. In this paper, we experimentally demonstrate the perfect cancellation of Brillouin scattering by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon-phonon interaction, enhancing or suppressing it.
The demand for high-performance chip-scale lasers has driven rapid growth in integrated photonics. The creation of such low-noise laser sources is critical for emerging on-chip applications, ranging from coherent optical communications, photonic microwave oscillators remote sensing and optical rotational sensors. While Brillouin lasers are a promising solution to these challenges, new strategies are needed to create robust, compact, low power and low cost Brillouin laser technologies through wafer-scale integration. To date, chip-scale Brillouin lasers have remained elusive due to the difficulties in realization of these lasers on a commercial integration platform. In this paper, we demonstrate, for the first time, monolithically integrated Brillouin lasers using a wafer-scale process based on an ultra-low loss Si3N4/SiO2 waveguide platform. Cascading of stimulated Brillouin lasing to 10 Stokes orders was observed in an integrated bus-coupled resonator with a loaded Q factor exceeding 28 million. We experimentally quantify the laser performance, including threshold, slope efficiency and cascading dynamics, and compare the results with theory. The large mode volume integrated resonator and gain medium supports a TE-only resonance and unique 2.72 GHz free spectral range, essential for high performance integrated Brillouin lasing. The laser is based on a non-acoustic guiding design that supplies a broad Brillouin gain bandwidth. Characteristics for high performance lasing are demonstrated due to large intra-cavity optical power and low lasing threshold power. Consistent laser performance is reported for multiple chips across multiple wafers. This design lends itself to wafer-scale integration of practical high-yield, highly coherent Brillouin lasers on a chip.
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