Intense Brillouin amplification in gas using hollow-core waveguides

Abstract

Among all the nonlinear effects stimulated Brillouin scattering offers the highest gain in solid materials and has demonstrated advanced photonics functionalities in waveguides. The large compressibility of gases suggests that stimulated Brillouin scattering may gain in efficiency with respect to condensed materials. Here, by using a gas-filled hollow-core fibre at high pressure, we achieve a strong Brillouin amplification per unit length, exceeding by six times the gain observed in fibres with a solid silica core. This large amplification benefits from a higher molecular density and a lower acoustic attenuation at higher pressure, combined with a tight light confinement. Using this approach, we demonstrate the capability to perform large optical amplifications in hollow-core waveguides. The implementations of a low-threshold gas Brillouin fibre laser and a high-performance distributed temperature sensor, intrinsically free of strain cross-sensitivity, illustrate the potential for hollow-core fibres, paving the way to their integration into lasing, sensing and signal processing.

Large evanescently-induced Brillouin scattering at the surrounding of a nanofibre

“…The tighter light confinement in nanofibre compared with hollow-core fibre results in a measured Brillouin gain coefficient in our 40 bar CO 2 gas filled nanofibre gas cell 5-times larger than in a hollow-core fibre under the same pressure [8], but it is expected that higher gains can be achieved by using noble gases (e.g. xenon) [40].…”

“…In these conditions, we have achieved a peak Brillouin gain coefficient of 18.90 ± 0.17 m −1 W −1 at 57 bar, which is 11 times higher than that obtained in a hollow-core fibre and is 79 times higher than that in a SMF. Furthermore, unlike in hollow-core fibres [8] where both optical and acoustic modes are confined in the hollow core, this work has demonstrated the first possibility to probe the acoustic wave in the surrounding medium of a waveguide using an all-optical method thanks to the strong Brillouin scattering generated by the evanescent field of the waveguide.…”

“…The generation of a confined elastic wave in the gas-silica rod assembling by the two components of optical field (guided and evanescent) is calculated by using the elasto-dynamic equation driven by the electrostrictive stress [42,43]. All calculations for CO 2 at 40 bar are realised using: an optical wavelength of 1550 nm, a refractive index of 1.01804 [8], an acoustic velocity of 250 m/s, and a density of 71.35 kg/m 3 . To exclude the contribution from the tapered regions, the Brillouin linewidth used in the simulation for 40 bar CO 2 is 14.2 MHz which is defined as twice the value of the left half-width-half-maximum of the spectrum fitted with a Lorentzian (i.e.…”

“…Brillouin scattering involves light-sound interactions and has been used in nonlinear optics [1][2][3][4], microwave photonics [5], slow and fast light [6], lasing [7], sensing [8] and imaging [9,10]. It has been observed in various platforms, including optical fibres [8,[11][12][13][14], whisperinggallery-mode resonators [15][16][17][18] and integrated waveguides [19][20][21][22][23][24][25].…”

Giant Brillouin Amplification in Gases

“…In our work, we used stimulated Brillouin scatt ering directly in the gas medium (such as air) fi lling a hollow-core fi ber to realize a massive optical amplifi cation, by a factor of 200,000. 3 We also demonstrated that the gain in a hollow-core fi ber can be much stronger than in a standard single-mode fi ber, and can, indeed, outperform any nonlinear gain in waveguide materials. In our experiments, we showed that the peak gain in these fi bers scales with the square of the gas pressure-and turns out, at a gas pressure of only a few tens of bars, to actually exceed the Brillouin gain observed in solid materials.…”