Forward Brillouin scattering in hollow-core photonic bandgap fibers

Abstract

We quantify the strength of stimulated forward Brillouin scattering in hollow-core photonic bandgap fiber through a combination of experiments and multi-physics simulations. Brillouin spectroscopy methods reveal a family of densely spaced Brillouin-active phonon modes below 100 MHz with coupling strengths that approach those of conventional silica fiber. The experimental results are corroborated by multi-physics simulations, revealing that relatively strong optomechanical coupling is mediated by a combination of electrostriction and radiation pressure within the nano-scale silica-air matrix; the nontrivial mechanical properties of this silica-air matrix facilitate the large optomechanical response produced by this system. Simulations also reveal an incredible sensitivity of the Brillouin spectrum to fiber critical dimensions, suggesting opportunity for enhancement or suppression of these interactions. Finally, we relate the measured and calculated couplings to the noise properties of the fiber as the foundation for phase-and polarization-noise estimates in hollow-core fiber. More generally, such Brillouin interactions are an important consideration in both the high and low optical intensity limits.

Frequency-domain technique to measure the inertial response of forward stimulated Brillouin scattering for acoustic impedance sensing

“…A variant of FSBS frequency sweeping methods have been described previously. [5][6][7] However, due to the presence of Kerr effect giving a similar signature in phase quadrature, the spectra of resonances are either distorted or must be manually processed to obtain an accurate decay time. Here, we demonstrate an acoustic wave frequency sweeping method by taking advantage of the contrast between the long inertial response of FSBS and the instantaneous nature of Kerr effect.…”

Guided-wave Brillouin scattering in air

“…While electronic nonlinearities are widely studied in such fibers [1][2][3], comparatively little is known of their acousto-optic (or optomechanical) interactions, and the dynamics, and noise that they can produce. Only recently has coupling between MHz elastic waves within the silica matrix been quantified [13], and identified as a source of noise in quantum optics [13,14].In this paper, we show that photon-phonon coupling mediated by air (gasses) within the hollow core of the fiber constitutes a much larger and perhaps more tailorable form of optomechanical coupling. Through a combination of theory and experiment, we show that the hollow core of the fiber acts as a conduit for guided acoustic waves in air.…”

“…nonchiral) and therefore f kl = 0 when k = l. Using to represent k = l and ⊥ to represent k = l, and following Refs. [13,24,25], the Brillouin gain for gases can therefore be written as:…”

“…While electronic nonlinearities are widely studied in such fibers [1][2][3], comparatively little is known of their acousto-optic (or optomechanical) interactions, and the dynamics, and noise that they can produce. Only recently has coupling between MHz elastic waves within the silica matrix been quantified [13], and identified as a source of noise in quantum optics [13,14].…”

“…In what follows, we consider forward stimulated Brillouin scattering (SBS) processes [13,[15][16][17][18][19][20][21][22], not to be confused with more widely studied backwards stimulated Brillouin scattering processes [23]. Through forward-SBS, co-propagating pump and Stokes waves of frequencies ω p and ω s are coupled through parametrically generated phonons of frequency Ω = ω p − ω s , as indicated by Fig.…”