Acoustic confinement and stimulated Brillouin scattering in integrated optical waveguides

Abstract

We examine the effect of acoustic mode confinement on Stimulated Brillouin Scattering in optical waveguides that consist of a guiding core embedded in a solid substrate. We find that SBS can arise due to coupling to acoustic modes in three different regimes. First, the acoustic modes may be guided by total internal reflection; in this case the SBS gain depends directly on the degree of confinement of the acoustic mode in the core, which is in turn determined by the acoustic V-parameter. Second, the acoustic modes may be leaky, but may nevertheless have a sufficiently long lifetime to have a large effect on the SBS gain; the lifetime of acoustic modes in this regime depends not only on the contrast in acoustic properties between the core and the cladding, but is also highly dependent on the waveguide dimensions. Finally SBS may occur due to coupling to free modes, which exist even in the absence of acoustic confinement; we find that the cumulative effect of coupling to these non-confined modes results in significant SBS gain. We show how the different acoustic properties of core and cladding lead to these different regimes, and discuss the feasibility of SBS experiments using different material systems.

Modeling light-sound interaction in nanoscale cavities and waveguides

“…The two basic contributions to AO coupling discussed previously, PE and MI, are still at stake, but in addition optical forces are induced in nanoscale waveguides, as exemplified by Brillouin scattering effects [15,69,70]. It has been predicted that photon and phonon confinement in a transversal dimension of the order of half the wavelength in nanoscale waveguides of mmlength has the potential to induce a giant Brillouin gain that could be equivalent to km-long silica fibers [71][72][73][74]. Both ES (volume) and optical surface forces such as radiation pressure (see Figure 2) were predicted to scale to very large values in nanoscale waveguides [15].…”

Inducing and harnessing stimulated Brillouin scattering in photonic integrated circuits

“…It should be noted that the above definition of the opto-acoustic overlap is an approximation, holding for waveguides that are sufficiently large that the longitudinal component of the electromagnetic field can be neglected, and for which coupling between the shear and longitudinal components of the acoustic field on boundaries can be neglected [98]. For very small waveguides, Eq.…”

“…For V core ≪ V clad , the acoustic mode is guided in the core and the resulting strong confinement leads Acoustic-optic confinement η regimes for an optical guiding device for different contrasts between the core (V core ) and cladding (V cladding ) acoustic velocity and its impact on the Brillouin gain. For V core ∼ V cladding acousto-optic overlap reduces due to radiating acoustic mode, while large acousto-optic overlap occurs for V core ≪ V cladding due to acoustic guidance and for V core ≫ V cladding (acoustic mode leakage regime) due to large acoustic impedance mismatch and thus large leakage time [98]. Copyright 2013, Optical Society of America.…”

“…The second regime where V core ∼ V clad corresponds to the radiative regime where the fundamental acoustic mode is near the cutoff [98]. In this regime, the coupling to a continuum of free acoustic modes reduces the acousto-optic overlap, resulting in reduced g B and an asymmetric gain profile.…”

Numerical modelling on stimulated Brillouin scattering characterization for Graphene-clad tapered silica fiber

“…The Brillouin peak gain is achieved under condition where the difference between pump and stoke frequency is equivalent to the Brillouin shift, [35,36]. (9) where is the numerical factor manipulated by fiber length and is approximated to a constant value ≈ 21. eff and ff are the effective area and effective length of fiber, respectively.…”