Strongly Nonlinear Slow Light Polaritons in Subwavelength Modulated Waveguides

Abstract

Slow light is a regime of reduced group velocity, resulting in increased photon density in optical pulses and enhanced nonlinear effects. Here, we propose the realization of slow light in the regime of strong light-matter interaction between waveguide photons and semiconductor excitons. We design a dielectric superlattice structure with a nearly-flat band characterized by low group velocity and group velocity dispersion, both required for enhancing nonlinear effects with ultrashort pulses. Furthermore, by applying this general framework to a perovskite-based structure, we demonstrate an enhancement of the single-particle phase shift by a factor of more than 20, representing a significant step toward the few-photon quantum regime. Our results provide a blueprint for accessible strong interactions in solid-state integrated optics.

Figures (3)

• Figure 1: Schematic of the designed slow polariton perovskite waveguide. (a) In a strip single-channel waveguide, the guiding layer is corrugated and includes one defect per supercell, whose periodic repetition forms a superlattice. (b) Effective refractive indices of the first TE fundamental mode for the geometry shown in panel (a) in etched ($n_1$) and raised ($n_2$) sections. (c) In the top view (xy plane), the geometry of superlattice reduces to a 2D problem. $L$ shows the size of the unit cell (supercell) in the superlattice. (d) Close-up view of the defect region and the two unit cells. The defect has the width $w_x$, and the period of the corrugation is $a_x$.
• Figure 2: Upper row: dispersion and modes of the periodic corrugated structure without defects. (a) Periodic modulation introduces a bandgap with upper and lower TE bands separated by a gap at the band edge ($ka_x=\pi$). (b) Electric field intensity profiles of TE modes corresponding to lower and upper modes at the band edge (points $e_1$ and $e_2$, respectively). (c) Group velocities of the two bands, vanishing at the band edge. Lower row: dispersion and modal properties of the corrugated structure with defects (superlattice). (d) Photonic dispersion of the upper (black), gap (red), and lower (blue) bands for a supercell of length $L$. The middle band is nearly flat. The horizontal dashed line shows the exciton energy. (b) Examples of electric field profiles corresponding to each band (points $i_1$, $i_2$ and $i_3$) in panel (a). In the flat band, the field is localized at the defect (centered). (c) Group velocities in each band. The solid curves show group velocities corresponding to the band mode in (d) with $N_g=32$. The dashed curve show the group velocity for $N_g=44$. Parameters are $a_x=0.13\,\mu$m, $h_a=0.08\,\mu$m, $h_x=0.3-2h_a\,\mu$m, $w_a=0.02\,\mu$m, $w_x=0.07\, \mu$m.
• Figure 3: (a) Snapshots of eigenmode wavepacket intensity in the slow-light and fast-light regimes. Initially, there is a Gaussian wavepacket (shown in red and black dashed lines for the fast and slow light, respectively) traveling along the x-axis. The red curve shows the wavepacket intensity after 10 ps of evolution, and the black curve shows the case of fast light. (b) Average nonlinear phase shift shown in red for the gap band. The black line shows the nonlinear phase shift accumulated in the fast-light regime. The green dashed curve shows the nonlinear phase shift for a strip-raised waveguide without any corrugation.