Abstract
We investigate the nonlinear response of photonic crystal waveguides with suppressed two-photon absorption. A moderate decrease of the group velocity (approximately c/6 to c/15, a factor of 2.5) results in a dramatic (x 30) enhancement of three-photon absorption well beyond the expected scaling, proportional, variant 1/v3g. This non-trivial scaling of the effective nonlinear coefficients results from pulse compression, which further enhances the optical field beyond that of purely slow-group velocity interactions. These observations are enabled in mm-long slow-light photonic crystal waveguides owing to the strong anomalous group-velocity dispersion and positive chirp. Our numerical physical model matches measurements remarkably.
Highlights
Slow-light nonlinearities have been remarkably observed through quantum coherence and interference in atomic systems, with group velocities of tens of meters per second and sub-100 kHz bandwidths[1, 2, 3, 4]
We investigate the nonlinear response of photonic crystal waveguides with suppressed two-photon absorption
We have demonstrated nonlinear scaling of the nonlinear enhancement beyond the limits of slow-light photonic crystal waveguides
Summary
Slow-light nonlinearities have been remarkably observed through quantum coherence and interference in atomic systems, with group velocities of tens of meters per second and sub-100 kHz bandwidths[1, 2, 3, 4]. In addition to the desirable Kerr term, each material has a nonlinear multiphoton absorption term This fundamental material property induces several detrimental effects, such as: (a) limiting the Kerr-induced phase-shift, called self-phase modulation (SPM); (b) inducing nonlinear and free-carrier absorption losses; (c) distorting the pulse via free-carrier dispersion; as well as (d) restricting the spectral range of any potential nonlinear optical devices such as all-optical switches[25]. Several early studies point out that the wavelength range of the two-photon absorption (TPA) tail depends strongly on the quality of the molecular beam epitaxy (MBE) sample growth [25, 26, 27] These fundamental obstacles must be overcome in order to achieve practical nonlinear devices, such as all-optical switches, on-chip.
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