Spatial homogeneity of optically switched semiconductor photonic crystals and of bulk semiconductors

Abstract

This paper discusses free carrier generation by pulsed laser fields as a mechanism to switch the optical properties of semiconductor photonic crystals and bulk semiconductors on an ultrafast time scale. Requirements are set for the switching magnitude, the time-scale, the induced absorption as well as the spatial homogeneity, in particular for silicon at λ = 1550 nm. Using a nonlinear absorption model, we calculate carrier depth profiles and define a homogeneity length ℓ hom . Homogeneity length contours are visualized in a plane spanned by the linear and two-photon absorption coefficients. Such a generalized homogeneity plot allows us to find optimum switching conditions at pump frequencies near ν/c=5000 cm −1 (λ = 2000 nm). We discuss the effect of scattering in photonic crystals on the homogeneity. We experimentally demonstrate a 10% refractive index switch in bulk silicon within 230 fs with a lateral homogeneity of more than 30 µm. Our results are relevant for switching of modulators in absence of photonic crystals.

Broadband sensitive pump-probe setup for ultrafast optical switching of photonic nanostructures and semiconductors

“…Our laser system provides high power pulses at two independently tunable frequencies, allowing us to adjust the pump frequency to optimize the optical penetration depth 14 and the probe frequency to scan across broad photonic gaps. The setup is based on a regeneratively amplified titanium sapphire laser that emits short 120 fs pulses at = 800 nm with a pulse energy of 1 mJ at a repetition rate of 1 kHz ͑Spectra Physics Hurricane͒.…”

“…[11][12][13] In these studies, one literally attempts to catch light with light. Therefore such switching processes are susceptible to perturbing effects such as absorption or ͑induced͒ inhomogeneity, 14 and sensitive experimental methods are required.…”

Ultrafast optical switching of photonic crystals

“…We have used Eq. 3.4 to obtain the nonlinear pump irradiance in the structure [117]. The two-photon absorption coefficient β is one of the three free parameters in our model.…”

Differential ultrafast all-optical switching of the resonances of a micropillar cavity

“…22 The frequency shift of each cavity resonance is detected by a 150 fs probe pulse whose timing is set by a delay stage. The probe is focused on the micropillar and is centered by maximizing the total reflected intensity.…”