Ultrafast Optical Switching in Three-Dimensional Photonic Crystals

We present the first experimental investigation of ultrafast optical switching in a three-dimensional photonic crystal made of a Si-opal composite. Ultrafast (30 fs) changes in reflectivity around the photonic stop band up to 1% were measured for moderate pump power $(70\mu \mathrm{J}/{\mathrm{c}\mathrm{m}}^2)$. Short-lived photoexcited carriers in silicon induce changes in the dielectric constant of Si and diminish the constructive interference inside the photonic crystal. The results are analyzed within a model based on a two-band mixing formalism.

Figure 1

Diagram illustrating the beam paths of the incident probe, the specular, and the Bragg diffracted beams. Inset schematically shows the faceted sample surface.

Figure 2

Measured (symbols) and calculated (solid lines) spectra of specular reflection ($R_0$) and Bragg diffraction efficiency ($R_d$). Experimental data are normalized to the maximum of the $R_d$ theoretical curve. Vertical arrows point the calculated positions of the photonic band edges when the imaginary part of dielectric constants is neglected.

Figure 3

Temporal evolutions of transient changes in specular reflection (dashed line) and Bragg diffraction efficiency (solid line). Inset shows the signal measured with 30 fs time resolution.

Figure 4

Calculated (solid line) and measured (symbols) spectra of the photoinduced relative changes in the total reflection. Dashed line shows the calculated relative changes in the specular reflection.