Optical bandpass switching by modulating a microcavity using ultrafast acoustics

We present time-resolved reflectivity spectra of the cavity mode in a II-VI semiconductor based planar microcavity that is modulated by a strain pulse injected using an ultrafast acoustics technique. The modulation occurs when the strain pulse passes interfaces of the layered cavity structure at which the electric field has an antinode. Maximum modulation is reached when the pulse enters or leaves the central cavity layer. The mode shifts in the cavity with a finesse of about 2000 are comparable to its mode linewidth, which shows that the proposed technique is prospective for ultrafast optical switching.

Figure 1

(Color online) (a) Scheme of the experimental setup and sample structure consisting of the aluminum transducer, the GaAs substrate, and the cavity, sandwiched between two Bragg mirrors. The indicated interfaces correspond to the antinodes of the confined electric field (modulus sketched by blue solid curve) as described in the text. The displacement pulse is injected via a laser pulse, indicated as an arrow at the left side. Right arrows show the white laser pulses for probing the reflectivity spectrum. (b) Reflectivity spectrum from the microcavity structure without influence of the displacement pulse. (c) Typical temporal and spatial shapes of the displacement pulse (black line) and the corresponding strain (gray line) during propagation through the sample. Dashed line indicates zero displacement or strain.

Figure 2

(Color online) Spectral/temporal contour plot of the reflectivity in presence of the displacement pulse propagating through the structure measured at a laser energy density of $P=6\text{mJ}/{\text{cm}}^2$ on the transducer $\left(T=10\text{K}\right)$. Black line shows the transfer-matrix calculation of the time evolution of the resonance mode energy for a Gaussian-shaped displacement pulse propagating with a velocity of 5365 m/s. Vertical dashed line indicates the time, when the middle of the cavity is maximum displaced.

Figure 3

(Color online) (a) Spectral/temporal contour plot of the reflectivity in the presence of the displacement pulse measured at a laser energy density of $P=12\text{mJ}/{\text{cm}}^2$ on the transducer $\left(T=10\text{K}\right)$. (b) Three spectral cuts in panel (a) corresponding to the delay times $t_{-1}=-23\text{ps}$ (red squares), $t=-150\text{ps}$ (thick solid line), and $t_1$ (blue circles). (Inset) Dependence of the maximum higher energy shift $\Delta E_{-1}$ on the excitation laser energy $P$.