Fig. 1. Finite difference Time Domain (FDTD) simulation of the frequency shift in a sample time-dependent single Fabry-Perot microcavity. The simulated cavity, resonant at vacuum wavelength λ=1550.25 nm, consists in a λ/2 layer (thickness = 388 nm with refractive index = 2) sandwiched between two 8.5-period Distributed Bragg Reflectors, fabricated by alternating high refractive index λ/4 layers (thickness = 129 nm with refractive index = 3) and low refractive index λ/4 layers (thickness = 194 nm with refractive index = 2). A Gaussian pulse of duration 20 ps is taken as the input. The dashed (solid) line shows the amplitude of the Poynting vector at the input (output) side versus time. The inset shows the spectra of respective electric fields (the resolution of the spectrum of the output is limited by the time window of the simulation).

Fig. 2. Simplified schematic representation of the CROW structure. For simplicity, we have represented the external dielectric mirrors with only 4 periods instead of 13, and the inter-cavity - coupling - mirrors with only 9 periods instead of 27. Only 2 cavities instead of 45 have been shown. Light travels in the positive x direction.

Fig. 3. Left panel: band structure of the 1D model of the CROW structure shown in Fig.2. The arrows indicate the frequency separation ΔΩ between the miniband and the nearest photonic states with the same k. Central panel: enlarged view of miniband. Right panel: trasmission spectrum and spectral shape of the signal pulse. This latter is chosen to fit in the region of the spectrum where the dispersion is linear and the transmittivity is flat and almost unity. Vertical axes have all the same (dimensionless) unit. For the actual parameters see text.

Fig. 4. FDTD simulation of the envelope of Poynting vectors at the input (dashed line, positive entering) and output boundary (solid line, positive exiting) of the coupled-cavities structure. Input and output boundaries are defined in Figure 2. The refractive index of all the layers is time-dependent, as shown by the right y-axis. Upper time scale is relative to the delay (τ₀) in a homogeneous medium with the average refractive index of the 1D-structure. The inset shows the spectra of the input and output pulse electric fields.

Fig. 5. (color online) A comparison between the calculated transmission spectra of the initial and shifted minibands in the case of a waveguide (a) and a 1D-multilayer structure (b). The miniband dispersion (full circles) in the 1D case is also plotted in (b).

Fig. 6. (color online) Successive snapshots of the electric field of the optical wave and of the index-driving microwave at 37, 56 and 75 ps. The differently colored electric fields have an illustrative scope and refer to a blueshift of the input pulse wavelength. The structure of the pulse electric field reflects the coupled cavity structure (maxima are located in correspondence of C layers.