Control of plasmon dynamics in coupled plasmonic hybrid mode microcavities

Hybrid plasmonic microcavities display localized electromagnetic states similar to the confined electronic levels in atoms and quantum wells. Exploiting this parallelism and concepts used in photonics, we describe a novel plasmonic device based on the coupling between a plasmonic microcavity and a photonic microcavity. We theoretically analyze the coupling effects and the plasmon dynamics in structures integrated in silicon optical waveguides. We observe a strong coupling behavior between the eigenmodes that leads to a periodic excitation of the plasmonic hybrid mode in analogy to a plasmonic pulsar. We demonstrate that the spectra—and thus the dynamics—of confined plasmons can be tailored with great versatility in plasmonic pulsars in the 100-fs scale. These structures open new ways in the design and conception of plasmonic and photonic applications and the control and manipulation of hybrid plasmons in the time domain.

Figure 1

Hybrid plasmonic structures based on optical microcavities. (a) Scheme of a plasmonic microcavity: the structure is formed by two gratings acting as DBRs enclosing an optical spacer; on top of the optical spacer an Ag layer separated by a SiO${}_2$ thin film generates the localized plasmonic–photonic mode. (b) Scheme of a plasmonic molecule formed by two concatenated plasmonic microcavities. (c) and (d) Calculated optical transmission for the single plasmonic and plasmonic molecule structure, respectively. (e) Calculated norm of the electric field component $E_x$ for an incident wavelength λ = 1296 nm for the single plasmonic microcavity. (f) Same as (e) but for the stopband wavelength λ = 1280 nm where no transmission occurs. (g) Calculated norm electric field component $E_x$ for a wavelength λ = 1284 nm in the plasmonic molecule structure with two coupled cavities (see Supplemental Material[34]).

Figure 2

Hybrid plasmonic–photonic pulsar. (a) Scheme of the structure: the pulsar is formed by two gratings acting as external DBRs enclosing two optical spacers separated by a coupling central DBR; on top of the right optical spacer an Ag layer separated by a 20-nm-thick SiO${}_2$ film generates the localized plasmonic–photonic mode. (b) Calculated optical transmission for the plasmonic pulsar structure for 3, 5, and 15 periods in the central DBR. The peaks for the five-period DBR at 1283 nm and 1312 nm correspond to the confined eigenmodes of the structure. (c) and (d) Calculated norm of the electric field in the $x$ direction for an incident wavelength λ = 1283 nm and 1300 nm, respectively, for the five periods’ central DBR structure (see Supplemental Material[34]).

Figure 3

Coupling effects in the plasmonic pulsar. (a) Wavelengths of the plasmonic pulsar modes as a function of the detuning of the photonic optical microcavity size with respect to the plasmonic hybrid mode cavity size. The number of periods of the cen-tral (external) DBRs are kept constant to 7 (20) periods. The size of the plasmonic cavity is 1290 nm. The color coding (red/blue) indicates the dominant character of the mode (plasmonic/photonic). (b) Corresponding linewidths of the modes.

Figure 4

Simulated time evolution in a hybrid plasmonic pulsar when the two eigenmodes are excited simultaneously. (a) Electric field corresponding to the time at $t$ = 55 fs where the field is strongly localized in the right (plasmonic) cavity. (b) Same as (a) but for the time $t$ = 140 fs when the field is localized in the left (photonic) cavity. (c) and (d) Magnified view of the electric field $|E_x|$ in the region of the hybrid plasmonic cavity for (a) and the photonic cavity for (b). (e) Time evolution of the total energy density in the structure integrated along the $x$ axis. The vertical dashed lines indicate the position of the photonic and plasmonic cavities. (f) Black (solid) and red (dashed) curves show the oscillation of the total energy density at the center of the photonic and plasmonic cavity, respectively, as a function of time (see Supplemental Material[34]).