Active Enhancement of Slow Light Based on Plasmon-Induced Transparency with Gain Materials

Abstract

As a plasmonic analogue of electromagnetically induced transparency (EIT), plasmon-induced transparency (PIT) has drawn more attention due to its potential of realizing on-chip sensing, slow light and nonlinear effect enhancement. However, the performance of a plasmonic system is always limited by the metal ohmic loss. Here, we numerically report a PIT system with gain materials based on plasmonic metal-insulator-metal waveguide. The corresponding phenomenon can be theoretically analyzed by coupled mode theory (CMT). After filling gain material into a disk cavity, the system intrinsic loss can be compensated by external pump beam, and the PIT can be greatly fueled to achieve a dramatic enhancement of slow light performance. Finally, a double-channel enhanced slow light is introduced by adding a second gain disk cavity. This work paves way for a potential new high-performance slow light device, which can have significant applications for high-compact plasmonic circuits and optical communication.

Keywords: gain material; metal-dielectric-metal; plasmon-induced transparency.

Figure 1

(a) 3D scheme of the plasmonic metal-dielectric-metal (MDM) waveguide system; (b) 2D scheme of this system from the view of z-axis. The geometry parameters are w = 100 nm, h = 205 nm, g = 19 nm, R = 141 nm; (c) The relationship between the effective refractive index (n_eef) of surface plasmon waves (SPWs) and the height at a wavelength of 1310 nm; (d) The distribution $\left|P_x\right|$ of the fundamental mode at 1310 nm when height is 100 nm.

Figure 2

(a) The transmission spectrum from finite-difference time-domain (FDTD) and coupled mode theory (CMT). The inset is the transmission spectrum without disk cavity; (b–e) The corresponding H_z distribution. For plasmon-induced transparency (PIT), the central transparent wavelength is 1328 nm, the valley values are at 1279 nm and 1378 nm.

Figure 3

(a) The spectrum of phase shift in no-gain PIT system; (b) The spectrum of delay time in no-gain PIT system.

Figure 4

(a) 2D scheme of gain-assisted PIT system from the view of z-axis. The geometry parameters are g′ = 41 nm, R′ = 149 nm; (b) Schematic of the energy transfer from a pumped four-level gain medium to the PIT resonance in plasmonic system; (c,d) The transmission spectrum with different gain coefficients.

Figure 5

(a–f) The phase shift and delay time corresponding to three different gain levels.

Figure 6

The relationship between transmission/delay time and gain coefficients at 1310 nm.

Figure 7

(a) 2D scheme of the gain-assisted double PIT system from the view of z-axis. The geometry parameters are g′ = 28 nm, g″ = 36 nm, R′ = 149 nm; (b) The transmission spectrum of double-disk system under the gain level $\eta =782 {\mathrm{cm}}^{-1}$. The insets are field distributions corresponding to the two central transparent wavelengths; (c) The phase shift spectrum of corresponding double PIT; (d) The delay time of corresponding double PIT.