Abstract
The optimization of laser resonators represents a crucial issue for the design of tera-hertz semiconductor lasers with high gain and low absorption loss. In this paper, we put forward and optimize the surface plasmonic metal waveguide geometry for the recently proposed tera-hertz injection laser based on resonant radiative transitions between tunnel-coupled graphene layers. We find an optimal number of active graphene layer pairs corresponding to the maximum net modal gain. The maximum gain increases with frequency and can be as large as ∼ 500 cm-1 at 8 THz, while the threshold length of laser resonator can be as small as ∼ 50 μm. Our findings substantiate the possibility of ultra-compact voltage-tunable graphene-based lasers operating at room temperature.
Highlights
The compact tunable sources of terahertz radiation are highly demanded in security, medical, and telecommunication applications [1,2,3]
Quantum cascade lasers (QCLs) are considered among most promising candidates to bridge the terahertz gap [4,5,6,7], but their operation is currently limited to the cryogenic temperatures only
We have proposed and substantiated the concept of injection THz laser based on the multiple graphene-layer structure exploiting the interlayer resonant radiative transitions and embedded in plasmonic waveguide
Summary
The compact tunable sources of terahertz radiation are highly demanded in security, medical, and telecommunication applications [1,2,3]. Under the population-inverted conditions, the stimulated electron tunneling accompanied by the photon emission is more probable than the inverse absorptive process Such a GL structure can serve as the laser gain medium with the lateral injection pumping. Are the gain-overlap factors, neff(ω, N) is the effective refractive index of the mode, Ez,y (x, z,ω ) are the components of the electric field in TM-mode, c is the light speed in vacuum, L is the waveguide width, κ is the dielectric constant of the barrier layer, σ zz (ω) and σ yy (ω) are the transverse and lateral dynamic conductivities of tunnel-coupled graphene double layer structure. The solution of the Maxwell equations with the pertinent complex permittivity of the surface plasmon waveguide and metal strips yields the spatial distributions of the electric fields, Ez,y (x, z,ω) in the propagating mode and the gain-overlap factors. In the calculations we have neglected the influence of GLs on the field distributions, because the electric field component along the GLs and, the surface currents are small in the TM mode, as we shall discuss below
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