Symmetrically structured plasmonic waveguide lasers with deep subwavelength confinement and low threshold

A hybrid plasma waveguide laser with a coupled metal-dielectric layer-semiconductor is designed to exploit the coupling between the tip of the gain medium and the metal layer to excite the plasma effect for optical field modulation and energy confinement. Considering the optical loss present in the metal, the laser is designed as a symmetric structure where the semiconductor and the insulating layer share the same metal layer. The experimental results show that the symmetric structure waveguide has a very low gain threshold, which is as low as 0.0073 1/μm for the optimal structure, thanks to the good equipartition excitation characteristics and the low loss of Na. In addition, the surface plasma and tip enhancement of the gain medium provide very strong energy confinement, which increases the value of the quality factor FOM to 3091. Furthermore, the fabrication error study shows that the proposed waveguide laser has a very high tolerance for fabrication errors. The fabrication error is extremely tolerant, and there is no decoupling of the symmetric structure within 30 nm of the fabrication error. This waveguide structure enhances the interaction between light and matter and makes it easier to achieve modulation of the optical field.