Nanolasers Based on Whispering‐gallery Resonances in Graphene Cavities with Hyperbolic Dispersion

We theoretically propose a novel nanolaser based on whispering-gallery resonances (WGRs) in spherical cavities with hyperbolic dispersion, composed of a dielectric core alternately wrapped by graphene and dielectric layers. First, we showed that the multilayer graphene-dielectric core-shell cavities have a negative dielectric constant in at least one direction and exhibit an unusual hyperbolic dispersion. Such cavities can support the whispering-gallery modes with resonance wavelengths much larger than the cavity sizes and can strongly confine the electromagnetic fields in deep subwavelength regions. Moreover, multiple dipole WGR modes with different orders can be excited by such cavities, accompanied by high Purcell factors and strong confinement electric fields within different dielectric layers. Therefore, by introducing gain into these different dielectric layers, lasing at different resonance wavelengths can be realized with a low lasing threshold. For the cavity with a diameter of 404 nm, the lasing threshold at a wavelength of 32.3 mu m is only 80.6 cm(-1). Furthermore, we demonstrated that by manipulating the refractive index of the dielectric layers, graphene Fermi energy, or the number of pairs of graphene and dielectric layers, the lasing wavelengths in a wide spectral range could be easily adjusted. Finally, even for the relatively simple core-shell cavity with only two pairs of graphene and dielectric layers, the ratio of resonant wavelength and cavity diameter for the TM1,1 mode is approximately 50, and the lasing threshold is only 90.74 cm(-1). This type of nanolasers has the characteristics of deep subwavelength, low threshold, and wide-band tunability. Hence, these lasers have great potential for applications in integrated terahertz devices.