Research On Low-Threshold Nanolaser Based On Bound States In The Continuum Of Grating Structure

With the rapid advancements in materials science and nanotechnology,miniaturization of lasers has emerged as a popular topic in photonics research.From the perspective of the developmental trajectory,laser’s sizes have evolved from solid and gas lasers at the meter-scale to the current nanometer-scale semiconductor nanolasers,spanning almost 10 orders of magnitude.The nanolaser is capable of producing coherent light at the nanoscale.The powerful local electromagnetic field at this scale greatly enhances light-matter interaction,creating an option that is more compact,faster,and more energy-efficient than its conventional counterparts.Due to these advantages,nanolasers are extensively utilized in various fields such as optical interconnections,near-field spectroscopy,sensing,optical detection of biological systems,and high-resolution imaging.The quality factor(Q-factor)is a parameter utilized to measure the performance of the laser.A high Q-factor of the optical cavity guarantees that photons remain in the cavity for an extended period,allowing for increased interaction with the gain materials.However,it is important to note that the efficiency of the light-matter interaction is not solely dependent on the lifetime of the light mode;the mode volume also plays a crucial role.Surface plasmon polariton modes are known to possess a significantly reduced mode volume compared to photonic modes.However,the Q-factors of these modes are generally low because of the metallic ohmic losses.All-dielectric nanomaterials with very low optical loss are utilized to avoid the ohmic loss of metal structures.Nevertheless,the radiation loss,which pertains to scattering in electromagnetic multipole modes that correspond to high refractive index nanoparticles,still remains a challenge in achieving high Q-factor resonance of nanostructures due to their dielectric properties.In recent years,bound states in the continuum(BIC)-a phenomenon that features infinite Q-factor and zero linewidth-have emerged as an effective means of achieving high-Q resonance in periodic structures.This discovery has driven the development of dielectric resonance nanophotonics and provided an essential physical mechanism for the construction of high-quality optical resonance in all-dielectric waveguide grating structures and two-dimensional grating metasurfaces.Bound states in the continuum(BIC)refer to localized states with energy embedded in a continuous spectrum that possess an infinite lifetime.However,in a real system,any loss results in the transformation of the bound state to a resonant state with a finite lifetime,which is commonly known as a quasi-BIC.This phenomenon finds application in various fields such as lasers,sensors,filters,absorbers,and nonlinear optics.This paper presents a numerical study on the low-threshold nanolaser featuring bound states in the continuum(BIC),which are supported using periodic grating structures.The primary research aims and conclusions are highlighted below:1.We propose an all-dielectric resonant waveguide grating(RWG)structure that is based on the quasi-bound state in the continuum(quasi-BIC)mode.This structure is capable of exciting the quasi-BIC mode of the waveguide structure.By varying the asymmetric parametersδ,the grating is transformed from the conventional two parts to the novel four parts configuration.Upon utilizing FDTD solutions software to simulate the laser behavior of the proposed all-dielectric resonant waveguide grating(RWG)structure,it was observed that the threshold of the nanolaser in the four-part grating-based RWG structure is nearly 20.86%lower than that of the conventional two-part grating structure under TE-polarized light.Moreover,the threshold of the RWG structure in the TM resonance mode is nearly 3.3 times lower than that of the conventional structure.Furthermore,it is noteworthy that the nanolaser threshold when exposed to TE-polarized light with the same geometrical parameters will be around ten times lower than that with TM-polarized light.2.We introduce a novel approach to excite bound states in the continuum(BIC)modes of two-dimensional grating nanostructures.This approach involves using nanopillars composed of highly refractive,all-dielectric materials such as In P or Si,which support in-plane radiation magnetic dipole resonances on metal films possessing high reflectivity properties and separated by a silica spacer layer.By simply varying the diameter of the nanopillars,we can flexibly adjust the BIC mode and Q-factor of this dielectric-metal hybrid nanostructure,and confine the electric field at this mode within the cylinder while maintaining a dipole-like distribution of the magnetic field in the horizontal plane.Through numerical simulations using FDTD,the laser generation is estimated to have a threshold value of only 5.31 m J/m~2,which is highly suitable for low-threshold nanolasers.