Design And Research Of Nano-Laser Based On Plasmon

With the development of photonic devices and nanotechnology,the requirements for miniaturization of devices are becoming more urgent,and lasers,which are one of the commonly used light sources for photonic devices,tend to be miniaturized.However,the physical volume of conventional lasers cannot be reduced to nanometer scale due to the large resonator and the inability to break through the diffraction limit.The wavelength of surface plasmon is smaller than taht of the light in free space,which gives an opportunity to break through the optical diffraction limit.Therefore,the laser based on surface plasmon amplification by stimulated emission of radiation(Spaser)can break through the diffraction limit and provides a new method to fabricate the nanolasers.This paper mainly includes the following two parts:1.Study on performance of Spaser based on Fano resonance.Metals are the essential materials for surface plasmon generation in Spaser devices,but there are irrevocable ohmic losses and radiation losses in metals,which will increase the Spaser threshold and make it more difficult for the construction and application.Therefore,how to reduce the radiation loss in the metal structure to achieve a low threshold Spaser has attracted extensive attention of researchers.Fano resonance is formed by the coupling of bright mode and dark mode,which has the characteristics of weak radiation.Therefore,low threshold Spaser can be realized with the help of Fano resonance cavity.We proposed a plasmonic tetramer structure with Fano resonance effect,which is composed of nanoantenna and T-shaped dimer.The scattering and absorption spectra are calculated by finite element software COMSOL,and the typical Fano resonance peak in the spectrum.Then we theoretically research on the Spaser characteristics based on the designed structure,the calculation results show that the model has a lower threshold of 0.0386,and the output laser has a narrow line width.By changing the geometric size of the metal structure,the output wavelength of Spaser can be tuanble,and the threshold value is still very low between 0.03 and 0.04 even after the geometric size changes.2.Research on performance of Spaser based on multi-resonance substrate.Firstly,we studied a Spaser model based on plasmon tetramer and simulated the proposed structure with COMSOL,which provides a new method for tuning the Spaser wavelength without changing the structure.The optical properties of the plasmon tetramer structure were studied in detail,and the source of the resonance mode was analyzed.The designed structure can generate three plasmon resonance modes,and the three surface plasmon resonance modes can be excited by the gain material to realize three different output wavelengths,which proves that our method can realize the wavelength tunability of Spaser in one structure.The influence of structure size on Spaser wavelength is also studied.After changing the length of metal arm in the vertical and horizontal directions of plasmon structure,the calculation results show that the Spaser wavelength also changes.That is to say,the structure we proposed can also change the Spaser wavelength by changing the geometrical size of the structure.