Far-Field Directional Luminescence Emission Enhancement Of Quantum Dots By Microlens Hybrid Structure

With the rapid development of electromagnetic numerical calculation and the continuous maturity of nano-fabrication processes,multi-functional,miniaturized and integrated micro-nano photonic devices have been designed and prepared,and have been widely used in the fields of biological sciences,energy utilization and high-speed optical communications.As one of the branches of micro-nanophotonic research,fluorescence detection has been used in biosensing,medical imaging,material analysis,material characterization analysis,illumination display,etc due to its high sensitivity and easy operation.However,in a homogeneous medium,the luminescence efficiency of fluorescent substances is relatively low and the limit of detector sensitivity,which seriously restrict the sensitivity of fluorescence detection.By enhancing the far-field directional emission of fluorescent substances,the signal collection of the detector can be effectively improved,and the sensitivity of fluorescence detection can be enhanced.Compared with other fluorescent substances,quantum dots are the best choice due to their unique optical properties.Therefore,it is important to study the fluorescence emission when micro-nano photonic structures and quantum dots are coupled.In this paper,the influence of micro-nano hybrid structures on the directional luminescence of quantum dots is systematically studied.The main research contents as follows:Firstly,a hybrid structure composed of a semicircle metal silver microfluidic channel and a microlens is proposed.The effect of the hybrid structure on the directional emission of quantum dots is studied by finite difference time domain method.The calculation results show that the emission is different when a single semicircle silver microfluidic channel and quantum dots with different polarization states are coupled.This is because the light waves emitted by the quantum dots with different polarization states interact with the metal microfluidic channel to form different optical coupling modes,which makes the quantum dots have different directional emission effects.Then the effect of metal microfluidic channel with different angle on quantum dots emission is studied.It is found that metal microfluidic channel with different angle have little effect on the directional emission of quantum dots.Finally,the effect of the hybrid structure composed of the semicircle metal microfluidic channel and microlens on the quantum dots directional emission is studied.It is found that when the support of the microlens is 3 ?m,the parameters of the microlens are 7 ?m and 1 ?m and the refractive index is 3,,high-intensity and high-directional fluorescence emission can be achieved compared to semicircle metal microfluidic channel.This is because that the support changes the optical path from semicircle silver channel to microlens,thus allowing the light to undergo sufficient phase changes before the light reaches the microlens,and finally achieve better interference in the far field than the situation without support.Then,a hybrid nano-antenna structure composed of silicon column dimer and titanium dioxide disk microlens is proposed to achieve highly directional fluorescence emission.The effects of different ratio of axis parameters of silicon column dimer and the hybrid structure of silicon column dimer and titanium dioxide disk microlens on the fluorescence directional emission are studied.The calculation results show that in the short and long wavelength band,the fluorescence enhancement of the quantum dots is different for the silicon column dimer antenna with different axis ratios,but the fluorescence enhancement is not much different near the center wavelength of 600 nm.The mechanism of silicon column dimer reinforced quantum dots emission is that the silicon column dimer will generate Mie resonance under the action of light wave,the electric field enhancement in the sub-wavelength region can be realized,known as electromagnetic hot spot.The quantum dots radiation rate near the electromagnetic hot spot is enhanced,and the fluorescence emission is enhanced.Then the effect of the combination of silicon column dimer and titanium dioxide disk microlens on the directional emission collection efficiency of quantum dots is analyzed.The results show that the hybrid structure composed of the silicon column dimer and the titanium dioxide disk microlens can realize the directional emission of quantum dots,and the light collection efficiency in the directional emission direction can reach 50%,which has important reference significance for achieving highly integrated single photon emitter and single molecule fluorescence enhancement.