| Semiconductor lasers are currently the most productive lasers,and their applications are extensive.A disadvantage of conventional semiconductor lasers is that the divergence angle is large and often requires a lens system to bunch.A vertical cavity surface emitting laser(VCSEL)is a semiconductor laser whose laser exit direction is perpendicular to the cavity surface.But it also has a large divergence angle,which limits its application in many fields.The use of a quantum dot light-emitting structure light source based on VCSEL has the advantages of high performance,small size,and low cost.At the same time,compared with the traditional distributed Bragg reflection(DBR)resonant cavity,the resonant cavity formed by the photon quasicrystal arrangement is structurally diverse,which indicates that it can be exhibited in a unique structure.And it’s different from previous features.A total reflection mirror composed of a photon quasi-crystal structure is used at the bottom of the light source,and a transmissive mirror with a photon quasi-crystal structure is used at the bottom.This design has a simple structure and a small volume,and is also advantageous for reducing the divergence angle.This thesis is a VCSEL consisting of a 460 nm quantum dot source and a Fibonacci photon quasicrystalline(FPQC)resonant cavity.It has the advantages of small size,low cost,small divergence angle,etc.The specific content of this article is as follows:1.The design of the quantum dot source provides a light source that can adjust the center wavelength of the spectrum for the VCSEL.It also has the characteristics of small volume and low threshold:(1)The luminescence model of the quantum dot is calculated by the finite element method design,and the desired emission spectrum is determined according to the difference in the concentration ratio of the doping materials.(2)In order to determine the threshold of the light source(the threshold current and voltage of the laser),the exact value of the threshold is determined from the sharp change in the spectrum at different voltages and the slope of the I-U curve of the source structure,respectively.2.The photon quasicrystalline resonator is designed to reduce the divergence angle,mode area and loss during propagation of the laser:(1)The Fibonacci order is selected as the order of the quasicrystalline structure,respectively.The purpose is to determine the number of layers of the mirror surface,by measuring the reflectivity of 1 layer,2 layers,...,10 layers quasicrystalline structure.Then the thickness of the first material is fixed.By changing the thickness of the second material,the reflectance is investigated.The same method is used to determine the thickness of the first material corresponding to the maximum reflectance,so that the thickness of each of the two materials at the maximum reflectance is found.A total reflection mirror with 460 nm emission spectrum at the center of the spectrum was finally obtained.(2)Optimize the transmission mirror surface in the same way.The two parameters of the divergence angle and the relative mode field area are mainly considered here.First,the number of layers of the transmission mirror was fixed.Second,the specific thickness of each layer was fixed.So,the reflection mirror and the transmission mirror surface of the cavity under the light source of 460 nm are obtained.3.Parameters and comparison of FPQC resonator laser and DBR resonator laser:(1)The overall structure and threshold of the two lasers are introduced.(2)According to the literature design,the DBR laser is optimized to achieve the optimal DBR cavity structure under the condition of the light source.(3)Comparing the parameters of far field divergence angle,relative mode field area and output spectrum,the advantages of FPQC resonator laser are obtained.In addition,as a quantum dot source of the laser source portion,an arbitrary spectral center can be obtained in the visible light range by changing the doping concentration,and it can be used as a light source for many lasers.At the same time,the 460 nm total reflection mirror on one side of the VCSEL resonator has a Fibonacci quasicrystalline structure and a small volume,which can be applied to radio frequency identification,antennas,sensors and the like.The resulting VCSEL of the FPQC resonator can be applied to the field of lasers with small divergence angles. |
