| In recent years,with the rapid development of the 5G network,Internet,and AR/VR technologies,we have entered a data-centric information age.Especially in next-generation optical communication systems,the amount of information transmission is increasing.At the same time,optical interconnect technology has quickly occupied the market with an irreversible trend.Vertical-cavity surface-emitting lasers(VCSELs)become an important light source for optical interconnect technology due to their advantages of small size,low power consumption,and easy integration.VCSELs needto continuously improve their performance to meet the requirements of the next generation of information technology,such as low power consumption,small volume,and low threshold current.Mirrors and active regions are very important components of the VCSELs,and they have an impact on the performance of the devices.In traditional VCSEL devices,distributed Bragg reflectors(DBRs)meet the laser lasing conditions,but also cause high series resistance and poor heat dissipation performance of lasers.In particular,the P-type DBRs seriously affect the performance of devices such as heat dissipation,power consumption,and threshold.In order to improve the performance of the VCSELs,it is necessary to focus on studying the P-side mirror structures of the VCSELs to improve the heat dissipation performance and reduce the power consumption.In addition,when the lattice constant of active regions matches that of the substrates and the mirrors,excellent performances of the devices can be achieved.For the oxide-confined VCSELs,the oxideconfined layers are usually placed in the P-side mirrors near the active regions.Therefore,the position of the oxide-confined layer should also be considered when designing the P-side mirror.The wavelengths of 850 nm,1310 nm and 1550 nm are the low-loss transmission windows of silica optical fiber.Consequently,they are widely used in optical communication.At present,the fabrication technology of short-wavelength VCSELs is relatively advanced,however,long-wavelength VCSELs still face many difficulties.These difficulties are mainly caused by lattice constant mismatching between mirrors and active regions.Therefore,when designing long-wavelength VCSEL devices,mirrors and active regions materials need to be considered.To achieve better development of 850 nm and 1.3 μm VCSEL devices in optical communication and other fields,it is a top priority to continuously improve their performances.However,the heat dissipation of the lasers can seriously affect device performances such as the threshold current,output power,and consumption.P-side mirrors seriously affect the heat dissipation of devices.To solve the above problems,a new type of two-dimensional photonic crystal mirror is proposed which has a smaller thickness,lower thermal resistance,and higher material thermal conductivity.It also avoids stress problems in subwavelength grating mirrors.Based on the above background,VCSELs with the two-dimensional photonic crystal mirrors as the P-side mirrors are studied in this paper.This work mainly studies VCSELs with wavelengths of 850 nm and 1.3 μm.The specific work and research results are as follows:(1)An 850 nm VCSEL,whose P-side mirror is the two-dimensional photonic crystal mirror,is proposed.Replacing the DBR of the VCSEL with two-dimensional photonic crystal mirror can effectively reduce device thickness and achieve single polarization of the device.The twodimensional photonic crystal mirror has relatively smaller thickness and higher material thermal conductivity.Therefore,the photonic crystal mirror is beneficial to reduce consumption and improve heat dissipation as well as optical performance of the device.Furthermore,its photonic crystal structure has a small etching depth and strong optical limiting.Therefore,it hardly affects the series resistance and current density.It is beneficial to further reduce the threshold current density of the laser.At the same time,stress in the subwavelength grating mirror is avoided,which is due to volume reduction when high aluminum component compounds are oxidized to AlOx.Based on the three-dimensional finite-difference timedomain method,the reflectivity of the two-dimensional photonic crystal mirror is analyzed to optimize the material structure and device structure.It is concluded that the high reflectivity bandwidth of the two-dimensional photonic crystal mirror is 106 nm,and the reflectivity at the lasing wavelength of 850 nm is 99.99%.Moreover,its thickness is 12.4%of the thickness of the DBR,61.7%of the thickness of the subwavelength grating mirror,and the thermal conductivity increased by 46%compared with the DBR.(2)The optical field distribution and the position of the oxideconfined layer of an 850 nm VCSEL are studied,which uses the twodimensional photonic crystal mirror as the P-side mirror.The optical field distribution and refractive index distribution of the VCSEL are analyzed to optimize the position of the oxide-confined layer.The position of the oxideconfined layer in the two-dimensional photonic crystal mirror is measured by making the position of the oxide-confined layer at the wave node of the intracavity optical stationary wave.(3)A 1.3 μm GaAs-based quantum dot VCSEL,whose P-side mirror is the two-dimensional photonic crystal mirror,is studied.Replacing the DBR of the VCSEL with the two-dimensional photonic crystal mirror can effectively reduce device thickness,improve heat dissipation and achieve single polarization of the device.In addition,the quantum dot active regions contribute to the successful fabrication of long-wavelength GaAsbased VCSELs,reducing the threshold current density and increasing the optical gain.The reflectivity of the two-dimensional photonic crystal mirror is analyzed to optimize the material structure and device structure.It is concluded that the high reflectivity bandwidth of the two-dimensional photonic crystal mirror is 133 nm.Its thickness is 473 nm,which is 9.7%of the thickness of the DBR.(4)The optical field distribution and the position of the oxideconfined layer of the 1.3 μm VCSEL are studied.The optical field distribution and refractive index distribution of the VCSEL are analyzed to optimize the position of the oxide-confined layer in the laser.The position of the oxide-confined layer in the two-dimensional photonic crystal mirror is determined by making the position of the oxide-confined layer at the wave node of the intracavity optical stationary wave. |
