Study On The Mode Control Of Vertical Cavity Surface Emitting Laser

Compared with the traditional edge emitting laser,the vertical cavity surface emitting laser?VCSEL?is widely applied for its unique advantages,such as natural single longitudinal mode,low threshold current,easy fabrication in two-dimensional arrays and circular output light spot.But VCSEL has a large transverse dimension and multi transversal mode excitation usually,which limits the application of VCSEL in the field of spectral analysis and optical communication.The traditional method of realizing single mode mainly involves epitaxial regrowth and accurate semiconductor etching,which make the fabrication of single-mode devices complicated and difficult to control,so there are great difficulties in achieving mass production.For achieving single mode in large oxidation aperture,in this paper,the higher order modes are suppressed by the surface relief and the dielectric film relief to obtain single mode.The influence of temperature on the device is solved by the gain-cavity mode detuning in structural design for stable single-mode operation at high temperature.In our experiment,single mode and single polarization are achieved via irregular elliptical dielectric film relief,the influence of dielectric film on VCSEL is also discussed.Firstly,in order to acquire VCSEL single transverse mode operation,we need to understand the relationship between transverse dimension and pattern distribution.For improving the output power and reducing the resistance of the device,a 7?m oxidation aperture is formed in the surface relief VCSEL.Multi-transverse modes will be lased with the current enhancement,we adopt the most effective surface relief technique to sovle this problem,the loss of higher order modes is increased by etching the cladding layer and DBR,which can increase the loss of higher order modes and improve the threshold gain of higher order modes,the fundamental transverse mode region remains unchanged so that the mode selection is realized.And for the dielectric film relief VCSEL with 6?m oxidation aperture,a?/4thickness of dielectric film is deposited on the surface of VCSEL,which will maximize the threshold gain for all modes,the fundamental transverse mode region of dielectric film is etched by dry etching and the higher modes region of dielectric film is reserved.By controlling the thickness and position of the dielectric film deposition to suppress the high order mode and obtain the single mode.In the experiment,we have prepared three kinds of single mode VCSEL devices.The first is the surface relief VCSEL device,stable single-mode operation at high temperature is produced by the surface relief integrated vertical cavity surface emitting laser?VCSEL?.Gain-cavity mode detuning technique is employed to realize high operating temperature for VCSEL.The surface relief is etched in the center of top side as a mode discriminator for fundamental mode output,and the threshold current minmum is 1.94mA at high temperature by gain-cavity mode detuning technique.Maximum single-fundamental-mode output power of 0.45mW at 80?is obtained,and the side mode suppression ratio?SMSR?is more than 30dB with the increasing temperature and current,respectively.The second is the VCSEL with circular dielectric film relief,we establish a novel method of controlling the transverse modes of vertical cavity surface emitting lasers?VCSELs?to achieve1mW single-fundamental-mode lasing.A dielectric mode filter is installed on top of the VCSEL.The dielectric layer?SiO₂?is deposited and patterned to modify the mirror reflectivity across the oxide aperture via antiphase reflections.This mode selection is nondestructive and universally applicable for other structures under single transverse mode.Destructive etching techniques?dry/wet?or epitaxial regrowth are also not required.This method simplifies the preparation process and improves the repeatability of the device.Measurements show that under continuous-wave current injection,the side-mode suppression ratio exceedes 30dB.The third is the VCSEL with elliptic dielectric film relief,the OPSR of elliptic dielectric layer VCSEL exceeds 16dB and the SMSR of elliptic dielectric layer VCSEL is larger than 25dB,maximum single-fundamental-mode output power of0.55mW at 25?is obtained,single mode and single polarization are obtained using the elliptic dielectric layer VCSEL.