Study On High Power Output And Mode Control Of Near Infrared Surface Emitting Laser

The external optical structure can be used as the external cavity of vertical-external cavity surface-emitting laser?VCSEL?,which can improve the output power and beam quality of VCSEL,such as the external cavity mirror,grating,frequency-doubling crystal and so on.The optically-pumped vertical external cavity surface emitting laser?VECSEL?made with external cavity mirror and the gain chip of VCSEL uses external light injection to generate excitation.Combining the advantages of the surface-emitting semiconductor laser and the optically-pumped solid-state laser,VECSEL not only achieves high power output,but also ensures high beam quality.Due to the flexible external cavity structure,VECSEL can achieve frequency conversion,wavelength tuning or mode locking.Combining semiconductor materials with a wide laser spectral range,VECSEL has a very wide wavelength range.Therefore,as soon as VECSEL technology appeared,it is one of the hottest research fields of semiconductor lasers.The undoped material of each layer inside VECSEL structure avoids the problems of light absorption.However,the key of high output power for VECSEL lies in the structure of internal active region with high gain.To achieve low power consumption under the high temperature,epitaxial structure of the VECSEL is optimized by using the commercial software PICS3D.The relationship between the structure of quantum well and the gain is simulated by the6)?method.Then,the gain spectra of quantum wells at different carrier density and temperature are compared,and the optimal composition and thickness of quantum wells are thus defined.The slight blue shift of the gain peak in the quantum wells with five different barriers accommodate the different emission thermal drift of the quantum wells at high temperature operation.With the Ga As P barriers at both sides of quantum wells can improve the gain characteristics of quantum wells efficiently.According to Sellmeier formula,the Al_xGa_1-xAs material system as DBR reflector is discussed,and then the transmission matrix is used to analyze the DBR reflectance spectrum and the distribution of the intensity of the light field in VECSEL.By the design and theoretical simulation of VECSEL structure,the VECSELs achieve 9.82 W unsaturated output at the about 976 nm wavelength.Under the external mirror with different reflectivity,the wavelength shift with the pumping power changed from 0.216 nm/W to 0.16 nm/W for the VECSEL.Thus,the internal heating effect is different for VECSEL with different mirrors.The divergence angle at two orthogonal directions is 9.2°and 9.0°,respectively.And the circle profile of optical field shows good symmetry.By comparing the nonlinear crystal,the LBO frequency-doubling crystal was determined,and the frequency doubling experiment achieved the output of more than 3W at 488 nm blue wavelength with the beam quality of less than 2.On the basis of the 980nm VECSEL,the design of the 1160nm VECSEL quantum well structure in the 1160 nm VECSEL is carrying out.Since In Ga As material with high In component is needed as quantum well,it leads to the generation of high strain,which is easy to cause strain accumulation.To solve the strain accumulation,the design structure of secondary strain compensation was proposed.The Ga As P with P component was used as the potential barrier,and Ga As P with high P component was used as the strain compensation layer.The VECSEL achieves the emission of 1164nm wavelength with a maximum laser power of 1.02w at the temperature of-20?.The divergence angles at orthogonal directions were 10.5°and 11.9°,respectively.The beam spot is circular symmetrical structure with good uniformity.Due to the temperature of active region with the variation of pump power,the experiment of switchable wavelength in the VECSEL can be realized without any element in the linear cavity through the design of the gain mismatch.The two wavelengths??950nm and 1000 nm within the spectral distance of 50nm were registered at more than 2W output power.This switchable wavelength operation provides a new possibility to achieve high power dual wavelength emission only using linear cavity.In addition,due to the traditional VCSEL lacking the ability to control the polarization characteristics,extensive attempts have been made to stabilize the polarization states of VCSELs,such as the use of fine metal-interlaced gratings,external optical feedback,electro-optic birefringence,photonic crystals,and high contrast grating structures.However,the large-scale fabrication of VCSELs with these complex processes is difficult to realize.Therefore,in this paper,by enhancing the anisotropic oxidation of the oxide layer,we propose a VCSEL with eye-shaped oxide aperture,realizing the control of mode and polarization.For apertures with dimensions of 2×4.6 and 3×6?m²,the orthogonal polarization suppression ratio?OPSR?of the VCSEL was 22 and 19d B,respectively.A single-mode suppression ratio?SMSR?of more than 25d B at an output power of 0.5m W was also achieved for the VCSEL with aperture dimension of 2×4.6?m².The proposed method to realize the mode and polarization control of VCSELs has great potential in future applications.