Development Of High Power And High Polarization 792 Nm Semiconductor Laser Module By Multiple Beam Combination Method

The 3～5μm mid-infrared laser is the most ideal atmospheric transmission window,which was widely used in the fields of air pollution monitoring,infrared imaging,sensing technology,surgery,free space communication,photoelectric countermeasure and other fields.As the pump source of optical parametric oscillator,the 792nm fiber-coupled semiconductor laser module first pumps the thulium-doped crystal and then pumps the holmium-doped crystal,which is the main method to produce mid-infrared laser in 3～5μm.The mid-infrared laser photoelectric countermeasure system prepared in this way has the advantages of high efficiency,good reliability and strong adaptability.792nm semiconductor laser chips and fiber-coupled semiconductor laser modules of high power,high polarization rate and high reliability are the core laser components of this mid-infrared laser electro-optical countermeasure system,which has received extensive attention in the world.High power fiber coupled laser needs multiple lasers beam combining,the quality of laser after beam combining depends on the performance of laser chip.The structure design of the laser,the epitaxial growth and the chip preparation process must be strictly controlled.Besides,the divergence angle of the laser directly emitted by the semiconductor laser is very large,and the beam quality of the fast axis and the slow axis is not consistent,which causes that the laser beam cannot be coupled directly into an optical fiber.In order to obtain a high output power fiber coupled module,the beam shaping,combination and fiber coupling are essential technological processes.In the experiments,considering that the size of optical element size is very small and the high positioning accuracy is required,how to achieve the precision assembly of optical devices is also the key factor affecting the quality of laser module.In this work,we have developed and grown the 792nm laser epitaxial wafer of In Ga As P/Ga In P material through the MOCVD equipment,and then fabricate laser chip by photolithography,etching,PECVD,metal evaporation,alloying and dissociation processes.We design optical system tocollimate the fast axis and slow axis and realize 24 chips fiber coupling.The output power of laser module is 232W at 10A continuous current,the degree of polarization is 94%and the electro-optic conversion efficiency is 48.6%.The main contents of this paper are as follows:（1）We have grown the high quality and low defect semiconductor laser epitaxial wafer through the MOCVD technology.We have designed the chip structure with broad waveguide large optical cavity,asymmetric wide waveguide structure and aluminum-free active layer.By broad waveguide large optical cavity,the size of a beam near-field mode is increase,the output optical power density is reduce,the output power is increased,and the service life of the device is improved.By adopting the asymmetric wide waveguide structure,the internal loss and waste heat of the laser are reduced,meanwhile,the differential quantum efficiency and the reliability are improved.By using the aluminum-free In Ga As P/Ga In P active layer to make the laser have high optical catastrophic power density on the cavity surface.（2）In this work,we fabricated laser chip by photolithography,etching,PECVD,metal evaporation,alloying and dissociation processes.We reduced the nonradiative recombination and improve the catastrophic optical damage level by facet passivation and facet coating,and used a COS（chip on submount）package to fabricate the single emitter laser and used various characterization methods to test device performance.At 25℃,the threshold current of single emitter COSis 1.55A,and the threshold current density is 190A/cm^-2.Under 10A current,the output power of the laser reaches 10.45W,the voltage is 1.88V,the electro-optical conversion efficiency is 55%,and the polarization degree of the device is 94%.With increasing the working current,the laser still has no catastrophic optical damage at 20A,which allows laser to work at higher current and higher power.（3）We improve the output power of semiconductor laser by beam combination technology.In this lettr,We used 24 high power and high polarization single emitter semiconductor lasers couple into 200μm fiber with a beam NA of 0.22.The laser module is aged for more than 4000hours at 12A and 25℃without obvious power degradation.The coupling laser module output power reaches 232W and the electro-optical conversion efficiency is 48.6%.