Research On 1550nm High Power Pulsed Semiconductor Lasers

In the applications of laser ranging,guidance and designation,1550nm lasers have some advantages such as better ability to penetrating smoke and fog,lower damage to human eyes,couldn't be detected by widely equipped silicon detector arrays compared to traditional lasers.InGaAlAs had higher?E_c,leading to better electron and hole confinement at high temperature and made it became an ideal material for 1550nm high power semiconductor lasers.A 1550nm InGaAlAs high power pulsed laser diode with output power of more than 10W were proposed.Based on strained quantum wells theory and material properties,the quantum well layers,barrier layers,cladding layers,waveguide layers and carrier blocking layer were designed to be In_0.68(Al_0.24Ga_0.76)_0.32As,In_0.44(Al_0.24Ga_0.76)_0.56As,InP,composition gradually variational In AlGaAs and In_0.52Al_0.48As respectively.The reflectivity of high-reflection films and antireflection films were optimized to be 98%and 11%respectively to obtain highest output power.Ridge waveguide parameters were analyzed by equivalent refractive approximation.With residual cladding layer thickness between 0.1⁰.3?m after etching,the optical field confinement and device reliability were guaranteed and waveguide width was designed to be 100?m.In order to further improve the output power and slope efficiency,on the one hand,the asymmetric separated confinement heterostructure?SCH?was adopted to improve slope efficiency and output power to 0.41W/A and 12.2W@30A.On the other hand,by pretreating facets in N₂ gases before coating and introducing a 25?m non-injection regions between p-electrode and p-InGaAs contact layer,the catastrophic optical damage?COD?threshold were increased and facet chemical damages were reduced.The failure of laser diodes generated from dark line defects,mechanical damages,solder failure and poor ohmic contacts.Aging screening,reducing defect density of semiconductor materials,solder,electrode and heat sink materials optimization and metal package with leakage rate below 5×10^-3 Pa cm³/s were adopted to improve reliability.MOCVD epitaxy,ridge waveguide etching and ohmic electrode preparation were optimized.MOCVD growth temperature,interfacial growth interruption time,chamber pressure and V/III ratio were optimized.XRD and PL test results show that the epitaxial quality was well.To obtain reverse-mesa ridge waveguide with smooth sidewall,low-viscosity and thinner photoresists were used,exposure time was shortened and dry reactive ion etching?RIE?was used.By controlling the AuGe Ni alloy annealing time,TiPt electrode heat treatment temperature and processing time,good ohmic contacts were obtained.Beam shaping was performed by cylindrical lens and the simulation results show that the vertical divergence angle was 0.92°.Test results show that all samples reached the design requirements:the output wavelength was within the range of 1550nm±20nm,the spectral width was below15nm,the peak output power was larger than or equal to 10W,the threshold current is less than or equal to 1A and the vertical divergence angle was less than or equal to 1°.After stored under high and low temperature and random vibration tests,optical power deterioration of all samples was below 10%while maintaining larger than 10W.After the electrical aging,one sample was failed and output power of two samples was below10W caused by sinter void.Sintered voids cause the heat generated during high power laser chip operation unable to effectively conduct to heat sink.The heat accumulated in the device and destroyed the internal structure,causing laser failure or output power degeneration.