| Vertical-cavity surface-emitting laser(VCSEL)is a new type structure of thesemiconductor lasers emerging in the1970s. Because of the unique structural features,such as using quantum wells as the gain medium, emitting light perpendicular to thedirection of the substrate and very short resonant cavity length, VCSEL has a large ofadvantages compared to the conventional edge-emitting lasers (EEL): easytwo-dimensional array integration, operating on dynamic single longitudinal mode,circular output beam with small divergence angle, highly fiber coupling efficiency andso on. Above advantages had made VCSEL devices become very important inphotoelectronics applications for optical fiber communication and opticalinterconnection. However, there are still some critical problems in developing lowerthreshold current, high power and stable temperature operation. One key constraint isthe more serious thermal effect in VCSEL compared to the EEL. Due to the thermaleffect, temperature rise in VCSEL leads to many changes of the performance of devices.Besides, the thermal characteristics in two-dimensional array VCSEL are more severeowing to horizontal current spread and the superimposed effect. In this paper,theoretical analysis, experimental measurement and device optimization areinvestigated on the thermal characteristics of high power980nm single and arrayVCSEL.The temperature properties of In0.2Ga0.8As/GaAs0.92P0.08quantum well are studied theoretically mainly from two aspects of the band and the gain. The influenceof temperature on the bandgap width and band offset are calculated. Change rates ofthe gain peak wavelength and the peak gain with temperature are obtained throughsimulating material gain spectrums at different temperatures. Based on thecharacteristic matrix method, reflectivities of P-DBR and N-DBR at varioustemperatures are calculated and the relationship between reflectivities and temperatureis analyzed. Above discussions provide a theoretical basis for studying temperaturecharacteristics of emitting wavelength, threshold current and output power of VCSELdevice and are instructive to optimize the thermal performance of VCSEL. Thetemperature characteristics of the near field are modeled theoretically, from whichinteraction of carriers, transverse modes and thermal effect is discussed qualitatively.Experiment measurements of thermal characteristics of VCSEL are carried outon the basis of theoretical simulations. Two methods of photoluminescence spectrumand electroluminescent spectrum are used to represent the change of the gainspectrum wavelength with temperature. Change rates of two methods are0.3643nm/Kand0.3873nm/K, respectively, which are almost equal and agree well with theoryvalues. In addition, the average temperature rise in active region is achieved throughmeasuring central wavelength shift of the electroluminescent spectrum at differenttemperatures in pulsed operation and central wavelength shift of theelectroluminescent spectrum at various CW injection current using VCSEL waferwith EEL structure. When CW injection current is500mA, the average temperaturereaches about353K. Thermal characteristics of single VCSEL devices with differentoxide apertures are studied experimentally in order to get better beam quality andhigher output power by choosing appropriate size of the oxide aperture. Singledevices with oxide apertures of415μm,386μm and316μm are made throughcontrolling the oxidation time. Diameters of the mesa and the P type contact are450μm and400μm, respectively. Thermal resistances of three devices are measuredbased on their different output characteristics under continuous-wave (CW) operationat room temperature. It is found that the smaller the oxide aperture is, the larger the thermal resistance of the device becomes. Temperature rise caused by self heating ofinjection current is obtained by comparing the relationship of the current, thewavelength and the temperature. At a CW injection current of1A, the temperature ofdevices with oxide aperture of415μm,386μm and316μm are32.4℃,35.2℃and76.4℃, respectively. Near field patterns are measured using a4f optical systembased on the optical system imaging mechanism. In order to demonstrate interactionof carriers, multi transverse modes and thermal effect, intensity distribution of thenear field and changes of mode size under CW and pulsed operation are compared.Combination of experimental results and theory investigations offers important basisfor further study on the thermal characteristics of high power VCSEL.Temperature distributions of4×4VCSEL array with0.5times,1times,1.5timesand2times the active region are simulated using COMSOL software based on finiteelement analysis. From simulated results we can see that the larger the unit spacing is,the less the thermal coupling between individual elements gets and the lower thetemperature of every element becomes. When unit spacing reaches1.5times theactive diameter, temperatures between elements at different positions decrease morethan25K comparing with50μm unit spacing which is close to room temperature. Anew array formation is designed through altering the configuration of elements so thatthermal coupling between elements can be reduced. It is found that the wholetemperature of the array greatly decreased without influencing the distribution of thefar field and even distribution of the temperature is reached.
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