| Because semiconductor lasers have the characteristics of high efficiency,long life,high beam quality,good stability,and compact structure,they have developed rapidly in recent years.Among them,the 915nm semiconductor laser has a very important role in the fields of pump source,laser imaging and so on.For a high-power wide-band 915nm semiconductor laser,the temperature rise has a greater impact on its performance due to its large injection current and high heat generation.Including its effect on the quality of the output beam of the device caused by the thermal lens effect,and the effect of temperature on the reliability of the work,etc.,have imposed restrictions on the actual application of the device.In this thesis,we take 915nm wide strip quantum well semiconductor laser as the main research object,and conduct in-depth evaluation and analysis of all aspects of the device from three aspects:theoretical elaboration,simulation and experimental test.First,we theoretically analyze the heat generation mechanism of semiconductor lasers,and the effects of temperature rise on their output power,threshold current,spectral characteristics,in-situ divergence angle,and working reliability and service life.The mechanism of heat generation,its thermal resistance and measurement methods are necessary introduced.Secondly,the influence of the thermal lens effect on the output characteristics of the915nm wide stripe semiconductor laser is analyzed,and computer simulation and experimental measurement are used for in-depth analysis.In computer simulation,ANSYS software was used to perform three-dimensional modeling of the semiconductor laser under study,and the finite element was divided to simulate the steady-state working state of the device.When the thermal power of the device is 10.3W,the central junction temperature reaches 40.9?.According to the obtained thermal distribution data,the focal length of the thermal lens is calculated to be approximately 109.5?m,and the slow axis divergence angle of the laser is approximately 4.7°.Using simulation data,the thermal resistance of the device is calculated to be 1.5K/W.It is also found from the analysis and simulation results that the thermal lens effect has a greater effect on the lateral waveguide,which causes the slow-axis divergence angle to increase significantly.In order to actually measure the effect of temperature rise on the output characteristics of a 915nm wide stripe strained quantum well semiconductor laser,a TEC-based bidirectional temperature control platform was built.The temperature control range of this platform can reach 5??80?,the temperature control precision is higher thaną0.1?,the cooling/heating power is?50W,the temperature control area is?50mm×50mm,and the temperature control parameters(PID)can be precisely adjusted by computer software.The temperature control platform was used to change the heat sink temperature of the semiconductor laser,and its optical power and wavelength were measured at different injection currents.At the same time,the slow axis divergence angle was measured using a CCD camera.We found that as the thermal power increased from 2.1W to 20.0W,the slow axis divergence angle increases from 2.6°to 5.0°,the wavelength shifts red,and the focal length of the thermal lens decreases.The coefficient of the laser wavelength's change with temperature is about 0.4nm/?.Comparing the experimental measurement results with the data obtained by simulation,the results obtained by the two tend to be consistent.Thirdly,the effects of temperature rise on the photoelectric characteristics and operating reliability of the 915nm wide quantum well semiconductor laser were analyzed in detail by experimental means.When studying the photoelectric characteristics,experimental measurements were performed on semiconductor lasers under steady-state and transient conditions:In steady state,when the temperature of the device increases from 25?to 80?,its output wavelength drifts from 915nm to 936nm,the wavelength temperature coefficient of the device is about 0.4nm/?,and the slope efficiency of the laser is 1.1W from 25?/A decreased to 0.9W/A at 80?,the threshold current increased from 1.0A to 1.3A,and the threshold current density increased from 0.14kA/cm~2 to 0.18kA/cm~2.Temperature has little effect on series resistance,the calculated characteristic temperature of the device is 89.4K.In the transient state,by changing the pulse width of the injected current,the duty cycle was gradually increased from 10%to 90%,and the laser indicators were measured when the current increased from 2A to 20A at each duty cycle.After analysis,it is found that as the duty cycle increases,the spectrum of the laser's output light appears red shifted.Under the condition that the duty cycle is constant,the output optical power of the laser is linearly related to the working current,and the slope efficiency of the device decreased From1.17W/A at 10%to 1.04W/A at 90%,and the threshold current increased from 0.67A to 1.01A.In the accelerated life test of a 915nm wide strip-shaped strain quantum well semiconductor laser,the operating current of the device was set to 20A,the heat sink temperature was set to60?and 80?,respectively,and the continuous 500 hours and more than 800 hours were performed.By monitoring the output power,the expected life of the laser at 60?is about45820 hours,and at 80?it is 20661 hours.Finally,experimental methods were used to measure and analyze the output beam quality related parameters of the 915nm wide quantum well semiconductor laser.In the thesis,the CCD optical imaging method was used to measure the laser far-field spots under different injection currents,and the spot sizes at different positions were obtained.The corrected spot radius was fitted by the least square method to obtain the M~2 of the device output beam It is found that with the increase of the working current,the beam waist width and the far-field divergence angle gradually increase.When the current increased from 2A to 20A,the beam quality factor M~2 increases from 5.44 to 11.76,and the beam quality gradually deteriorates.By studying the output characteristics,especially thermal characteristics,of the 915nm high-power wide-bar quantum-well semiconductor laser,the relationship between the threshold,slope efficiency,spectrum,beam quality,and reliability of this type of device as a function of operating temperature was initially obtained,which deepened the accuracy of The recognition of the thermal lens effect of the lateral waveguide of the wide strip laser has established a simplified calculation method for the thermal lens effect of the laser far field.The above research and the obtained results have a certain supporting role for further optimizing the structure of the 915nm high-power wide-bar quantum-well semiconductor laser,so as to obtain the rapid development of high beam quality and high power working devices. |
PDF Full Text Request