Study Of Thermal Behavior Of High-power Diode Laser Array

In recent years, with the continuous development of high power diode lasertechnology, they have access to a wide range of applications successfully in the fieldof industrial, military, scientific research, medical, direct material processing, and soon. In order to expand the applied fields of high-power diode laser further, it becomesto be the only way for the development of high-performance diode laser technologythat improving the electro-optical properties of devices, as well as reliability and life,continuously. However, as the diode laser output power improve, the heat generated inactive region also increase continuously, which result in the device junctiontemperature rise serious. It is well know that the excessive junction temperature ofdiode laser will cause a series of problem, such as thresh current increasing, slopeefficiency&output power decreasing, lasing wavelength shifting, spectral of diodelaser array broadening, and so on. It not only has critical effects on the stability of theelectro-optical performances, but also poses a serious threat to device reliability andlifetime. Based on the mentioned consideration, Aiming at enhancing the thermalmanagement level of device, and to achieve the purpose of stabilizing the deviceelectro-optical properties and improving device reliability and life, it is more andmore crucial for diode laser to analyze the thermal behaviors systematically and todevelop thermal design and optimization effective.Firstly, the thermal behaviors of conduction cooled diode laser arrays packagedwith different packaging processes were analyzed respectively, by the combinedmethods of numerical simulation and experimental analysis in this thesis. Themodeling results obtain the temperature distributions of device and its active region atcontinuous wave (CW) mode, present the characteristics of changes of thecomponents of thermal flux in active region, and reveal the thermal resistancecontributions from the important elements of the laser structure, such as laser chip,solder layer and heat-sink, to the total thermal resistance of a laser packagequantitatively; it is found that the characteristics of conduction cooled devices withdifferent packaging processes are similar and the differences only lie in the diversityof each key parameters, by comparative analysis of modeling results; due to theintroduction of sub-mount, the thermal management of devices packaged with hardsolder process is more serious than that of conventional devices packaged indium solder process. In order to validate the accuracy and reliability of modeling results, thethermal properties of devices are tested and characterized under CW mode byexperimental means, a large amount of verifications and analysis have been donebetween the experimental results and theoretical calculations. The results show thatthe experimental values are consistent with theoretical calculated values.For the conduction cooled diode laser arrays operated in pulse state, the devicespackaged with indium solder are taken as a representative case, the simulationsanalyze the transient state thermal behaviors of these devices, and elaborate the effectof heat accumulation and the dynamic thermal balance process of devices from thenon-steady-state to steady-state; In addition, the thermal crosstalk among emitters inthe one-dimensional arrays are modeled and analyzed basing on the devices packagedwith hard solder technology, of which the thermal management is more serious. At thesame time, the validating experiments are fulfilled. The experimental results show thatthe numerical results are conformed to the measured experimental results qualitatively,although they are not equal.Secondly, for the thermal reaction of high power diode laser array with voids insolder layer, the effects of solder voids, including the factors of its locations, shapeand voids sizes, on the temperature distributions of active region and facettemperature of devices are studied systematically and obtained. Besides all, themodeling results reveal the quantitative relationship between voids sizes and localtemperature rise, and that between the output power and thermal reactions of soldervoids. Moreover, from an experimental perspective, how thermal reactions of soldervoids influence the performances of devices are tested and analyzed qualitatively.Under the guidance of analysis studies, the high power diode laser array with goodperformances was produced.Finally, basing on the aforementioned modeling conclusions, for the poorthermal management of devices packaged with hard solder technology, this paper notonly analyze and discuses the influence factors of thermal crosstalk among emitters inthe arrays, but also presents some thermal optimizations for devices from thechip-level and packaging-level angles, respectively. The optimization results proposethe strategies about how to decrease thermal crosstalk and enhance the efficiency ofwaste heat conduction down away the array; more important, it lays the foundation forreducing the device thermal resistance and improving the dissipating efficiency.Under the guidance of modeling conclusions, the devices with copper-tungsten sub-mount and that with copper-diamond sub-mount are prepared respectively, andthe conventional devices packaged indium solder are also produced. After the contrastanalysis of performances of these three type devices, it is found that the performancesof devices with copper-diamond sub-mount are better than that of devices withcopper-tungsten sub-mount, although the packaging process of devices withcopper-diamond sub-mount is immature. What is more, its performances almost aswell as that of traditional devices packaged with indium solder. At this point, theproblem of how to achieve high output power while maintaining or even to improvedevice reliability and lifetime is solved by this measure successfully.