Study On The Dissipation And Packaging Of High Power Laser Diode Module

High power laser diode array module is an integrative high-technology of 21 century. It has absolutely advantages, such as smaller body,simpler structure,lower expenses,higher efficiency and longer life-span etc, and with the wider range of its wavelength,higher output power emerging, it has played more and more important part in industry, medicine, display, national defence and the area of pumping solid laser, it is a pop research in laser technology field nowadays, and is predicted to be the mainstream of developing economy and defence constructing.Thermal dissipation is one of the key problems in the research of high power laser diode arrays, the basic way to solve this problem is nice packaging. In this thesis, different structures, heat sinks and packaging ways are studied. Some achievements are obtained.Firstly, starting with the exploration of laser's heat sources, this paper analyzed the heat characters of lasers according to the heat transfer theory. We know that there are three sources: 1) Heat released from the non-radiative recombination of electrons and holes when current injects into the active region; 2) After reaching the threshold value, the correlated processes of photon absorption in active region, including heat produced by the spontaneous radiation recombination , free carrier absorption, and other kinds of scattering, diffraction and absorption to photons; 3) The joule heat released from the Ohmic losses after the injecting current augmented. Then the total heat resistance of laser diode was calculated according to heat transferr theory, and the temperature characters of laser diode were tested after experiments, since that we know the heat specialties of laser radically. The high output power of laser brings up corresponding high dissipation power, if heat converted from dissipation power is not removed in time, the junction temperature will be inevitably raised, accordingly it will ascend the threshold current, abase the efficiency, remove the laser wavelength, and deathfully descend the life-span of laser in evidence.Through the discussing of laser's heat specialties, we know that the heat dissipation is so important to make a high efficiency, high reliability semiconductor laser, moreover nice packaging is the key to solve the problem. At the beginning of this chapter, two key problems of laser packaging was introduced, one is accurate aiming of laser bar and heatsink, and the other one is well thermo-electricity contact, and how to settle these problems are also promoted. Combining with encapsulation forms in existence and United States patents, different packaging structures were classified and compared. Basing on different joint modes of laser bar and heatsink, it was divided to direct connection and bracket fabric. These two typical structures are discussed separately including their packaging ways and difficulties. Also a new simple module structure is designed and a 10 bar array is fabricated.Microchannel heatsink which is one of active heatsinks is used to cool high power laser stacks module in this paper. Based on the analysis of relative essays inside and outside the country, the heat sink materials, cooling liquid, the heatsink structure, and the bonding of laser bar are optimized in order to increase the transfer efficiency. Considering the practical manufacturing condition, an Oxygen-free copper microchannel heatsink consisting of five copper sheets is designed and fabricated utilizing the technology of deep photolithography, mechanical machining, and bonding with medium. By testing, the total thermal of the microchannel heatsink for cooling high power semiconductor laser stacks is 0.645°C/W, which is content with the desire of thermal dissipation.After fabricating the microchannel heatsink, the packaging structure of laser stack module is designed. The conventional laser stack usually adopts bio-sintering technique to dissipate the heat from both P and N sides of laser bar, but this kind of packing will increase the space between bars nearby, then depress the packing integration. The other packaging way combines the single integrating and bio-sintering technic, it not only reduces the heat resistance, but also improves the integrity density. But the laser stack module is difficult to disassemble after it is packaged. The whole work efficiency of the module will be affected if one bar of the laser stack is abruptly invalid. Therefore, each bar is sintered on one piece of microchannel to form a encapsulating unit, then it can be cooled efficiently, packaged in high density, and disassembled at liberty, which improves the stability and reliability of the module. When the output power is much higher, we need to add a piece of fast dissipating material (diamond artificially growing is chose at present) between chips and heatsink to conform an encapsulating unit, then laser diode module is stacked by multilayer units introduced just now. We also consider and resolve the problems of electro-contact, waterproof and the heat character consistency.Finally, a 15 layers laser stack module was successfully packaged. The peak wavelength of the laser stack array is 808.57 nm, and at input current of 200μs, 1000Hz, the peak output power of the whole module is 1500W at the 20% duty cycle. In the whole process, there was no phenomenon of short circuit and water leaking. Fig.2 is a 15 bar laser stack packaged by microchannel heatsink.