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Micro Fluidic Optoelectronic Packages based on LTCC
Keywords: LTCC, Laser Diode, Micro-fluidic
Many laser systems today use laser diodes as the primary emitters, or assemblies of these diodes to pump traditional laser crystals such as Nd:YLF. These diodes are packaged into water cooled assemblies and by their nature dissipate enormous amounts of heat, with waste heat fluxes on the order of 2000 W/cm2. Assemblies of these diodes require large amounts of electrical current for proper operation, and the device operating temperature must be carefully controlled in order to avoid a shift in the output wavelength. Typical current densities are on the order of 2000 A/cm2. The traditional solution to this problem has been the development of copper multilayer coolers. Diodes are bonded to these metal structures and liquid coolant is circulated through the metal layers in order to cool the diode bar. Assemblies of laser diodes are then formed by stacking these diode bars and coolers. Several problems exist with this approach including the erosion of the copper coolers by the coolant, a requirement for the use of de-ionized water within the system, and a significant CTE mismatch between the diode bar and the metal cooler. The authors have developed a cooler based on LTCC. These coolers have been created with a modified LTCC process flow and include an array of impingement jets and fluidic channels embedded in the ceramic material. The benefits of this approach include a much closer CTE match between the LTCC and the diode bar as well improved erosion resistance. In addition, since the LTCC is a dielectric, electrical isolation between the laser diode and the coolant can be achieved, thereby eliminating the need for de-ionized water. This paper will describe the fabrication process for these coolers in detail as well as present performance data for the LTCC coolers relative to traditional copper coolers.
Edward F. Stephens, Director of Engineering
Northrop Grumman - Cutting Edge Optronics
St. Charles, MO

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