The aim of the project is to develop high power/high reliability near-IR diode laser bars to address the needs of both telecommunication and industrial markets in terms of lifetime and cost per watt. Material defects, thermal management and mechanical stresses are now main critical issues, which need to be solved to achieve higher reliability and higher output power from potentially efficient bars. This project addresses these critical issues by developing an industrial methodology to screen high performance laser bars (at 980nm and 808nm), combined with an advanced stress-free bar packaging on expansion-matched micro-channel coolers. The main objective is to demonstrate a reliable (2000h) 100W-CW bar. The achievement of this performance is expected to give a strong impact on reliability at reduced power levels: a projected lifetime, acceptable by the telecommunication market, of 100000 h is expected from 20/30W-CW bars at 980nm.
This project covers the R&D of the future generation of near-IR high-power/high reliability laser-bars for telecommunication and industrial applications. It is based on the development of industrial screening tools and advanced packaging technologies able to efficiently select, mount and cool high performance bars on optimum coolers. Based on non-destructive photo-current and photo-luminescence spectroscopies, an industrial screening methodology will be designed in order to select high quality sources of bars and to monitor the optimisation of the different packaging steps (soldering, bonding, burn-in). The development of new expansion-matched micro-channels coolers and the associated soldering process will be another major issue of this work. The expected result o is a reliable (2000h) 100W-CW bar and a projected lifetime for 980nm 20/30W bars of 100000 h.
The aim of the work is to develop the future generation of high-power/high reliability diode-laser-bars by combining advanced screening methodologies with the new expansion-matched micro-channel heat-sinks. Different non-destructive screening techniques based on optical spectroscopies will be developed and used to screen different material sources of high performance laser bars, including Al-free materials. Advanced micro-photoluminescence techniques will be used for mapping the defect and strain on the output facets which are known to influence laser degradation and reliability. Photo-current spectroscopy and the derived "laser beam induced current" technique will be investigated as complementary or alternative methods. New expansion-matched Cu micro-channel coolers will be developed for stress-free bar-packaging.
Two innovative solutions will be considered:
i) integration of a low expansion metal sheet into the micro-channel assembly,
ii) integration of a copper-tungsten bar-submount on the top of the micro-channel assembly.
Monitored by the stress-sensitive spectroscopic techniques developed in the project, soldering processes based on hard-solder (Au-Sn) and soft solder(In) will be optimised to reach the "stress-free condition". Micro-Raman spectroscopy and direct thermal imaging with an IR camera will be used to assess the quality of the solder joint and the performance of the heat-sink, while the laser is operating. To establish correlations between reliability and packaging-induced stress and to produce ageing models suitable for bars operating up to 30mW/µm, ageing tests (1000-2000h) will be carried out. Standard reliability analysis methods will be applied to the degradation and ageing data. Laser degradation and failure modes will be physically investigated on the aged bars mainly by cathodo-luminescence and photo-luminescence microscopy.
M6: Qualification of optical spectroscopy methods for bar screening.
M12: Assessment of the strain measurement methodology.
M15: Advanced expansion-matched heat-sinks available.
M21: Reduction of stress level in mounted bars by a factor of 2.
M24: Packaged bars for 100W-CW application available for lifetime testing
M27: Reliability at 100W-CW > 2000h. Extrapolated lifetime at 20/30W-CW higher than 100000 h (980nm).
Funding SchemeCSC - Cost-sharing contracts
NG7 2RD Nottingham