TITLE: Process to Mitigate Catastrophic Optical Damage to Quantum Cascade Lasers
TECHNOLOGY AREA(S): Air
ACQUISITION PROGRAM: PMA272
Tactical Aircraft Protection Systems
OBJECTIVE: Develop an
optimized fabrication process for quantum cascade lasers (QCLs), such as facet
passivation and high thermal conductivity coatings, in order to mitigate the
impact of the QCL’s operating lifetime due to catastrophic optical damage
DESCRIPTION: Employment of high-power
QCLs for aircraft protection against shoulder-fired heat-seeking missiles is
among the most critical applications for these devices. The ongoing Common
Infrared Countermeasures (CIRCM) program represents the first program of record
for the QCL technology. The program puts QCLs on the path toward wide
acceptance in DoD applications.
CIRCM is focused on the development of, and transition to, a large throughput
production of a compact and lightweight QCL-based Directed Infrared Counter
Measure (DIRCM) system, capable of addressing the threats posed to rotary wing
aircraft by the proliferation of the Man-portable air defense system (MANPADs).
A relatively low (conservative) continuous wave optical power on the order of
1W is targeted in this program. However, a higher optical power, exceeding 5W
for a single emitter, would significantly improve system characteristics.
The maximum optical power level for state-of-the-art QCLs is primarily limited
by COD of the output laser facet: QCLs tend to fail at optical power densities
on the order of 10MW/cm2, which roughly corresponds to total power level of 3W
for narrow-ridge (10micron-wide) devices. Despite the fact that QCLs are
projected to be the cornerstone of a number of next generation infrared systems
for various DoD applications, COD failure mechanisms have not been studied for
these devices. The lack of reliable experimental data on laser failure and the
absence of a practical COD model make it impossible to properly evaluate mean
time between failure (MTBF) for future infrared products comprising QCLs.
Preliminary QCL COD elevations [Ref 1] show that the two most typical failure
scenarios for high-power buried-heterostructure QCLs mounted epi-down on
submounts with a high thermal conductivity are: (1) Rapid degradation (on a
scale of microseconds) in laser performance occurs when optical power density
at the output facet significantly exceeds 10MW/cm2. Output facet inspection in
this case shows a significant damage with a drop of melted material often observed
near the active region area. The inspection results suggest that, similar to
short-wave infrared diode lasers, the QCL damage occurs due to a thermal
runaway process that results in the active region material melting, an
irreversible damage to the laser. The positive feedback loop responsible for
the QCL rapid degradation has never been clarified for QCLs and there is no
active research being carried out to increase the COD threshold and, therefore,
increase optical power level for traditional Fabry-Perot emitters. (2) For a
lower power level, in the range from 5 to 10MW/cm2, hermetically packaged QCLs
can reliably operate for >1,000h [Ref 2]. However, eventually they still
catastrophically fail. The most likely explanation for the failure is device
aging accompanied by defect diffusion to the output facet at elevated
temperatures, which in turn lowers COD threshold. Again, the natures of the
defects, time-scale for their development, and conditions that influence their
formation have never been studied for QCLs.
Therefore, it is the goal of this topic to develop optimum fabrication
processes, such as facet passivation and high thermal conductivity coatings
that will mitigate the aforementioned reliability issues.
PHASE I: Design and
demonstrate feasibility of a model capable of identifying the positive feedback
loop responsible for the thermal runaway in QCLs, describing the rapid output
facet degradation, and determining the COD threshold for typical edge emitting
QCLs. The model development will require fitting to thermal and time-resolved
optical experimental data. The Phase I effort will include prototype plans to
be developed under Phase II.
PHASE II: Develop a prototype
fabrication process employing the model designed in Phase I. Perform experimental
data collection to refine the model via study of immediate (microsecond scale)
damage at high power level, long term degradation, and defects formation
analysis. Based upon the improved device model, develop QCLs with increased COD
threshold (higher power single emitters) and estimate MTBF for various
PHASE III DUAL USE
APPLICATIONS: Develop a cost-effective process for manufacturing
high-reliability QCLs that are to be transitioned and integrated into DIRCM
systems for field deployment in a Navy platform.
Commercialize the technology based on the reliability evaluations from this
program for law enforcement, marine navigation, commercial aviation enhanced
vision, medical applications, and industrial manufacturing processing.
1. Lyakh, A., Maulini, R.,
Tsekoun, A., Go, R., and Patel, C.K.N. “Tapered 4.7µm quantum cascade lasers
with highly strained active region composition delivering over 4.5 watts of
continuous wave optical power.” Optics Express, 2012, Vol. 20, Issue 4, pp.
2. Miftakhutdinov, D.,
Bogatov, A., and Drakin, A. “Catastrophic optical degradation of the output
facet of high-power single-transverse-mode diode lasers.” Quantum Electronics,
Vol 40, No 7, 2010.
3. Hu, Y., Wang, L., Zhang,
J., Li, L., Liu, J., Liu, F., and Wang, Z. “Facet temperature distribution of a
room temperature continuous-wave operating quantum cascade laser.” Journal of
Physics D: Applied Physics, Vol 45, No 32, 15 August 2012.
4. MIL-STD-810G, Department
of Defense Test Method Standard for Environmental Engineering Considerations
and Laboratory Tests. United States Department of Defense. 31 October 2008.
KEYWORDS: QCL; Wall-Plug
Efficiency; Thermal Load; Scaling; MWIR; Brightness
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