We present a laser drilling technology eminently suitable for structuring of solid glass preforms for microstructured optical fibers (MOF). This technology allows fiber designs that can not be easily adressed by stack and draw technology. As an example, we present a four ring hexagonal hole structure drilled in a silica rod over a length of 80 mm at ILT. The fiber drawn from this preform was used for absorption measurements and fiber Bragg grating inscription experiments at IPHT. Geometrical aspects are compared to those of a MOF with a similar structure made by the stack and draw technology.
High-power diode lasers in the mid-infrared wavelength range between 1.8μm and 3.0μm have emerged new
possibilities for solid-state pumping and direct material applications based on water absorption with favoured
wavelengths at 1.94μm and 2.9μm. GaSb based diode lasers are naturally predestined for this wavelength range.
We will present results on MBE grown (AlGaIn)(AsSb) quantum-well diode laser single emitters and laser arrays at
different wavelengths between 1.8μm and 3.0μm. At 1.94μm different epitaxial designs have been investigated in order
to optimize the GaSb based diode lasers for higher wall-plug efficiency and higher brightness. More than 30%
maximum wall-plug efficiency in cw operation for single emitters could be demonstrated for resonator lengths of 1mm.
At 2.25μm a high wall-plug efficiency of 24% has been measured. For 2mm resonator length by using asymmetric
waveguide structures the wall-plug efficiency could be doubled. Fast axis far field widths of 70 degree (95% power
included) have been demonstrated. At 2.9μm emitting wavelength broad-area lasers with 2mm resonator length with
360mW at 10°C heat sink temperature are presented. We have also started to transfer the concepts for higher brightness
to this wavelength regime.
19-emitter laser arrays emitting at 1.94μm have been packaged on actively cooled heat sinks. Comparable high wallplug
efficiencies have been measured with p-side down and p-side up packaging. In all configurations far field widths
are well below 90 degree (95% power included). Finally a record value of 140W have been measured for a stack built
of 10x 20% fill factor bars emitting at 1.91μm.
The reliability of high-power diode laser bars is limited by the thermo-mechanical stress occurring during the packaging
process and operation. The stress is caused by the mismatch of the thermal expansion coefficients between heat sink and
laser bar. In general the stress influence grows with the bar size. The development of tapered laser bars leads to higher
cavity lengths so the thermo-mechanical stress in the longitudinal direction becomes more important. In this work the
packaging influences on different sized laser bars are compared. At first thermal and thermo-mechanical influences are
evaluated in FEM-simulations. Afterwards laser bars of different lengths and widths are mounted and characterized. The
occurring strain is analyzed by electroluminescence using the correlation between stress and polarization properties of
the laser bar radiation. Because of the correlation between temperature and wavelength, a thermal analysis of the
mounted laser bars can be done by emitter resolved spectra scanning. The influence on reliability is analyzed in an aging
study with intermediate characterization steps.
We developed a high brightness fiber coupled diode laser module based on single diode lasers providing more than 60
Watts output power from a 100 micron fiber at the optimum fiber laser pump wavelength of 976 nm. The advantage of
using multiple single emitters on a submount compared to using bars or mini bars is the direct fiber coupling by use of
optical stacking and the fact that no beam transformation is needed. We achieved best brightness with a high fill factor,
optical efficiency of more then 80% and wall-plug efficiency of more then 40%. The use of single emitters on a
submount also extends the life span due to reduced failure (xn vs. x) per device (n individual emitters vs. n emitters on a
bar (mini array)). Low drive current enables modulation.