David Venables

Advancements in laser diode chip and packaging technologies for application in kW-class fiber laser pumping

A new 100μm aperture, 920nm laser diode chip was developed to improve fiber coupling efficiency and reliability. These chips have been assembled into single-emitter and multi-emitter packages with 105μm diameter fiber-coupled output. The single-emitter package is rated for 12W operation, while the multi-emitter package is rated at 140W. Power conversion efficiency is 50%. Over one year of accelerated active life testing has been completed along with a suite of passive, environmental qualification tests. These pumps have been integrated into 2kW, 4kW, and 6kW fiber laser engines that demonstrate excellent brightness, efficiency, and sheet metal cutting quality and speed.

High-power, high-efficiency fiber-coupled multimode laser-diode pump module (9XX nm) with high reliability

We have developed a single-emitter multi-mode laser-diode-pump platform for high efficiency, brightness and high reliability in a small form factor. This next-generation package is scalable to higher optical power and offers a low-cost solution for industrial applications, such as fiber lasers, graphic arts and medical. The pump modules employ high coupling efficiency, >90%, high power-conversion efficiency, >50%, and low thermal resistance, 2.2°C/W, in an electrically-isolated package. Output powers as high as 18W have been demonstrated, with reliable operation at 10W CW into 105μm core fiber. Qualification results are presented for 0.15NA and 0.22NA fiber designs.

A high power high-brightness multi-single-emitter laser pump platform

A platform has been developed for high-power, high-brightness, multi-single-emitter laser pumps for fiber lasers, directdiode, and other applications. Using multi-mode fiber with 105μm core and 0.22 NA, fiber-coupled optical power up to 100 Watts and a brightness as high as 100 kW/mm2/sr can be achieved. Common schemes for increasing brightness include spatial, wavelength, and polarization-beam combination of multiple single-emitters. Spatial multiplexing has been chosen for this platform to leverage JDSUs proven reliability of highpower single-emitter packages and passive optical components. In one configuration, we achieved >60W fiber coupled optical power, 50 kW/mm2/sr, and 45% wall-plug-efficiency using 105 μm core, 0.22 NA fiber from this platform. An optional VBG can also be placed inside the package for achieving spectral locking over a 16 nm wavelength range.

Recent progress in fiber-coupled multi-mode pump module and broad-area laser-diode performance from 800-1500 nm

We present performance improvements of fiber-coupled pump modules and broad-area lasers at 8xx nm, 9xx nm and 14xx nm wavelengths. Broad-area lasers with a 200 μm aperture at 808 nm for direct diode applications emit 11W CW and 30W pulsed. Pump modules at 830 nm for printing applications show excellent linearity, power stability of 2% and 95% of the power within 0.12 NA into a 50 μm core fiber at 1W CW. Broad-area lasers at 880 nm for pumping applications emit 18W CW with a peak wallplug efficiency of 64%. An improved design of 9xx pump modules is demonstrated with built-in feedback-protection (>30 dB at 1060 nm) that allows safe operation in multi-kW peak-power fiber lasers. Up to 3W of optical power with slope efficiency and peak wallplug efficiency of 0.64 W/A and 46%, respectively, is presented for 14xx nm broad-area lasers with a 100 μm wide aperture.

Long-Term Aging and Quick Stress Testing of 980-nm Single-Spatial Mode Lasers

Single-spatial mode lasers emitting at 980 nm are studied during continuous-wave long-term operation and ultra-high power short-term operation (stress-test) up to 13.5 W. We find that both tests eventually activate the same degradation mechanism, namely internal catastrophic optical damage. In the case of ultra-high power operation, we show that the mechanism that initializes this effect is a lateral widening of the optical mode, resulting in increased absorption outside the waveguide. Defects formed during long-term aging may eventually lead to the same effect. Stress testing allows for activation of several degradation mechanisms in a device one after the other and for distinguishing between mechanisms induced by aging and independent ones. Stress tests could pave the way toward more time-efficient testing, e.g., for comparison of different technology variants in development.

830nm high power single mode DFB laser for high volume applications

We report an 830nm high power single spatial mode DFB laser design in the AlGaAs/GaAs system that offers performance close to a Fabry-Perot design as well as manufacturing yield compatible with volume production. Single-mode power in excess of 200mW at case temperature up to 600C is consistently obtained for current below 300mA. This performance level is enabled by use of an efficient, partially-corrugated design and a 2nd order grating located on the p-side. Through careful design and an optimized epitaxial re-growth on the grating, promising reliability results compatible with uncooled application are demonstrated.

Rapid stress-testing vs. long-term aging: a case study of 980-nm emitting single-spatial mode lasers

The degradation behaviors of 980-nm emitting nominally identical single-spatial mode lasers are studied during continuous wave long-term operation and during single-pulse stress tests. Both tests activate internal catastrophic optical damage as sudden degradation mechanism limiting the device lifetime. In case of high power stress-testing, the mechanism that initializes this effect is a spatial widening of the optical mode, resulting in increased absorption outside the waveguide. A similar disturbance to the optical mode is caused by defects that are generated during long-term operation. Thus two very different aging regimes eventually result in the same degradation scenario. We find that single-pulse stress-testing allows for activation of several degradation mechanisms in a device one after the other. Moreover, it becomes possible to distinguish between effects induced by gradual degradation and such that are independent on operation time. Thus stress-testing is considered a complementary tool, which might pave the way towards more economic device testing.

Analysis of 980nm emitting single-spatial mode diode lasers at high power levels by complementary imaging techniques

Pulsed operation of standard 980-nm emitting single-spatial-mode high power diode lasers at multi-watt power levels is studied. Primary emission, short wavelength infrared emission, as well as the spatio-temporal evolution of the near field are recorded. This approach allows for the determination of the operation parameters during which single-mode operation is maintained. This gives limits of safe operation far beyond the standard specifications as well as information about the relevant degradation mechanisms in this regime. Reference experiments with a set of long-term operated devices reveal gradual aging signatures and the starting points of the relevant aging processes become detectable. They are compared with those obtained from the devices operated under pulsed conditions.