KEYWORDS: Epitaxy, High power lasers, Reliability, Laser development, Metalorganic chemical vapor deposition, Laser applications, Yield improvement, Manufacturing, Laser systems engineering
Industrial quality high power laser bars operated at 250 W output power are in volume production. Beyond the output power high conversion efficiency, polarization purity and beam quality are key requirements in high power applications. The latter requires controlling the chip beam parameter, especially the slow axis blooming, as well as the flatness or “smile” of the packaged device. The chip and package endurance must be carefully considered in the design. Our new MOCVD-based high power laser platform enables power conversion efficiencies of above 65% over the entire 920 nm to 1080 nm wavelength range at 250 W output power and at drive currents ranging from 250 to 285 A. Endurance test results show the high reliability of the chip and the fully AuSn hard soldered micro channel cooler package. Random emitter failures are the single relevant degradation mechanism present. At normal operating condition a degradation rate as low as 0.2% in 1000 h operation, obtained in 13’000 h test time indicates a MTTF of 100,000 h. Results of the QCW life-tests are in agreement with the CW tests and confirm the robustness of the fully AuSn hard soldered assembly. Also the micro channel cooler shows no sign of degradation from corrosion. The established 250 W MOCVD-epitaxy based platform is now paving the way to 300 W and later 350 W output power. Devices with 420W peak power and rollover currents of 550 A at 1040 nm wavelength were demonstrated.
We report on the development of the latest generation of high power laser diodes at 14xx nm wavelength range suitable for industrial applications such as plastics welding and medical applications including acne treatment, skin rejuvenation and surgery. The paper presents the newest chip generation developed at II-VI Laser Enterprise, increasing the output power and the power conversion efficiency while retaining the reliability of the initial design. At an emission wavelength around 1440 nm we applied the improved design to a variety of assemblies exhibiting maximum power values as high as 7 W for broad-area single emitters. For 1 cm wide bars on conductive coolers and for bars on active micro channel coolers we have obtained 50 W and 72 W in continuous wave (cw) operation respectively. The maximum power measured for a 1 cm bar operated with 50 μs pulse width and 0.01% duty cycle was 184 W, demonstrating the potential of the chip design for optimized cooling. Power conversion efficiency values as high as 50% for a single emitter device and over 40% for mounted bars have been demonstrated, reducing the required power budget to operate the devices. Both active and conductive bar assembly configurations show polarization purity greater than 98%. Life testing has been conducted at 95 A, 50% duty cycle and 0.5 Hz hard pulsed operation for bars which were soldered to conductive copper CS mounts using our hard solder technology. The results after 5500 h, or 10 million “on-off” cycles show stable operation.
The conventional distributed feedback (DFB) edge-emitting lasers with buried gratings require two or more epitaxial
growth steps. To avoid the problematic overgrowth we have used laterally-corrugated ridge-waveguide surface gratings,
which also enable easy integration of the resulting laterally-coupled DFB (LC-DFB) lasers with other devices and are
applicable to different materials, including Al-containing ones. The paper presents the modeling and design
particularities of LC-DFB lasers, the fabrication process, involving a highly productive and cost-effective UVnanoimprint
lithography technique, and the characteristics obtained for the LC-DFB lasers fabricated from GaAs-, GaSband
InP-based epiwafers. The first batches of GaAs-based LC-DFB lasers, emitting at 894 nm, GaSb-based LC-DFB
lasers emitting at 1.946 μm and InP-based LC-DFB lasers, emitting at 1.55 μm had relatively low threshold currents, a
high side-mode-suppression-ratio and exhibited linewidths in the range of 1 MHz and below, showing that the LC-DFB
lasers are an effective low-cost alternative for the conventional buried-grating DFB lasers.
The conventional distributed feedback and distributed Bragg reflector edge-emitting lasers employ buried gratings,
which require two or more epitaxial growth steps. By using lateral corrugations of the ridge-waveguide as surface
gratings the epitaxial overgrowth is avoided, reducing the fabrication complexity, increasing the yield and reducing the
fabrication cost. The surface gratings are applicable to different materials, including Al-containing ones and can be easily
integrated in complex device structures and photonic circuits. Single-contact and multiple contact edge-emitting lasers
with laterally-corrugated ridge waveguide gratings have been developed both on GaAs and InP substrates with the aim to
exploit the photon-photon resonance in order to extend their direct modulation bandwidth. The paper reports on the
characteristics of such surface-grating-based lasers emitting both at 1.3 and 1.55 μm and presents the photon-photon
resonance extended small-signal modulation bandwidth (> 20 GHz) achieved with a 1.6 mm long single-contact device
under direct modulation. Similarly structured devices, with shorter lengths are expected to exceed 40 GHz small-signal
modulation bandwidth under direct modulation.
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