Handheld fiber laser welding is increasingly replacing arc welding as the technology of choice, driving strong demand for components that enable cost-efficient designs. In a first step, this trend has driven the development of multi-mode edge-emitting laser diodes in the 9xx nm wavelength range that, depending on emitter width, nowadays routinely achieve output power levels in the range of 35-45 W. We report on our recent developments of even more powerful single emitter laser diodes at Coherent Corp. to support novel and even more cost-efficient fiber laser architectures. Our newest generation of edge-emitting devices provides reliable output power levels in CW operation of up to 65 W from a 320 μm-wide emitter.
GaAs-based high-power laser diodes in the 9xx nm wavelength-range are at the heart of modern materials processing systems. The continuing increase in reliable operating power and efficiency of these diodes has been one of the driving factors behind their wide adoption in fiber laser and direct diode systems and has been a major factor fueling the growth of the materials processing market.
II-VI as a leading manufacturer of both VCSEL and edge-emitting GaAs-based laser diodes has pioneered the adoption of 6-inch GaAs laser diode technology in high-volume manufacturing. In this presentation we will review the developments of the high power pump laser diode market in recent years that required the adoption of larger diameter wafer substrates, discuss selected highlights and challenges of our 6-inch GaAs laser production, and present latest chip performance results.
We report on our recent developments at II-VI Laser Enterprise of laser diode sources for the 79x nm range. High power conversion efficiency in excess of 62% was demonstrated. For high power applications like Thulium fiber laser pumping we have achieved an output power of more than 12.5W in CW operation for 94 μm wide broad-area single-emitters. We added the functionality of wavelength stabilization to the laser diodes by using a distributed feedback grating (DFB). Locking has been obtained over the full current range between 1A and 4A tested so far with some margin for temperature variation. For efficient fiber laser pumping the laser diodes were integrated in a multi-emitter platform, achieving 38 W out of a 105 μm fiber within 0.15 NA.
We report on the development of high power, 9xx-10xx nm laser diode bars for use in direct diode systems and for solidstate and fibre laser pumping with applications in industrial markets. For 1 cm wide bars on micro channel cooler (MCC) we have achieved a reliable output power of 250 W across the 900 nm – 1060 nm range. At this output power level we have achieved power conversion efficiencies of 65-66 % and 90 % power content slow axis beam divergence of ~6.5°. Results of a 6400 h life test show an average power degradation of 0.6 % per 1000 h at this operating power level. We will also show results of high power bars assembled on the new OCLARO conductive cooler, the BLM. This new cooler has a small footprint of 12.6 mm × 24.8 mm and is designed for lateral or vertical stacking of diodes in multi kilowatt systems but with the benefits associated with a conductive cooler. The thermal properties are shown to be the same as for a standard CS mount. 1 cm wide high fill factor bars and 0.5 cm wide low fill factor half bars assembled on the BLM operate at 63-64 % power conversion efficiency (PCE) with output powers of up to 250 W and 150 W, respectively.
We report on laser diode bars with wavelengths ranging from 793 to 1080 nm and optimized for high power and high
temperature operation. For 808 nm bars output power values of 300 W at 300 A drive current and 200 μs pulse length
have been recorded at a cooler temperature of 75°C. Extending our wavelength range to 1080nm we report on bars with
>65% power conversion efficiency in CW operation and more than 500 W output power for a wide range of qCW
modes. Finally, the properties of a 6-bar stack with 3 kW output power at 460 A drive current and 200 μs pulse width
will be discussed.
The attractiveness of bars for industrial applications depends strongly on the reliable high brightness operation. For 9xx bars we report on high filling factor configurations with 200W reliable output power. Our low filling factor devices with output power between 40W and 90W have proven to operate reliably at output power densities of 85mW per 1µm stripe width, showing power wear-out degradation of less than 0.5% per 1000h operation time. For shorter wavelengths we present solutions for 808-880 nm bars. For our 808nm bars we observe power degradation of less than 4% after 8000h hard-pulse life test at 75W output power.
Tunable laser diodes with a tuning range of several tens of nanometers are generally being acknowledged as key components for future generation optical networks. However, all presently available devices suffer from several serious drawbacks. The most well-known issue is the time-consuming calibration procedure that has to be carried out for every single device.
Recently the so-called sampled or superstructure grating tunable twin-guide or (S)SG-TTG laser diode has been suggested to overcome some of the prevailing problems. In this paper we will present tuning characteristics of first devices and discuss the influence of facet reflections on the tuning behaviour.
The widely tunable twin-guide laser diodes operate around 1.55 μm and have a continuous tuning range of ~ 2 nm. However, by utilizing Vernier-effect tuning, the overall quasi-continuous tuning range is extended to 28 nm. Within this tuning range, five supermodes can be continuously tuned without the occurrence of any mode hops. The side-mode suppression ratio is kept between 25 and 37 dB.
Widely tunable lasers are generally considered as the transmitters of future WDM optical communications. Electronically tunable edge-emitting laser diodes are of particular interest as they can switch the wavelength in tens of nanoseconds and thus offer great potential for new networking concepts such as optical packet or burst switching, label switching, bandwidth on demand, ... In this paper we discuss new concepts for such widely tunable laser diodes which are studied in the framework of the European IST project NEWTON (NEw Widely Tunable laser diodes for Optical Networks).
Widely tunable lasers are generally considered as key components of future optical communication networks. However, practically all widely tunable lasers that have been fabricated so far suffer from drawbacks, like elaborate calibration procedures that are required for each specific device, low output powers, and limited direct modulation capabilities.
To overcome the aforementioned issues, the sampled or superstructure grating tunable twin-guide or (S)SG-TTG laser diode has been suggested recently. In this paper we will focus on the operation principle, the fabrication, and performance of the first widely tunable twin-guide laser diodes.
The devices operate at ~ 1.55 µm wavelength. By means of Vernier effect tuning, the continuous tuning range of ~ 2 nm is extended to an overall tuning range of 28 nm. Within this tuning range, five supermodes are useable and can be continuously tuned without any mode hops. The side-mode suppression ratio remains between 25 and 37 dB over the whole tuning range. Without any tuning currents applied, a maximum output power of 12 mW has been achieved.
Different design approaches and the corresponding fabrication technology of widely tunable lasers with vertically integrated Mach-Zehnder interferometer (VMZ) have been investigated with respect to the spectral selectivity and tuning performance. Calulations show for designs with InGaAsP bulk material as active region that a tuning range of 75nm and a side-mode suppression ratio (SSR) of more than 30dB are feasible. The tuning range can be further extended using multiple quantum well heterostructures as active regions. They enable tuning ranges covering the whole material gain spectrum, but with a reduced SSR. Due to the codirectional mode coupling of the laser, the use of an appropriate facet coating allows an enlargement of the SSR to more than 30dB even for the large tuning range designs. We present the different design concepts and discuss the theoretical data as well as the first experimental results of the corresponding VMZ-laser devices. The measured spectrum of the laser shows an SSR close to the theoretically predicted value.
The influence of two monolayer (ML)-thick AlAs under- and overlayers on the formation and properties of self-assembled InAs quantum dots (QDs) has been studied using transmission electron microscopy, photoluminescence (PL) and electroluminescence. The main purpose of this work was to achieve high internal quantum efficiency of the active medium and temperature stability of the laser diodes. Single and multiple layers of 2.0-2.4ML InAs QDs with various combinations of under- and overlayers were grown on GaAs (001) substrate by molecular beam epitaxy inside a AlAs/GaAs short-period superlattice. It was found that a 2.4-ML InAs QD layer with GaAs underlayer and 2-ML AlAs overlayer exhibited the lowest QD surface density of 4.2x1010 cm-2 and the largest QD lateral size of about 19 nm as compared to the other combinations of cladding layers. This InAs QD ensemble has also shown the highest room temperature PL intensity with a peak at 1210 nm and the narrowest linewidth, 34 meV. Fabricated edge-emitting lasers using triple layers of 2.2-ML InAs QDs with AlAs overlayer demonstrated 120 A/cm2 threshold current density and 1230 nm emission wavelength at room temperature. Excited state QD lasers have shown high thermal stability of threshold current up to 130 degree(s)C.
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