Single-transverse-mode semiconductor laser diodes with broad emission spectrum in pulsed or CW regime are attractive
as seed sources in fiber laser systems. Stimulated Brillouin scattering can be a limiting factor in such systems, causing
damaging high power pulses to reverse propagate in the fibre. The effect can be significantly mitigated by broadening
the linewidth of the seed laser. Here we report on such a seed source capable of operating in either CW or pulsed mode
with a center wavelength at around 1060 nm and spectral full width at half maximum of greater than 10 nm. The new
source is based on well-established ridge waveguide pump laser technology, modified for operation in a
superluminescent regime. A coupling efficiency of ~80 % into a single mode fiber is achieved. Our time resolved
spectral studies show that the device is demonstrating fast modulation rate and very high peak optical power up to 1 W
while maintaining a broad emission spectrum greater than 10 nm.
We report on reliable single-mode laser modules at 1060 nm used in pulsed operation for efficient seeding of fiber amplifiers. The modules incorporate InGaAlAs single quantum well diodes with a design inherited from telecom qualified devices. Pulse parameters can be widely varied with laser intrinsic modulation capability in GHz range. 2.5 W peak power is exhibited in a single-mode fiber at a current of 5 A with 200 ns pulses. Reliability is proven by lifetest in pulsed operation up to 3.5 A. Wavelength stabilization with fiber Bragg gratings is obtained over a wide range of operating conditions.
The performance of high-power pump-laser modules is strongly influenced by their thermal properties. In this paper we discuss the optimization of the device performance with respect to thermal properties, output power, wavelength stability, and device reliability using the example of our newest pump-laser generation that has been developed and qualified to support the high-end market of erbium-doped fiber amplifiers. A comparison of device properties obtained from modeling and measurements is presented at each design step. We report on the performance of fiber Bragg grating-stabilized telecom-grade modules yielding 600 mW fiber-coupled light output power.
Based on the most recent generation of Bookham's laser diode bars in the 9xx nm wavelength range which are able to deliver in excess of 250 W of output power from 50% filling factor 2.4 mm cavity length design, we have developed low 20% fill-factor bar devices for high brightness applications. Close to 200 W of output power has been achieved in CW mode from actively cooled micro-channel cooler devices without signs of damage. Mounted on conductively cooled copper blocks, still more than 130 W (CW) has been obtained, indicating the high conversion efficiency of >60% reducing the thermal load on the mounting assembly. Based on extensive reliability testing in excess of 5000 h and at power densities ranging up to 36mW/um and beyond, highly reliable operation of 20% fill-factor bars is expected. To facilitate fiber coupling into wide-core multi-mode fibers a further reduction of the emitter aperture has been realized. From a single 3.6 mm cavity length by 800 um wide emitter design ("MaxiChip") about 50 W output power has been obtained in CW mode from devices mounted on standard conductively cooled 1x1 inch copper blocks. While CW operation has been thermally limited, extremely high peak power operation can be expected in qCW operation. Due to the narrow aperture of this MaxiChip efficient and easy coupling into wide aperture multimode fibers can be achieved.
In this communication we present the characteristics of Bookham's MU7-9xx-01 laser module with multimode fiber output. This latest generation of our multimode modules is designed for light output power of up to 7 W in uncooled operation in the wavelength range between 915 nm and 975 nm. The key element of the module is our new SES8-9xx-01 broad area single emitter. These high power lasers in the 9xx nm wavelength range show a high slope efficiency of up to 1.2 W/A in CW room temperature operation. High efficiency combined with low threshold current and low operation voltage result in a maximum wall plug efficiency of above 65%. Almost 4000 h lifetest data at accelerated conditions are available for the laser diodes. The data give estimated reliability values of below 5 kFIT at operating conditions (between 8 A and 8.5 A injection current at up to 35°C heat sink temperature). The robustness of the new lasers is also illustrated by the fact that no catastrophic mirror damage was observed up to 22.5 W of light output power. The low divergence of the laser beam allows coupling into multimode fiber with 0.15 or 0.22 numerical aperture (NA) with a coupling efficiency above 90% at operation condition. Maximum ex-fiber light output powers of 11.5 W are shown. On module level around 2000 h lifetest data are accumulated without any failure or sign of degradation.
We report on the development of a new cost-effective, small form-factor laser source at a wavelength of 980 nm. The laser module is based on proven technology commonly used for pump laser modules deployed in fiber amplifiers of telecommunication networks. The package uses a state-of-the-art 14-pin butterfly housing with a footprint of 30x15 mm2 with a Fabry-Perot AlGaAs-InGaAs pump laser diode mounted inside having an anti-reflection coating on its front facet. The light is coupled into a single-mode polarization-maintaining fiber with a mode-field diameter of 6.6 micrometer. The spectral properties of the source are defined by a fiber Bragg grating (FBG) that provides feedback in a narrow reflection band. The laser back facet and the FBG form a long resonant cavity of 1.7 m length in which laser light with a low coherence length of a few cm is generated. This configuration with the laser being operated in the coherence-collapse regime has the advantage of being robust against variations in the optical path, thus enabling stable and mode-hop free emission. The laser module has the following properties: a continuous-wave fiber output power exceeding 800 mW, a spectral bandwidth of less than 50 pm, a root-mean square power variation of less than 0.2 % from DC to 2 MHz over the entire power operating range, and a polarization extinction ratio of more than 20 dB. This is a compact, low noise, high power source for frequency conversion with nonlinear optical materials, such as blue light generation.
Reliable power scaling by stretching the cavity length of the laser bars ranging from 1.2 mm to 3.6 mm at constant filling factor of 50% is demonstrated. While a relatively short cavity length of 1.2 mm allows for thermally limited CW output powers in excess of 180 W, extremely high 325 W at 420 A (CW, 16°C) have been achieved by leveraging the enhanced thermal properties of a 3.6 mm cavity length on standard micro-channel coolers. A high electro-optical conversion efficiency of 62% and 51% respectively is attributed to the low internal losses from an optimized waveguide design and the excellent properties of the AlGaAs-material system accounting for low thermal and electrical resistance. Multi-cell lifetest data at various operation conditions show extremely low wear-out rates even at harsh intermittent operation conditions (1-Hz type, 50% duty-cycle, 100% modulation). At 100 W output power 300 Mshots corresponding to 64000 h mean-time-to-failure (MTTF) have been extrapolated for 20% power drop from initial 2000 h and 4000 h lifetest readouts of a 1.2 mm cavity design. Similar results have been obtained for our next generation of ultra high power laser bars enabling reliable operation at 120 W output power and beyond. From 2.4 mm cavity length bars we have obtained 250 W of CW output power at 25°C while extrapolated reliability data at 120 W and 140 W power levels of up to 2000 h duration indicates that such devices are able to fulfill the requirements for lifetimes in the 20 - 30 kh range.