Bernd Valk

Laser welding for fiber pigtailing with long-term stability and submicron accuracy

Laser welding as a means for optical packaging, providing long-term stability and submicron precision, has been implemented for fixing single-mode fibers or fiber arrays to integrated optical waveguides of GaAs and InP optoelectronic chips. Fixing accuracies better than 0.5 μm are achieved by applying a new method of corrective welding. Devices such as high-power LEDs featuring low spectral modulation, 980-nm laser diodes, integrated reflective Mach-Zehnder modulators (GaAs), and 1 x 2 InP switches have been packaged and used in system test beds.

9xx high-power broad-area laser diodes

In this communication we report on the performance characteristics of Bookham’s latest generation of 915-990 nm broad area single emitter (BASE) laser diodes with around 90 μm wide aperture. Representative high power devices in the wavelength range of 950-960 nm, mounted p-side down onto expansion matched assemblies using our highly reliable AuSn-solder technology, reveal a high slope efficiency of around 1.05 W/A during CW operation at 25°C heat sink temperature. Coupling efficiency into multi-mode fiber with 0.15 or 0.22 numerical aperture exceeds 93% mainly due to the low vertical divergence of the laser beam. In addition, low laser threshold and series resistance enable more than 62% maximum wall plug efficiency of the present generation of the laser diodes. Preliminary tests of new prototypes reveal already excellent performance characteristics of the next generation device with up to 19.9 W light output power in pulsed operation and 16 W for thermally limited CW operation.

Recent developments for BAR and BASE: Setting the Trends

Bars with high and low filling factors serve the different schemes for beam transformation and fiber coupling. We report on highly efficient 8xx bars for operation in excess of 100 W and reliable broad-area single-emitter lasers (BASE) with 90 um aperture being capable to deliver in excess of 10 W from a 105 um core fiber. For 9xx bars we present solutions with power levels per device ranging from 60 W to 300 W corresponding to linear power levels beyond 8.5 W per 100 um stripe width indicating convergence of BAR and BASE devices. Life test results for these devices will be shown and high brightness fiber coupled solutions will be discussed.

Broad area single emitter (BASE) modules with improved brightness

High power pump modules are used for industrial as well as telecom applications such as for fiber lasers and cladding pumped erbium doped fiber amplifiers (EDFA) [Lichtenstein, N., et al., 2004]. Key element of a pump module is a single emitter laser diode, which normally has an aperture of around 90 mum, in order to provide best coupling into an optical multi-mode fiber with a 105 mum core diameter. Increasing the brightness of the pump module lends additional flexibility in the design of fiber lasers and amplifiers and enables higher output power. In this communication we report on two approaches to increase the brightness of our latest generation of high power pump modules. Within the first approach the electro-optical performance of the single emitter laser diode is improved by optimizing Bookhams mature chip technologies such as InGaAs/AlGaAs structures grown by MBE, the ridge-waveguide manufacturing process, the E2 facet passivation and the mounting technology. The combination of improved chip design and new coupling scheme leads to reliable broad area modules with outstanding brightness.

Improved brightness on broad-area single emitter (BASE) modules

In this communication we report on the approaches to increase the brightness of Bookhams latest generations of high power pump modules. Since the single-emitter laser diode is the essential building block in all module designs, the optimization of the device design towards higher wall-plug efficiency, higher brightness and better reliability is one focus of the ongoing development efforts at Bookham. By using an analytical simulation tool critical parameters for efficient emitter-fiber coupling as the beam divergence and coupling scheme could be identified.

CW to QCW power scaling of high-power laser bars

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.

Automated assembly processes of high power single emitter diode lasers for 100W in 105 μm / NA 0.15 fiber module

Modules consisting of multiple single emitters pose demanding challenges on assembly, production capabilities and cost. A fiber coupled module has been produced delivering 100 W optical power from a 105 μm, NA 0.15 fiber. The module consists of two times six vertically stacked single emitters combined by polarization multiplexing. Special attention was paid to the development of a very robust low cost pigtail. The developed semiautomatic highly accurate process enables assembly times way faster than possible in a purely manual procedure. The achievable yield in combination with low material costs proofs the excellent potential for the manufacturing of cost efficient laser modules.

9xx high power pump modules

In this communication we present the characteristics of Bookhams 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.

Fiber coupled high-power multi-mode diode pump lasers

In the past decade of development in fiber laser technology, the market share of high power full fiber lasers has expanded tremendously to replace traditional gas and solid laser systems. While fiber lasers offer advantages of compact dimensions, high conversion efficiency, and full fiber integration, cost is still a major challenge for fiber laser manufacturing. With an increasing power rating, high power diode pump lasers become the most critical component to control the cost margin of fiber laser. Oclaro offers the most complete solution of fiber coupled diode lasers for fiber laser customers with platforms of multi-mode single emitter, multi emitters and mini-bar fiber coupled, with the benefit of competitive

Packaging and performance of a high-speed indium phosphide access switch

/W margin and Telcodia standard high reliability performance .