FaBriDi - Fiber coupled high brilliance diode lasers
Fig. 1. Exemplary optical system for coupling of DBR tapered diode laser radiation into a single-mode fiber.
Fig. 2. Coupling efficiency η into a single-mode fiber in dependence on fiber facet misalignment measured at a constant operating point of the diode laser with input power reduced to 100 mW.
Efficient high-power lasers in continuous-wave (CW) operation emitting spectrally narrow-band near-infrared radiation in spatial fundamental mode are desired for applications such as pumping of solid-state and fiber lasers as well as for frequency conversion. A distributed Bragg reflector (DBR) tapered diode laser is well-suited to fulfil these requirements. However, this diode laser type is characterized by an astigmatic beam, and the properties of its beam change slightly in dependence on the operation conditions. It is therefore challenging to use such a laser source. The Ferdinand-Braun-Institut (FBH) works on beam shaping and coupling into single-mode and low-mode-number fibers in order to maintain the high spectral brightness and to simplify the use of these laser light sources.
At the FBH, coupling of DBR tapered diode laser radiation into single-mode and low-mode-number fibers has been investigated systematically in a bench-top setup. An exemplary optical system for coupling of DBR tapered diode laser radiation into a single-mode fiber is presented in Fig. 1. The aim is to improve the spatial properties of the spectrally narrow-band, high-power laser radiation. In particular, a stigmatic, nearly Gaussian laser beam independent of the taper current and thus independent of the optical power level shall be provided. The scope of the experiments comprises the investigation of coupling efficiency into optical fibers in dependence of spatial laser beam properties, position of optical lenses, misalignment of fiber input facet position (exemplarily depicted in Fig. 2) as well as in dependence of input power. Furthermore, the spatial and spectral properties of the laser radiation behind the optical fibers are determined. Up to date, a maximum power of more than 3 W ex single-mode fiber with a core diameter of approx. 6 µm at a coupling efficiency in excess of 60% has been reached.
This ongoing work is funded by the German Federal Ministry of Education and Research in the frame of the InnoProfile-Transfer joint research project "FaBriDi" under contract No. 03IPT613A. The results of laboratory experiments will contribute to the development of compact fiber coupled high-power laser modules based on DBR tapered diode lasers emitting single-frequency laser radiation at 920, 980, and 1064 nm.
Publications:
C. Fiebig, S. Pekarek, K. Paschke, M. Uebernickel, T. Südmeyer, U. Keller, G. Erbert, "High-brightness distributed-bragg-reflector tapered diode lasers: pushing your application to the next level", Proc. SPIE, vol. 7918, no. 79180R (2011).
C. Fiebig, G. Blume, C. Kaspari, D. Feise, J. Fricke, M. Matalla, W. John, H. Wenzel, K. Paschke, G. Erbert, "12W high-brightness single-frequency DBR tapered diode laser", Electron. Lett ., vol. 44, no. 21, pp. 1253-1255 (2008).
Outlook:
D. Jedrzejczyk, P. Asbahr, M. Pulka, B. Eppich, K. Paschke, "High-power single-mode fiber coupling of a laterally tapered single-frequency diode laser", to be published in IEEE Photonics Technology Letters.
D. Jedrzejczyk, P. Asbahr, M. Pulka, B. Eppich, K. Paschke, "Coupling of DBR tapered diode laser radiation into a single-mode-fiber at high powers,” to be presented at LASE SPIE Photonics West 2014, Paper 8965-47.
FBH research: 26.11.2013