Quantum-dot based saturable absorber for mode locking of fibre lasers

R. Herda, O.G. Okhotnikov, E.U. Rafailov, M.A. Cataluna, W. Sibbett, P. Crittenden, A. Starodumov
2005 2005 IEEE LEOS Annual Meeting Conference Proceedings  
We demonstrate stable mode locking in a Yb-based fiber laser by using a multiple layer quantum-dot saturable absorber mirror. 2.8 ps pulses at 1042nm were produced at an average modelocked power of 5mW. OCIS codes: (140.0140) Lasers and laser optics, (140.7090) Ultrafast lasers, (999.9999) Quantum dot Significant progress in the fabrication of quantum-dot (QD) lasers using molecular beam epitaxy (MBE) has allowed the realisation of both edge-emitting lasers and vertical-cavity surface emitting
more » ... y surface emitting lasers that produce relatively high cw powers [1] . Notably, devices based on QD structures are becoming of interest in ultrafast physics (generation/amplification of femtosecond pulses), because one of the key parameters which influences the emission/absorption spectra and the optical gain in QD devices, is the spectral latitude associated with the distribution of dot sizes [2, 3] . Although the semiconductor saturable absorber mirrors (SESAM), which have had considerable success in mode-locking of various types of lasers have, until now, depended on quantum wells, but we believe that SESAMs based on QD structures have the potential to generate ultrashort pulses. Particularly, the fast carrier dynamics of QD structures facilitates the use of such a structure as a fast saturable absorber to mode-lock solid-state lasers [4] . SESAM technology has helped considerably the development of mode-locked fiber lasers. The main features of these fiber-based devices -high efficiency, reliability and small footprint -make them promising candidate sources for applications occupied more traditionally by ultrafast solid-state lasers. The broad fluorescence spectrum makes different fiber gain media attractive for tunable and ultrashort pulse sources. Recently pulse trains covering the extensive range from 895nm to 1560 nm were reported using neodymium, ytterbium and erbium mode-locked fiber lasers [5, 6, 7] . In this work we present experimental data that demonstrates mode-locked operation of a Yb-doped fiber laser by using a 80 layer QD structure combined with a distributed Bragg reflector (DBR) as a saturable absorber mirror. The QD SESAMs were grown by NL Nanosemiconductor GmbH. The distributed Bragg reflector was formed by 33 pairs of quarter lambda Al 0.9 Ga 0.1 As/GaAs. In the absorbing part of the structure 8 multiple stacks of 10 InGaAs QD layers spaced with 10nm of GaAs were deposited. The linear and nonlinear reflectivities of the SESAM are shown in Figure 1 a) and b) respectively. Figure 1. a) Typical reflectivity spectra and b) nonlinear reflectivity measured at 1042 nm of the QD SESAM structure with 80 layers. The modulation depth was measured to be 17.6 % and the saturation energy was 591 µJ/cm 2 . In our experiments we used Yb-doped fibre as a gain medium placed in the linear cavity as shown in Figure 2 . The laser cavity contained a 75 centimeter-long piece of Yb -doped fibre having absorption of 434 dB/m at 980 nm. The active fibre was pumped 830 0-7803-9217-5/05/$20.00©2005 IEEE
doi:10.1109/leos.2005.1548265 fatcat:vwxac7jitfeincxst53zzrtxn4