fs pulse generation with MIXSEL (mode-locked integrated external cavity surface emitting laser) based on quantum dot amplifying and absorbing elements (QD-MIXSEL)
Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Final Report Abstract
The main focus of QD-MIXSEL project was to realize the first compact semiconductor based high-power femtosecond laser source for frequency comb generation based on a QD gain region monolithically integrated with a fast QD saturable absorber. The motivation behind the use of QDs was the ability to tailor the optical properties over a wide range by exploiting additional geometry-based degrees of freedom of zero-dimensional system. The main strength of this joint collaborative project was that the specific expertise of the three different international groups were brought together for a successful investigation of the problem and for the device development with a high relevance for the future applications. The investigated within QD-MIXSEL project QD material had to be optimised to fulfill the different requirements depending on the applications. For the VECSEL a high optical gain is important, therefore QDs with high-quality and high density were necessary. For SESAM structures, low saturation power and ultrashort lifetimes are needed, which can be achieved by introduction of recombination centers. Beside this, the saturable absorber layers additionally have to withstand a longer high-temperature growth procedure for the epitaxial formation of distributed Bragg reflectors (DBR). Following the project-related results on the QD-VECSEL (C. G. E. Alfieri et al. 2018) achieved by the project partner at ETH with new records in pulse duration and peak power, we have further optimized the QD quality. A reduction in PL linewidth from 54 meV down to 26 meV with increased intensity measured at 10 K as well as a high dot density of 1.8 x 10^11 cm^-2 for a single QD layer was achieved. A significant improvement of the device performance is expected by implementing these optimized QDs utilizing the much higher spectral gain based on the reduction of the size distribution and increasing the QD density. With the new approach for QD-based SESAMs implementing high-quality InxGa1−xAs QDs grown at high temperature and p-type doping we have demonstrated the first antiresonant QD- SESAM with high-temperature stability suitable for the monolithic integration into MIXSEL devices. It could be experimentally demonstrated that the τ1/e value of the recovery time as well as the saturation parameters can be adjusted to a level comparable to the reference state-of the art defect-related QW-SESAM by a post-growth annealing step. Since these developed absorbers have much higher optical quality compared to the QW reference, their high-speed performance can survive a long-term MBE overgrowth at 600°C, which is essential for growth of MIXSEL structures. The project brought significantly new knowledge in the field, showing, that the fast decay rates in saturable absorbers based on non-radiative recombination centres can be successfully substituted by an enhanced radiative recombination in high optical quality QD absorbers using a p-type high-density modulation doping. We strongly believe that ongoing mode-locking experiments will confirm the high performance of the developed QD-SESAMs. After that QD-MIXSEL structures will be realized. Simulations of the MIXSEL using an advanced FDTD code revealed, as expected, that the pulses obtained depend strongly on material parameters which at 1 µm are not fully known. Nevertheless, an important finding is the fact that when the pulses are very short (1 ps or shorter), they are affected by coherent interactions as when ultrashort pulses propagate in a semiconductor optical amplifier.
Publications
- “Optical efficiency and gain dynamics of modelocked semiconductor disk lasers”, Optics Express 25 (2017) 6402-6420
C. G. E. Alfieri, D. Waldburger, S. M. Link, E. Gini, M. Golling, G. Eisenstein, U. Keller
(See online at https://doi.org/10.1364/OE.25.006402) - “High-power sub-300- femtosecond optically pumped quantum dot semiconductor disk lasers”, IEEE Photonics Tech. Lett. 30 (2018) 525-528
C. G. E. Alfieri, D. Waldburger, M. Golling, U. Keller
(See online at https://doi.org/10.1109/LPT.2018.2801024) - “Mode-locking instabilities for high-gain semiconductor disk lasers based on active submonolayer quantum dots”, Phys. Rev. Applied 10 (2018) 044015
C. G. E. Alfieri, D. Waldburger, J. Nürnberg, M. Golling, L. Jaurigue, K. Lüdge, U. Keller
(See online at https://doi.org/10.1103/PhysRevApplied.10.044015) - "Optimization of size uniformity and dot density of InxGa1−xAs/GaAs quantum dots for laser applications in 1 µm wavelength range", Journal of Crystal Growth 517 (2019) 1-6
T. Finke, V. Sichkovskyi, J. P. Reithmaier
(See online at https://doi.org/10.1016/j.jcrysgro.2019.04.002) - “Sub-150-fs pulses from a broadband optically pumped MIXSEL”, Optics Letters 44 (2019) 25-28
C. G. E. Alfieri, D. Waldburger, J. Nürnberg, M. Golling, U. Keller
(See online at https://doi.org/10.1364/OL.44.000025) - “Tightly locked optical frequency comb from a semiconductor disk laser”, Optics Express 27 (2019) 1786-1797
D. Waldburger, A. S. Mayer, C. G. E. Alfieri, A. R. Johnson, X. Ji, A. Klenner, Y. Okawachi, M. Lipson, A. L. Gaeta, U. Keller
(See online at https://doi.org/10.1364/OE.27.001786) - "Temperature resistant fast InxGa1−xAs/GaAs quantum dot saturable absorber for the epitaxial integration into semiconductor surface emitting lasers", Optics Express 28 (2020) 20966
T. Finke, J. Nürnberg, V. Sichkovskyi, M. Golling, U. Keller, J. P. Reithmaier
(See online at https://doi.org/10.1364/OE.396198)
