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LASER SYSTEMS AND MATERIALS
Pulses features of the self-Q-switched erbium fiber lasers
A.M.Smirnov123, A.V.Dorofeenko1-3'4'5, A.A. Rybaltovsky1, O.V.Butov1
*
ALT'22
1- Kotelnikov Institute of Radioengineering and Electronics of RAS, Mokhovaya 11-7, Moscow 125009, Russia 2- Faculty of Physics of Lomonosov Moscow State University, Leninskie Gory 1-2, Moscow 119991, Russia
3- Moscow Institute of Physics and Technology, 19 Institutskiy pereulok, Dolgoprudny 141700, Russia
4- Institute for Theoretical and Applied Electromagnetics RAS, 13 Izhorskaya, Moscow 125412, Russia
5- Dukhov Research Institute of Automatics, 22 Suschevskaya, Moscow 127055, Russia
The universal dependence of the pulse frequency and duration on the operation power in heavily doped erbium passive Q-switch fiber lasers has been experimentally discovered and theoretically confirmed. It was found that the frequency and duration of pulses are determined by the laser output power and coincides for 1490 nm and 976 nm wavelength pumping regardless of the operation wavelength, fiber core doping level, temperature and cavity length. The frequency and duration of pulses dependencies on lasing power are characterized by equal slopes on a double logarithmic scale in the measured pump power range [1] (Fig.1). The pulses formation is caused by the lasing process itself and the pulse parameters primarily depend on the lasing power. A doping growth leads to the erbium clusterization increase with up-conversion increasing at the lasing wavelength. As a consequence, the pulse duration reduces and the pulses frequency increases, other input conditions being equal.
Fig. 1 Dependence of the frequency (a) and pulse duration (b) for 976 nm and 1490 nm wavelength pumping on on the lasing power.
An optical fiber preform was synthesized using both the modified chemical vapor phase deposition (MCVD) and surface plasma chemical vapor deposition (SPCVD) technologies. To achieve a high concentration of erbium oxide in glass (at the level of 0.3 mol.% Er2O3) with a minimum level of gray losses SPCVD technology was used. The absorption level at the 1528-1535 nm wavelength of erbium doped fibers varied from 5.3 dBm to 183 dBm. The fiber laser cavity was based on the classical Fabry-Perot scheme. Fiber Bragg gratings (FBGs) inscribed directly in the active fiber core were used as cavity mirrors.
A comparative analysis of the Q-switched lasers operation with different erbium doping level for 1490 nm and 976 nm wavelengths pumping was performed. Resonant excitation at a wavelength of 1490 nm leads to a sharp increase in the pulse frequency and duration reduction compared to 976 nm wavelength excitation. Considering the model presented in Ref. [2], it was assumed that the duration and repetition frequency of pulses are determined by the rate of up-conversion at the lasing wavelength. The occurrence of pulses happens due to the lasing process itself. Taking into account the difference between the lasing efficiency when pumped at 976 nm and 1490 nm wavelengths, the heating caused by the up-conversion at the lasing wavelength can be the primary one.
We acknowledge the support by the Russian Science Foundation Project 20-72-10057.
[1] A.M. Smirnov and O.V. Butov, Pump and thermal impact on heavily erbium-doped fiber laser generation, Optics Letters, vol. 46, pp. 86-89 (2021).
[2] A.M. Smirnov, A.P. Bazakutsa, Y.K. Chamorovskiy, I.A. Nechepurenko, A.V. Dorofeenko, and O.V. Butov, Thermal Switching
of Lasing Regimes in Heavily Doped Er3+ Fiber Lasers, ACS Photonics, vol. 5, № 12, pp. 5038-5046 (2018).
