CC BY
17The 30th International Conference on Advanced Laser Technologies
ALT'23
LS-O-5
Harmonic mode-locking and multi pulse generation of Holmium-doped fiber laser with the ring cavity
S.A. Filatova1 V.A. Kamynin1, A.D. Zverev1, A.I. Lobanov1, P.V. Balakin12, Y.G. Gladush3, D.V. Krasnikov3,
A.G. Nasibulin3, V.B. Tsvetkov1
1 - Prokhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow, Russia 2 - MIREA - Russian Technological University, 78 Vernadsky Avenue, 119454 Moscow, Russia 3 - Skolkovo Institute of Science and Technology, Nobel Str. 3, Moscow, 121205, Russia
*email address: [email protected]
High repetition-rate mode-locked fiber lasers operating in the 2-3.5 ^m spectral range are in demand for numerous applications in the fields of science and technology because of ultrashort pulse duration and compact size. Such sources are promising for burst-mode generation, polymer micromachining, medicine, free space optical communication, and etc [1]. Holmium-doped (Ho) fiber takes main advantages of longer gain wavelength up to 2.2 ^m and larger emission cross-section. The simplest methods to increase repetition rate of passively mode-locked fiber laser are shortening cavity length and harmonic mode-locking (HML) [2].
This work focuses on the study of different types of passive mode-locking in a Ho-doped fiber laser with the ring cavity and the possibilities of obtaining harmonic mode-locking. Passive mode-locking was implemented based on the polymer-free single-walled carbon nanotubes (SWCNT) saturable absorber [3], nonlinear polarization evolution (NPE) and hybrid mode-locking [4].
Fig. 1. (a) Experimental setup of the NPE mode-locked Ho-doped fiber laser, (b) oscillogram of the burst-mode generation with 7 ultrashort pulses
in the burst, (c) radio frequency spectrum at the repetition rate of 588 MHz.
The cavity of Ho-doped fiber lasers consists of 2 m Ho-doped fiber pumped by the Yb-doped fiber laser at 1128 nm through a 1125/2100 nm wavelength division multiplexer (WDM), fiber coupler, polarization controllers (PC), isolator, polarizer in the case of NPE mode-locking as in Fig. 1(a), and FC/APC connectors with saturable absorber. In the case of hybrid mode-locking, NPE and SWCNT were combined in one cavity. The cavities length varied in the range of 7.5-8.8 m, depending on the mode-locking type.
In the case of NPE mode-locking, the burst-mode generation with a pulse repetition rate of «1.4 GHz and varying number of ultrashort pulses within a burst (up to 10 pulses) was obtained (Fig. 1(b)). The maximum pulse repetition rate obtained at a pump power of 2.9 W was 588 MHz with a signal-to-noise ratio (SNR) of «50 dB (Fig. 1(c)). In the case of hybrid mode-locking, the maximum pulse repetition rate obtained at a pump power of 3.2 W was 614 MHz with a SNR of «60 dB. In the case of mode-locking based on SWCNT, single-and dual-wavelength generation, as well as the unstable harmonic mode-locking with a maximum pulse repetition rate of «166 MHz, were obtained. The dependences of pulse repetition rate and average output power on the pump power were obtained.
This study was funded by a grant of the Russian Science Foundation № 22-72-00126 (development and study of fiber lasers characteristics).
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