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0Double harmonic mode-locking in soliton fiber ring laser
V.A. Ribenek1*, P.A. Itrin1, D.A. Korobko1, A.A. Fotiadi12
1- Ulyanovsk State University, 42 Leo Tolstoy Street, Ulyanovsk, 432970, Russian Federation
2- Electromagnetism and Telecommunication Department, University of Mons, Mons, B-7000, Belgium
* ribl98@mail.ru
Passive harmonic mode-locking (HML) of a soliton fiber laser locked to optoacoustic resonance (OAR) in the cavity fiber ensures high-frequency laser operation, high pulse stability, and low timing jitter [1]. However, the pulse repetition rate (PRR) of such lasers is limited to ~1 GHz for standard fibers due to the available acoustic modes [1-4]. Here, we address these limitations by demonstrating a soliton fiber laser built from standard fiber components and subjected to double harmonic mode-locking (DHML) [5].
In our experiment, the laser adjusted to operate at 15-th harmonic of its cavity matching the OAR (TR2,9 GAWBS mode) at ~200 MHz (Fig.1) could be driven to operate at a high harmonic of this particular OAR frequency, thus reaching ~12 GHz (Fig.2, a). This breakthrough is made possible through controllable optoacoustic interactions in a short, 50 cm segment of unjacketed cavity fiber implemented through its stretching (Fig.1). We propose that the precise alignment of the laser cavity harmonic and fiber acoustic modes leads to a long-lived narrow-band acoustic vibration. This vibration sets the pace for pulses circulating in the cavity by suppressing modes that do not conform to the Vernier principle. The surviving modes, equally spaced by the OAR frequency, in cooperation with the gain depletion and recovery mechanism, facilitate the formation of stable high-frequency pulse sequences, enabling DHML. In this process, the OAR rather than the laser cavity defines the elementary step for laser PRR tuning (Fig.2, a). Throughout the entire PRR tuning range, the soliton fiber laser exhibits enhanced stability, demonstrating a better than ~40 dB supermode suppression levels (SSL), improved pulse timing jitter and relative intensity noise (RIN) (Fig.2, b-d).
Fig. 1. Experimental setup of the soliton NPE laser (a); Guided Fig. 2. The PRR as a function of the increasing pump power (a) and acoustic wave Brillouin scattering (GAWBS) spectra recorded with the SSL (b), timing jitter (c) and RIN (d) as functions of the PRR 1-km G.652.D fiber (Fujikura) (b). measured in HML (blue) and DHML (red) regimes.
The work was funded by the Russian Science Foundation (23-79-30017).
[1] A.N. Pilipetskii, E.A. Golovchenko, C.R. Menyuk, Acoustic effect in passively mode-locked fiber ring lasers, Optics Letters 20, 907-909 (1995).
[2] E.M. Dianov, A.V. Luchnikov, A.N. Pilipetskii, A.M. Prokhorov, Long-range interaction of picosecond solitons through excitation of acoustic waves in optical fibers, Applied Physics B 54, 175-180 (1992).
[3] W. He, M. Pang, D.H. Yeh, P.S.J. Russell, Optoacoustic mode-locking based on micro-core photonic crystal fibre, in 2021 26th Microoptics Conference (MOC), 1-2 (2021).
[4] V.A. Ribenek, P.A. Itrin, D.A. Korobko, A.A. Fotiadi, Double harmonic mode-locking in soliton fiber ring laser acquired through the resonant optoacoustic coupling, APL Photonics 9(5), 056105 (2024).
