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5*
ALT'23
The 30th International Conference on Advanced Laser Technologies
LS-O-6
Optimization of the length of the cavity of an erbium fiber laser with a sub-GHz repetition rate of ultrashort pulses
A. Zverev1, V. Kamynin1, V. Tsvetkov1, S. Sverchkov1, V. Velmiskin2, B. Denker1, Y.
Gladush3, A. Nasibulin3
1- Prokhorov General Physics Institute of the Russian Academy of Sciences, Russia 2- Scientific Center for Fiber Optics, Russian Academy of Sciences, E.M.Dianova of the Russian Academy of Sciences,
Russia
3- Skolkovo Institute of Science and Technology, Moscow, Russia
Main author email address: [email protected]
Fiber sources of ultrashort pulses (USPs) with a sub-GHz repetition rate are in demand for various applications, including analog-to-digital converters[1], study of supercontinuum generation[2], and highresolution microscopy[3]. The repetition frequency of the gigahertz level can be obtained by implementing harmonic mode locking or in lasers with an extremely short cavity based on heavily doped active fibers and hybrid components.
976 nm
a) Laser b) c)
diode
Output
PC
103.50 103.51 103.52 103.53 103.54 Frequency, MHz
298 299 300 Frequency, MHz
Fig.1. a) Initial scheme of an erbium fiber laser (resonator length 1.93 m). SWCNT - connected ferrules, between which there are single-walled carbon nanotubes; A hybrid is a fiber element that combines the properties of a WDM, an insulator and coupler; PC - polarization controller. The pumping direction is shown in red. b) RF spectrum of initial signal; c) RF spectrum of final signal (resonator length 0.6 m).
In this work, we studied the possibility of increasing the repetition rate of ultrashort pulses by using a heavily doped active fiber and a hybrid (optical splitter (coupler), wavelength division multiplexer (WDM), insulator) in an erbium fiber laser with a ring cavity. The initial experimental setup is shown in Fig. 1 (a). As an active medium, we used a 12 cm the composite fiber with a phosphate glass core with a high concentration of erbium ions and a silica glass cladding. The composite fiber was pumped by the laser diode at a wavelength of 976 nm through a hybrid. The coupler split was 85/15 (15% yield). To be able to adjust the generation mode, the circuit included a polarization controller. Passive mode locking was provided by single-walled carbon nanotubes synthesized in an aerosol placed between two FC/APC optical connectors (SWCNT [4]). The resonator length in this case was exactly 1.93 m.
The laser generated ultrashort pulses with a repetition rate of 103.5 MHz (RF spectrum of the signal Fig.1 (b)) and a duration of 5 ps at a central wavelength of 1535 nm. The spectrum width was 1 nm (Fig. 1 (b)). The output radiation power was 0.48 mW. With a decrease in the resonator length, stable modes were also obtained with ultrashort pulse repetition frequencies of 129 MHz (resonator length Lr = 1.55 m), 153 MHz (Lr = 1.3 m), 214 MHz (Lr = 0.9 m), 247 MHz (Lr = 0.8 m).
Next, we removed the polarization controller from the circuit and reduced the length of the resonator as much as possible (without changing the length of the active fiber) to 0.6 m.
In this case, we also managed to obtain a stable mode of single-pulse generation. The laser generated ultrashort pulses with a repetition rate of 298.5 MHz (RF spectrum of the signal Fig. 1 (c)) and a duration of 1.6 ps at a central wavelength of 1543 nm. The spectrum width was 1.3 nm. The output radiation power was 1.64 mW.
Thus, we have carried out an optimization of the ring laser circuit, as a result, sources with a repetition rate
of ultrashort pulses from 100 to 300 MHz have been obtained.
The work is supported by the Russian Science Foundation (#23-79-30017)
[1] Valley, G. C. Photonic analog-to-digital converters. Optics express, 15(5), 1955-1982, (2007).
[2] Korobko, D., et al. "Control of supercontinuum generation due to soliton propagation in fibers with varying dispersion." Optik: 171032, (2023).
[3] Potma, Eric O., et al. "High-sensitivity coherent anti-Stokes Raman scattering microscopy with two tightly synchronized picosecond lasers." Optics letters 27.13,1168-1170, (2002).
[4] Kaskela, Antti, et al. "Aerosol-synthesized SWCNT networks with tunable conductivity and transparency by a dry transfer technique." Nano letters 10(11), 4349-4355 (2010).
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