CC BY
18LS-I-9
Dual-comb mode-locked lasers based on intrinsic polarization-
multiplexing
Maciej Kowalczyk1*, Lukasz Sterczewski1, Xuzhao Zhang2'3, Valentin Petrov4, Zhengping
Wang2, Jaroslaw Sotor1
1-Laser & Fiber Electronics Group, Faculty of Electronics, Wroclaw University of Science and Technology,
Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
2- State Key Laboratory of Crystal Materials, Shandong University, 250100 Jinan, China 3- Center of Nanoelectronics, School of Microelectronics, Shandong University, Jinan 250100, China
4- Max Born Institute for Nonlinear Optics and Ultrafast Spectroscopy, Max-Born-Str. 2a, 12489 Berlin,
Germany *m.kowalczyk@pwr.edu.pl
Recently, a great number of applications relying on dual-comb laser systems emerged. This primarily includes various spectroscopic techniques, but it also covers ranging, microscopy or communication. Standard realization of the dual-comb laser setup is based on a pair of mutually-coherent mode-locked lasers. However, it has been demonstrated that the experimental setup can be significantly simplified, if two individual pulse trains are simultaneously emitted from the single free-running laser [1].
In this paper we describe a novel, unprecedentedly simple technique for dual-comb generation from a single-cavity femtosecond solid-state laser [2]. Our concept relies on intrinsic polarization-multiplexing originating from double refraction inside a birefringent gain medium. In contrast to previous demonstrations, it does not require any additional components to be introduced to a standard laser resonator. Despite its simplicity, all the cavity components are common for both beams, supporting high relative coherence of the free-running combs.
We demonstrate the experimental implementation of this new scheme in a diode-pumped Yb:Ca3NbGa3Si2O14 (CNGS) mode-locked laser, with its setup schematically depicted in Fig. 1. The oscillator generates two orthogonally-polarized beams with a central emission wavelength around 1050 nm and the repetition rate difference of 4.73 kHz. The pulse durations of the combs amount to 88 and 93 fs, making this source the first sub-100 fs single-cavity dual-comb ytterbium-based laser source. Moreover, we also show that by changing the net cavity dispersion the laser can simultaneously operate in two distinct dispersion regimes with one beam following the conservative soliton pulse formation (pulse duration of 117 fs) and the other being strongly chirped (2360 fs).
Fig. 1. Schematic of the dual-comb Yb:CNGS laser. Due to a double refraction inside the birefringent active crystal two orthogonally-polarized beams corresponding to extraordinary (e) and ordinary (o) rays are generated. The picture (*) presents a real image of the two beams incident on one of the cavity mirrors.
The phase stability of the generated soliton combs was carefully analysed indicating sub-kilohertz relative linewidth over 10 dual-comb beating periods, which, to the best of our knowledge, is the best noise performance ever demonstrated for a solid-state dual-comb laser. The excellent mutual coherence of the combs allowed us to perform free-running spectroscopic measurements of the fused silica etalon over second time scales with mode-resolved precision.
This work was supported by National Science Centre (NCN, Poland; 2015/18/E/ST7/00296).
[1] R. Liao, H. Tian, W. Liu, R. Li, Y. Song, and M. Hu, "Dual-comb generation from a single laser source: principles and spectroscopic applications towards mid-IR - A review," J. Phys.: Photonics 2, 042006 (2020).
[2] M. Kowalczyk, L. Sterczewski, X. Zhang, V. Petrov, Z. Wang, and J. Sotor, "Dual-comb femtosecond solid-state laser with inherent polarization-multiplexing," arXiv:2009.05454 (2020).
