All-fiber All-normal-dispersion Femtosecond Laser with Nonlinear
Multimodal Interference-based Saturable Absorber
Uğur Teğin1,2 and Bülend Ortaç1
1. National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara, Turkey
2. Present address: Optics Laboratory and Laboratory of Applied Photonics Devices, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
Chong et al. demonstrated a stable passively mode-locked all-normal-dispersion fiber laser and pulse generation is attributed to the strong spectral filtering of chirped pulses, dissipative soliton pulses [1]. In the following years, with very-large-mode-area fibers the energy and power scalability of the dissipative soliton pulses is demonstrated. Recently, multimodal interactions are subject to device studies with various configurations. Nazemosadat et al. theoretically proposed a short graded-index multimode fiber segment in between single mode fiber as a saturable absorber [2]. On the other hand, with similar device structure an all-fiber bandpass filter is later presented both numerically and experimentally [3].
Here, we demonstrate the first all-fiber integrated all-normal-dispersion Yb-doped oscillator with the nonlinear multimodal interference based saturable absorber capable of generating ultrashort pulses. The experimentally demonstrated self-starting cavity is presented in Fig.1.a. The oscillator forms dissipative solitons at 1030 nm with 5.8 mW average power and 44.25 MHz repetition rate (Fig.1.b-d). We record the RF spectrum with 1 kHz span and 10 Hz resolution bandwidth and observed an outstanding sideband suppression ratio around 70 dB (Fig.1.b). Mode-locked cavity generates chirped pulses with ∼5ps duration and these pulses are externally compressed to 276 fs with a grating compressor (Fig.1.e). We use PICASO algorithm to retrieve temporal pulse shape from spectrum and autocorrelation traces. The algorithm registers the retrieved pulse duration is 236 fs as presented in Fig.1.f. Numerical simulations are performed to investigate cavity dynamics, and obtained results are well matched with experimental observations.
Fig. 1 (a) Schematic of the oscillator. (b) Short range RF spectrum and long range RF spectrum (inset) (c), Spectra of dissipative soliton pulse from the output couplers on logarithmic and linear scale (inset). (d) Autocorrelation trace of the chirped pulses obtained directly from output coupler C1. Inset: single-pulse train. (e) Autocorrelation trace of the dechirped pulses obtained from output coupler C1 (solid) and theoretical fit with Gaussian pulse shape (dashed). Inset: in logarithmic scale. (f) PICASO retrieved de- chirped pulse shape.
In conclusion, we numerically and experimentally present a new method to generate dissipative soliton pulses in a low-cost all-fiber laser configuration. Proposed cavity design is based on nonlinear multimodal interference to ensure saturable absorber and bandpass filtering necessary to generate dissipative soliton pulses. We believe the reported laser configuration is an attractive method for generating ultrashort dissipative soliton pulses and can find application high stability required research areas such as optical metrology.
References
>1@ A. Chong, J. Buckley, W. Renninger, F. Wise, “All-normal-dispersion femtosecond fiber laser,” Opt. Express 14, 10095 (2006). >2@ E. Nazemosadat, A. Mafi, “Nonlinear multimodal interference and saturable absorption using a short graded-index multimode optical fiber,” J. Opt. Soc. Am. B 30, 1357 (2013).
>3@ W. S. Mohammed, P. W. Smith, X. Gu, “All-fiber multimode interference bandpass filter,” Opt. Lett. 31, 2547 (2006). (a) (b) (c) (d) (e) (f) 978-1-7281-0469-0/19/$31.00 c2019 IEEE
