Abstract
We propose a nanotube-based erbium-doped fiber laser that can deliver conventional soliton (CS) and stretched pulse (SP) based on D-shaped fiber saturable absorber (DF-SA) where evanescent-field interaction works. The novel Nanotube-based Fiber Laser can generate SP or CS by tuning pump power and polarization controller (PC) properly. The net cavity dispersion of laser is slightly negative. In our experiment, by optimizing the PC in the cavity, CS and SP can be obtained at the central wavelengths of 1530.6 nm and 1530.3 nm due to on carbon nanotubes and the spectral filtering effect induced by nonlinear polarization rotation. Although the acquired CS and SP nearly have the same central wavelengths, they show distinct optical spectra, 3-dB bandwidths. The proposed fiber laser with switchable CS and SP is attractive for ultrashort pulse generation and fast measurements in practical applications.
Highlights
Due to their excellent features of generating ultra-short pulses, passively modelocked fiber lasers have drawn a lot of attention [1] [2] [3] [4]
In the fiber laser cavity, a 980 nm laser diode (LD) is used as pump source via a 980/1550 nm wavelength-division multiplexer (WDM) coupler; an 18-m erbium-doped fiber (EDF) with the group velocity dispersion (GVD) parameter of -9 ps/nm/km and the absorption of 3 dB/m at 980 nm acts as the gain media; a polarization controller (PC) in the cavity is used to adjust the state of polarization; the 10% port of a 90/10 coupler is adopted to extract the laser for measurement; the D-shaped fiber saturable absorber (DF-saturable absorbers (SAs)) integrated into the cavity is made by using an optical-deposition technique to deposit single-wall carbon nanotubes (SWNTs) on the D-shaped fiber (DF) [56]; a polarization independent isolator (PI-ISO) is adopted to realize unidirectional operation
The central wavelength of the conventional soliton (CS) locates at ~1530.6 nm, which is mainly determined by the diameter distribution of nanotubes in SWNT-SA, the intracavity loss, the transmittance peak of birefringence-induced filter, and the gain profile of EDF [42] [60]
Summary
Due to their excellent features of generating ultra-short pulses, passively modelocked fiber lasers have drawn a lot of attention [1] [2] [3] [4]. There are many investigators that pay great attention to SWNTs as SAs. A fiber laser generating a 74 fs pulse with 63 nm spectral width based on nanotube mode locker have been proposed by Popa et al [34]. Broadband operation which is the superior feature of SWNTs can be realized by mixing SWNTs with different diameters, because the diameter and chirality of nanotubes determine the absorption peak of SWNTs [35]
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