CNT-based saturable absorbers with scalable modulation depth for Thulium-doped fiber lasers operating at 1.9 μm

Abstract

In this work, we demonstrate a comprehensive study on the nonlinear parameters of carbon nanotube (CNT) saturable absorbers (SA) as a function of the nanotube film thickness. We have fabricated a set of four saturable absorbers with different CNT thickness, ranging from 50 to 200 nm. The CNTs were fabricated via a vacuum filtration technique and deposited on fiber connector end facets. Each SA was characterized in terms of nonlinear transmittance (i.e. optical modulation depth) and tested in a Thulium-doped fiber laser. We show, that increasing the thickness of the CNT layer significantly increases the modulation depth (up to 17.3% with 200 nm thick layer), which strongly influences the central wavelength of the laser, but moderately affects the pulse duration. It means, that choosing the SA with defined CNT thickness might be an efficient method for wavelength-tuning of the laser, without degrading the pulse duration. In our setup, the best performance in terms of bandwidth and pulse duration (8.5 nm and 501 fs, respectively) were obtained with 100 nm thick CNT layer. This is also, to our knowledge, the first demonstration of a fully polarization-maintaining mode-locked Tm-doped laser based on CNT saturable absorber.

Generating Picosecond Pulses With the Largest Number of Lasing Wavelengths by an All-Fiber Optical Parametric Oscillator

“…The mode-locked erbium-doped fiber laser was designed to generate picosecond laser pulses at 1550 nm band. It has a ring cavity structure and utilizes single wall carbon nanotube (SWNT) film as a saturable absorber [11,12]. A segment of erbium-doped fiber (EDF) is used as the gain medium, and pumped by a 976 nm laser diode (LD) through a 980/1550 nm wavelength division multiplexer (WDM).…”

Generation of multi-solitons and noise-like pulses in a high-powered thulium-doped all-fiber ring oscillator

“…Nonetheless, mode-locking threshold power noticeably falls with cavity length increase which is inherent to NPE mode-locking mechanism due to evident enhancement of lumped nonlinearity governing polarization ellipse rotation in a cavity with extended length. Thus, according to our observations, there are two possible ways for single soliton generation to be realized in the developed scheme of the TDF mode-locked laser, which are both based on the mode-locking threshold reduction below fundamental soliton energy limit: (i) noticeable cavity elongation leading to inevitable decrease in soliton energy and power 12 or (ii) implementation of a saturable absorber with reduced saturation power (and energy) such as carbon nanotubes or graphene instead of or together with NPE 2 . However, the first solution should have additional experimental confirmation.

Figure 7( a ) Energy and ( b ) peak power of a single soliton at the laser output for the minimum possible pulse duration and for the durations obtained from the experiment, depending on the cavity length.

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“…Thulium-doped fiber (TDF) mode-locked lasers are highly promising for spectroscopic and sensing applications, including gas-tracing, light detection and ranging systems (LIDARs), seed sources for mid-IR optical parametric oscillators (OPOs) and supercontinuum generation, biomedical applications, optical communications, micromachining and defense 1 . To date, the generation of conservative 2–4 , dispersion-managed 5,6 and dissipative solitons 7,8 and similaritons 9 has been realized in TDF lasers using various mode-locking techniques, including Kerr-nonlinearity-based nonlinear polarization evolution(NPE) 4–6,8–10 , nonlinear loop mirrors 11,12 , various saturable absorbers (SESAM 7,13 carbon nanotubes 2,14,15 , graphene 16,17 , and other 2D structures 3,18 ) and hybrid techniques 19,20 . This provides great flexibility in the configurations of lasers and to the variety of ultra-short pulse characteristics available.…”

Dynamics of carbon nanotube-based mode-locking fiber lasers

“…© Springer Nature Limited 2018; (F) ∼1900 nm using Tm-doped fiber laser. Sobon et al [126]. © Springer Nature Limited 2017; (G) ∼2100 nm using Ho-doped fiber laser.…”