Concentration effect of carbon nanotube based saturable absorber on stabilizing and shortening mode-locked pulse

Abstract

We comprehensively investigated the concentration effect of dispersed single-walled carbon nanotubes (SWCNTs) in polymer films for being a saturable absorber (SA) to stabilize the mode locking performance of the erbium-doped fiber laser (EDFL) pulse through the diagnosis of its nonlinear properties of SA. The measured modulation depth was from 1 to 4.5% as the thickness increased 18 to 265 microm. The full-width half-maximum (FWHM) of the stable mode-locked EDFL (MLEDFL) pulse decreased from 3.43 to 2.02 ps as the concentrations of SWCNTs SA increased 0.125 to 0.5 wt%. At constant concentration of 0.125 wt%, the similar pulse shortening effect of the MLEDFL was also observed when the FWHM decreased from 3.43 to 1.85 ps as the thickness of SWCNTs SA increased 8 to 100 microm. With an erbium-doped fiber length of 80 cm, the shortest pulse width of 1.85 ps were achieved at 1.56 microm with a repetition rate of 11.1 MHz and 0.2 mW of the output power under an output coupling ratio of 5%. An in-depth study on the stable mode-locked pulse formation employing SWCNTs SA, it is possible to fabricate the SWCNT films for use in high performance MLEDFL and utilization of many other low-cost nanodevices.

Passive mode locking of ytterbium- and erbium-doped all-fiber lasers using graphene oxide saturable absorbers

“…The saturable absorption effect is observed in semiconductor type SWCNTs. After that, SWCNTs have been widely applied for mode locking fiber lasers [3][4][5][6][7][8][9][10][11] and solid-state lasers [12][13][14]. Because the energy band gap strongly depends on nanotube's diameter [15], it is required to precisely control the CNT diameter to tune the absorption band of CNT SAs for mode locking laser at a specific wavelength.…”

Mode-locked fiber laser using SU8 resist incorporating carbon nanotubes

“…The mixture of SU8-2075 and cyclopentanone was made by using 4 ml and 1 ml, respectively. Adding SWCNTs at a concentration of 0.125 wt% is an adequate amount to obtain well dispersed SWCNTs and also to observe stabilized shortened pulses [16]. The simplest way to implement a SA with this composite is by making a thin film that can be placed between two angled fiber connectors.…”

“…The cell was separated to obtain a film whose thickness was equal to the thickness of the spacer. The thickness of the film was 100 μm and was chosen according to reference [16]. A small piece of the film (2 mm X 2 mm) was cut and placed between two FC/APC connectors in order to have an all-fiber SA device.…”

“…This is directly related to the polymer solvent, but also with the amount of SWCNTs that we want to incorporate. Therefore, the choice of film thickness and concentration of the SWCNTs is essential for obtaining stable and short mode-locked pulses [12,16]. Furthermore, we also have to consider the mechanical and thermal properties of the polymer.…”

Fabrication of SU8/SWCNT films as saturable absorbers

“…The mixture of SU8-2075 and cyclopentanone was made by using 4 ml and 1 ml, respectively. The amount of SWCNTs was calculated to have a concentration of 0.125 wt% since this has been shown to be an ideal concentration when dealing with thin films of composite materials containing SWCNT [9]. In order to fabricate thin films of the SU8/SWCNT composite, we fabricated a glass cell whose walls have been covered with PDMS.…”