Femtosecond Er-Doped All-Fiber Laser with High-Density Well-Aligned Carbon-Nanotube-Based Thin-Film Saturable Absorber

Abstract

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.5 mW in an erbium-doped ring laser with the hybrid mode-locking of a VDVA-SWNT SA in combination with the effects of nonlinear polarization evolution. Dechirped pulses with a duration of 180 fs were generated, with a repetition rate of about 42.22 MHz. The average output power standard deviation was about 0.06% RMS during 3 h of measurement.

Generation of similariton-like pulse bunch in erbium-doped fiber laser with hybrid mode-locking

“…Single-walled boronnitride carbon nanotubes (C:BNNT) 15 play the role of a slow SA and provide self-triggering of mode locking. The mechanism of nonlinear polarization evolution (NPE) serves as a fast SA 16 . To adjust the generation regime, a polarization controller (PC) is used.…”

High-Density Well-Aligned Single-Walled Carbon Nanotubes for Application as a Saturable Absorber with a High-Pass Filter Effect in an Erbium-Doped Ultra-Short-Pulse Fiber Laser

“…The carbon nanotube compact was cut into 1 μm thick samples using UltraCut E. The completed SA samples were obtained by pouring cut HDWA-SWCNT compacts with an aliphatic epoxy resin. The main optical characteristics of the obtained film were carefully studied in our previous publication . The resulting SA has such advantages over standard nanotubes as a shorter response time and a greater modulation depth (Table ).…”

“…In this case, as seen in the laser scheme, we used two polarization controllers (PC) to adjust the mode-locking and an isolator–polarizer to achieve the NPE effect. The second regime achieved by the hybrid mode-locking mechanism, a film of high-density well-aligned single-walled carbon nanotubes (HDWA-SWCNTs) was introduced into the laser cavity, which was located between two FC/APC connectors and played the role of a slow saturable absorber. , The Raman spectrum and SEM of the nanotubes used are shown in Figure a,b, respectively. The HDWA-SWCNTs remained after treatment with a diameter of up to 1.2 nm, corresponding to the 225.7 cm –1 radial breathing mode of the Raman spectra.…”

“…The main optical characteristics of the obtained film were carefully studied in our previous publication. 27 The resulting SA has such advantages over standard nanotubes as a shorter response time and a greater modulation depth (Table 1). However, a dramatic advantage of aligned nanotubes is their polarization dependence of absorption.…”

“…Passive stabilization methods address the more fundamental causes of noise and are based on optical principles . When talking about passive methods to reduce intensity noise, saturable absorbers play a significant role not only in the formation of mode-locking but also in the stabilization of output pulse characteristics. − To date, in order to achieve a stable mode-locking in USP lasers, various SAs have been developed such as SA based on the nonlinear polarization evolution (NPE), − as well as SESAM saturable absorbers, carbon nanotubes, ,, and films of transition metal dichalcogenides. − Furthermore, it is especially worth highlighting hybrid mode-locking methods, which means the use of two saturable absorbers in the same cavity, for example, the use of NPE and carbon nanotubes SA . Hybrid mode-locking simplifies the mode-locking process in the cavity by taking advantage of two saturable absorbers with different characteristics.…”