Generation of ultra‐fast laser pulses using nanotube mode‐lockers

Abstract

We report a simple way to fabricate a high optical quality single wall carbon nanotubes (SWNTs) polyvinyl alcohol (PVA) composite. The composites demonstrate strong saturable absorption at ~1.5 µm, the spectral range for optical communications. These are used as mode-lockers in a fiber laser. We achieve ~713 fs pulse generation and up to 8 mW output power.

Ultrafast stretched-pulse fiber laser mode-locked by carbon nanotubes

“…Ultrasonicating the mixture resulted in a uniform solution which was then drop-cast on a Petri dish. Slow evaporation (1-2 weeks) under ambient temperature and pressure in a desiccator gave a free standing SWNT-PVA composite, 50 µm thick with homogeneously dispersed tubes [7,11,13]. The film was then dried at 45 °C .…”

“…Alternative saturable absorbers based on single wall carbon nanotubes (SWNTs) and graphene are at the centre of an intense research effort [7,8], due to their broad operation range, low saturation power, easy fabrication, mechanical and environmental robustness, and quick recovery times . These have been used to mode-lock fiber [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], waveguide [24], solid-state [25][26][27], and semiconductor lasers [28]. Present mode-locking technology typically relies on soliton-like operation.…”

Wideband-tuneable, nanotube mode-locked, fibre laser

“…Yet, it degrades the mode-locking performance, resulting in less output power or longer pulses. In our case, the contributions to the non-saturable losses may include residual absorption due to amorphous carbon, metal catalysts and tubes not in resonance with the incident light, scattering from residual bundles, absorption and refraction from the polymer matrix 16 , and linear coupling loss between fibre ends 34 . By further engineering film thickness and nanotube loadings and alignment, devices with minimized non-saturable loss could be obtained.…”

“…Semiconductor saturable absorber mirrors are widely used in fibre lasers [4][5][6] , but their operating range is typically limited to a few tens of nanometres 7,8 , and their fabrication can be challenging in the 1.3 -1.5 mm wavelength region used for optical communications 9,10 . Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness [11][12][13][14][15][16] . Here, we engineer a nanotube -polycarbonate film with a wide bandwidth (>300 nm) around 1.55 mm, and then use it to demonstrate a 2.4 ps Er 31 -doped fibre laser that is tuneable from 1,518 to 1,558 nm.…”

“…SWNTs show large optical nonlinearity 25 , ultrafast carrier relaxation time 26 and high damage threshold 27 . They are compatible with optical fibres, and mode-locked laser operation at $1.5 mm has been demonstrated 15,16,[27][28][29][30][31][32] . The variation of nonlinear absorption is determined by the number of tubes in resonance with the incident light.…”