Passive Q-switching of a fiber optic laser induced by carbon black pigment solution

Abstract

In this paper, we report an experimental study of passive Q-switching in a fiber optic laser induced by a carbon black pigment solution with reverse saturable absorption (RSA) properties. The solution was contained in a borosilicate capillary tube with an inner diameter of 125 μm and a length of 1.5 cm, which facilitated the alignment of the optical fibers and the integration of the solution for nonlinear characterization and pulse generation in a laser cavity. The solution was characterized by Fourier Transform Infrared (FTIR) spectroscopy and non-linear analysis was performed using the P-scan technique at 1550 nm by a high-gain amplifier using a pulse width of 10 ns and a frequency of 2 kHz. The results show a nonlinear absorption coefficient ($\beta$) of 1.49 × 10⁻⁶ m/W and a third-order nonlinear susceptibility (χ⁽³⁾) of 8.2 × 10⁻¹⁶ m²/V². The pulses generated in an optical fiber laser with a ring-cavity configuration, using the carbon black pigment solution, showed an initial repetition frequency of 16 kHz at a pump power of 33 mW, which increased to 36 kHz when the power was raised to 130 mW, emitting at a wavelength of 1533 nm. To the best of our knowledge, this is the first demonstration of using carbon black pigment solutions for pulse generation in optical fiber lasers, which is an accessible, efficient, and low-cost alternative for optical communication applications.