H. Ahmad, N.A.M. Rusni, M.Z. Samion
This study investigates the use of Rhodamine 6G as a new saturable absorber (SA) for achieving passive mode-locking in thulium-holmium-doped fiber lasers (THDFLs) operating in the 2 μm wavelength region. An arc-shaped fiber host enables effective interaction of the evanescent field with the Rhodamine 6G layer. The spiral-like surface morphology and nanocrystalline features of the Rhodamine 6G SA were confirmed through field emission scanning electron microscope (FESEM) analysis. With a modulation depth of 15.2 %, the Rhodamine 6G-based SA successfully initiated fundamental mode-locked pulses at a frequency of 14.6 MHz, accompanied by a signal-to-noise ratio (SNR) of 68.7 dB. Stability analysis conducted over an 8-hour operation period showed only minor SNR fluctuations, with a maximum deviation of 1.1 dB, indicating excellent long-term stability. Additionally, by increasing the pump power, the mode-locked laser was able to generate higher-order harmonic mode-locked pulses, achieving up to the 9th harmonic, corresponding to a frequency of 131.6 MHz. This demonstration indicates that Rhodamine 6G is an excellent, low-cost, and efficient organic dye-based SA that is capable of supporting both stable fundamental and harmonic mode-locking in fiber lasers operating in the 2 μm region. © 2025 Elsevier Inc.
Photonics Research Centre, Universiti Malaya, Kuala Lumpur, 50603, Malaysia; Physics Department, Faculty of Science, Universiti Malaya, Kuala Lumpur, 50603, Malaysia; Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Negeri Malang, Jalan Semarang 5, Malang, 65145, Indonesia; Distinguished Visiting Professor, Universiti Kuala Lumpur British Malaysian Institute (UniKL BMI), Batu 8, Jalan Sungai Pusu, Selangor, 53100, Malaysia
