Characterization of thulium-doped fiber as active gain medium at 2000 nanometer wavelength region

Abstract

Driven by huge demands and needs, the communication industry has tremendously grown in all over the world. With the development of low loss optical fiber as the main optical communication medium, high power tunable laser and other related auxiliary components are developed to practically opt as an alternative to the electrical communication system. In conjunction with the rapid growth of data traffic and high bandwidth demands, 2 µm wavelength region has been looked out for. In this study, the generation of thulium-doped fiber laser is thoroughly investigated especially in generating pulsed laser. Passively Q-switched thulium-doped fiber laser (TDFL) is successfully experimented by using graphene-based saturable absorber (SA) as a Q-switcher in modulating the intra-cavity loss experienced by the fiber laser system. In the generation of Q-switched TDFL, the laser system has been set up in two configurations; ring cavity and linear cavity. The comparison of the laser performance in terms of frequency, output power, pulse width, and pulse energy differ significantly to each laser cavity. Moreover, the effects of nonlinearities also contribute to the generation of the Q-switched TDFL. These effects can be seen in the wider spectrum of the Q-switched TDFL as being compared to the spectrum of the continuous wave (CW) laser. In this study, four set ups of Q-switched TDFL in ring cavity using four different SAs have been investigated whereas a set of Q-switched TDFL experimented in a linear cavity. Besides that, this study also focuses on the designations of thulium-doped fiber amplifier that can be applied for future generation in optical communication. As aforementioned, 2 µm wavelength region has been the interest of the optical communication society at present. In this study, the thulium-doped fiber amplifier (TDFA) is demonstrated through simulation by OptiSystem v. 13. The basic single stage TDFA is successfully demonstrated and this design is made comparable to the dual-stages TDFA which utilized the pump distribution technique. In the dual-stages with distributed pumping configuration, the pump power is distributed into two stages. Fifty percent of the pump power is being used in the first stage while another fifty percent is being used in the second stage. Tri-stages TDFA is also being demonstrated through the OptiSys and it had been made comparable to the dual-stages TDFA where both TDFAs are utilizing the same enhancement technique. It is shown that the dual-stages TDFA has successfully decreased the noise figure of about 2 dB. All TDFAs were investigated in achieving high gain, high output power with low noise figure.