Design and characterization of narrow linewidth fiber laser for wireless communication

Abstract

Ultra-high network capacity becomes more desirable mostly fueled by the widespread adoption of wireless communication and 3G cellular mobile radio system. Narrow linewidth fiber laser has become an essential criterion to realize high-speed data transmission technology. Optical filters are used widely as narrowing element in fiber laser system. A design of Erbium-Doped Fiber Laser (EDFL) configuration is constructed by incorporating different optical filters. The EDFL using Ultra-Narrow Bandwidth tunable filter (UNB-Tunable Filter) shows potential to become an ideal system with the ability to have high Optical-Signal-to- Noise-Ratio (OSNR), moderate output power and wide tunability. The Single Longitudinal Mode (SLM) and ultra-narrow linewidth was realized using Stimulated Brillouin Scattering (SBS) effect and 100 m highly nonlinear fiber. The proposed laser was operated in all-fiber ring configuration where the SBS effect takes place at the amplified output power of 26 dBm. Four Brillouin Stokes are produced spanning from 1550.17 nm to 1550.65 nm. Then, the amplified output was reduced to ~13 dBm intentionally to produce only the first Stokes. The Fabry-Perot filter (F-P filter) was applied to suppress the Brillouin Pump (BP) output signal to generate SLM laser. By utilizing delayed self-heterodyne measurement technique, the linewidth of 0.7 kHz was obtained which is the narrowest Brillouin linewidth reported so far. The application of narrow linewidth presented based on dual-wavelength fiber laser (DWFL). By implementing UNB-Tunable Filter and a Fiber Bragg Grating (FBG) within the EDFL ring configuration, the DWFL was successfully demonstrated. By varying the bandwidth of UNB-tunable filter from 50 pm to 650 pm, the DWFL spacing increased from 2 pm to 58 pm. The 2 pm DWFL found to be the narrowest spacing reported, which is really difficult to get due to mode competition faced by the cavity. The proposed design produced beat frequency spectrum of 0.25 GHz to 7.27 GHz corresponding to the DWFL output spacing of 2 pm to 58 pm. The obtained frequency will find applications and significantly potential in sensing and wireless communication.