An ultra-narrow linewidth multiwavelength fiber laser without linear gain

Abstract

An ultra-narrow linewidth multiwavelength Brillouin fiber laser is demonstrated. Erbium-doped fiber amplifier with linear gain is not used in the structure to avoid the signal broaden. Multiwavelength output with identical interval and ultra-narrow linewidth will be obtained through the experiment. Because the whole system works with a simple structure, it can work stably and has a good application performance in the future. A one-way feedback multiwavelength Brillouin fiber laser structure has been designed. A 2x2 3dB coupler, a 8 km-long single-mode fiber (SMF), a distributed feedback(DFB) semiconductor laser and two optical circulators are included in the structure. A segment of 8 km-long single-mode fiber (SMF) between the two ports of a 2x2 3 dB coupler is used as Brillouin gain loop. A distributed feedback semiconductor laser works as the Brillouin pump (BP). Laser output and feedback are realized by two optical circulators. We adopt the Brillouin pump power at 80 mW. Seven Stokes signals can be observed excluding BP. The Brillouin frequency shift is 0.088 nm compares with the wavelength of BP. We have measured multiwavelength Brillouin fiber laser spectrum ten times in 50 minutes. The experiment result shows that the multiwavelength output of Brillouin fiber laser is very stable. The 3 dB linewidth of the output laser is 5 kHz measured by the frequency spectrum analyzer.