Widely tunable wavelength spacing dual-wavelength single longitudinal mode erbium doped fiber laser

• The lasing wavelength spacing is widely tunable in a range from 2 nm to 18 nm.
• The birefringent fiber filter benefits the simultaneous oscillation of dual-wavelength in a single laser cavity.
• The output peak power of the lasing dual-wavelength is approximately equalized at room temperature.
• The single longitudinal mode operation of the lasing dual-wavelength is verified by Fabry–Perot scanning interferometer.
• The modulation performance of single lasing wavelength is proved to be good according to the clear eye diagram.

A simple widely tunable wavelength spacing dual-wavelength single longitudinal mode (SLM) erbium doped fiber laser (EDFL) based on cascaded fiber Bragg gratings (FBGs) and birefringent fiber filter is proposed and demonstrated. Experimental results show that the lasing wavelength spacing is widely tunable in a range from 2 nm to 18 nm, which has potential to generate frequency tunable terahertz (THz) waves by beating the lasing dual-wavelength in a high speed photodetector. The birefringent fiber filter acts as an ultra-narrow bandpass filter and benefits the simultaneous oscillation of dual-wavelength in a single laser cavity. The output peak power of the lasing dual-wavelength is approximately equalized at room temperature, and a high optical signal-to-noise ratio (OSNR) is realized in the whole tuning range. The SLM operation of dual-wavelength fiber laser is verified by Fabry–Perot (F–P) scanning interferometer, and the clear eye diagram proves that the proposed fiber laser is effective in the application of fiber optic communication system.