Mode-hop-free single-longitudinal-mode erbium-doped fiber laser frequency scanned with a fiber ring resonator

We describe the experimental construction of a single-longitudinal-mode erbium-doped fiber ring laser equipped with a ring resonator filter. The system is designed to avoid mode hopping and can be frequency scanned for spectroscopic sensor applications. We modified a conventional ring resonator filter to have the capability to reduce transmittance of unwanted modes, which is essential for frequency scanning without mode hopping.