Dual-Wavelength Erbium-Doped Fibre Ring Laser by Cascading Tunable Bandpass Filter with Bandstop Filter

A novel fibre ring laser is proposed and successfully demonstrated. By cascading a tunable bandpass filter with a bandstop filter to construct the desired narrow dual-transmission-peak spectrum, and employing a segment of unpumped erbium-doped fibre as a saturable absorber, a stable fibre ring laser is achieved at room temperature. The proposed laser can operate in dual-wavelength with the wavelength spacing of 0.48 nm and the extinction ratio more than 50 dB or switch between the two wavelengths by adjusting a polarization controller. The stability is investigated experimentally and explained theoretically.