Triple-wavelength laser from a femtosecond laser directly-written fiber cavity for microwave generation

We report an all-fiber triple-wavelength single-frequency distributed Bragg reflector (DBR) laser for 1-10 GHz microwave (MW) generation. The DBR cavity contains a non-polarization-maintaining Er fiber and a pair of fiber Bragg gratings (FBGs) made using a femtosecond laser line-by-line (LbL) direct-writing method. Such a configuration combining a short cavity and radial asymmetry leads to frequency locking and phase controlling of multi-wavelength fiber lasers. A 1.59-µm triple-wavelength laser with high coherence, spectrum purity, and polarization purity has been demonstrated; 3-6 GHz triple-frequency MW was generated.