AbstractA simple microwave signal source is proposed by connecting two single‐longitudinal‐mode erbium‐doped distributed Bragg reflector fiber lasers in series. For using same pump LD, mutual injection locking of two fiber lasers is achieved. The two single‐longitudinal‐mode lasers have 0.048 nm wavelength difference. By beating the two wavelengths at a photodetector, stable microwave signal at 6.17 GHz is achieved at room temperature. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 177–179, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24840