Fig.7 displays the influence of BP wavelengths on the MBEFL performance. The experimental results show that the laser can be tuned from 1547 to 1569 nm without any free-running cavity modes. Once BP wavelength is chosen beyond this wavelength range, the unstable free-running cavity modes are observed around 1560 nm. For the wavelength ranging from 1557 to 1563 nm, the number of lasing lines is the maximum, while beyond this wavelength region, the number reduces rapidly. In short, the tuning range of MBEFL depends on the gain competition between the Stokes lasing lines and the free running cavity modes.