As the TLS is turned off, the unstable self-lasing cavity modes are
intrinsically generated and dominate the laser oscillation around
1557–1563 nm owing to the mode competition in EDFL. The mode
competition limits the tuning wavelength range and impacts the
power stability of the suggested BEFL. In order to suppress the free-
running cavity modes, BP wavelength is required to match with the
self-lasing modes wavelength to improve the performance of the
laser. Hence, we set BP at a wavelength of 1557 nm.