Energy tunability of BMSs. (a) Harmonic mode-locking order and repetition rate of BMSs realized via tuning the polarization state of light at pump power of ~10 mW. (b) Single-pulse energy versus different harmonic mode-locking orders. (c) Pulse trains and (d) radio frequency spectra of the 5th harmonic mode-locking BMSs. (e) Pulse trains and (f) radio frequency spectra of the 85th harmonic mode-locking BMSs.