Passively harmonic mode-locked fiber laser with switchable repetition rate based on a 45° tilted fiber grating

A passively harmonic mode-locked erbium-doped fiber laser was built up based on nonlinear polarization rotation(NPR) technique with switchable repetition rates. A 45 tilted fiber grating(45TFG) integrated in the cavity was considered as an ideal polarizer, which was combined with two polarization controllers to realize NPR mechanism. Under fixed pump power of 673 mW, a group of harmonic mode-locked pulses from 1st to 37th could be obtained only through adjusting the two polarization controllers carefully. The laser can produce stable pulses with the maximum repetition rate of 783 MHz which corresponds to 37th harmonic order, and the sidemode suppression ratio (SSR) of 37th harmonic mode is 41 dB. High repetition rate and stable pulses can be used in applications, such as modern optical communication system and optical sensors.