Polarization maintaining harmonically mode-locked fiber laser with suppressed supermode noise due to continuous wave injection

Abstract

We report on experimental studies of a SESAM mode-locked Er-doped fiber laser completely spliced from polarization-maintaining fiber components. With the fiber mode spot properly aligned to the SESAM, the laser operates harmonic mode-locking (HML) available in a whole range of pump powers up to ∼355mW with the supermode suppression level (SSL) less than 25 dB. Importantly, the HML laser generates the pulses in a linear polarization state and enables the pulse repetition rate (PRR) up to ∼1145 MHz. In our experiments we show that an optical injection of an external continuous wave (CW) into the laser cavity improves the stability of the laser operation in HML regime resulting in an increase of the SSL by 20–30 dB. Besides, the CW injection is able to expand the range of pump powers available with HML laser providing an increase of the maximal laser PRR up to ∼2195 MHz. Importantly, the implemented optical injection does not affect high purity of the laser polarization state. The presented numerical simulations enable qualitative explanations of the effects observed experimentally.