Bi_2O_2Te Nanosheets Saturable Absorber-Based Passive Mode-Locked Fiber Laser: From Soliton Molecules to Harmonic Soliton

摘要

As a recent addition to the emerging 2D bismuth oxychalcogenides (Bi_2O_2X,where X = S, Se, and Te), atomically-thin bismuth oxytellurium (Bi_2O_2Te)exhibits unique thermoelectric and photoelectric properties. In this study,high-quality Bi_2O_2Te nanosheets (NSs)-based saturable absorber (SA) witha modulation depth of 8.2% is developed using the liquid phase exfoliation(LPE) method and is successfully applied to a passively mode-lockedEr-doped fiber laser (EDFL) for the first time (with reference to the availableliterature). Due to the excellent nonlinear saturable absorption propertyof Bi_2O_2Te NSs, various switchable and stable mode-locking states can berealized in the same EDFL, including fundamental frequency conventionalsoliton (CS), soliton molecules, and harmonic mode-locking (HML) states.Among them, the CS pulse at 7.48 MHz (fundamental frequency) with ahigh signal-to-noise ratio (SNR) of 67.25 dB is obtained. The 2nd, 3rd, and4th-order soliton molecules are observed with a soliton pulse separation of≈6.2 ps. Moreover, for HML, a maximum repetition rate of 1.78 GHz (i.e., correspondingto the 238th-order harmonic) is obtained. The results reveal thatBi_2O_2Te NSs demonstrate excellent nonlinear optical modulation propertiesand can serve as a fundamental basis for promotion of academic researchand innovation of engineering applications involving ultrafast photonics.