GeSe Nanosheet-Based Modulator for Generating Switchable High-Order Harmonic Mode-Locked Pulses

A modulator with favorable nonlinear saturable absorption properties is fabricated by dropping GeSe nanosheets onto a tapered fiber. The order-switchable high-order harmonic mode-locked (HML) pulses are acquired in an Er-doped fiber (EDF) laser based on this modulator. The modulation depth of the GeSe nanosheets-based modulator is measured to be 15.94%, meaning it can be used as a saturable absorber (SA). Conventional soliton pulses with a fundamental repetition frequency of 2.18 MHz and a center wavelength of 1556.76 nm were obtained by employing a GeSe-SA in an EDF laser. By tuning the polarization controller and increasing pump power, high-order HML pulses appear in this laser with orders switchable between 20, 25, 30, 46, and 52. These experimental phenomena and data indicate that GeSe nanosheets could be regarded as a candidate material to yield high-order HML pulses, which has prospective application value in ultrafast photonics.