Bidirectional ultrafast fiber laser mode-locked with ethylene glycol

A bidirectional fiber pulsed-laser utilizing ethylene glycol as a mode-locker has been successfully proposed and demonstratedfor the first time. The glycol saturable absorber (SA) is createdby filling ethylene glycol into a cannula,which serves to connect the end facets of two optical patch cords, ultimately forming a sandwich structure. The modulation depth of the glycol-SA is 9.6%, being adequate for mode-locking operation. Based on such an SA, the laser pulses propagating in the clockwise and counterclockwise directions are both achieved by adjusting the polarization state and pump power in the cavity to balance the intra-cavity dispersion and nonlinearity. The obtained laser pulse in one direction operates at the fundamental frequency of 24.31 MHz, with a center wavelength of 1568.28 nm and a 3 dB bandwidth of 0.65 nm; the pulse in the other direction transmitting in the same frequency rate, has a center wavelength of 1568.34 nm and a 3 dB bandwidth of 0.68 nm. With the superiority of fast response time, broad working bandwidth, high damage threshold, low cost,and simplicity in fabrication,this SAs have expansive application prospects in ultrafast photonics and nonlinear optics.