LP₁₁ Mode All-Fiber Ultrafast Laser at 1.3 <i>μ</i>m by Using Bismuth Telluride as an Optical Modulator

This work reports higher order LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes in ultrafast mode-locked fiber laser at the O-band regime. The mode-locking was achieved by using bismuth telluride (Bi<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Te<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>) as an optical modulator in a praseodymium-doped fluoride fiber (PDFF) laser which operates at 1300.5 nm. Bi<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Te<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> was prepared by liquid phase exfoliation (LPE) process and then it was drop-casted onto the arc-shaped fiber, which behaves as an optical modulator. The mode-locking was obtained within the pump power range of 106.8 to 133.2 mW. The pulse repetition rate was at 0.407 MHz with a signal-to-noise ratio (SNR) of 53.4 dB. The ultrafast pulses of 890 fs duration with a pulse energy of 2.4 nJ were achieved. At the output, by using the offset splice spot (OSS) technique the higher-order modes were excited in the two-mode fiber (TMF). These higher-order modes were LP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes with a two-lobe structure visualized using the Thorlabs beam profiler.