Hybrid structure based on no-core and graded-index multimode fibers as saturable absorber for a self-starting mode-locked Yb-doped fiber laser
Sunita Thulasi, S. Sivabalan
Abstract
We demonstrate an all-fiber ytterbium (Yb)-doped mode-locked oscillator using a hybrid structure based on no-core fiber graded-index multimode fiber (NCF-GIMF) as the saturable absorber (SA). The proposed SA exhibits unique characteristics such as large-power tolerance, high modulation depth of 24.7%, and low saturation intensity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>11.01</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">M</mml:mi> <mml:mi mathvariant="normal">W</mml:mi> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">c</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> , which help to achieve a stable mode-locking operation. The all-normal and self-starting oscillator generates stable ultrafast pulses with a repetition rate of 21.35 MHz, pulse energy/average output power of 120 pJ/2.7 mW, and a pulse duration of 2.4 ps at a central wavelength of 1034.2 nm. The output pulses are then dechirped to 300 fs using an external grating compressor and possess high stability with a radio frequency spectrum of 58 dB. These results show that the NCF-GIMF-based SA can be used as an effective photonic device for high energy wave breaking free pulse generation.