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The other core component is the saturable absorber (SA), which is the key to achieving single longitudinal mode operation and obtaining narrow linewidth laser output.
Its working principle is based on using unpumped thulium-doped fiber as a dynamic narrowband filter. As shown in the principle diagram, with the increase of input light intensity, the SA reaches absorption saturation, and the output light intensity is significantly improved. Through calculation, we know that the FWHM of a 1-meter-long SA is 22.6 MHz, which perfectly matches the 17 MHz cavity mode spacing. This precise matching ensures the effective realization of single longitudinal mode output. |
IEEE/ICACT20260337 Slide.09
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