This work presents a systematic study on the integration of highly nonlinear fiber (HNLF) into an actively mode-locked nanosecond erbium-doped fiber laser (EDFL) cavity, while assessing the performance and stability of high order harmonics (up to the 105th order) via comparative analysis of setups with a standard single-mode fiber and their respective HNLF-integrated setups, specifically characterizing the impact of nonlinearity on peak power, full-width-at-half-maximum (FWHM), and pulse stability. The results indicate that adding HNLF enhances peak power, particularly at lower harmonic frequencies, while improving the FWHM values. Peak power and FWHM were found to be dependent on both the modulator driving signal’s frequency and its peak-to-peak voltage. In the non-HNLF setup, the peak power varied from 3.8 dBm to −6.19 dBm, and the FWHM ranged from 12.5 ns to 7.5 ns. In contrast, in the HNLF-integrated setup, the peak power ranged from 4.62 dBm to −3.37 dBm, and the FWHM varied from 10.5 ns to 9.5 ns as the modulator driving frequency was adjusted. The configuration with HNLF integration presents additional measurable improvements not only in pulse power and FWHM but also in several measures of spectral quality. The integrated configuration achieved an optical signal-to-noise ratio (OSNR) of 69.89 dB as compared to the length-matched standard SMF-28 configuration’s OSNR of 61.56 dB; and a side mode suppression ratio (SMSR) of 68.7 dB at a modulation frequency of 9.78 MHz, which was 6.6 dB greater than that of the corresponding non-HNLF configuration. Thus, the contribution of HNLF integration not only extends to pulse shaping but also encompasses simultaneous enhancements in optical signal quality and pulse train coherence, both of which are directly applicable to optical communications and sensing applications.
Unalan et al. (Sun,) studied this question.
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