Generation of cylindrical vector dissipative soliton using an ultra-broadband LPFG mode converter with flat conversion efficiency

Abstract

Dissipative solitons (DSs), which are pulses with high pulse energy and a broad rectangular output spectrum, have several applications. In a fiber system, the generation of higher-order DS requires a mode converter with a high and flat conversion efficiency that can cover the working waveband. The requirements on high and flat conversion efficiency as well as broadband working waveband is a great challenge for a traditional mode converter. This study presents an L-band mode-locked fiber laser with a 3-dB bandwidth of more than 47 nm and a first-order cylindrical vector (CV) mode DS output based on an ultra-broadband long-period fiber grating (LPFG). The fabricated mode converter is a novel cascading LPFG with an ultra-broadband working bandwidth and flat conversion efficiency which could meet the demand of DS mode conversion. The 15-dB bandwidth is 149.76 nm, from 1515.36 nm to 1665.12 nm. Furthermore, the conversion efficiency in the range of the output spectrum is 98.60 ± 0.23%. The single-, double-, and triple-soliton output characteristics and their real-time spectra are observed using time-stretched dispersion Fourier transformation (TS-DFT) technology. Experimental results demonstrate that the first-order CV mode DS laser can maintain its dynamics after mode conversion under the accuracy of detection system, implying that the LPFG works only as a mode converter. The broadband DS laser with CV mode output in the L-band has been presented for the first time in study, to the best of our knowledge. This study is also the first to detect real-time characteristics for a higher-order mode-locked fiber laser using the TS-DFT technology. The proposed type of LPFG is s good candidate for generating higher-order mode lasers with an all-fiber structure.