Two new two-dimensional covalent–organic frameworks are synthesized using a three-connected building block, showing ultrahigh iodine capture capacities of 5.625 g g−1 and 4.820 g g−1 on account of physical–chemical adsorption.

In this investigation, a convex-shaped fiber ring (CSFR)-based single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) is proposed and experimentally verified. The CSFR, composed of only two optical couplers and forming a double-ring architecture, is employed to serve as a high quality mode filter to eliminate the dense longitudinal modes of the EDFL. The unpumped erbium-doped fiber in the Sagnac loop is utilized to produce the ultra-narrowband auto-tracking filter effect as a saturable absorber to guarantee the SLM out. The experimental results show that the linewidth of the proposed EDFL is 840 Hz with a high optical signal to noise ratio of 63 dB. In addition, the stability of the EDFL with the maximum output power fluctuation of 0.01 dB and the maximum central wavelength variation of 0.01 nm, in both the short-term and the long-term observations. Hence, we obtained a SLM EDFL with extremely high stability, ultra-narrow linewidth and high optical signal to noise ratio (OSNR). INDEX TERMS Single longitudinal mode (SLM), erbium-doped fiber laser (EDFL), saturable absorber.

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