A sensitivity enhanced temperature sensor with cascaded tapered two-mode fibers (TTMFs) based on the Vernier effect is proposed and experimentally demonstrated. It is confirmed that series connection exhibits higher extinction ratio than parallel one both by theory and experiments, which provides guidance for related experiments. In experiments, two TTMFs have the same single-mode fiber-TTMF-single-mode fiber configuration, while the free spectral ranges (FSRs) are chosen with slightly difference by modifying the parameters in the tapering process. Experimental results show that the proposed temperature sensor possesses sensitivity of −3.348 nm/°C in temperature measurement range from 25 °C to 60°C, 11.3 times sensitivity enhancement in comparison with single TTMF. Benefiting from advantages of high temperature sensitivity, simplicity of manufacture and long distance sensing, this novel sensitivity enhanced temperature sensor can be applied to various particular fields, such as oil wells, coal mines and so on.

We report on two-dimensional (2D) hexagonal boron nitride (hBN) as saturable absorber (SA) material in a passively Q -switched erbium-doped fiber laser (EDFL) operating at 1.5 µm. The 2D hBN film as an SA is fabricated and transferred onto the optical fiber tip by natural deposition technology. In the Q -switched operation, we obtain stable Q -switched laser operation with a maximum average 10% output power of 2.25 mW, corresponding to a repetition frequency of 55.5 kHz, shortest pulse width of 6.77 µs, and single pulse energy of 40.49 nJ. The achieved PQS at 1.5 µm EDFL with 2D hBN as an SA may have potential applications in many novel 2D materials and all-fiber lasers.

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We propose and demonstrate a wavelength switchable mode-locked Erbiumdoped fiber laser with carbon nanotubes for mode-locking and a tapered two-mode fiber (TTMF) based filter for wavelength selection. The TTMF based filter constructed with singlemode fiber-TTMF-single-mode fiber configuration, features smooth interference spectrum. It is attributed to that only two modes are involved into the interference in the specially designed TTMF, which is confirmed by both simulations and experiments. Moreover, the free spectral range (FSR) of the TTMF based filter can be arbitrarily chosen by controlling the taper diameter. Depending on the FSR of the TTMF based filter, the central wavelengths of the mode-locking operation of the Erbium-doped fiber laser based on carbon nanotubes can be switched between two wavelengths with FSR of 8.5 nm and three wavelengths with FSR of 3.1 nm, respectively. This fiber laser is flexible source for various applications.

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