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A compact Q-switched 2.78 μm Er 3+ :ZBLAN fiber laser is demonstrated, in which gold nanocrystal (GNC) film is used as both a saturable absorber and a high reflection mirror. The GNC film is deposited on the end facet of a commercial optical fiber by an ion sputtering technique. It is a simple and efficient method to fabricate a saturable absorber device. Using the GNC film, stable Q-switching is obtained with the repetition rate varying from 22.945-94.144 kHz. The minimum pulse width of 0.81 μs is obtained with a signal-to-noise ratio of 37 dB, the corresponding pulse energy is up to 3.58 μJ, and the average output power is 337 mW at the maximum pump power of 7.45 W. This letter reveals that gold nanomaterial is a reliable optical material for pulse generation at the mid-infrared waveband.

A new type of optical fiber sensor based on an asymmetric structured microfiber modal interferometer is proposed and demonstrated. The sensor head is simply made of singlemode fiber using the electrical arc discharge technique. Owing to the reflection spectrum dips formed by the interference between the cladding modes and the core mode, measurements of temperature and the refractive index (RI) can be obtained by monitoring the wavelength shifts of the interference spectrum. Experiments show that the sensor exhibits a good response to temperature and the ambient RI variation, with maximum sensitivities of 0.079 nm °C-1 and -49.957 nm/RIU, respectively. The merits of its cost-effective and simple fabrication makes this sensor a promising device for sensing applications.

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We propose and demonstrate a coating-enhanced dual-microspheric structure fiber sensor that measures temperature and refractive index simultaneously. The claddings of the two microspheric structured fibers are spliced together and the ends of the fibers are coated with a layer of gold film to increase reflection, thereby forming a dual-microspheric structure sensor head. Our experimental results show that the temperature sensitivity and the refractive index can reach 65.77 pm °C−1 and −19.7879 nm RIU −1 , respectively. Compared with the uncoated sensor, the refractive index sensitivity is significantly improved by the gold film. This work suggests a low-cost, high-resolution and convenient fiber-based method to achieve multifunctional sensing applications.