A graphene coated microfiber Bragg grating (GMFBG) for gas sensing is reported in this Letter. Taking advantage of the surface field enhancement and gas absorption of a GMFBG, we demonstrate an ultrasensitive approach to detect the concentration of chemical gas. The obtained sensitivities are 0.2 and 0.5 ppm for ${\mathrm{NH}}_3$ and xylene gas, respectively, which are tens of times higher than that of a GMFBG without graphene for tiny gas concentration change detection. Experimental results indicate that the GMFBG-based ${\mathrm{NH}}_3$ gas sensor has fast response due to its highly compact structure. Such a miniature fiber-optic element may find applications in high sensitivity gas sensing and trace analysis.

We find that the random fiber laser (RFL) without point-reflectors is a temperature-insensitive distributed lasing system for the first time. Inspired by such thermal stability, we propose the novel concept of utilizing the RFL to achieve long-distance fiber-optic remote sensing, in which the RFL offers high-fidelity and long-distance transmission for the sensing signal. Two 100km fiber Bragg grating (FBG) point-sensing schemes based on RFLs are experimentally demonstrated using the first-order and the second-order random lasing, respectively, to verify the concept. Each sensing scheme can achieve >20dB optical signal-to-noise ratio (OSNR) over 100km distance. It is found that the second-order random lasing scheme has much better OSNR than that of the first-order random lasing scheme due to enhanced lasing efficiency, by incorporating a 1455nm FBG into the lasing cavity.

In this paper, we reported the realization of 2nd-order random lasing in a half-opened fiber cavity, which is formed by a FBG with central wavelength at the 1st–order Raman Stokes wavelength and a single-mode fiber (SMF) performing as a random distributed feedback mirror. Using this proposed method, the threshold of 1st-order (2nd-order) random lasing is reduced to 0.7 (2.0) W, which is nearly 2 times lower than that observed in a completely-opened cavity.

Light sources with high radiance are increasingly required for full-field real-time imaging. Conventional lasing sources are poorly suited for such imaging due to their high spatial or temporal coherence, which generates a speckle that deteriorates image quality. Here, a random fiber laser with multitransverse modes is used as an illumination light source to effectively reduce the speckle in imaging. Low spatial coherence and low temporal coherence of the random fiber laser give birth to significant reduction in the speckle. Under the power-limited condition, the multimode random fiber laser is verified to have a comparable or even better imaging quality compared to a multimode amplified spontaneous emission source. Furthermore, its potential to generate ultrahigh power of up to hundreds of Watts with extremely-high spectral density would make a breakthrough in the development of a new generation of high-power low-coherence light sources for many speckle-free imaging applications, where conventional light sources are not usable. As the multimode random fiber laser can naturally inherit all the advantages of single-mode random fiber lasers, including flexible wavelength, robust structure, and high power, this paper may provide a platform to develop powerful low-coherence light sources to meet wide range requirements of the full-field real-time speckle-free imaging.

This paper proposes a novel concept of refractive index sensing taking advantage of a high-refractive-index-contrast optical Tamm plasmon (OTP) structure, i.e., an air/dielectric alternate-layered distributed Bragg reflector (DBR) coated with metal. In the reflection spectrum of the structure, a dip related to the formation of OTP appears. The wavelength and reflectivity of this dip are sensitive to variation of ambient refractive index, which provides a potential way to realize refractive index sensing with a large measuring range and high sensitivity.

In this paper, we make a comprehensive study on a highly efficient half-open cavity design for high power random fiber laser (RFL). With the theoretical analysis, we optimize the cavity's fiber length for getting higher output power within the scheme, i.e., shorter fiber length is preferred for efficiently harvesting the first order random lasing at the open end of the cavity. As the verification of the theory, we experimentally demonstrate a high output power (7 W), highly efficient (70% optical conversion efficiency) RFL working at 1140 nm, using 10 W 1090 nm laser as the pump source and only 1 km standard single-mode fiber as the distributed cavity.