Multi-wavelength (MW) laser sources with high optical signal-to-noise ratios (OSNR) are of great interest for optical communications with ultrahigh data capacity as well as microwave and terahertz photonics. In this paper, we report the first demonstration of MW Brillouin random fiber laser in the telecom spectral window around 1.5 μm based on a unique random fiber grating (RFG). Random feedback by enhanced distributed Rayleigh scattering from the RFG basically enables a high-efficiency random lasing resonance of the Stokes wave via stimulated Brillouin scattering in optical fibers. A subfiber loop eventually delivers the cascading process for the high-efficiency generation of up to a 14-order Stokes' comb with an ultrahigh OSNR of 41 dB and an optimized peak power discrepancy of 3.4 dB. Thanks to Rayleigh scattered random feedback from the RFG, single longitudinal mode operation of the Stokes laser emission is achieved.

Highly sensitive and broadband ultrasound (tens of megahertz) detectors can extend the capabilities of photo-acoustic imaging in biomedical application and nondestructive test inspection. Here ultra-compact fiber-based multi-mode dual-cavity Fabry-Perot interferometer (DC-FPI) ultrasound sensors are proposed by splicing three sections of cleaved standard single-mode fibers with the fiber off-core cross section in the middle. The contrasts, reflectivity, and linewidths of the DC-FPIs have been comprehensively characterized. The broadband frequency responses, ranging from 5 kHz to 45.4 MHz, are demonstrated by using the high harmonics of a piezoelectric transducer centered at 3.7 MHz. In addition, the influences of different resonant modes in the DC-FPI on the ultrasound frequency response have been demonstrated. The high-frequency and broadband response of such a simple and cost-effective ultrasound device offers new opportunities to the industrial ultrasound-based and advanced biomedical applications.

We report a high-efficiency (25%) Brillouin random fiber laser (BRFL) with Brillouin gain medium of 2-km polarization maintaining fiber (PMF) as well as distributed Rayleigh scattering feedback from 500-m PMF. The characteristics of lasing efficiency and relative intensity noise (RIN) have been comprehensively studied comparing with the BRFLs with half-open ring cavity and bidirectional pumping linear open configuration. The enhanced lasing efficiency using PMF-BRFL with half-open ring cavity enables sub-kHz linewidth, lower phase fluctuation and frequency jitter comparing with phase locked pump laser, thanks to the polarization-matched efficient Brillouin gain in PMFs. The RIN and frequency instability of the proposed PMF-BRFL induced from external disturbance, e.g., mechanical and thermal noise, have been effectively suppressed with respect to conventional SMF-based BRFL.

Vortex beams have attracted much attention in recent years due to unique features of the phase or polarization singularity in the center part of beams. Various applications have been explored by the vortex beams including optical communication, optical tweezer, etc. Especially, the vortex beams for optical sensing applications have emerged. Compared with the traditional Gaussian beams, the vortex beams enable the optical sensing with the degree of freedom by controlling the spin and orbital phase and polarization. In this review article, we have discussed the theory of polarization and phase vortices, and then summarized the vortex beam generation in optical fiber and their sensing applications. It is hoped that the article can intrigue further research interest and development in fiber vortices for sensing applications.

A linearly polarized Brillouin random fiber laser (LP-BRFL) with distributed feedback along 2 km polarization-maintaining fibers (PMFs) is demonstrated. The laser was built up using a bidirectional pumping mechanism in an all-PMF configuration, yielding a radiation with 8% power efficiency and more than 25 dB polarization extinction ratio. A high lasing efficiency is achieved due to the polarization-matched Brillouin amplification and distributed feedback along kilometer long PMFs. The relative intensity noise and the thermal-induced frequency noise of this random laser have also been measured and compared to that of a custom single-mode-fiber-based random laser and a conventional phase-locked laser.

An all-silica Fabry-Perot interferometer (FPI) based on a microbubble for high-pressure and high-temperature measurements is proposed and demonstrated. The microbubble-based air cavity is fabricated using a hollow silica tube and a single-mode optical fiber for pressure sensing. The suitable thickness between the two end faces of the microbubble enables the silica cavity to be used for temperature sensing. The wavelength shift of the reflection spectrum versus pressure is linear, and the sensitivity reaches −5.083 nm/MPa at room temperature (20 °C) within the range of 0 − 4 MPa. The temperature sensitivity reaches 12.715 pm/°C within the range of 20 − 700 °C. The very low temperature-pressure cross-sensitivity of the two cavities indicates that the proposed FPI sensor offers great potential for simultaneous high-pressure and high-temperature measurements in harsh environments.