The detection of the surrounding environment is one of the most fundamental challenges in optical fiber sensors research. In this Letter, we report two new, to the best of our knowledge, phenomena in large effective area fiber (LEAF), which are the linear dependence of the radial acoustic mode induced forward Brillouin scattering (FBS) spectral linewidth on temperature and the linear dependence of the radial acoustic mode induced FBS spectral frequency shift on acoustic impedance. By utilizing these linear relationships, we present a novel temperature and acoustic impedance simultaneous measurement method based on FBS in LEAF. With a fiber Sagnac loop structure, the obtained measurement uncertainties of temperature and acoustic impedance surrounding LEAF are 0.1°C and 0.006 k g / ( s ⋅ m m 2 ) , respectively. The corresponding measurement uncertainties in the form of relative percentage values are 0.5% and 0.4%, respectively.

A novel method for simultaneous measurement of temperature and pressure based on forward Brillouin scattering (FBS) in double-coated optical fiber is proposed. A new phenomenon, which is the linear relationship between frequency shift of the FBS spectra induced by radial acoustic modes and pressure surrounding the sensing fiber, is theoretically analyzed and experimentally verified. Another new interesting feature is observed that the frequency shift-pressure coefficients of different radial acoustic modes are different. Based on the phenomena that different radial acoustic modes have different frequency shift-temperature and frequency shift-pressure coefficients, we propose a brand-new method to achieve the simultaneous measurement of temperature and pressure by using the frequency shift information of two FBS scattering peaks. In a proof-of-concept experiment, a double-coated single-mode fiber is used as the sensing fiber, and the temperature and pressure measurement errors are 0.13 °C and 0.05 MPa, respectively. The proposed method is expected to become a simple, accurate, durable and stable sensing method for simultaneously measuring temperature and pressure, which has great potential in many practical applications.

We propose an elliptical-core mode selective photonic lantern (EC-MSPL), which can be well matched to mode division multiplexing (MDM) systems without multiple-input multiple-output (MIMO). The taper region of the small package satisfying the adiabatic condition is obtained through two-stage taper related parameter optimization, which can reduce the length of the taper region without affecting the PL performance. Finally, we simulated the results for step-index EC-MSPL and graded-index EC-MSPL at taper lengths of 10 cm and 5 cm, respectively, using the beam propagation method. Both types of PL can achieve low-loss mode conversion and crosstalk below -15.6dB at 1550nm wavelength. At the same time, the coupling efficiencies of the two PL modes in the S+C+L bands are higher than 85% and 71%.

The trench-assisted multimode fiber TA-OM4 is used as a sensing fiber to achieve a higher signal-to-noise (SNR) in Brillouin optical time domain sensors, due to its high stimulated Brillouin threshold and high modulation instability threshold. The Brillouin gain spectrum (BGS), stimulated Brillouin scattering (SBS) and modulation instability (MI) thresholds of TA-OM4 at 1550 nm are characterized and demonstrated theoretically and experimentally. The SNR improvements of TA-OM4 over G655 and G657 at the end of 15.5 km-long fibers, which are respectively 1.1 dB and 2.3 dB are verified experimentally. We achieve a temperature uncertainty of 0.3°C in 15.5 km TA-OM4 with 5 m spatial resolution by use of a Brillouin optical time domain reflectometry (BOTDR) sensor. The good bend resistance and high SBS and MI thresholds of TA-OM4 with better SNR improvements over SMFs works at the extreme bending conditions.

A novel distributed strain and temperature fast measurement method in Brillouin optical time-domain reflectometry (BOTDR) system based on double-sideband (DSB) modulation is proposed. The single-wavelength probe light is modulated into dual-wavelength probe light with a fixed phase difference by using carrier suppressed DSB modulation. The interaction between the Brillouin scattering signals corresponding to dual-wavelength probe light forms a Brillouin beat spectrum (BBS). The distributed temperature and strain are obtained by only measuring the peak power trace of the BBS and one of the slope power trace of the two Brillouin gain spectrum (BGS) corresponding to dual-wavelength probe light. The proposed method does not require scanning the Brillouin spectrum and does not require using optical fibers with multiple Brillouin scattering peaks as sensing fibers, and thus features fast measurement speed and wide variety of sensing fiber types. In a proof-of-concept experiment, the temperature uncertainty of 1.3 °C and the strain uncertainty of 36.3 με are respectively achieved over a 4.5-km G.657 fiber with 3 m spatial resolution and 30 s measurement time. The experimental measurement uncertainties of temperature and strain of the proposed method are almost equivalent to that of the method by using BGS scanning and special fibers.

A novel fast measurement method based on Brillouin gain spectrum (BGS) and Brillouin beat spectrum (BBS) in a complex index profile fiber has been proposed to realize simultaneous measurement of distributed temperature and strain. An interesting phenomenon that the temperature/strain sensitivities of the power on the BGS slope and the power on the BBS peak are very different has been discovered and utilized for temperature and strain sensing. By means of only measuring the power trace of the BGS slope and the power trace of one BBS peak along the sensing fiber, the distributed temperature and strain can be measured by using the Brillouin optical time-domain reflectometry (BOTDR) without scanning the Brillouin spectrum. The temperature and strain measurement uncertainties of the proposed method are one order of magnitude lower than that of the BBS-based measurement method. In a proof-of- concept experiment, the temperature and strain of the 2 km large effective area fiber (LEAF) are measured at a spatial resolution of 3 m within 18 s.