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.

A novel distributed strain and temperature measurement method based on Brillouin beat spectrum (BBS) in a complex index profile fiber are proposed. The BBS corresponds to the optical interaction of different acoustic modes. For a large-effective-area fiber (LEAF), the first peak of BBS is contributed by the first and second acoustic modes, while the second peak in BBS is contributed by the first and third accoustic modes. Through determining power changes in the peaks of BBS due to strain and temperature variation along a LEAF, the distributed strain and temperature can be measured by the homodyne Brillouin optical time-domain reflectometry (BOTDR) without scanning the Brillouin spectrum. The strain and temperature at the end of a 4.5-km LEAF are measured at 3-m spatial resolution in 140 s.

In this paper, we investigate third-order nonlinearities in aluminum-doped zinc oxide (AZO) thin film by the Z-scan method at a wavelength of 1064 nm. We carried out experiments under different pulse widths (26 ns, 62 ns, and 101 ns) and energy densities (5.3 J/cm2, 10.6 J/cm2, and 15.9 J/cm2) and obtained the nonlinear absorption coefficient, nonlinear refractive index, and third-order nonlinear susceptibility of AZO thin film. The Z-scan results show that AZO thin film exhibits a larger nonlinear refractive index (-5.48×10-13 m2/W) and third-order nonlinear susceptibility (1.97×10-6 esu) than those of some other semiconductor materials at the wavelength of 1064 nm. This suggests that AZO thin film may be a very promising nonlinear medium for nonlinear photonics applications in the tens of nanoseconds regime.

We propose a novel topological photonic crystal nonlinear laser power limiter based on topological edge states and optical Kerr effect. In the proposed laser power limiter, a one-dimensional photonic crystal in topological edge state allows the relatively weak signal light with a certain wavelength to pass through with high transmission, but blocks most of the intense hostile or accidental laser with the same wavelength due to the change of topological edge state generated from optical Kerr effect. Taking a 1064 nm wavelength as an example, we have designed such a nonlinear laser power limiter corresponding to the wavelength. When the optical power density is low (less than 0.12 MW/cm²), the light transmission can reach 82.54%, and the transmission can be reduced to 1.04% when the optical power density is increased to 11.66 MW/cm². Therefore, this method provides a new promising approach to realize laser protection at the desired wavelength.

We study the nonlinear optical limiting effect of graphene dispersions in ethanol and acetone at a wavelength of 1064 nm. The nonlinear optical limiting effect of graphene dispersion under three different linear transmittances (about 70%, 80%, and 90%), two different thicknesses (1 and 3 cm), and two different solvents (ethanol and acetone) are measured. The influences of concentration, thickness, and solvent on the nonlinear optical limiting effect of the graphene dispersion are analyzed. The experimental results show that the concentration and solution thicknesses have great influence on the optical limiting ability of graphene dispersions. The graphene dispersions with ethanol and acetone as solvents can be used to achieve excellent nonlinear optical limiting effects. The optical limiting ability of the graphene dispersion in acetone is better than that of the graphene dispersion in ethanol.