Brillouin scattering properties of lanthano-aluminosilicate optical fiber

Bragg Grating Assisted Sagnac Interferometer in SiO2-Al2O3-La2O3 Polarization-Maintaining Fiber for Strain-Temperature Discrimination

Polarization-maintaining fibers (PMFs) have always received great attention in fiber optic communication systems and components which are sensitive to polarization. Moreover, they are widely applied for high-accuracy detection and sensing devices, such as fiber gyroscope, electric/magnetic sensors, multi-parameter sensors, and so on. Here, we demonstrated the combination of a fiber Bragg grating (FBG) and Sagnac interference in the same section of a new type of PANDA-structure PMF for the simultaneous measurement of axial strain and temperature. This specialty PMF features two stress-applied parts made of lanthanum-aluminum co-doped silicate (SiO2-Al2O3-La2O3, SAL) glass, which has a higher thermal expansion coefficient than borosilicate glass used commonly in commercial PMFs. Furthermore, the FBG inscribed in this SAL PMF not only aids the device in discriminating strain and temperature, but also calibrates the phase birefringence of the SAL PMF more precisely thanks to the much narrower bandwidth of grating peaks. By analyzing the variation of wavelength interval between two FBG peaks, the underlying mechanism of the phase birefringence responding to temperature and strain is revealed. It explains exactly the sensing behavior of the SAL PMF based Sagnac interference dip. A numerical simulation on the SAL PMF's internal stress and consequent modal effective refractive indices was performed to double confirm the calibration of fiber's phase birefringence.

Sapphire derived fiber based Fabry-Perot interferometer with an etched micro air cavity for strain measurement at high temperatures

A sapphire derived fiber (SDF) based Fabry-Perot interferometer (FPI) with an etched micro air cavity for strain measurement at high temperatures is proposed. The FPI is formed by splicing a section of SDF between an etched single mode fiber (ESMF) and a capillary. The SDF's core containing 51.3mol.% aluminum provides the intrinsic Fabry-Perot interferometer cavity with an enhanced fringe contrast through the narrow etched air cavity reflector. Because the different Poisson effects of the cladding and the core have different deformations under axial stress, the transverse strain imposed from the cladding to the core was introduced to the additive model. The strain sensitivity of the FPI was theoretically analyzed and experimentally demonstrated at room temperature. A thermal annealing process was performed to study the stability in high temperatures and to release the residual stress during the sensor's fabrication. The strain calibration was carried out subsequently from 20℃ to 1000℃. Benefiting from the doping in the core and diffusion in the cladding of the high temperature resistant material Al₂O₃, the proposed sensor was proved to operate well in 950℃ and was also characteristized by a sensitivity of 1.19 pm/µɛ and 1.06 pm/µɛ in the process of loading and unloading strain separately.

Highly nonlinear yttrium-aluminosilicate optical fiber with a high intrinsic stimulated Brillouin scattering threshold

Highly nonlinear (high-NA small-mode-area) optical fibers also possessing an intrinsically high stimulated Brillouin scattering threshold are described. More specifically, silica clad, yttrium-aluminosilicate core fibers are shown to exhibit an intrinsically low Brillouin gain coefficient between 0.125 and 0.139×10^-11  m/W and a Brillouin gain linewidth of up to 500 MHz. Losses on the order of 0.7 dB/m were measured, resulting from impurities in the precursor materials. Nonlinear refractive index values are determined to be similar to that of silica, but significant measurement uncertainty is attributed to the need to estimate dispersion curves since their direct measurement could not be made. The interest for highly nonlinear optical fibers with a low intrinsic Brillouin gain coefficient is expected to continue, especially with the growing developments of narrow-linewidth high-energy laser systems.

Single- and few-moded lithium aluminosilicate optical fiber for athermal Brillouin strain sensing

Results are presented toward realizing a true single-mode fiber whose Brillouin frequency shift is independent of temperature, while its dependence on strain is comparable to conventional high-silica-content single-mode fibers. Demonstrated here is a fiber with a negative thermal sensitivity dν/dT of -0.26  MHz/K and a strain sensitivity of +406  MHz/%. The suppression of the Brillouin thermal response is enabled by the large thermal expansion coefficient of the group I oxide-containing silica glass network.

High temperature sensing with fiber Bragg gratings in sapphire-derived all-glass optical fibers

A structured sapphire-derived all-glass optical fiber with an aluminum content in the core of up to 50 mol% was used for fiber Bragg grating inscription. The fiber provided a parabolic refractive index profile. Fiber Bragg gratings were inscribed by means of femtosecond-laser pulses with a wavelength of 400 nm in combination with a two-beam phase mask interferometer. Heating experiments demonstrated the stability of the gratings for temperatures up to 950°C for more than 24 h without degradation in reflectivity.

Materials Development for Next Generation Optical Fiber

Optical fibers, the enablers of the Internet, are being used in an ever more diverse array of applications. Many of the rapidly growing deployments of fibers are in high-power and, particularly, high power-per-unit-bandwidth systems where well-known optical nonlinearities have historically not been especially consequential in limiting overall performance. Today, however, nominally weak effects, most notably stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) are among the principal phenomena restricting continued scaling to higher optical power levels. In order to address these limitations, the optical fiber community has focused dominantly on geometry-related solutions such as large mode area (LMA) designs. Since such scattering, and all other linear and nonlinear optical phenomena including higher order mode instability (HOMI), are fundamentally materials-based in origin, this paper unapologetically advocates material solutions to present and future performance limitations. As such, this paper represents a 'call to arms' for material scientists and engineers to engage in this opportunity to drive the future development of optical fibers that address many of the grand engineering challenges of our day.