Distributed opto-mechanical analysis of liquids outside standard fibers coated with polyimide

The analysis of surrounding media has been a long-standing challenge of optical fiber sensors. Measurements are difficult due to the confinement of light to the inner core of standard fibers. Over the last two years, new sensor concepts have enabled the analysis of liquids outside the cladding boundary, where light does not reach. Sensing is based on opto-mechanical, forward stimulated Brillouin scattering interactions between guided light and sound waves. In most previous works, however, the protective polymer coating of the fiber had to be removed first. In this work, we report the opto-mechanical analysis of liquids outside commercially available, standard single-mode fibers with polyimide coating. The polyimide layer provides mechanical protection but can also transmit acoustic waves from the fiber cladding towards outside media. Comprehensive analysis of opto-mechanical coupling in coated fibers that are immersed in liquid is provided. The model shows that forward stimulated Brillouin scattering spectra in coated fibers are more complex than those of bare fibers, and strongly depend on the exact coating diameter and the choice of acoustic mode. Nevertheless, sensing outside coated fibers is demonstrated experimentally. Integrated measurements over 100 meters of fiber clearly distinguish between air, ethanol and water outside polyimide coating. Measured spectra are in close quantitative agreement with the analytic predictions. Further, distributed opto-mechanical time-domain reflectometry mapping of water and ethanol outside coated fiber is reported, with a spatial resolution of 100 meters. The results represent a large step towards practical opto-mechanical fiber sensors

Opto-Mechanical Interactions in Multi-Core Optical Fibers and Their Applications

[EN] Optical fibers containing multiple cores are being developed towards capacity enhancement in space-division multiplexed optical communication networks. In many cases, the fibers are designed for negligible direct coupling of optical power among the cores. The cores remain, however, embedded in a single, mechanically-unified cladding. Elastic (or acoustic) modes supported by the fiber cladding geometry are in overlap with multiple cores. Acoustic waves may be stimulated by light in any core through electrostriction. Once excited, the acoustic waves may induce photo-elastic perturbations to optical waves in other cores as well. Such opto-mechanical coupling gives rise to inter-core cross-phase modulation effects, even when direct optical crosstalk is very weak. The cross-phase modulation spectrum reaches hundreds of megahertz frequencies. It may consist of discrete and narrow peaks, or may become quasi-continuous, depending on the geometric layout. The magnitude of the effect at the resonance frequencies is comparable with that of intra-core cross-phase modulation due to Kerr nonlinearity. Two potential applications are demonstrated: single-frequency opto-electronic oscillators that do not require radio-frequency electrical filters, and point-sensing of liquids outside the cladding of multi-core fibers, where light cannot reach.This work was supported in part by a Starter Grant from the European Research Council (ERC) under Grant H2020-ERC-2015-STG 679228 (L-SID), in part by the Israeli Ministry of Science and Technology under Grant 61047, and in part by the Spanish Ministry of Economy and Competitiveness under the DIMENSION TEC2017 88029-R Project. H. H. Diamandi was supported by the Azrieli Foundation for the award of an Azrieli Fellowship. The work of J. Madrigal was supported by Universitat Politecnica de Valencia scholarship PAID-01-18. The work of D. Barrera was supported by Spanish MICINN fellowship IJCI-2017-32476.Diamandi, HH.; London, Y.; Bergman, A.; Bashan, G.; Madrigal-Madrigal, J.; Barrera, D.; Sales Maicas, S.... (2020). Opto-Mechanical Interactions in Multi-Core Optical Fibers and Their Applications. IEEE Journal of Selected Topics in Quantum Electronics. 26(4):1-13. https://doi.org/10.1109/JSTQE.2019.2958933S11326

Invited Article: Distributed analysis of nonlinear wave mixing in fiber due to forward Brillouin scattering and Kerr effects

Forward stimulated Brillouin scattering (F-SBS) is a third-order nonlinear-optical mechanism that couples between two co-propagating optical fields and a guided acoustic mode in a common medium. F-SBS gives rise to nonlinear wave mixing along optical fibers, which adds up with four-wave mixing induced by the Kerr effect. In this work, we report the distributed mapping of nonlinear wave mixing processes involving both mechanisms along standard single-mode fiber, in analysis, simulation, and experiment. Measurements are based on a multi-tone, optical time-domain reflectometry setup, which is highly frequency-selective. The results show that F-SBS leads to nonlinear wave mixing processes that are more complex than those that are driven by the Kerr effect alone. The dynamics are strongly dependent on the exact frequency detuning between optical field components. When the detuning is chosen near an F-SBS resonance, the process becomes asymmetric. Power is coupled from an upper-frequency input pump wave to a lower-frequency one, and the amplification of Stokes-wave sidebands is more pronounced than that of anti-Stokes-wave sidebands. The results are applicable to a new class of distributed fiber-optic sensors, based on F-SBS

Supplementary document for The all-optical Stern-Gerlach effect in the time domain - 6828128.pdf

Mathematical analysi

Forward stimulated Brillouin scattering and opto-mechanical non-reciprocity in standard polarization maintaining fibres

Abstract Opto-mechanical interactions in guided wave media are drawing great interest in fundamental research and applications. Forward stimulated Brillouin scattering, in particular, is widely investigated in optical fibres and photonic integrated circuits. In this work, we report a comprehensive study of forward stimulated Brillouin scattering over standard, panda-type polarization maintaining fibres. We distinguish between intra-polarization scattering, in which two pump tones are co-polarized along one principal axis, and inter-polarization processes driven by orthogonally polarized pump waves. Both processes are quantified in analysis, calculations and experiment. Inter-modal scattering, in particular, introduces cross-polarization switching of probe waves that is non-reciprocal. Switching takes place in multiple wavelength windows. The results provide a first demonstration of opto-mechanical non-reciprocity of forward scatter in standard fibre. The inter-polarization process is applicable to distributed sensors of media outside the cladding and coating boundaries, where light cannot reach. The process may be scaled towards forward Brillouin lasers, optical isolators and circulators and narrowband microwave-photonic filters over longer sections of off-the-shelf polarization maintaining fibres

Optical fiber point sensors based on forward Brillouin scattering

[EN] Forward Brillouin scattering interactions support the sensing and analysis of media outside the cladding boundaries of standard fibers, where light cannot reach. Quantitative point-sensing based on this principle has yet to be reported. In this work, we report a forward Brillouin scattering point-sensor in a commercially available, off-the-shelf multi-core fiber. Pump light at the inner, on-axis core of the fiber is used to stimulate a guided acoustic mode of the entire fiber cross-section. The acoustic wave, in turn, induces photoelastic perturbations to the reflectivity of a Bragg grating inscribed in an outer, off-axis core of the same fiber. The measurements successfully analyze refractive index perturbations on the tenth decimal point and distinguish between ethanol and water outside the centimeter-long grating. The measured forward Brillouin scattering linewidths agree with predictions. The acquired spectra are unaffected by forward Brillouin scattering outside the grating region. The results add point-analysis to the portfolio of forward Brillouin scattering optical fiber sensors.Bar-Ilan UniversityShemer, K.; Bashan, G.; Zehavi, E.; Diamandi, HH.; Bernstein, A.; Sharma, K.; London, Y.... (2022). Optical fiber point sensors based on forward Brillouin scattering. Optics Express. 30(22):39321-39328. https://doi.org/10.1364/OE.4696233932139328302