Advances in Opto-mechanics in Standard and Multi-core Fibers

In recent years a new class of optical fiber sensing has been established based on Forward stimulated Brillouin Scattering (F-SBS) [1]. In this work we report advances in distributed sensing of fluids outside bare and polyimide coated standard single mode fiber [2]. Comprehensive analysis of F-SBS is presented for a coated fiber in an arbitrary liquid. The model suggests that the decay rates of stimulated acoustic waves in a given medium vary significantly with the exact coating radius and among different modes. Pre-calibration of the fiber under test is therefore required. With proper choice of modes, distributed analysis is achieved over 1.6 km-long coated fiber that is entirely immersed in liquid. The measurements properly identify and locate a 200 meters-long fiber section that was immersed in ethanol, while the rest of the fiber was kept in water. The spatial resolution of the protocol was 75 meters.

In an extension of this work, a model for nonlinear wave mixing among co-propagating optical tones has been formulated, bringing together F-SBS and Kerr effect contributions [3]. The model predicts that nonlinear wave mixing involving F-SBS is markedly different from four-wave-mixing due to the Kerr effect alone. When the frequency difference between adjacent tones matches an F-SBS resonance the process becomes asymmetrical. Power is transferred from a high-frequency pump wave to a lower-frequency one, and the nonlinear amplification of Stokes-wave sidebands is more pronounced than that of anti-Stokes-wave terms. The model is in excellent agreement with distributed measurements based on multi-tone optical time-domain reflectometry over 8 km of fiber.

Lastly, F-SBS was also studied in multi-core fibers. The stimulated acoustic waves induce inter-core cross-phase modulation among the constituent cores of the fiber, even in the absence of direct optical coupling [4]. We recently showed that such crosstalk may close an electro-opto-mechanical feedback loop that runs across two different cores. Pump light in one core stimulated acoustic waves, and the phase modulation of a probe wave in a different optically isolated core is detected and fed back to modulate the pump. With sufficient optical power, acoustic and radio-frequency noise in the hybrid cavity may be driven into stimulated oscillations of acoustic waves. Narrow linewidths below 100 Hz are observed [5] for wideband (500GHZ) pump light.

[1] Y. Antman, et al, "Optomechanical sensing of liquids outside standard fibers using forward stimulated Brillouin scattering," Optica 3, 510-516 (2016)

[2] G. Bashan, et al, "Optomechanical time-domain reflectometry," Nature Communications 9, 2991 (2018).

[3] Y. London, et al," Distributed analysis of nonlinear wave mixing in fiber due to forward Brillouin scattering and Kerr effects" upcoming APL photonics.

[4] H. H. Diamandi, et al, "Opto-mechanical inter-core cross-talk in multi-core fibers," Optica 4, 289-297 (2017).

[5] H. H. Diamandi, et al, "Highly-coherent stimulated phonon oscillations in a multi-core optical fibers," Scientific Reports 8, 9514 (2018).