Opto-Mechanical Inter-Core Cross-Talk in Multi-Core Fibers

Multi-core fibers (MCFs) consist of several cores that are assembled together. These fibers are widely regarded as the leading solution to the optical communications capacity crunch. The most prevalent paradigm for the design and employment of MCFs relies on the suppression of direct coupling of optical power among cores. However, the cores are mechanically coupled as they are parts of a single, unified structure. This brings about inter-core opto-mechanical coupling: acoustic modes of the fiber's entire cross section may be stimulated by light propagating in one core, and modulate light that is propagating in all other cores. Moreover, MCF geometry removes the radial symmetry of standard single-mode fibers, in which the single core is located on-axis. This symmetry breaking allows for the optical stimulation of a much broader variety of general guided acoustic modes, which cannot be observed in standard fibers.

In this seminar I present the analysis of opto-mechanical inter-core crosstalk among optically-isolated cores in a commercially available MCF, validate the model predictions experimentally, and discuss the implications of the results on various potential applications of MCFs, such as future communication systems. The analysis suggests that the spectrum and magnitude of inter-core opto-mechanical coupling may be quantified in terms of an equivalent nonlinear coefficient, with units of [W´km]^-1 , in analogy with the intra-core Kerr effect. Equivalent nonlinear opto-mechanical coefficients as large as 1.3 [W´km]^-1  were measured. The magnitude of the effect, at particular resonance frequencies, may be larger than that of intra-core Kerr nonlinearity. Quasi-continuous modulation spectra involving general torsional-radial modes are demonstrated.
While opto-mechanical inter-core crosstalk is unlikely to restrict the performance of optical communication over MCFs, the mechanism may find applications in sensing, microwave photonics and fiber lasers.

* This research was carried out towards the Master degree in Electrical Engineering at Bar-Ilan University, under the supervision of Prof. Avi Zadok