Seminar: Electro-Optics and Microelectronics Seminar
Mode-Selective Optical and Opto-Mechanical Interactions in Few-Mode Fibers
Date:
October,18,2026
Start Time:
14:00 - 15:00
Location:
506, New Zisapel Building
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Lecturer:
Ori Pearl
Research Areas:
| Optical fibers guide light in discrete spatial modes. Each mode has a different propagation constant and transverse field distribution, which affect the interactions that can occur within the fiber. Conventional single-mode fibers support only one guided core mode. Few-mode fibers, in contrast, support several distinct modes within the same simple fiber geometry. In these fibers, the choice of spatial mode becomes an additional degree of freedom for controlling optical and opto-mechanical interactions. Selecting the optical mode can change phase matching, spatial symmetry, and modal overlap. It can therefore determine which optical or acoustic states participate in the interactions, with potential applications in fiber sensing. In this work, two mode-selective interactions were studied in a commercial few-mode fiber. First, intermodal forward stimulated Brillouin scattering was investigated between the LP₀₁ and LP₀₂ core modes. Their different propagation constants generate an electro-strictive driving force with a substantial axial wavenumber and an appreciable axial component. The process therefore involves the excitation of mechanical modes of the fiber which hybridize between transverse and axial displacement components. A full vector model describing the scattering process will be presented. The predictions of the model agree well with measurements. The results include acoustic branches which originate from axial modes at cutoff, observed in forward Brillouin scattering for the first time. Measurements in air and ethanol also revealed distinctly different linewidth responses for predominantly radial and axial acoustic modes, reflecting their different mechanical character. In the second part, coupling from the LP₀₁, LP₀₂, and LP₁₁ core modes to optical cladding modes was studied using a fiber Bragg grating. The results show that the incident core mode controls both the coupling strength and the families of accessible cladding modes through radial overlap and azimuthal symmetry. Together, the two studies show that selecting the optical spatial mode can open different optical and acoustic coupling pathways, without modifying the underlying fiber structure. Ori Pearl is an M.Sc student in Electro-Optics at Bar-Ilan University, under the supervision of Prof. Avinoam Zadok. His research focuses on forward Brillouin scattering and opto-mechanical interactions in optical fibers.
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