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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.

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Microwave Photonics Systems Based on Whispering-gallery-mode Resonators
12:18

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Published on: August 5, 2013

Mode coupling in a multimode optical fiber with microbends.

L Jeunhomme, J P Pocholle

    Applied Optics
    |February 16, 2010
    PubMed
    Summary
    This summary is machine-generated.

    This study examines how fiber optic cable deformations affect radiation patterns. Findings reveal strong coupling between fiber modes, crucial for understanding signal loss and cabling requirements.

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    Area of Science:

    • Optical Engineering
    • Materials Science

    Background:

    • Multimode optical fibers are susceptible to signal degradation from physical deformations.
    • Understanding mode coupling is essential for predicting signal loss in fiber optic systems.

    Purpose of the Study:

    • To experimentally observe and theoretically model the radiation pattern of short multimode fibers under induced deformations.
    • To quantify the relationship between deformation amplitude, mode coupling, and excess loss.

    Main Methods:

    • Experimental measurement of radiation patterns for fibers with varying induced deformations.
    • Theoretical modeling based on strong coupling assumption between two specific fiber modes.
    • Numerical evaluation of coupling coefficients and excess loss.

    Main Results:

    • Experimental results show good agreement with theoretical predictions.
    • Quantified coupling coefficients and excess loss as a function of deformation amplitude.
    • Identified key requirements for fiber optic cabling to minimize deformation-induced signal loss.

    Conclusions:

    • The study validates a theoretical model for multimode fiber deformation effects.
    • Provides practical insights into the impact of physical stress on optical signal integrity.
    • Offers guidance for optimizing fiber optic cable design and installation practices.