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Related Concept Videos

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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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...
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Transmission Line Design Considerations01:23

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Aluminum has become the material of choice for overhead transmission lines, surpassing copper due to its abundance and cost-effectiveness. The most prevalent type is the aluminum conductor, steel-reinforced (ACSR), which combines aluminum strands around a steel core. Other variants include all-aluminum conductors (AAC), all-aluminum alloy conductors (AAAC), aluminum conductor alloy-reinforced (ACAR), and aluminum-clad steel conductors. Advanced designs, such as aluminum conductors with steel...
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Fiber Reinforced Concrete01:22

Fiber Reinforced Concrete

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Fiber-reinforced concrete significantly enhances the structural and nonstructural properties of traditional concrete by incorporating fibers like steel, glass, and polymers. These fibers, varying from natural ones such as sisal and cellulose to manufactured ones like polypropylene and Kevlar, are mixed into hydraulic cement with aggregates. Steel fibers, often preferred for their robustness, contribute to improved ductility, toughness, and post-cracking performance. The concrete is classified...
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Spin–Spin Coupling Constant: Overview01:08

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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
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A coaxial cable consists of a central copper conductor used for transmitting signals, followed by an insulator shield, a metallic braided mesh that prevents signal interference, and a plastic layer that encases the entire assembly.
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Efficient integrated tri-modal coupler for few-mode fibers.

Julian L Pita Ruiz, Lucas G Rocha, Jun Yang

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    This study presents a high-efficiency vertical grating coupler for few-mode fibers, enabling efficient coupling for multiple spatial modes. This technology is key for advancing high-capacity optical networks using space division multiplexing.

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    Area of Science:

    • Photonics and Optical Engineering
    • Integrated Optics
    • Fiber Optic Communications

    Background:

    • Few-mode fibers (FMFs) support multiple spatial modes, offering higher bandwidth potential than single-mode fibers.
    • Efficiently coupling light into and out of specific modes in FMFs is a critical challenge for realizing their capacity.
    • Existing mode couplers often suffer from low efficiency or complexity, hindering practical applications.

    Purpose of the Study:

    • To demonstrate a high-efficiency vertical grating coupler capable of addressing multiple modes (LP01x, LP11ax, LP11bx) in a graded-index few-mode fiber.
    • To design and fabricate a compact and efficient mode coupler compatible with complementary metal-oxide-semiconductor (CMOS) processes.
    • To validate the performance of the coupler through experimental measurements of coupling efficiency for each targeted mode.

    Main Methods:

    • Utilized inverse design to create a non-uniform, straight, bidirectional grating coupler.
    • Integrated two mode-selective directional couplers and two tapers to enhance mode selectivity and efficiency.
    • Fabricated the device using electron-beam lithography with a minimum feature size of 100 nm.
    • Experimentally measured coupling efficiencies for the LP01x, LP11ax, and LP11bx modes.

    Main Results:

    • Achieved high coupling efficiencies of -3.0 dB for LP01x, -3.6 dB for LP11ax, and -3.4 dB for LP11bx modes.
    • Demonstrated a CMOS-compatible fabrication process suitable for mass production.
    • The device design effectively addressed the specific modes of the graded-index few-mode fiber.

    Conclusions:

    • The developed vertical grating coupler offers high efficiency for multiple modes in few-mode fibers.
    • Its CMOS compatibility and high performance position it as a key enabling device for future high-capacity optical communication networks.
    • The technology supports space division multiplexing (SDM) strategies, crucial for meeting increasing data demands.