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

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

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 involved orbitals. The...

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Related Experiment Video

Updated: May 31, 2026

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System
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Published on: July 18, 2015

High-performance and compact binary blazed grating coupler based on an asymmetric subgrating structure and vertical

Junbo Yang1, Zhiping Zhou, Honghui Jia

  • 1State Key Laboratory on Advanced Optical Communication Systems and Networks, Peking University, Beijing 100871, China.

Optics Letters
|July 19, 2011
PubMed
Summary
This summary is machine-generated.

This study presents a compact silicon-on-insulator fiber-to-waveguide grating coupler achieving high coupling efficiency. The novel asymmetric subgrating design enables vertical fiber alignment and efficient light transfer for photonic integrated circuits.

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Area of Science:

  • Photonics
  • Integrated Optics
  • Nanophotonics

Background:

  • Efficient fiber-to-waveguide coupling is crucial for optical interconnects.
  • Subwavelength gratings offer advanced light manipulation capabilities.

Purpose of the Study:

  • To design a high-performance, compact fiber-to-waveguide coupler.
  • To achieve high coupling efficiency and vertical fiber alignment.

Main Methods:

  • Design of a binary blazed subwavelength grating coupler on silicon-on-insulator.
  • Optimization of waveguide and grating parameters (thickness, period, height, fill factor).
  • Utilizing an asymmetric subgrating structure for vertical coupling.

Main Results:

  • Calculated coupling efficiency of 69% at 1.52 μm and 65% at 1.55 μm.
  • Achieved a 1 dB wavelength bandwidth of approximately 80 nm.
  • Potential for up to 80% efficiency with added Bragg reflectors.

Conclusions:

  • The designed grating coupler offers high performance and a compact footprint.
  • The asymmetric subgrating enables efficient vertical fiber coupling.
  • The device is compatible with standard CMOS processing, facilitating integration.