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Related Concept Videos

Imperfections in Crystal Structure: Point, Line and Plane Defects01:25

Imperfections in Crystal Structure: Point, Line and Plane Defects

A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...
Imperfections in Crystal Structure: Stoichiometric Point Defects01:26

Imperfections in Crystal Structure: Stoichiometric Point Defects

Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
Imperfections in Crystal Structure: Non-Stoichiometric Defects01:29

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...
Symmetry Elements in a Crystal01:27

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Crystal symmetry operations are isometric transformations that map objects onto indistinguishable copies while preserving distances, angles, and volumes. The simplest symmetry operation is translation, which shifts the entire infinite crystal lattice parallelly by a translation vector.Crystallographic rotations involve rotations by an angle of 2π/n around an axis without changing the positions of points on the axis. It is called the rotational axis of the symmetry, denoted by n. The combination...

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Related Experiment Video

Updated: Jun 22, 2026

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation
13:02

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Published on: February 25, 2017

Defect modes in multisection helical photonic crystals.

Fei Wang, Akhlesh Lakhtakia

    Optics Express
    |June 6, 2009
    PubMed
    Summary

    Defect modes in helical photonic crystals (HPCs) exhibit coupled or uncoupled behavior based on twist defects. This influences spectral holes, transitioning from reflection to transmission as thickness increases.

    Area of Science:

    • Photonics
    • Condensed Matter Physics
    • Materials Science

    Background:

    • Helical photonic crystals (HPCs) exhibit unique optical properties due to their periodic helical structure.
    • Defect modes in photonic crystals can be engineered to control light propagation and localization.
    • Twist defects introduce localized states within the photonic bandgap.

    Purpose of the Study:

    • To investigate the behavior of defect modes in four-section helical photonic crystals with three twist defects.
    • To analyze the influence of twist angle and crystal thickness on defect mode coupling and spectral characteristics.
    • To explore the transition of spectral holes from reflection to transmission based on defect mode coupling.

    Main Methods:

    • Numerical simulation of four-section helical photonic crystals.

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    Published on: February 25, 2017

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  • Analysis of defect modes introduced by twist defects at section interfaces.
  • Investigation of optical response to normally incident plane waves with different circular polarizations.
  • Examination of spectral hole evolution with increasing crystal thickness.

    • Main Results:

    • Two distinct defect modes are identified, localized at different defect sites.
    • Defect mode coupling is controlled by the twist angle (phit), leading to either coupled or uncoupled behavior.
    • Uncoupled modes result in two co-handed reflection holes (small thickness) evolving to two cross-handed transmission holes (large thickness).
    • Coupled modes lead to three co-handed reflection holes (small thickness) evolving to one stable cross-handed transmission hole (large thickness).
    • Simultaneous occurrence of two spectral hole types at a single resonance wavelength is achievable for uncoupled modes.

    Conclusions:

    • The coupling of defect modes in HPCs significantly dictates their optical response.
    • Crystal thickness and twist defects are critical parameters for controlling spectral hole characteristics.
    • Engineered defect modes in HPCs offer potential for novel optical devices and applications.