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|December 20, 2007

Summary

This summary is machine-generated.

Omnidirectional reflection is achieved using Bragg structures with sufficient refractive index contrast. Chirping or grading periodicity allows wide spectral ranges with modest index contrast, enabling arbitrary spectral shapes.

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Area of Science:

Optics and Photonics
Materials Science

Background:

Optical refraction limits external rays incident on high-refractive-index media to a small internal cone angle.
Periodic Bragg structures can overcome this limitation by reflecting light over a wider angular range than the internal cone.

Purpose of the Study:

To investigate the conditions for omnidirectional external reflection using Bragg structures.
To explore methods for achieving wide spectral gaps and arbitrary spectral shapes with reduced refractive index contrast.

Main Methods:

Analysis of refractive index ranges for omnidirectional reflection.
Theoretical proposal of chirping or grading the periodicity of Bragg structures.

Main Results:

Omnidirectional external reflection is possible with sufficient internal refractive-index contrast.
Chirping or grading periodicity enables coverage of wide spectral ranges with modest index contrast.
The graded-periodicity approach is effective when the average refractive index exceeds 2.

Conclusions:

Modifying Bragg structure periodicity offers a pathway to broadband and shape-tunable spectral reflection.
This approach reduces the need for high refractive index contrast, making the technology more accessible.