Please explain the microscopic structure of an FBG in layman’s terms. How does it reflect specific wavelengths through periodic variations in the refractive index?
An FBG’s microscopic structure can be understood as a segment within the core of an optical fiber where the refractive index (the property that describes how light bends as it passes through a material) changes periodically, like a series of tiny, evenly spaced “stripes” or gratings.
When broadband light (light containing a wide range of wavelengths) travels through the fiber and encounters this grating, most wavelengths pass through undisturbed. However, a very specific wavelength, known as the Bragg wavelength, is reflected back. This occurs because the spacing of these periodic variations in the refractive index precisely matches a condition for constructive interference for that particular wavelength, effectively “bouncing” it back. Other wavelengths do not meet this condition and continue to propagate through the fiber.
This phenomenon makes FBGs highly sensitive to external changes like temperature and strain, which can alter the grating’s spacing and thus shift the reflected Bragg wavelength. This characteristic is leveraged in various sensing applications.
DCYS offers a range of bare fiber Bragg gratings suitable for various applications and packaging needs. An example of a bare FBG is shown below:
You can learn more about our bare FBG products through the following links:
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