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Core Removal
D-fiber Etching Description

D-fiber etching can be used for two purposes:
  1)To remove the cladding and expose the core
  2)To remove part of the core itself
Both of these processes are used here at BYU, the first for making surface relief fiber Bragg gratings and the second for core replacement technologies. The goal is to perform these processes on a contiguous piece of optical fiber without destroying the integrity of the fiber. For core removal, it is also desirable to provide a gradual transition into the core.

D-Fiber Doping Profile
The optical fiber has the following materials:
  1. Undoped outer cladding
  2. Fluorine doped inner cladding
  3. Germania doped core
  4. Undoped region near the center of the core that is a result of the manufacturing process

Selective Chemical Etching
In addition to changing the index of refraction, the doping also changes the rate at which the material etches in hydrofluoric (HF) acid.
Doping Index of refraction Relative etch rate
Undoped 1.444 1.0
Fluorine doped 1.441 ~1.4
Germania doped 1.476 ~11x
Here is a little simulation of the core being etched from a fiber.
  1. The red part represents the germania-doped core.
  2. The outer blue part is the fluorine-doped cladding.
  3. The blue in the center is a region of undoped silica in the core.
Press the play button to see the animation.
Since the core etches much more quickly than the cladding, we can remove or partially remove it, while maintaining the main shape of the fiber.
A groove is created in the core region.

D-Fiber Etching Process
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  1. Fiber Preparation

  2. Fiber Holder

  3. Dip Etch

Etched Fiber Profiles

See the entire Fabrication Process

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