# Divergence angle of light exiting a nano-etched single mode fiber

• melnop
In summary, a single mode fiber with a NA of 0.12 and a silver-coated tip with a 200 nm diameter hole acts as a point source for light at 830 nm. However, when the light is shorter than 830 nm, the fiber may have multiple modes. To calculate the cone of light from the silvered end, the intensity profile can be found by using the diffraction formula for single-slit diffraction.
melnop
I am working with a single mode fiber at 830 nm with a NA of 0.12 (http://www.thorlabs.com/thorcat/19600/P3-830A-FC-2-AutoCADPDF.pdf). One end has a fiber tip coated in silver with a small hole of 200 nm diameter to essentially create a point source. My advisor told me that the fiber has a few modes when the light traveling through is shorter than 830 nm. I know that the acceptance angle may be calculated easily for a normal fiber, but I'm not sure how the small hole will affect things.

How could I calculate the cone of light that is coming out of the silvered end?

(I have included a diagram for clarity)

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• FIBdFiber.jpg
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## 1. What is the divergence angle of light exiting a nano-etched single mode fiber?

The divergence angle of light exiting a nano-etched single mode fiber is a measure of how much the light spreads out as it exits the fiber. It is typically measured in degrees and can vary depending on the specific characteristics of the fiber and the light source.

## 2. How does the divergence angle of light exiting a nano-etched single mode fiber affect its performance?

The divergence angle of light exiting a nano-etched single mode fiber can affect its performance in several ways. A larger divergence angle can result in more light being lost or scattered, reducing the overall efficiency of the fiber. It can also impact the accuracy and precision of the light signal being transmitted.

## 3. What factors can influence the divergence angle of light exiting a nano-etched single mode fiber?

Several factors can influence the divergence angle of light exiting a nano-etched single mode fiber, including the size and shape of the etched pattern, the refractive index of the fiber, and the wavelength of the light being transmitted. Other variables, such as temperature and mechanical stress, can also play a role.

## 4. How can the divergence angle of light exiting a nano-etched single mode fiber be measured?

The divergence angle of light exiting a nano-etched single mode fiber can be measured using various techniques, such as imaging the output of the fiber and analyzing the image to determine the angle. Other methods include using specialized instruments like beam profilers or using mathematical calculations based on the fiber's physical properties.

## 5. Can the divergence angle of light exiting a nano-etched single mode fiber be controlled or adjusted?

Yes, the divergence angle of light exiting a nano-etched single mode fiber can be controlled or adjusted to some extent. The design and fabrication of the fiber can be optimized to achieve a desired divergence angle, and certain materials or coatings can be applied to help minimize the angle. However, there are limitations to how much the angle can be controlled, and it may vary slightly due to external factors during use.

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