How can I determine the length of a Multimode fiber?

In summary, the conversation is about a step index single-multi-single mode fiber with equal lateral splicing offset at both junctions. Refractive indexes, offset, and radius of cores are given. The device is fed by a broad-band source and the spectral response collected by an Optical Spectrum Analyzer is given. The period of oscillations in the spectral response has been measured using Matlab. The person is seeking advice on how to determine the length of the multimode fiber using the measured period, and has looked at articles investigating the use of this structure as a sensing device but did not find a relation. They are then advised to use an Optical Time Domain Reflectometer to measure the length, taking into account any refractive index or impedance mismatch. A
  • #1
mefisto
I have a step index SMS (single-multi-single mode fiber) with an equal lateral splicing offset at both junctions.
Refractive indexes, offset and radius of cores are given.
This device is fed by a broad-band source and the spectral response collected by an Optical Spectrum Analyzer is given.

The spectral response has an evident oscillating behavior and I have measured the period of oscillations thanks to Matlab

Can you suggest me how to determine the length of the multimode fiber using the measured period ? I can neglect dispersion. I have looked at articles that investigate the use of this structure as a sensing device , but I did not find a relation, since the length was always given .
thanks in advance.
 
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  • #2
To measure fibre length, use an Optical Time Domain Reflectometer, OTDR. It sends short pulses of light up the line to reflect from the mismatch, or the open far end. The time to reflection, adjusted for group velocity due to RI, gives twice the line length.

If there is a refractive index or impedance mismatch in the system then you will see standing wave patterns. I expect the SW pattern will be due to some small junction interface, so will not give fibre length. How long do you think your fibre is, 1mm, 1m or 1km?

Can you please post the graph that shows the oscillation, with a clearly readable horizontal axis.

Edit:
Look at pages 20 to 25 in this file.
http://122.physics.ucdavis.edu/sites/default/files/files/Electronics/TransmissionLinesPart_II.pdf
 
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FAQ: How can I determine the length of a Multimode fiber?

1. How does the length of a multimode fiber affect its performance?

The length of a multimode fiber can impact its performance in terms of signal loss and distortion. The longer the fiber, the more likely there will be a decrease in signal strength and an increase in errors.

2. Is there a standard measurement for determining the length of a multimode fiber?

Yes, the standard measurement for multimode fiber length is meters (m).

3. What factors can affect the accuracy of measuring the length of a multimode fiber?

Factors that can affect the accuracy of measuring the length of a multimode fiber include the quality of the fiber, the type of connectors used, and environmental conditions such as temperature and humidity.

4. How can I measure the length of a multimode fiber?

The most common way to measure the length of a multimode fiber is by using an optical time domain reflectometer (OTDR), which sends a light pulse down the fiber and measures the time it takes for the reflection to return. Other methods include using a measuring wheel or a tape measure.

5. Are there any limitations to measuring the length of a multimode fiber?

Yes, there are limitations to measuring the length of a multimode fiber. These include the maximum distance that an OTDR can accurately measure, which is typically around 2-3 kilometers, and the need for clear access to both ends of the fiber for accurate measurements.

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