Experimenting the Speed of Light with Optical Fibers

In summary, I did an experiment on the speed of light with different length of optical fibers. I found that when I used long fibers like for example 50 meters or 20 meter, it showed a value inferior to the speed of light even after multiplying the refraction index of 1.49. But when I used optical fiber of short length, for example when I compare the difference between a 10 meters optical fiber and a 0.60 meter one, I got a result that is almost the same as the speed of light. I think that the longer it gets the more impurities it has and if those impurities can slow it down. I'm not sure if that's how it works, but it's something to think about.
  • #1
ATH500
6
0
I did an experiment on the speed of light with different length of optical fibers.
I know that the fiber has a refraction index of 1.49.
I would like to know if I need to take in account the total internal reflection of the optical fibers too.
Because when I use long fibers like for exemple 50 meters or 20 meter, it shows value
inferior to the speed of light even after having multiplied the refraction index of 1.49.
I get 218x10^6 m/s or 198 x 10^6...

But when I use optical fiber of short length, for example when I compare the difference between a 10 meters optical fiber and a 0.60 meter one, I got a result that is almost the same as the speed of light: 291326041 meters/second.

I will post the results I got when doing the experiment with the optical fibers and the oscilloscope.

Here are four results for a length of 10 meters:
10_m_essai_2.png

10_m_essai_3.png

10_m_deroulee.png

10_m_roulee.png


Here is the result for 20 meters:
20_m.png


For 50 meters:
50_m.png


For 0.60 meter:
delai_electronique_62_00ns_60c.png


For 0.615 meter:
delai_electronique_66_00ns_61_.png


I would like to know why do I get value of the speed of light that are inferior the more the length of the fiber increase.

Thank you,
Pascal
 
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  • #2


I think you do need to take into account of the total internal reflection since this means that the ray travels for a longer distance than the length of the fiber.
 
  • #3


So, does anyone else have any other ideas about this ?
 
  • #4


Keep in mind that I'm no expert. The speed of individual photons, however, is always c. It's the interactions with atoms that slows down the propagation speed in a medium. It would make sense, then, that a longer path involves more interactions.
 
  • #5


Are you sure that's how it works ? I thought that the refraction index took care of all this and that it already take in account the interactions inside the same material. Because my optical fiber is made of the same material all along it must the refraction index should not change because every particle of that material already slows down 1.49 time the speed of light.

I wonder if the longer it gets the more impurities it has and if those impurities can slow it down...
 
  • #6


ATH500 said:
Are you sure that's how it works ?

No, I'm not; that's why I told you to keep in mind that I'm no expert. I was just giving you my best high-school drop-out's guess about the situation.
 
  • #7


It's a red LED input flashing at 100Hz. And when the receptor perceives light from the LED, it drops in voltage and we can see the effect on the oscilloscope. The LED correspond to the yellow graph and the receptor to the blue graph. I wonder if the impurities or the total internal reflection in the fiber has an effect.
 

1. How do optical fibers help in experimenting the speed of light?

Optical fibers are thin, flexible strands of glass or plastic that are used to transmit light signals. By using these fibers, scientists are able to create a controlled environment in which they can measure the speed of light. The fibers also allow for the manipulation and redirection of light, making it easier to conduct experiments.

2. What is the process of experimenting the speed of light with optical fibers?

The process involves sending a pulse of light through the optical fiber and measuring the time it takes to travel a certain distance. This is repeated multiple times and the average speed is calculated. The distance is then adjusted and the process is repeated to obtain more data points. The speed of light can then be calculated using the formula speed = distance/time.

3. How accurate are the results obtained from experiments with optical fibers?

The use of optical fibers allows for a high level of accuracy in experimenting the speed of light. By controlling the environment and minimizing external factors, scientists are able to obtain precise measurements. However, it is important to note that the speed of light is affected by various factors, such as the medium it is traveling through, and the results may vary slightly.

4. What are the applications of experimenting the speed of light with optical fibers?

Experimenting the speed of light with optical fibers has many practical applications in the field of telecommunications. By understanding the speed of light and how it interacts with fibers, scientists are able to develop faster and more efficient communication systems. This technology is also used in medical imaging and other scientific research.

5. Are there any limitations to experimenting the speed of light with optical fibers?

One limitation is that the speed of light can only be accurately measured in a vacuum, as it is affected by the medium it is traveling through. This means that the results obtained from experiments with optical fibers may not be 100% accurate. Additionally, the technology used in the experiments may have limitations in terms of precision and measurement capabilities.

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