Transverse mode output from a multimode fiber using TEM00 laser source?

In summary, if a TEM00 output laser source is used as input into a multimode optical fiber, it is possible for the output of the optical fiber to be multimode. This is due to mode coupling and modal dispersion, which causes energy to leak from the TEM00 to higher modes as the beam propagates. This can cause signal attenuation and make the signal unreadable if the multimode segment is longer.
  • #1
babreopti
2
0
If a TEM00 output laser source (regarding both cases of single frequency vs multifrequency) is used as input into a multimode optical fiber, is it possible for the output of the optical fiber to be multimode?
 
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  • #2
I think that it's inevitable- google "modal dispersion". Because a multimode fiber supports many transverse modes, energy will leak from the TEM00 to higher modes as the beam propagates due to mode coupling which varies as the square root of the length.
 
  • #3
Actually that is one of the labs for telecom students: what happens if we mix single- and multi-mode fibres on a path between two singlemode telco devices running with 40 GHz clocks (using amplitude modulation, NRZ-OOK, so the frequency if modulation is equal to bit rate)?
Simple answer is: it works if the MM fiber is pretty short (tens of meters) - just signal is attenuated due to different apertures of core fibres; but if the MM segment is longer, modal dispersion obscures the signal to make it unreadable.
Full answer is: watch the output signal on the oscilloscope to see the dispersion.
 

1. What is a transverse mode output?

A transverse mode output refers to the spatial distribution of the laser beam's intensity and phase within the cross-section of the beam. This is determined by the structure of the laser cavity and the characteristics of the laser source.

2. What is a multimode fiber?

A multimode fiber is an optical fiber with a larger core diameter that allows multiple light rays to propagate through it at the same time. This allows for the transmission of multiple signals or modes simultaneously.

3. What does TEM00 laser source mean?

TEM00 stands for "Transverse Electromagnetic Mode 00" and refers to the fundamental mode of a laser beam, which has a Gaussian intensity profile and a single lobe in the transverse direction. This is considered the most stable and desirable mode for many applications.

4. How does a TEM00 laser source produce a transverse mode output in a multimode fiber?

The TEM00 laser source produces a transverse mode output in a multimode fiber by using a collimating lens to convert the laser beam into a collimated beam with a specific diameter. This beam is then coupled into the multimode fiber, which allows for the propagation of multiple modes. The fundamental mode (TEM00) is then selectively coupled into the fiber, resulting in a transverse mode output.

5. What factors can affect the quality of the transverse mode output from a multimode fiber using a TEM00 laser source?

Several factors can affect the quality of the transverse mode output, including the alignment of the laser beam with the fiber, the beam diameter, and the length and quality of the fiber. Other factors such as temperature and environmental conditions can also impact the output. To achieve the best results, it is important to carefully control and optimize these factors.

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