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I know what modes in an optical fiber mean but what are exactly mode groups in an optical fiber?

From what I read until now, I have the impression that modes that have close propagation constants belong to the same group. But how 'exactly' do we group modes?

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If you look at the eigenmode in the fiber, there is non mode group due to each mode has its own propagation constant even though they are very close.

Let us talk about the linear polarization mode in weakly guide fiber. Some modes will linearly combine since their propagation constants can be seen as identical and then they form LP mode, e.g. TE01, TM01 and HE21 generate LP11 mode. Actually, such LP11 mode is indeed a mode group because it contains degenerated modes, polarization degenerated and spatial degenerated, i.e. LP11x, LP11y, LP11o, LP11e. Hence LP11 mode group has four modes: LP11ox, LP11oy, LP11ex and LP11ey.

Being in your mind, there are only eigenmodes exist in the fiber. Other types of mode are just another way to express them.

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  • $\begingroup$ 1)I'm familiar with the LP modes and the two different polarizations of a mode but what do LP11e, LP11o , LP11ox ... refer to ? $\endgroup$ – ghfalcon7 Apr 26 '14 at 21:19
  • $\begingroup$ 2)Can you give me some book references to fully understand the concept of modes in optical fibers ? $\endgroup$ – ghfalcon7 Apr 26 '14 at 21:20
  • $\begingroup$ One classic reference is D. Marcuse, "The impulse response of an optical fiber with parabolic index profile", Bell System Technical Journal V 52 N 7, pp 1169-1174, 1977. Online here $\endgroup$ – The Photon Aug 4 '14 at 22:01
  • $\begingroup$ So in summary: mode groups are different eigenmodes that seem to be the same in the weak guidance approximation, is this what you are saying? I've not heard the term "mode group" before, but the TE01, TM01 and HE21 do indeed have different propagation constants in the full vector model, although they are very very close. See chapter 12 of Snyder and Love "Optical Waveguide Theory". $\endgroup$ – WetSavannaAnimal Aug 22 '15 at 13:35
  • $\begingroup$ @ghfalcon7 See chapter 12 of Snyder and Love "Optical Waveguide Theory" $\endgroup$ – WetSavannaAnimal Aug 22 '15 at 13:36

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