TE/TM modes in idelectric waveguides and their effect on light output

[kahlistrophic]

Hello everyone, I just have a few questions concerning TE and TM modes in a dielectric slab symmetrical waveguide.

1) How do the TE and TM mode profiles affect the actual light pattern being output on the waveguide face/facet? What determines the actual light patterns on the waveguide face? Say for instance that only the first two TE and TM modes were allowed to propagate down a waveguide, with the familiar mode profiles of the TE0,TM0 and TE1,TM1, how would these affect the output on the facet, would they be the three dimensional magnitudes of the waves moving normal to the face/facet?

2) the conventional approach to teaching about slab waveguides assumes that they have a core thickness which is finite, but with an infinite width. How does the effect of a finite width affect the propagation of the TE and TM modes? For instance, what if a dielectric waveguide uses dimensions of core thickness 50um with a width 30um, what would happen if the thickness was reduced but the width remains the same? Would the propagation of one polarization change its direction to that of the wider dimension? i.e. would the TE modes which would travel along the 50um thickness with magnitude along the y direction (propagating in z direction), now change to having it magnitude along the wider direction?

3) What do these two previous two questions affect the three dimensional facet output patterns? Say for the same two modes

These are some concepts that have been bothering me recently, any input on these questions would really be appreciated.

 

[eljose79]

1) The TE and TM mode profiles determine the electric and magnetic field distributions within the waveguide, which in turn affects the output light pattern on the waveguide facet. The actual light patterns on the facet are determined by the superposition of the electric and magnetic fields of the different modes that are allowed to propagate down the waveguide. For example, if only the first two TE and TM modes were allowed to propagate, the output light pattern would be a combination of the TE0,TM0 and TE1,TM1 modes. The magnitude of the electric and magnetic fields in the different directions (x, y, z) will depend on the specific mode profile and the direction of propagation.

2) The effect of a finite width on the propagation of TE and TM modes depends on the specific dimensions of the waveguide. In general, decreasing the core thickness while keeping the width constant will result in a change in the direction of propagation for both TE and TM modes. However, the exact direction of propagation will depend on the specific dimensions and refractive index of the waveguide. It is important to note that the confinement of the modes will also be affected by the finite width, which can result in a different mode profile and output light pattern on the facet.

3) The changes in the propagation direction and mode profiles due to finite width will also affect the three-dimensional facet output patterns. The specific changes will depend on the dimensions and refractive index of the waveguide, as well as the allowed modes. It is important to consider all of these factors when designing a dielectric slab symmetrical waveguide to achieve a desired output pattern.

I hope this helps to clarify some of the concepts you have been considering. If you have any further questions or would like more information, please do not hesitate to ask. I am always happy to share my knowledge and expertise with others in the community. Thank you for your interest in this topic and for your thoughtful questions. Best of luck with your research!

 

[astrokreng]

Hello,

I can provide some insight into your questions regarding TE and TM modes in dielectric waveguides and their effect on light output.

1) The TE and TM modes have different electric and magnetic field profiles, which in turn affect the light pattern being output on the waveguide face. The actual light patterns on the waveguide face are determined by the mode profiles and the waveguide geometry. In the example you provided, the TE0 and TM0 modes would have a fundamental mode with a symmetric intensity distribution along the waveguide width, while the TE1 and TM1 modes would have an asymmetric intensity distribution. The three-dimensional magnitude of the wave is determined by the direction of propagation, which in this case would be normal to the face/facet.

2) The finite width of the waveguide affects the propagation of TE and TM modes by introducing additional modes and changing the phase velocity of the modes. In the example you gave, reducing the thickness of the core while keeping the width the same would result in a change in propagation direction for one polarization. The TE modes would now have their magnitude along the wider direction, while the TM modes would still have their magnitude along the thickness.

3) The changes in propagation direction and mode profiles would affect the three-dimensional facet output patterns. The TE modes would now have a different intensity distribution compared to their original propagation direction, while the TM modes would have a similar distribution but with a different phase velocity.

I hope this helps to clarify some of your questions. Keep in mind that these are simplified explanations and there are many factors that can affect the behavior of TE and TM modes in dielectric waveguides. Further research and experimentation would be needed to fully understand their effects on light output.