Hi support team,
In Sequential example 2 in the article 'Simulating diffraction efficiency of a volume holographic grating using Kogelnik’s method',
you refer to Hologram Waveguide as:
It says that, the material on both sides of the hologram during construction is acrylic. Can you explain why? according to picture above the hologram has one side acrylic and air on the other side.
Thank you,
Tali M.
Best answer by Csilla Timar-Fulep
View originalHi Tali
This is due to the way we record the hologram:
In the sequential 2 example, to make beam 2, you will need to set a prism when recording:
Sandrine
Hello All,
My doubt is can we used a single slab of glass as a waveguide? How can we get the TIR effect in a waveguide?
How we can check the final FOV as output?
Sandrine Hi
Thank you for your reply.
In this sequential 2 example, you mentioned above, one has to fill construct wave in 'surface type', which construct beam is it refer to, beam1 or 2?
For transmission holograms, construction beams come from the same side of the hologram surface. Inversely, for reflection holograms, construction beams come from opposite sides of the hologram surface. So how can I set this?
Thanks in Advance,
Tali M.
Hi Tali
The construction wavelength is for both beams: beam 1 and beam 2.
Have a look at the help file for Hologram 2 (The Setup Tab > Editors Group (Setup Tab) > Lens Data Editor > Sequential Surfaces (lens data editor) > Hologram 2). It explains how to set it up.
If it is still not clear, let us know.
Sandrine
Hi Sandrine,
Thank you for your reply.
However I still don't understand, how it can be the same wavelength for both beams: beam 1 and beam 2.
For transmission holograms, construction beams come from the same side of the hologram surface. and for reflection holograms, construction beams come from opposite sides of the hologram surface. Opposite sides of the hologram can be two different materials, no?
So how can I set the same wavelength for two different materials?
Thanks,
Tali M.
+2
Hi Tali,
Thanks for getting back to us!
The hologram deviates ray paths according to the following equation:
This equation above doesn't consider the index of the materials at two sides of the hologram surface. If one of the rays is from different material, then we should multiply its unit vector by the index where the ray is in. For example, if the hologram is attached on a glass with index of n_g and is used in reflection, then we should write incident readout beam and the refracted beam as n_g*r'_r and n_g*r'_o. This is already handled by OpticStudio.
However, the construction beams are always assumed to be in the AIR, as you mentioned. There is no parameter for defining the index of the material where the construction beams are. In cases where the hologram is optically manufactured in a non-AIR material, the construction wavelength should be effectively changed from λ_c to λ_c/n_g.
Please note that, when the index of the materials at two sides of the hologram are different, we should expect rays to be diffracted to different directions. This is exactly what we would expect for a grating diffraction. Shown below is a sketch that depicts this concept.
Please also note that to use a hologram in reflection, its Material must be set to “MIRROR”. This explicitly indicates OpticStudio that rays propagate in the opposite direction after hitting the hologram surface.
You may find more information about this in the Help at:
The Setup Tab > Editors Group (Setup Tab) > Lens Data Editor > Sequential Surfaces (lens data editor) > Hologram 1 and Hologram 2
and in this knowledgebase article:
How to model holograms in OpticStudio · MyZemax
I hope this helps, but if you have further questions, please ask!
Best,
Csilla
Dear Csilla,
Thank you so much for your help and elaborated explanation
Maybe I'm missing something with the definitions.
Let's look at two examples marked in red below:
(e) and (c) are both represent reflection holograms, construction beams come from opposite sides of the hologram surface.
1) Type (e) (Hologram 2) is used to model 'holographic waveguide for Augmented Reality'
and the construction of its hologram is done with an extra prism, so I understand why the construction
wavelength is the same for construction beam1 and construction beam2 during construction process.
2) Do you have an example (application) for type (c) hologram1?
Thanks,
Tali M.
Hi Tali
We don't have examples for Hologram 1.
If you have a set-up in mind, would you mind sending us a sketch of the construction and set-up and then we can help you with the OpticStudio file? Thank you.
Sandrine
No, Sandrine I don't have.
I hoped to understand better via another example..
Thanks,
Tali
Hi Tali!
Sorry for the late reply. I will check with my colleagues. I was hoping someone from our community will have an example?
Thank you.
Sandrine
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