Hi Tali

I think Holographic Waveguide presents unique advantages. The difference is not only the fabrication.

I have found that article that gives an interesting insight: https://research.fb.com/wp-content/uploads/2020/12/Design-and-Fabrication-of-Freeform-Holographic-Optical-Elements.pdf

Sandrine

Dear Sandrine, 

Thank you for your reply. But I can't find in your referral article the advantage of  'Holographic Waveguide' from  

''Modelling a holographic waveguide for Augmented Reality (AR) systems'.

The article  https://research.fb.com/wp-content/uploads/2020/12/Design-and-Fabrication-of-Freeform-Holographic-Optical-Elements.pdf

talk about Holographic Freform Elements, and I wish to understand the advantage of Holographic waveguide that is realized in OpticStudio as Hologram1 and Hologram2.

I thought the difference between Holographic Freeform and Holographic waveguide is achieving better performance at higher FOV, but both of them talks about FOV ~10[deg]

Will appreciate your insights.

Thanks, Tali M.

Hi Tali

The article I sent had a section comparing HOE vs traditional optics (thickness constraint, selectivity of HOE which is the ability to only diffract light from specific incoming angles or at specific wavelengths, and multiplexability of HOE which is the ability to superpose different configurations of volume gratings).

That being said, I don't have experience in these kinds of systems. Both articles work with the same kind of FOV because the articles AR with freeform and AR with holographic waveguide are focused on OpticStudio modelling. I will check with my colleagues that wrote the holographic article. They may have a better insight. 

In the meantime, you may have already found it but this article has a comparison table on AR Optical Combiners:  https://www.sciencedirect.com/science/article/pii/S258900422030585X.

Sandrine

Hello Tali,

This is a quite big question. I didn't carefully search literatures but below is some of the big difference I can say. Hopefully this is a good reference to you.

1. Holographic waveguide should give you smaller form factor. This is the biggest advantage that makes people choose diffractive optics instead of free-space optics.

2. Hologram provides higher see-through transmittance. With freeform, you need a half mirror which can decrease the incident light amplitude by 30%~70%. However, holographic film works based on wavelength- and angular selection. Normally you can have a better brightness when seeing the outside world through the holographic waveguide.

3. HOE is more difficult to be mass fabricated. At least it's not as common as the refractive or mirror optical elements.

Note it's possible you use more than two HOEs, or you can include both freeform and HOE in one system. In that case, you should have more freedom in the design.

Please let me know if you need any more comment.

Thank you.

Best regards,

Michael

Dear Michael,

Thank you for your informative reply. 

1) Can you please explain what you mean by ' smaller form factor'?

2) Is it true to say that better performance at higher FOV and wider spectral range can be achieved more easily with Holographic Freeform     

     rather than with Holographic waveguide (HOE)

Thanks in Advance, 

Tali M.

Hi Tali,

Thank you for reply. Please find my comments below.

1) I'm not sure if there is a 'definition' for form factor, but when I say smaller, I meant simply it looks more like a normal glasses that people is harder to notice it's an AR device. The following article might be a reference to you.

https://www.sciencedirect.com/science/article/pii/S2096579619300038

2) This really depends on how you design your device. Even for 'waveguide type AR', I can think of several different ways to design. And you could have both freeform and waveguide in your system at the same time. No matter what type of design you choose, usually you need to compromise all performance as well as size of the system. You cannot simply simply compare FOV of two systems with ignoring all other factors. I think you will need to carefully consider all factors and then choose the best design type for you. I have found a review reference for your reference as below.

https://www.cell.com/iscience/pdf/S2589-0042(20)30585-X.pdf

Hi Michael,

Great!

Thank you for your elaborated reply.

Tali M.