Volume Bragg Grating?

[Ramsey_innovations]

I was wondering if anyone here has any experience working with VBG's, more particularly multiplexed VBG's for spectral combining.

I'm interested because, from what I've read, they offer spectral combining with supreme efficiency and a very high damage threshold.

There is a company local to me by the name of Optigrate who is a leading producer of these gratings. If anyone could help me to gain some technical understanding of the pro's and con's of implementing these as combiners I would be greatly appreciative.

If it seems promising I'm considering approaching this company with the intention of possibly partnering with my company to produce a modular combiner which I have invented over the course of 4-5 years.

I need to hear from someone with some real working knowledge of these optics so I can gain as much understanding about them before approaching their research engineers, as I do not want to miss something integral and sound like a baffoon.

Thanks!

 

[Meatball]

With Braggs, there is a bit more calculation to do, before you are implement any single optic. It really depends on your particular plan. They are essentially mirrors with very low losses when the Bragg condition is "true", and when its not true the beam simply goes through the optics.

You can make the Bragg condition "true" or "untrue" with a change in wavelength, or the incident angle. For this to work, you must first have a grating distance to design your "circuit" around.

So again... it depends on what you really need. If you can ($)afford($) the efficiency, then its still only one way of doing a simple task. There are probably dielectric mirrors out there with only slightly more losses, but are similar in price.

 

[Ramsey_innovations]

Thank you for the information, that sounds congruent with some things I have read. Basically the main advantage is efficiency. What about the limitations with the number of beams that can be combined though? I have heard, at least with holographic VBG's, that it may be possible to combine tens if not hundreds of wavelengths with extremely low losses. Also, as I understand it, these are limited to spectral combining meaning combing of identical wavelengths is out.

Again thanks for the response, greatly appreciated.

 

[Meatball]

Theoretically, that should probably work very well I suppose. If you are wanting to combine a large number of wavelengths, then the VBG route would definitely be the more precise method of adding in wavelengths one at a time, but that comes with the assumption that your laser beams are especially narrow banded. That being said, laser diodes may see some of the lowest efficiency curves achievable from a laser through a VBG since LDs are not known for their narrow bandwidth or constancy of lasing wavelength which is lots of times a function of operating temperature. DPSS, gas or any other SS laser should able to show huge efficiency plots through the optic if the setup is clean, and solid in design.

Right, spectral combination is the only combination these can do, because if two beams of the same wavelength need to both make the Bragg condition "true" from opposite sides of the optic, they will simply both reflect off their respective sides and go their own ways.

Now as to the limit of the number of beams that can be combined... well.

Lets just say that's largely a function of the budget you have to work with.

You can always decide to go with very elaborate setups capable of combining say 25 beams together, but the design must be perfect and will probably be designed around some kind of particular laser module with "X" physical dimensions to it. This would be so that worn out modules can be easily swapped out and replaced without any kind of optical circuit redesign.

I'm trying to find a paper I read once which described how you can heat or cool a VBG, "tuning" it to precisely meet the Bragg condition for one of say "Y" number of incident beams on the optic. The Bragg distance changes slightly with optic temperature, so again the more $$$ you have to work with, the more suitable and better fit for the job, the VBG becomes.

Hopefully that makes sense?

 

[Ramsey_innovations]

Yes, that makes perfect sense. I now see the potential issues with diode/semiconductor based lasers. I hadn't considered the wavelength variations from diode to diode as well as shift during operation. It makes sense though since the VGB's are so wavelength discriminatory as opposed to say a dichroic filter which can provide a wide spectral bandwidth of either transmission or reflection. Thanks, that is really helpful.
If you do find the paper that would be great, but don't worry about it too much you've already provided a great deal of assistance.
You've been a great help :beer:
Thanks,
James