Using laser light with DMD DLP chip

Hello Sean,

Welcome to the DLP section of the TI-E2E Community.

Thank you for your inquiry.  Here are some answers to your questions:

1) Does TI have any DLP/DMD systems that can be used with IR light along the 10.6um wavelength?  Even if the items are not rated for use, are there any contacts that have used this technology successfully with these products?

The limiting factor with light of this wavelength is the pixel pitch (distance between mirror centers).  The largest pixel pitch that we currently have available in our Discovery kits is 13.68 um.  Then next smaller is 10.8 um.  Both of these are on the same order as the wavelength that you wish to use. 

The diffraction efficiency is very low indeed for wavelengths greater than 1/4 l.  At this wavelength of light the DMD will act more as a rough mirror than a switch.

2) Is there a new document discussing using laser light with DLP technology?

The document you referenced is being redone and reformated for our updated website.  We hope to release it soon.  You may be able to find a cached copy of the older one on some search engines.

3) Does the Light Commander have any options for the 10.6um wavelength light?

For the reasons given in the answer to your first question, the answer is no.

Thanks for the quick response.

I'm not familiar with the terminology of "pixel pitch".  You said it is the distance between the mirror centers.  Is this the actual linear measurement between the mirrors on the DMD (similar to dot pitch in printing)?  Can you explain in a little more detail why this is an issue when along the same order of the light wavelength?

In my conceptual application I will only need static IR images that need to be held for a few seconds, then no light emitting for a number of seconds (IR source turned off), and then a different static IR image held for a few seconds, and so on.  Because I am looking at using static images, I conceptually designed the optics to have a larger distance between DMD and projection lense hoping to capture only the collimated light (possibly even use a collumating lense if needed).  My theory is that this would eliminate diffracted beams and only give me the appropriate image with no "shadowing" or noise (if the mirrors stay static even a slight difference of diffraction shouldn't be a problem...at the right distance).  Does my description make any sense at all?  Any thoughts on the design/potential problems?

If the above application seems to theoretically make sense, what intensity IR incident light can the DMD handle without destroying it?  I may be able to live with 20% efficiency depending on what intensity I can apply.

Thanks,

Sean

Hi Sean,

The DMD is an array of square mirrors, like a grid on graph paper.  The distance from one line to the next is like the pixel pitch.  This means that the DMD acts as a two dimensional diffraction grating. 

For more information about diffraction gratings see:  http://en.wikipedia.org/wiki/Diffraction_grating

When the grating pitch (i.e. "pixel pitch" for DMDs) is on the same order as the wavelength of light being used there is only one diffraction order available in the hemisphere -- namely the 0^th order, which is the same as the reflection from a mirror.  To be usable you need non-zero orders to switch between.   

The diffraction orders are an interaction between the wavelength of light usedand the spatial coherence of the DMD (i.e. regularly spaced mirrors).

I hope this helps.

Fizix

Hi Sean,

There is another challence if you want to use CO2 Lasers with a DLP apart from the pixel pitch. In front of each DLP is a safety glass - This glass has a high absorption of your CO2 Laser, so you should remove it. But if you do this (i tried and failed) you can get problems with electrostatic charging of the mirrors. 

A solution to this problem could be that Ti produce a DLP with a Zn-Se window instead of the glass - i  asked them but they denied - but maybe you can ask too.

If you are successful it would be nice when you tell me how it's going.

Best regards

Elke

Hello Sean,

I wanted to add that in case you wish to take off the window in order to be able to work with the DMD at that frequency, you should consider 0.7" DMD for example and not the 0.55" which would be much more difficult to handle with regards to removal procedure.

Instead of using the DMD with a designated imaging lens it would be possible to form a pattern which by means of diffraction will produce the image you want.

If you wish to do that it would require a binary phase mask transmission design that you could feed the DMD with.  The DMD will work similar to a binary DOE.

now if you design a transmission in which a lens in being taken in consideration then you could filter out the undesired orders and have 1st order appear where you want it to.

This would also be much easier to install since you do not really have to run fine adjustments for the illumination, as long as you have a conjugating beam propagating the DMD you will be able to obtain the image.  The coverage of the DMD will dictate the resolution of the image, in case you have low coverage- you will get the image but with higher granularity level (It is recommended to have maximum coverage due to the high energy you wish to work with).   Since you wish to work with high power IR source, I'd try working at lowest possible D.C.

Please take in consideration that in case that data you wish to project is asymmetric then this would probably not be a good solution for you since in binary structures there is a twin image artifact that would overlay the data.

 Regards,

Yuval

Dear Sean

We are currently working on a mini module based on a LD (5W) at 808nm designated to replace the current IR LED in the LC.

In case you wish to use laser with your kit maybe this could address your requirements, however 10.6um is too far in the IR range to be able to use it with.

If you are interested in working at the NIR range then this module could fit.

Can you elaborate on your application ? is 10.6um a requirement ?

Best Regards,

Yuval Kapellner

EKB Technologies Ltd

A DLP Design house

www.ekb.co.il

Hi Elke,

Perhaps you may wish to share your experience on removing the DMD cover glass so we can learn from it?