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Wavelength applied in DMD-based system

Jack Bunn
Prodigy 60 points

Hi, All:

I am trying to use a IR source and DLP1700 together to build a system. The source is working at 6 micron. From full-wave simulation I found that when I change the binary state of the micromirror array, the steering beam seemed not changed. And I acknowledged from this forum that because the wavelength is too ”large“ for DMD, and it is not able to resolve the change of binary state. 

http://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/f/94/p/58488/221034.aspx

I would like to know the largest wavelength can be applied for DMD. 

Another question is about the window. I found the function of the window as below:

http://focus.ti.com/pdfs/dlpdmd/Type_A_window_transmission_Discovery_Website.pdf

I would like to know if for practical use, I am not able to apply wavelength that is larger than 2000 nm for DMD in order to get low reflection. What if I remove the window and use a self-designed fiter instead of it?

Best regards.

Jack

  • 0
    TI__Genius 9935 points

    Jack,

    Welcome to the DLP & MEMS E2E forum.

    Your simulations are showing you the problem of the individual pixel mirrors being too close in size to the wavelength of the illuminating light. The 7.6 um pitch of the DLP1700 is very nearly the same as the wavelength of the light, therefore the mirror will not act as a specular reflector, but as a scattering element. Apart from window transmission and other considerations, a mirror is not effective at wavelengths which are greater than about 1/6 the linear dimension of the mirror, determined by the system tolerance for scattering vs reflection.

    The window on the DMD1700 can not be removed or changed. The cavity which is formed by the window must remained sealed from exposure to the environment. Any compromise of this environment will cause the DMD to fail.

    Even though the DMD1700 datasheet says "Designed for Use with Broadband Visible Light (420 nm - 720 nm)", as you can see from the curves in the other link which you gave, the window can be used at longer wavelengths in the NIR with some reduction in throughput.TI can not guarantee any performance outside the data sheet specs. However, you could try wavelengths up to perhaps 1 um, making your own judgment of acceptable performance.

    Best regards,

    Pascal

  • 0 in reply to Pascal DLP
    Prodigy 60 points

    Dear Pascal:

    Thanks very much for your reply.

    Does TI have other micromirror arrays (with larger dimensions, e.g. 20 micron pitch) that is suitable for longer wavelengths application?

    Regards,

    Jack

  • 0 in reply to Jack Bunn
    TI__Genius 9935 points

    Jack,

    The DMD with the largest dimension micromirror is the .7 XGA (1024x768) which is available for the DLP Discovery 4100 kit. This DMD has a mirror pitch of 13.6 um. This DMD is available with a NIR window anti-reflection coating. See this link for transmission curves: http://focus.ti.com/analog/docs/memsmidlevel.tsp?sectionId=622&tabId=2455

    The DLP Discovery 4100 kit is available only through our Design House partners.

    For additional information, please see the following link:

     

    http://focus.ti.com/docs/toolsw/folders/print/dlpd4x00kit.html

    Best regards,

    Pascal

  • 0 in reply to Pascal DLP
    Prodigy 60 points

    Hi, Pascal:

    Thanks very much.

    I also found a DLP chip set, http://www.dlp.com/dlp/regional/uk/discovery/discovery3000.aspx,

    For my research, I need to find a DMDs, which doesn't have to with high performance. It should be able to applied to 3 micron or even larger wavelengths.

    Another consideration is the price, I would like to build a low-cost system, so the price cannot be too high for a single DMD.

    So can you give some suggestion which one is better for my specific application?

    Cheers

    Jack

  • 0 in reply to Jack Bunn
    TI__Genius 9935 points

    Jack,

    The DLP Discovery 3000 kit is no longer available. Please look at the DLP Discovery 4100 Kit. Go to http://ti.com/mems and click on the link "Developer Kits" under "Getting Started". The Discovery 4100 offers the same DMDs as the discontinued Discovery 3000 kit. The Discovery 4100 is only available through one of our DLP Design Houses (click on the "Buy Now" link under the Discovery 4100). You will find that the Discovery 4100 is not inexpensive, though.

    For cost effectiveness, I recommend that you look at the LightCommander development kit. The DMD which comes with the LightCommander is the .55 XGA with 10.8 um mirror pitch. The LC kit also features a 4 LED illuminator: R G B and NIR (850 nm). I recognize that this is far shorter wavelength than you have mentioned).

    Best regards,

    Pascal

  • 0 in reply to Pascal DLP
    TI__Genius 9935 points

    Jack (and others who may have read this),

    I spoke too quickly, and made a mistake. The DLP Discovery 3000 Kit is still available through DLI (http://www.dlinnovations.com). The selection of DMDs available for the DLP Discovery 3000 is different from the DLP Discovery 4100. See http://www.dlinnovations.com/index.php?page=products&section=d3000&subsection=chipset

    Sorry for any confusion.

    Best regards,

    Pascal