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DLP6500FYE: DLP® products forum

shengtao sun
Prodigy 80 points
Part Number: DLP6500FYE
We were trying to use DMD chip to generate specific patterns, powered by laser sources. The DMD generates abnormal scattering stripes additional to the desired patterns. The scattering-like patterns are superimposed onto the desired patterns. 
  • 0
    Prodigy 80 points

    The upper image is the pattern generated and the lower image is the projection through a projector lens. The scattering-like patterns are marked in this image.

  • 0
    TI__Guru 54705 points

    Hello Shengtao,

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

    Please show the GUI setup information/screens and attach a file with at least the image file you are loading to the DMD.  
    Without more information it will be difficult to assist you well.

    Also can you tell me about your camera capture parameters?

    Fizix

  • 0 in reply to Fizix
    Prodigy 80 points

    The setting and image are attached and I am using an IR camera so I am not sure if I can pull out the complete settings of the camera.

  • 0 in reply to shengtao sun
    TI__Guru 54705 points

    Hello Shengtao,

    I notice in your settings you have it set to 1 bit over 105 µs.  Please change it to 8 bit (it will adjust the exposure to 4046 µs).  I assume from the image you are attempting to to display gray stripes with one black stripe.  What you are displaying is black stripes (since the gray is below the threshold value).  I do not completely understand the picture though. 

    It would help to know how you are triggering (or if you are triggering) the camera to capture the image.  You can use the Trigger Out 2 for that if needed.

    Also in the picture can you tell me what it is being projected on?  Is this a flat surface and is it uniform in color?

    Fizix

  • 0 in reply to Fizix
    Prodigy 80 points

    Well the problem is not about the color actually. I also used only black and white image and this is what I have after the dmd. The projected surface is a flat surface and it is white background with a checkerboard on it. It will look just the same with a white paper. I would like to know what is the cause of these fade stripes beside the pattern I want and how to solve this problem.

  • 0 in reply to shengtao sun
    TI__Guru 54705 points

    Hello Shengtao,

    Are you able to see this with your eye or is this only in the camera images?

    If it is visible with your eye, then I wonder if this is a coherency effect:

    • Is the illumination beam collimated?
    • Do you have a lens system that is imaging the DMD pattern onto your target? 
      • If not, then you may be seeing diffraction effects of the pattern that is on the DMD.
      • How do they change if you move further or closer to the DMD?

    Also, what is the wavelength of the light?

    FIzix

  • 0 in reply to Fizix
    Prodigy 80 points

    Hello Fizix

    The wavelength is 980nm which is NIR. I can't see this directly with my eyes but it looks the same as the picture with an IR card. I use laser beam and it is collimated and expanded before it reach the DMD. Then after the reflection of the DMD it went through a concave lens for further expanding.

    Shengtao

  • 0 in reply to shengtao sun
    TI__Guru 54705 points

    Hello Shengtao,

    I suspect that you are seeing the diffraction orders of the pattern superimposed on the primary image.

    Try displaying a single stripe and taking a picture of the result and posting it.

    Fizix

  • 0 in reply to Fizix
    Prodigy 80 points

    Single stripe looks like this.

  • 0 in reply to shengtao sun
    TI__Guru 54705 points

    Hello Shengtao,

    It is clear to me that you are getting edge diffraction from the stripe(s) and in the single stripe image it looks like slit diffraction and in the multi-stripe images it looks like orders from the multiple slits.

    Fizix

  • 0 in reply to Fizix
    Prodigy 80 points

    Hi Fizix

    If so how could I remove these edge diffraction stripes?

    Shengtao

  • 0 in reply to shengtao sun
    TI__Guru 54705 points

    Hello Shengtao,

    The edge diffraction and the "multi-stripe" diffraction is a fundamental property of the interaction of monochromatic coherent collimated light.

    You could try re-imaging the surface of the DMD at your target rather than working in the collimated domain.  

    This may be challenging if the final image you want is much larger (i.e. magnified) than the DMD array.

    Fizix

  • 0 in reply to Fizix
    Prodigy 80 points

    Hello Fizix

    Currently we are trying to average out the edge diffraction by breaking the pattern into smaller parts and using minimum exposure time to display them. I have one question about the DMD setting. How does the "color" tab in the gui work? Does it change DMD's reaction to different colors?

    Shengtao

  • 0 in reply to shengtao sun
    TI__Guru 54705 points

    Hello Shengtao,

    The color tab in the DMD is only for Solid State Illumination (SSI) control.  The DMD is reflective so, there is nothing that can change it's reaction to different colors of light.

    However, the edge diffraction will change with wavelength according to wave mechanics.

    I would take the single slit pattern you saw, and do a Fourier transform and put that pattern on the DMD to see if you can get a better image.  However, If you are sending only binary patterns it may be challenging since your pattern will only have 0 or 1 for phase.

    Fizix