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DMD reflection image quality

Hi, I am using Discovery™ 4100 Starter Kit with 0.55'' XGA DMD. We are using our own optics and did a simple test to focus a fiber laser beam (visible spectrum) to the DMD with an angle of 24 degrees (roughly) with the normal of the mirror, what we got is a  reflection in the center (white) together with many similar array images around the center image. And the surrounding array images are colorful rather than white. How can we obtain a clear reflection center only? Why there is so many arrays around it? Thanks.

  • Hello Huan,

    Welcome to the DLP section of the Texas Instruments E2E community.

    I am glad to see that you are using the D4100 kit.  

    I am a little bit confused by the description of a "fiber laser beam" (visible spectrum).  From your description of the results it appears that you have many wavelengths in the beam.   Do you know what the Numerical Aperture of the illumination is at the DMD? 

    The DMD acts as a grating and will cause some separation of colors.  This is normal and is a result of diffration off the the DMD array (it behaves as a grating).  You can generally reduce the effect with a larger Numerical Aperture on the Illumination side, but it cannot be completely eliminated.

    I hope this is helpful.

     

    Fizix.

  • Thank you for your reply.

    We do not use any focusing lens when illuminate the DMD and we just use the original laser beam. It has wavelength cover the visible range. So do you mean that with a focusing lens to illuminate the DMD will reduce the grating effect? And currently when we increase the power of the laser beam, the image array brightness also becomes stronger and we are not sure which image is the true reflection. Is there anyway to get a better quality? We are doing this with simple optics (collimator, mirrors) and our goalis to have a simple spectrum shaping. So is it a must to have a specifically designed optics (such as prism, focus lens)?

    Thanks a lot!

    Huan

  • Hello Huan,

    The focusing lens will not reduce the diffraction as much as it will cause the color spots (diffraction orders) to overlap more resulting in less noticable color separation.

    Fizix