• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 747 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DLP 9000 FLS Contrast Ratio

Phil Chapnik
Prodigy 20 points

I am trying to find out the contrast ratio for the DLP 9000 FLS chip. That is, when the chip is fully illuminated with the 24 degree illumination cone, and all of the mirrors are in the "on" state, then a certain amount of light is reflected towards the projection lens entrance pupil. When the all of the mirrors are in the "off" state, there is still some light reflected into the projection lens due to scattering form the mirror edges and the dead area between the micro mirrors. What is the ratio of the "on" to "off" light energy reflected into the lens entrance pupil?

I am assuming the visible wavelength band.

I have heard of a Dark Chip, but do not find much information on it. It is my understanding that the Dark Chip adds some absorbing material between (or below) the micro-mirrors to cut down on the scattered light. If this is true, is the 9000 FLS chip available with this feature? And if so, what is the contrast ratio as a “dark chip”?

  • 0
    TI__Expert 6370 points

    Hi Phil,

    The contrast of your system will be specific to your optical design. For information on reflectivity check out the Micromirror Optical Characteristics section of the DLP9000 Datasheet. For information on Window Transmission, check out this app note.

    All current DLP DMDs are "dark chips," as you call them. So yes, the DLP9000FLS is a dark chip.


    Best regards,

    Trevor

  • 0 in reply to Trevor Dowd
    Prodigy 20 points
    I am trying to obtain the highest possible contrast. I will be using off-axis illumination (no TIR prism) and am also planning on using the full numerical aperture capability of the chip. So the question I am asking is basic to the DLP chip itself, not the optical system. The answer would be dependent upon the scattering characteristics of the chip given illumination to fill the +/-12 degree cone angle, but no more than +/-12 degrees (as then the contrast ratio would depend upon the optical design).

    When the chip is illuminated with a +/-12 degree cone angle (covering the active area), then the light that falls between the mirrors bounces around underneath, some being absorbed by the "dark chip" technology and the rest re-emitted through the inter-mirror cracks. This re-emitted light will cover more than +/-12 degrees due to scattering (maybe covering +/-90 degrees?). If my projection optics only works at f/2.4 ( +/-12 degree cone NA), then the amount of stray light that from the cracks will be lesser value.

    If all of the mirrors are in the "off" position, then the only light that gets through the projection optic will be that from the inter-mirror cracks, and possibly some from the edges of the mirrors. These two sources of stray light will set the limit on the contrast ratio. So what is the ratio of light that is directed into the projection optic when the mirror are "on" versus "off"?
  • 0 in reply to Phil Chapnik
    TI__Expert 6370 points
    Hi Phil,

    I am going to have my colleague take a look at your question. There might be a slight delay due to the holidays, thanks for your patience.

    Best regards,
    Trevor
  • 0 in reply to Phil Chapnik
    TI__Guru 54705 points

    Hello Phil,

    The contrast ratio is comprised primarily of the following factors:

    • Reflectivity of the aluminum µ-mirrors (including surface roughness at the wavelength being used) which is very flat over the visible range 
    • Effective fill factor integrated over the input cone.
    • Diffraction efficiency (at the wavelengths of interest - both for off and on states) integrated over this input and output cones.
    • Tilt angle of the actual device (between 11 and 13 degrees). This affects the potential overlap of the input and input cones.

    With all of the above you must integrate over the output cone for on and off.  The challenge is that it is driven mostly by the off state light which is very small and even small changes can have a profound effect on the value.  The single biggest killer of contrast ratio is light leakage at the point where the input cone and output cone nearly meet. 

    You can improve the overall on state light by expanding the cone past +/- 12 degrees perpendicular to the line connecting the center of the input and output cones.

    I hope this is helpful. 

    Fizix

    P.S. The OEM contrast ratio's of projectors is based on measurements they make on a fully designed system.