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DLP Discovery 4100 Development Kit _ DMD application

Jing Lu69
Prodigy 55 points

Hi,

We have the DLP Discovery 4100 Development Kit with .55 type X DMD. And we use it to modulate the laser source in a microscope. I have two questions:

1. Can we set some of the DMD micro-mirrors to PARK position (0 degree), instead of +12 or -12 degree?

2. We found some interference fringe on our CCD camera after DMD was power on.  Is that normal?

Thank you in advance for your help.

Jing

  • 0
    TI__Guru 54285 points

    Hello Jing,

    1.  Once a DMD is powered up there are only two operational states -12° and +12°.  Parking is a powered off condition and the mirrors are only nominally at 0°. 

    2.  This is generally caused by highly collimated lasers with a very small effective NA.  What is the appearance of the fringes?  are they like a bulls-eye or more like a set of parallel lines (or other)?

    a.  If they are like a bulls-eye, this is likely your optical path that is creating Fresnel zones of constructive and destructive interference centered on the optical axis of the lens due to path length differences.

    b.  If they are parallel lines, then you can try decreasing or increasing your incident angle a little to determine the relationship.

    c.  For other, you will need to experiment to see if you can discover the mechanism generating the fringes.

    One thing to try is to use a beam expander and a faster lens to create a more angularly distributed illumination (larger NA). 

    What is your illumination angle?

    Fizix

  • 0 in reply to Fizix
    Prodigy 55 points
    Hi Fizix,

    Thank you for your reply.

    Our system is a line scan microscope, hence the beam on DMD is a line generated by cylindrical lens with meridian NA=0.0135 and sagittal NA=0. And the fringes on image obtained by line-CCD are horizontal parallel lines.

    I tried changing the incident angle, the lines were changing in amplitude and position.

    Jing
  • 0 in reply to Jing Lu69
    TI__Guru 54285 points

    Hello Jing,

    Since your system is using a cylindrical lends then the straight lines could be the equivalent of concentric circles with spherical lenses.

    My hunch is that the lines represent constructive and destructive interferences due to different path lengths to the target surface through the cylindrical lens.  I would expect the "fringe" lines to be parallel to the focus line of the meridian of the lens (i.e. the same direction as the center ridge of the lens.

    You may want to try a beam expander in the meridian direction and a larger meridial NA to see if this mitigates the RMS peak to valley differences in the lines.

    Fizix