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Original question:

DLP4500: 3D scan setting point could problem

DLP4500: Reflect the coherent light without shifting the phase

Liu Yang
Expert 8875 points
Part Number: DLP4500

Hi team,

We would like to reflect the coherent light in a collimated state (plane wave) in the DMD.
Because the mirrors are tilted as shown in the attached figure, the optical path difference occurs in front of and behind each mirror. In other words, I think the wavefront will shift.

optical distance.pdf

Is it possible for the DMD to reflect without shifting the phase?
I think if two DMDs are used directly, the optical path difference will be eliminated, is it possible?
If there is any good method, please teach.


Beat Regards,
Tom Liu

  • 0
    TI__Mastermind 23070 points

    Hello Tom,

    Welcome to DLP forum and thank you for your interest in DLP technology.

    You observation is correct and it will create diffraction. DMD modulates the light by tilting mirrors t to ON and OFF stage. The row of mirrors  will create diffraction grating for a coherent light. However, it diffraction efficiency ( loss of light due to diffraction) varies with wavelength. You may be able to  minimize this effects at blaze frequency.

    The shifting the phase can not be avoided. 

    "I think if two DMDs are used directly, the optical path difference will be eliminated, is it possible?"

    This is technically feasible.  However,alignment of two DMDs will be very challenging especially planarity alignment

    regards,

    VIvek.