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DLP4710: TIR/RTIR Design Method

Wei Quan Chiang
Prodigy 70 points
Part Number: DLP4710

Hello Sirs,

I would like understand how to design a TIR/RTIR for this DLP4710.

1. What is the pros and cons between TIR/RTIR?

2. How to decide the angle of the prism? Is there any specific angle needed to hit at DMD?

3. How to calculate the distance between DMD and TIR/RTIR?

4. How to calculate the distance between TIR/RTIR and the projector lens?

Thank you.

  • 0
    TI__Mastermind 22830 points

    Hello Wei,

    Please review the following post. It will answer your first question. Meanwhile, I will with my colleague and get response to your other questions. 

    https://e2e.ti.com/support/dlp/f/94/p/900052/3334727

    However, we may be limited in scope of answering your question. Most of the these information are available in the optical text books.

  • 0 in reply to Vivek Thakur
    Prodigy 70 points

    Vivek Thakur said:

    Meanwhile, I will with my colleague and get response to your other questions. 

    Sure, thanks in advance.

  • 0 in reply to Wei Quan Chiang
    TI__Mastermind 22830 points

    Hello Wei,

    Thank you for  your patience. I  will need some more time to get back to you.

    regards,

    Vivek

  • 0 in reply to Vivek Thakur
    TI__Mastermind 22830 points

    Hello Wei,

    Thank you for your patience. Please find the response to your questions:

    1. What is the pros and cons between TIR/RTIR?

      The attached PDF file has detailed comparison - TIR-RTIR.pdf

    2. How to decide the angle of the prism? Is there any specific angle needed to hit at DMD?

    The angle at the DMD is the illumination angle, which is usually two times the mirror tilt angle so that the on-state rays leave perpendicular to the array and to prevent flat state light from getting into the image. The angle of the prism is determined by the index of the material and the critical angle. For RTIR, the angle is always a 90 degree prism for the outgoing path because the path-in-glass has to be constant across the field of the array for the projection lens, or there will be tilt errors like astigmatism and keystone distortion.

    3. How to calculate the distance between DMD and TIR/RTIR?

    It is not a firm number. Most users like to minimize this gap space to 1 or 2 mm, sometimes more depending on how much mechanical space is needed in front of the DMD to mount it. The desire to minimize it comes from minimizing the back working distance (BWD) to the projection lens, which influences the size of the lens and thus the cost.

    4. How to calculate the distance between TIR/RTIR and the projector lens?

    There is no firm calculation. It depends on how much lens shift is going to be used, if any, and the clearance of the lens barrel with the wedge prism (for a TIR prism). For RTIR, it also depends on mechanical clearances mostly with the DMD package and connections. In both cases, if XPR actuator is to be used, there will be some space required between the lens and the prism to mount that.

    Hope this answers your questions.

    regards,

    Vivek

  • 0 in reply to Vivek Thakur
    Prodigy 70 points

    Hello Vivek,

    Answers provided above are quite straight forward and clear.

    Sincerely thanks for your time and help!