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TIDA-00554: Extending bandwidth to cover up to 2250 nm

Michael Barger
Prodigy 70 points
Part Number: TIDA-00554
Other Parts Discussed in Thread: DLP2010NIR, DLP4500NIR

Has anyone looked into how challenging it would be to modify this spectrometer design to cover wavelengths up to 2250 nm? Of course, modification to the optics and software will be needed, but are there any deal-breakers that I should look out for?

Thanks!

  • 0
    TI__Mastermind 20045 points

    Hello Michael,

    Please allow us to look into this and we'll get back to you next week. Sorry for the delay.

    Thanks,

    Kyle

  • 0 in reply to Kyle Rakos
    Prodigy 70 points

    No problem, Kyle. I'm looking forward to hearing back from you!

  • 0
    TI__Intellectual 1375 points

    Hi Michael,

    It is possible. Both the DLP2010NIR and DLP4500NIR DMDs are compatible with wavelengths from 700-2500nm. The software for NIRscan Nano was actually designed with this flexibility in mind, so there should not be a huge amount of software work. Most of the effort would be in the optics and mechanics:

    • An extended InGaAs detector would be needed vs the standard InGaAs detector that is used in the NIRscan Nano reference design. If selecting a cooled detector, a TEC driver would need to be provided.
    • A completely different optical design would be needed. If using lenses instead of mirror optics, a different lens material would be needed compared with the material used in the lenses in NIRscan Nano. See for reference the lens material used in the NIRscan reference design: http://www.ti.com/tool/TIDA-00155
    • Because of the different optics design, grating angles, etc, a completely new mechanics design would also be required to hold the optics.
    • The Analog front end would likely need modification since the output of the detector would change.

    During the optical design phase, there are many tradeoffs to take into account to balance wavelength resolution, signal throughput (which affects SNR), and cost.

  • 0 in reply to Eric Pruett
    TI__Intellectual 1375 points

    Also, I should mention that in dispersive optics designs there are additional challenges when a design requires imaging wavelengths from a span greater than one octave (1125-2250nm would be one octave, 900nm-2250nm would be greater than one octave). So depending on your desired wavelength range, that could drive the complexity of the optics design.

  • 0 in reply to Eric Pruett
    Prodigy 70 points

    Eric,

    All of what you've written here matches my own analysis, so thank you for corroborating everything.

    For this design, TI used several custom optics: for example, those from Optimax. Are those proprietary to TI, or does TI write releases so that others can purchase those same lenses directly?

    Lastly, on the issue of aliasing from 2nd-order diffraction (what I believe you're referring to regarding spans greater than an octave), is it fair to say that there is no way to prevent that issue once the light has hit the diffraction grating? (For example, in order to provide for 750-1125 nm in addition to 1125-2250 nm, those should be two separate, filtered light paths with separate diffraction gratings.)

    Michael Barger

  • 0 in reply to Michael Barger
    TI__Genius 10925 points

    Hi Michael, 

    Kindly wait for few more days, we will look into this and get back ASAP!

    Thanks & Regards,

    Hirak.

  • 0 in reply to Hirak Biswas
    Prodigy 70 points

    No problem, Hirak. Thanks for the update!

  • 0 in reply to Michael Barger
    TI__Mastermind 22830 points

    Hi Michael,

    The Zmax files for the optical components are published in the reference design.Please feel free to use them.

    you wrote -

    Lastly, on the issue of aliasing from 2nd-order diffraction (what I believe you're referring to regarding spans greater than an octave), is it fair to say that there is no way to prevent that issue once the light has hit the diffraction grating? (For example, in order to provide for 750-1125 nm in addition to 1125-2250 nm, those should be two separate, filtered light paths with separate diffraction gratings.)

    Your understanding is correct , you can can prevent it once it hits the diffraction grating. You could use either a two separate light  paths or time multiplex by using a switching filter. Switching filter may help in lower cost.

    regards,

    Vivek