Polarization Gratings

What is Polarization Grating?

A polarization grating (PG) is a “thin film prism” that combines the functions of a hyper efficient polarizer and a unique beam splitter into a thin film.

How It Works

PGs diffract incident light into two beams in the ± first orders (no higher order diffraction), with the output beams having opposite circular polarizations. The diffraction angle is determined by the design of the film. Polarized incident light diffracts completely into a single + or – order.

Line Art drawing of PG lens

Traditional Grating

  • 100-200um Thicknes
  • Multiple Orders
  • Limited to Narrow Spectrum

ImagineOptix PG

  • 2-4um Thickness
  • +/- 1st Order Only
  • Can be Tuned for Narrow or Broardband

Technical Details

Specifications

  • Efficiency:  Up to 99% diffraction efficiency (less than 1% leakage into the zero order), up to 95% transmittance
  • Typical Diffraction Angles: up to ±20˚ (higher angles possible for custom applications)
  • Typical Bandwidths (narrowband type): ±6% around 1550nm, 800nm, 633nm, 532nm, or 455nm; other wavelengths custom
  • Typical Bandwidths (broadband type): 450-650nm, 500-900nm, 1-4 µm; other wavelength ranges custom
  • Size: up to 120 x 120mm sq; round samples custom
  • Wavefront: lambda/5 typical, up to lambda/30 custom

Benefits

PGs have 99% diffraction efficiency in most cases, and propagate both polarizations in a “forward” direction, making them uniquely suited as polarization elements and beam splitting elements. Additionally, PGs combined with LC cells are ideal for polarization-based switching elements because they “re-direct” light into one of two directions depending on the polarization state of the incident light.

  • Additional Information

    We pioneered the defect-free PG starting in 2005 and we are the pioneer of broadband techniques through multiple twists. We use these principles to tailor nearly any achromatic and chromatic spectra and we enjoy the challenge of tailoring our technology to new applications. If you have a unique optical challenge that doesn’t exactly fit our typical specifications, we encourage you to contact us to explore what is possible.

    Polarization Gratings (PGs) are basis for IO technology platforms

    • Polarized diffraction
      • Right & left circular
      • +/- 1st orders only
    • Highly efficient
      • Low leakage: <1%
    • Tunable operation
      • Broadband
      • Narrowband
    • Wide Angle Version Available

    Features

    • Periodic Optical Axis formed in LCs
    • Affects the Geometric Phase
      (not conventional phase or Bragg)
    • Polarizing Beam Splitter
      (with excellent LCP/RCP)

    Theory Predictions, Exp. Confirmed

    • 100% single-order diffraction
    • Polarization-sensitive 1st orders
    • ~ 500 lines/mm and smaller (≥ 2 µm period)
    • Wide wavelength tuning (350 – 5000 nm)

    Best of “thick” and “thin” gratings.

     

    • 1st order efficiency ratio depends on circular polarizations
    • 0th order efficiency depends only on PG construction
    • Polarization of 1st order is always orthogonal to input circular
    • Dependent

     

     

     

     

     

     

     

     

    PG Efficiency w/Respect to Input Angle

    • Dependent on grating period and wavelength
    • Leakage increases with angle
    • Small grating periods have higher sensitivity
    • Large grating periods can be fairly insensitive
    • In general falloff of efficiency is relatively slow

     

     

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