Comparison of Polarizer Technologies

The Moxtek® wire grid polarizer technology provides a consistent, highly durable solution to high quality LCoS display technology with a perfect polarization match to the LC imager. Latest improvements in the polarizing beam splitter (PBS) technology enable a 10% improvement in efficiency. This technical article offers a comparison between imaging needs and how Moxtek is improving its products. It explains how competing technologies in LCoS projectors compare in terms of brightness, performance, durability and reliability.

Efficiency (Tp*Rs) for a polarizing beamsplitter can be defined as the perfection with which a polarizer converts randomly polarized light into (reflected) s and (transmitted) p polarized light. In case all the light is converted, the beamsplitter will be 100% efficient. Actually, some light is absorbed, some s is transmitted and some ‘p’ is reflected, reducing the efficiency.

The Moxtek standard PBS is typically 81% efficient at 550nm wavelength. This efficiency has been dramatically improved with improved manufacturing techniques and new wire grid technology.

Figure 1 shows the improvement in efficiency for the Moxtek High Efficiency PBS (HEPBS) versus standard PBS. This represents a 10% improvement.

Beamsplitter Efficiency Comparison (Typical)

Figure 1. Beamsplitter Efficiency Comparison (Typical)

Comparison of Other Technologies

Table 1- “Comparison of Technologies”, shows a comparison of wire grid polarizer, stretched polymer absorbing films (dichroic polarizers), and Brewster’s angle polarizers (MacNeille cubes).

Table 1. Comparison of technologies

Element ProFlux Wire Grid Dichroic Polarizer MacNeille Polarizer
Polarizing Mechanism Polarizer using a nano-structured thin film Resonant absorption in thick stretched film Reflects s-polarization and transmits p-polarization
Significance A perfect polarization match to the LC imager, even skew rays can align to the LC. PBS: f/1.5 and below. PPL: f/1.0 and below. Thick polarizing film results in beam depolarization Polarization irection depends on incoming ray: skew rays are not aligned to LC
Contrast Excellent brightness, contrast, and on-screen uniformity Reduced contrast and uniformity Reduced contrast and uniformity
Durability Made from all inorganic materials for high durability Polymer film degrades over time and in high flux conditions Requires polymer waveplate for correct polarization

Flatter response of ProFlux polarizer across both wavelength and angle creates a more uniform picture from the projector. The wide acceptance angle enables small optical designs while maintaining color and contrast uniformity. Figure 2 shows an angular map comparison of the Proflux Beam Splitter and the MacNielle Cube.

Figure 2 shows the center of the circle is a 45° angle of incidence on the plate. The circle radius is 33°, representing behavior over an f/0.9 cone. The ProFlux beam splitter shows no TIR cutoff, and can be used at a much smaller than the MacNielle PBS, retaining high contrast.

Figure 3, “AOI Comparison for Proflux Wire Grid and Dichroic Polarizers”, shows how the flat response of ProFlux for rotation in both axes is an indication of its superior performance with skew ray polarization. Dichroic sheet depolarization reduces the ability to maintain high polarization contrast in optical systems.

Angular Map Comparison

Figure 2. Angular Map Comparison

AOI Comparison for ProFlux Wire Grid and Dichroic Polarizers

Figure 3. AOI Comparison for ProFlux Wire Grid and Dichroic Polarizers

Conclusion

A significant benefit of the ProFlux PBS over a MacNeille cube is the direction of polarization. A cube polarizes in a direction defined by the orientation of the incoming ray, that is, by the plane of incidence. Since the plane of incidence changes as the skew ray direction changes, uniform polarization over a large cone is impossible for a standalone cube PBS.

ProFlux PBS, on the other hand, polarizes relative to the direction of the wire grid structure. Rays along the principal axis, as well as skew rays, are all polarized in the same direction. This is called a Cartesian polarizer and is a critical quality for good PBS polarization. Using ProFlux PBS polarizers creates improved full screen performance by providing uniform polarization brightness and contrast across the entire angular aperture at the PBS. The ProFlux PBS is available as HEPBS, providing a 10% improvement in efficiency.

This information has been sourced, reviewed and adapted from materials provided by Moxtek, Inc.

For more information on this source, please visit Moxtek, Inc.

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