ILCC 2008 - Photonics and Display applications (APP)
Polarization-Independent Liquid Crystal Microdisplays Using LC Polarization Gratings: A Viable Solution
Liquid Crystal (LC) Polarization Gratings (PGs) are one of the most viable means of achieving real polarization independent modulation, which benefits from the unique feature of these thin diffraction gratings including polarization independent zero-order diffraction and coupling only between zero- and first-orders with nearly 100% efficiency. Our early attempts to exploit these properties with transmissive substrates led to the first successful experimental realization of LCPGs with low scattering and >95% hologram efficiency. A proper choice of photo-alignment and LC materials was the principal reason for this initial success. Further, a general relationship of the material and grating parameters was derived using elastic continuum principles, which was in agreement with experiment. Moreover we found that these properties can be electrically modulated with contrasts approaching 150:1 over the entire visible range, with switching times of several ms.
More recently, we have advanced significantly by fabricating high quality LCPGs on reflective substrates (both aluminum mirrors and 256x256 pixel silicon backplane). We have developed a prototype projector, matching the microdisplay with an LED light source in a field-sequential-color configuration. Because the LC thickness in the reflective-mode is half of the transmissive-mode, we have succeeded in using LC materials with birefringence of ~0.14 to obtain sub-millisecond total switching times. On the theoretical side, an extended Jones Matrix method now allows us to describe the optical properties at oblique incidence angles, which can be related to experimentally measured data. Our best LCPGs can diffract light with separation > 15 degrees, and electrically switch the energy in the first orders with contrasts in excess of 1000:1. We have recently quantified the dependence of this electrical contrast in terms of other material parameters, and are currently attempting to increase this threshold even further. Here we identify the key innovations in our processing and elaborate on all the above-mentioned results.
RKK, COH, MJE
[MJE] My comments are integrated above. In addition, I have the following questions:
- Where did you get the "10 times faster" number? It sounds wrong to me...
- Also, where did you get the 400:1 number "over the entire visible range"? It was never more than 150:1 in LEDs.