We have evaluated a new concept for a variable light valve and thermal insulation system based on nonimaging optics. The system incorporates compound parabolic concentrators and can readily be switched between an open highly light transmissive state and a closed highly thermally insulating state. This variable light valve makes the transition between high thermal insulation and efficient light transmittance practical and may be useful in plant growth environments to provide both adequate sunlight illumination and thermal insulation as needed. We have measured light transmittance values exceeding 80% for the light valve design and achieved thermal insulation values substantially exceeding those of traditional energy efficient windows. The light valve system presented in this paper represents a potential solution for greenhouse food production in locations where greenhouses are not feasible economically due to high heating cost.
Transparent electrically-conductive nanoporous thin films can be used as electrodes to attract dye ions from solution to
modulate the reflectance of a surface. Here we demonstrate that this technique can be used to create diffraction gratings
that can be modified by the application of a small electrical potential with a selected spatial distribution. Using
nanoporous ITO films fabricated by Glancing Angle Deposition, we have produced variable diffraction gratings,
fabricated by a variety of methods, including lithography combined with etching techniques or direct patterning using
focused ion beam etching. We demonstrate modulation of the diffraction pattern by employing electric force to attract
the dye ions into the nanoporous electrode, thereby introducing a substantial local change in the effective refractive
index value and thus altering the resultant diffraction pattern and, in some cases, yielding diffractive orders that lie
between those associated with the underlying grating. These new orders are easily distinguished and their intensity can
be substantially modified by controlling the applied voltage. Because this technique can work with very small pitch
gratings, this approach has the potential to enable new applications that may not be readily achieved using conventional
liquid crystal technology.
We present a novel method of modulating total internal reflection (TIR) from an optical surface using a solution of dye ions in combination with a nanostructured electrode. Previous work using the electrophoretic movement of pigment particles to modulate TIR was limited by agglomeration of the pigment over time. Dye ions do not suffer from this limitation, but because of their small size they have significantly smaller absorption cross-section per unit charge than pigment particles which are generally two orders of magnitude larger. This significantly limits the maximum absorption caused by electrostatic attraction of the ions to a transparent conductive electrode. This can be overcome by using a transparent conductive nanoporous thin film as the electrode in which the porosity increases the effective surface area, allowing more dye ions to move into the evanescent wave region near the nanoporous transparent electrode and thus substantially increases the amount of absorption. In this paper, we demonstrate the modulation of TIR by observing the time-dependent variation of the reflectance as the dye ions are moved into and out of the evanescent wave region. This approach may have applications in reflective displays and active diffractive devices.
High Dynamic Range displays offer higher brightness, higher contrast, better color reproduction and lower power
consumption compared to conventional displays available today. In addition to these benefits, it is possible to leverage
the unique design of HDR displays to overcome many of the calibration and lifetime degradation problems of liquid
crystal displays, especially those using light emitting diodes. This paper describes a combination of sensor mechanisms
and algorithms that reduce luminance and color variation for both HDR and conventional displays even with the use of
highly variable light elements.
This paper begins by "re-introducing" the phenomenon of total internal reflection and the associated critical angle,
including a careful discussion of the extent to which the "total" in TIR is truly total, and the "critical" in critical
angle is truly critical. Although in one sense these points are largely of theoretical interest, they also have an applied
aspect in relation to controlling TIR. From this perspective, two practical applications of TIR are discussed. The
first involves illuminating engineering applications with prism light guides, and the second concerns electronic
image displays employing frustrated TIR. In both cases the unique attributes of TIR play a key role in the efficiency
and practicality of these applications.