As the phenomenon "color" is involved in almost each production where is a great demand for inexpensive and precise colorimeters. Today there are in principle two kinds of colorimeters: three-channel colorimeters (which are cheap but not accurate) and array spectrometers (which offer a high accuracy at a high price). Liquid crystals have the potential to allow accurate color measurements at a low price. We show three different schemes of colorimeters and actual measurements. The accuracy of our colorimeters is better than 0.005 for each color coordinate.
Multiple pass liquid crystal devices have potential applications as wavelength selective elements for both illumination and measurement systems, the peak in the wavelength transmission of a single birefringence device when repeatedly applied gives a narrow peak in transmission. Most liquid crystal display devices are optimized for operation at 550 nm where the effects of dispersion are of secondary importance, however in applications using multiple devices to create a tuneable filter the effects of dispersion are particularly significant. Typically birefringence data is only available at a specific wavelength or at a specific temperature, this is especially true of commercial liquid crystal that are characterized for 550 nm device operation. To allow computation of both temperature and wavelength dependence the variation of liquid crystal refractive indices over a two dimensional temperature -- wavelength plane has been extrapolated from single wavelength or single temperature data. The effect of this variation in the birefringence of the liquid crystal material in possible filter configurations to determine the wavelength dependence has been evaluated. Though reducing the effective operating range of a given device design a useful tuneable filter function is still achieved. To achieve the same tuning range as would be predicted without the effects of dispersion a more complex stack of devices is required.
Liquid Crystal Filled Polymer Structure (LiCFiPS) Devices consist of a polymer structure, which performs the desired spatial phase modulation of the incident light, filled with lqiuid crystal to permit modulation of this optical function. Potentially fabrication of this type of device, by established polymer hot rolling or embossing techniques, may be carried out at very low cost. Devices incorporating a complex polymer structure will inevitably have liquid crystal aligned at varying orientations to the surface. Switchable gratings with the liquid crystal aligned in the plane of the grating but either parallel or perpendicular to the grating rulings have been investigated as the two extremes of alignment. Good results have been achieved for parallel aligned devices, however devices with the liquid crystal aligned perpendicular to the grating lines show defects and inhomogeneities. Computational models of these devices show features that correspond well with the observed switching characteristics and have been used to explore routes to the design of improved devices. While such devices might not offer the ultimate versatility of matrix addressed SLM devices they do offer switchable optical devices at very low cost.
Liquid crystal filled polymer structures provide switchable optical devices at low cost and with low driving voltages. One such device is a switchable optical grating, current models of these do not fully explain the effects seen within the devices that have been constructed. A new modeling technique has been implemented to better understand these. A comparison of the use of the Oseen-Frank and Landau-De Gennes free energy equations is given. Data from an experimental device is compared to that from simulation and it is shown that the simulation provides both similar results and an aid to understanding the real device.
Films of Poly-Tetra-Fluoro-Ethylene (PTFE) have been shown to be very effective alignment agents for liquid crystal materials. Such films may be deposited in a one step dry process offering advantages in terms of both time and simplicity over deposition of polyimide or SiO<SUB>2</SUB> alignment layers. This is most appropriate for applications where a test device is required as part of a rapid prototype for ergonomic and similar testing. Earlier work has identified suitable deposition parameters (temperature, surface pressure, velocity) for production of PTFE films but with single films there is still typically some variation in the alignment due to the machined surface of the PTFE bar itself. In this work multiple film deposition using a 'step and repeat' has been investigated as means of achieving improved alignment uniformity and has been found effective in test devices of several cm<SUP>2</SUP>. Electro-Optic measurements on a multiple pixel test device show little spatial variation in the threshold voltage illustrating the possibility of matrix addressing a PTFE aligned prototype device. In conclusion PTFE films offer a very rapid method of producing alignment layers for devices having reproducible and uniform electro-optic characteristics.