Effect of dispersion on the wavelength dependence of cascaded liquid crystal devices

Abstract

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.