Comparison of variable birefringence devices and Fabry-Perotetalons for use as tunable filters

A comparison is made of three device configurations which can be used as tunable filters: a Fabry-Perot etalon used in transmission (FPT), a Fabry-Perot etalon used in reflection (FPR), and a variable birefringence filter used in transmission (VBF). Initial conditions are defined for the achievement of a contrast ratio of 100:1, and the implications of these results on material choice discussed. The effect of nonuniform device thickness on contrast ratio is analyzed for all three cases. Analytic expressions are derived which predict the behavior of the contrast ratio under differing device conditions and which give rule-of-thumb values for the maximum acceptable thickness variation for a given contrast ratio. Using these expressions it is shown that the configuration least sensitive to variations in thickness is the VBF, with the FPT coming second and the FPR last. Experimental studies were carried out on three devices-a piezoelectric tunable air-spaced Fabry-Perot etalon, an electrooptically tunable liquid-crystal Fabry-Perot etalon, and an electrooptically tunable liquid-crystal variable birefringence filter     

High-performance tunable filter

The tuning performance of a liquid-crystal, electro-optically tunable, Lyot filter is described. This filter is widely tunable across the visible region up to a wavelength of approximately 630 nm and has very high performance characteristics that are preserved over the entire tuning range. These include a narrow passband of 0.1 nm, a large-aperture performance of at least 30 mm, a wide field of view of ?8.5 degrees , and the ability to be tuned to an accuracy that is one tenth of the linewidth of the passband. Possible applications for such a filter include remote sensing, multispectral sensing, and laser environmental and underwater monitoring.     

Wavelength Dependence of Optical Bistability in Molecular-beam-deposited ZnSe Interference Filters

Abstract

Complete ZnSe interference filters exhibiting optical bistability have been fabricated using ultrahigh-vacuum molecular-beam techniques. The wavelength dependence of the critical switching power was measured at five wavelengths between 521 and 676 nm for a filter with two-period ZnSe/BaF₂ multilayer reflectors and an initial assessment has been made of their long-term operational stability.     

A double-element broad-band liquid crystal tunable filter-factorsaffecting contrast ratio

A double-element broad-band liquid crystal tunable filter consisting of a high-order quartz wave plate in series with a very-low-order electrooptically tunable liquid crystal phase plate and placed between crossed polarizers is described. A possible application for such a device is protection against intrusive laser radiation. The advantage of this double-element filter over a single-element low-order LC filter is that it increases the wavelength resolution of the device, which, when operated in the protect mode, allows continued sensing of the scene. Experimental and theoretical studies were made of the contrast ratios obtainable with such a filter