Resonant element reflect6/10/2023 ![]() We begin this chapter by summarizing the physical basis for this class of tunable filters. In short, we employ a resonant waveguide grating supporting leaky modes that is tuned by micro-electro-mechanical (MEMS) means. In the present contribution, we introduce a new tunable filter concept for potential application in multispectral and hyperspectral imaging systems. The former is based on stacks of birefringent liquid-crystal plates integrated with polarizers, whereas the latter is diffractive in nature. Among these, tunable liquid-crystal and acousto-optical filters represent two prominent device classes ( Gat, 2000 Vo-Dinh et al., 2004). Gat lists principal attributes of ideal tunable filters and describes examples of filters employed to date ( Gat, 2000). The capability of the tunable filters central to these spectral imaging methods defines the quality of the data sets collected. Its application to real-time guidance in surgery is promising ( Vo-Dinh et al., 2004). In medicine, hyperspectral in-vivo diagnostics of tissue may avoid excision and permit in situ analysis ( Vo-Dinh et al., 2004). Examples include spatio-spectral diagnostics in agricultural crop management, true-color night vision, forensics, and archaeology and art ( Gat, 2000). Each of these methods is connected with a plethora of useful applications. Thus, in multispectral imaging, relatively few wavelengths are used to carry the spatial information, whereas in hyperspectral imaging, the number of wavelength channels may reach ~100 ( Vo-Dinh et al., 2004). Hyperspectral imaging is a similar concept principally differentiated from multispectral imaging in that many more wavelengths and narrower spectral passbands are employed. Under time-varying conditions, the data cube would be multidimensional in (x, y, λ, t) space. The resulting spectral image cubes contain intensity and wavelength (λ) data at each pixel in the 2D image ( Gat, 2000). By using rapidly tunable filters and two-dimensional (2D) image planes such as those provided by charge-coupled device (CCD) detectors, data sets containing spatial (x, y) and spectral information are acquired. Multispectral imaging refers to a combination of spectroscopy and photography.
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