Preparation and Spectrum Characterization of a High Quality Linear Variable Filter

Abstract

To meet the requirements for lightweight, miniaturized dispersive optical systems for space applications, linear variable filters with a high transmittance and spatial dispersion coefficient are proposed. The filters were produced with dual ion beam sputtering, where a single layer thickness variation was achieved with a deposition rate adjustment based on a linear variable correction formula. A linear variable trend matching method was used to correct the film thickness based on the reduction of the mismatch error between two materials: Ta2O5 and SiO2. The influence of the spectral and spatial measuring average effects was addressed by sampling the spot size optimization. This paper presents an all-dielectric linear variable filter that operates between 520 and 1000 nm, with an excellent linear dependence of 40 nm/mm over 12 mm. The linear variable filter possessed a 2.5% bandwidth, and its transmittance was found to be >80% at the central wavelength of the band, with a 0.1% transmittance in the cut-off region. These results indicate great potential for optical devices for space applications, and the developed process has good reproducibility and stability.

Simple but effective: strong efficiency boost for a linear variable filter-based spectrometer

“…To date, several types of LVF have been developed, including metal-dielectric 13 and all-dielectric structures. [14][15][16][17][18][19][20][21][22] The latter ones became more prevalent and are already commercially available, 16,17 with wavelength ranges covering, e.g., 320 to 560, 450 to 850, and 800 to 1100 nm, 16 or infrared (IR) regions, such as 0.9 to 1.70 or 2.5 to 5.0 μm. 17 Numerous applications and devices based on LVFs have been reported, such as gas 19 and liquid 20 measurements, thin-film measurements, 21 broadband spectrometers for current NASA space missions, 22 order sorting filters for commercial grating spectrometers, 24 multispectral and hyperspectral imaging, 25,26 commercially available LVF monochromators, 27 and hyperspectral video cameras.…”

“…Filter-based spectrometers can have an extremely compact and rigid design without any moving parts, consisting of only a filter array or longitudinally variable filter placed in front of a sensor array, for example, a chargecoupled device (CCD) or complementary metal-oxide-semiconductor, to capture a spectrum in one shot. A variety of spectral filters and structures, often micrometer-sized, have been developed, such as plasmonic color filters, 4,5 photonic crystal arrays, 6 single nanowires, 7 absorptive filter arrays composed of either conventional colloidal quantum dots 8 or perovskite quantum dots, 9 Fabry-Pérot (FP) filter arrays, [10][11][12] and linear (also called "continuously") variable filters [13][14][15][16][17][18][19][20][21][22] [linear variable filters (LVFs)]. An important benefit of such types of spectrometers compared to grating-based spectrometers is the possibility of detecting a broad spectral range with high spectral resolution despite their small size.…”

Synthesis of nanostructure Ta2O5 coatings using plasma reactive sputtering technique for optical filter application

“…"Where R is the reflectance, and can be expressed by the relation" [11]: R=1-A-T…..( 4 Because the wave goes through the medium, the termination coefficient is connected to the exponential rot of the wave [5]: "Kex=αλ/4π…….."( 5) "Where λ: is a wavelength of the incident radiation".…”

Tunable Perfect Narrow-Band Absorber Based on a Metal-Dielectric-Metal Structure

“…Compared to plasmonic structures, unpatterned thin films made up of one or more films of dielectric or metallic materials are widely used as color filters [34,35], antireflective coatings [36,37], and reflector mirrors [38,39]. Many traditional optical coatings rely on the Fabry-Perot interference effect to achieve a specific function.…”