Widely tunable Fabry-Perot filter based MWIR and LWIR microspectrometers

Ebermann, Martin; Neumann, Norbert; Hiller, Karla; Gittler, Elvira; Meinig, Marco; Kurth, Steffen

doi:10.1117/12.919169

Cited by 15 publications

(6 citation statements)

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“…It is reported that the IR filtering based on the MEMS-FP have been developed successfully, and the working wavelength already covers a relatively wide range including near-IR [4][5][6], mid-IR [7,8], and far-IR [9]. The main features of the MEMS-FP device are that one of the mirrors must be moved so as to change the optical path of interference beams traveling in the FP cavity and, thus, the filling factor is very low and generally less than 0.6.…”

Section: Introductionmentioning

confidence: 99%

Electrically tunable infrared filter based on the liquid crystal Fabry–Perot structure for spectral imaging detection

Zhang¹,

Muhammmad

Luo³

et al. 2014

Appl. Opt.

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An electrically tunable infrared (IR) filter based on the liquid crystal (LC) Fabry-Perot (FP) key structure, which works in the wavelength range from 5.5 to 12 μm, is designed and fabricated successfully. Both planar reflective mirrors with a very high reflectivity of ∼95%, which are shaped by depositing a layer of aluminum (Al) film over one side of a double-sided polished zinc selenide wafer, are coupled into a dual-mirror FP cavity. The LC materials are filled into the FP cavity with a thickness of ∼7.5 μm for constructing the LC-FP filter, which is a typical type of sandwich architecture. The top and bottom mirrors of the FP cavity are further coated by an alignment layer with a thickness of ∼100 nm over Al film. The formed alignment layer is rubbed strongly to shape relatively deep V-grooves to anchor LC molecules effectively. Common optical tests show some particular properties; for instance, the existing three transmission peaks in the measured wavelength range, the minimum full width at half-maximum being ∼120 nm, and the maximum adjustment extent of the imaging wavelength being ∼500 nm through applying the voltage driving signal with a root mean square (RMS) value ranging from 0 to ∼19.8 V. The experiment results are consistent with the simulation, according to our model setup. The spectral images obtained in the long-wavelength IR range, through the LC-FP device driven by the voltage signal with a different RMS value, demonstrates the prospect of the realization of smart spectral imaging and further integrating the LC-FP filter with IR focal plane arrays. The developed LC-FP filters show some advantages, such as electrically tunable imaging wavelength, very high structural and photoelectronic response stability, small size and low power consumption, and a very high filling factor of more than 95% compared with common MEMS-FP spectral imaging approaches.

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Section: Introductionmentioning

confidence: 99%

Electrically tunable infrared filter based on the liquid crystal Fabry–Perot structure for spectral imaging detection

Zhang¹,

Muhammmad

Luo³

et al. 2014

Appl. Opt.

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“…Tuning is accomplished by actuating the movable plate via voltage or piezoelectrically, thereby modulating the cavity gap. 4,5 These filters have demonstrated quality factors of 40 -100 with a wide tuning range throughout both midwave and longwave IR spectrum. However, tuning speeds are limited to tens of Hz.…”

Section: Introductionmentioning

confidence: 99%

Fast, electrically tunable filters for hyperspectral imaging

et al. 2014

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Tunable, narrow-wavelength spectral filters with a ms response in the mid-wave/long-wave infrared (MW/LWIR) are an enabling technology for hyperspectral imaging systems. Few commercial off-the-shelf (COTS) components for this application exist, including filter wheels, movable gratings, and Fabry-Perot (FP) etalon-based devices. These devices can be bulky, fragile and often do not have the required response speed.Here, we present a fundamentally different approach for tunable reflective IR filters, based on coupling subwavelength plasmonic antenna arrays with liquid crystals (LCs). Our device operates in reflective mode and derives its narrow bandwidth from diffractive coupling of individual antenna elements. The wavelength tunability of the device arises from electrically-induced re-orientation of the LC material in intimate contact with antenna array. This re-orientation, in turn, induces a change in the local dielectric environment of the antenna array, leading to a wavelength shift.We will first present results of full-field optimization of micron-size antenna geometries to account for complex 3D LC anisotropy. We have fabricated these antenna arrays on IR-transparent CaF 2 substrates utilizing electron beam lithography, and have demonstrated tunability using 5CB, a commercially available LC. However, the design can be extended to high-birefringence liquid crystals for an increased tuning range. Our initial results demonstrate >60% peak reflectance in the 4-6 µm wavelength range with a tunability of 0.2 µm with re-orientation of the surface alignment layers. Preliminary electrical switching has been demonstrated and is being optimized.

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“…Spectrometers [1][2][3][4][5][6][7] in the mid-wave infrared (MWIR: 3 to 5 μm) and long-wave infrared (LWIR: 8 to 12 μm) wavelength ranges are of interest for infrared (IR) spectroscopy, [8][9][10][11] multi/hyper-spectral imaging, [12][13][14][15][16] and compositional analysis 11,17 due to their inherent ability to identify the unique absorption and/or reflected spectra of elements and compounds. Multi/hyper-spectral imaging is commonly differentiated based on the number of spectral channels, where hyperspectral imaging systems generally collect more than 100 adjoining spectral bands and multispectral imaging systems typically acquire <20 non-adjoining spectral bands, 12,16,18,19 even though there is no agreement on precise values.…”

Section: Introductionmentioning

confidence: 99%

Ge/BaF2 thin-films for surface micromachined mid-wave and long-wave infrared reflectors

Gill

Tripathi

Keating

et al. 2022

J. Optical Microsystems

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High performance distributed Bragg reflectors (DBRs) are key elements to achieving high finesse MEMS-based Fabry-Pérot interferometers (FPIs). Suitable mechanical parameters combined with high contrast between the refractive indices of the constituent optical materials are the main requirements. In this paper, Germanium (Ge) and barium fluoride (BaF 2 ) optical thin-films have been investigated for mid-wave infrared (MWIR) and long-wave infrared (LWIR) filter applications. Thin-film deposition and fabrication processes were optimised to achieve mechanical and optical properties that provide flat suspended structures with uniform thickness and maximum reflectivity. Ge-BaF 2 -Ge 3-layer solid-material DBRs have been fabricated that matched the predicted simulation performance, although a degradation in performance was observed for wavelengths beyond 10 μm that is associated with optical absorption in the BaF 2 material. Ge-Air-Ge 3-layer air-gap DBRs, in which air rather than BaF 2 served as the low refractive index layer, were realized to exhibit layer flatness at the level of 10 to 20 nm across lateral DBR dimensions of several hundred micrometers. Measured DBR reflectance was found to be ≳90% over the entire wavelength range of the MWIR band and for the LWIR band up to a wavelength of 11 μm. Simulations based on the measured DBR reflectance indicates that MEMS-based FPIs are able to achieve a peak transmission of ≳90% over the entire MWIR band and up to 10 μm in the LWIR band, with a corresponding spectral passband of ≲50 nm in the MWIR and <80 nm in the LWIR.

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Widely tunable Fabry-Perot filter based MWIR and LWIR microspectrometers

Cited by 15 publications

References 0 publications

Electrically tunable infrared filter based on the liquid crystal Fabry–Perot structure for spectral imaging detection

Electrically tunable infrared filter based on the liquid crystal Fabry–Perot structure for spectral imaging detection

Fast, electrically tunable filters for hyperspectral imaging

Ge/BaF2 thin-films for surface micromachined mid-wave and long-wave infrared reflectors

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