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In this paper we present basic designs, operation concepts and some application examples of a novel microspectrometer for the spectral range of 3-5mum, which is based on a pyroelectric detector with an integrated micromachined Fabry-Perot filter (FPF). We discuss the influence of different optical setups on the spectral resolution and the signal-to...
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Citations
... Neumann et al. (2009) illustrate the cross section of the optical cavity. 40 The distance between the reflective surfaces can be modulated using control electrodes. This precise modulation of the cavity distance is achieved using the FPI Evaluation Workbench software suite, facilitating interferencebased wavelength selection. ...
An optical sensing approach that balances portability with cost efficiency has been designed for the reliable monitoring of fugitive methane (CH4) emissions. Employing a LiTaO3-based pyroelectric detector integrated with micro-electro-mechanical systems and a broad infrared source, the developed gas sensor adeptly measured CH4 concentrations with a low limit of detection of about 5.6 ppmv and showed rapid response times with t90 consistently under 3 s. Notably, the novelty of our method lies in its precise control and reduction of CH4 levels, enhanced by wavelet denoising. This technique, optimized through meticulous grid search, effectively mitigated noise interference noticeable at CH4 levels below 10 ppmv. Postdenoising, nonlinear regression analyses based on the modified Beer–Lambert equation returned R² values of 0.985 and 0.982 for the training and validation sets, respectively. In conclusion, this gas sensor has been shown to be able to meet the requirements for early warning of CH4 leakage on the surface in various carbon capture, utilization, and storage projects such as enhanced oil or gas recovery projects using CO2 injection.
... So far, the electrically tunable spectral filters based on the micro-electronic mechanical system Fabry-Perot (MEMS-FP) have already been designed and fabricated successfully. Their working wavelength already covers several typical regions such as the visible [5], near-infrared [6][7][8], mid-infrared [9,10], and far-infrared [11]. Generally, the key MEMS-FP microcavity is driven by static electricity to mechanically change the FP microcavity depth and thus achieve the spectral selection and adjustment. ...
An electrically tunable infrared (IR) filter based on a key cascaded liquid-crystal Fabry–Perot (C-LC-FP) working in the wavelength range of 3–5 μm is presented. The C-LC-FP is constructed by closely stacking two FP microcavities with different depths of 12 and 15 μm and fully filled by nematic LC materials. Through continuous wavelength selection of both microcavities, radiation with a high transmittance and narrow bandwidth can pass through the filter. According to the electrically controlled birefringence characteristics of nematic LC molecules, the transmission spectrum can be shifted through applying a dual voltage signal over the C-LC-FP. Compared with common LC-FPs with a single microcavity, the C-LC-FP demonstrates better transmittance peak morphology and spectral selection performance. To be more specific, the number and the shifted scope of the IR transmission peak can be decreased and widened, respectively.
... Meanwhile, with the development of Micro-Electro-Mechanical Systems (MEMS) and Micro-Opt-Electro-Mechanical Systems (MOEMS), the electrically tunable filter based on the structure of MEMS-FP has been utilized in spectral imaging application. The wavelength of the resonant peak, determined by the depth of the FP cavity, has already covered several typical regions such as visible [6], near-infrared [7,8], mid-infrared [9], and far-infrared [10]. Although the size of the device has been significantly reduced and the transmission spectrum can be adjusted electrically, the mechanical moving parts of MEMS-FP filter limit its reliability in some applications. ...
... Generally, the distance between the top and bottom mirror in the MEMS-FP can be varied and then maintained through electrostatic attraction. 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. ...
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.
An arrayed electrically tunable infrared (IR) filter based on the key structure of liquid crystal FabrÿCPerot (LC-FP) working in the wavelength range from 2.5 to 5 μm is designed and fabricated successfully. According to the electrically controlled birefringence characteristics of nematic LC molecules, the refractive index of LC materials filled into a prefabricated microcavity can be adjusted by the spatial electric field stimulated between the top and bottom aluminum (Al) electrodes. As a crucial component of the filter, the Al film with a typical thickness of ∼30 nm acts as the electrode as well as the reflective mirror. The particular functions, including key spectral selection and spectral adjustment, can be realized by the developed LC-FP filter driven electrically. Our experiments show that the maximum transmittance of the transmission peaks is ∼24%, and the transmission spectrum can be shifted remarkably through applying different voltage signals with a root mean square value range from 0 to ∼21.7 Vrms. The experimental results are consistent with the simulation according to the model constructed by us. As a 2 × 2 or four-channel IR filter, the top electrode of the device is composed of four same sub-electrodes. Each channel in the device is powered separately and synchronously to select desired transmission spectrum, which means that the device can be used to obtain spectral sub-images in different spectral bands in one shot.
This report presents recent advances in the design and fabrication of a tunable Fabry-Pérot interferometer (FPI) with subwavelength grating (SWG) reflectors, as well as measurement results and applications. The FPI is designed as wavelength selecting element for highly miniaturized mid-wave infrared spectrometers. The optical resonator of the FPI is built between two highly reflecting mirrors. The mirrors are integrated in a supporting MEMS structure with one electrostatically movable and one fixed mirror carrier. The FPI is fabricated in a bulk micromachining batch process on wafer level from two silicon substrates. The substrates are bonded together with an intermediate SU-8 layer. The reflectors are made of aluminum subwavelength gratings, structured on a thin LP-Si3N4 membrane by nanoimprint lithography. The subwavelength structures build a frequency selective surface with high reflectance and low absorbance in a defined spectral range. Simulations and optimization of the design were done using finite element method with a 3D EM frequency domain solver. Comparison of simulation results and measurements of fabricated reflectors and FPIs are in very good agreement. The FPIs are used in the 5th interference order and can be tuned from 3.5 μm to 2.9 μm electrically. The measured maximum transmittance is between 70 % and 50 % and the measured FWHM bandwidth is lower than 50 nm. The new subwavelength grating reflectors can be integrated in a MEMS batch process more cost-efficient than previously used reflectors of dielectric layer stacks.
A III-nitride based tunable hyperspectral detector pixel is described with the potential for real time detection in a wide range of wavelengths including near infrared (NIR). This detector has intrinsic hyperspectral pixels, each pixel being tunable in real time through a range of wavelengths determined by pixel design. This will eliminate the need for external gratings and filters, substantially decreasing weight, size, and complexity and increasing robustness. The single pixel detector discussed here offers the potential of wavelength spectroscopy from UV to NIR. To allow for dynamic tunability a multilayered AlxGa1-xN (0
We report on the recent progress made toward development of a III-nitride based tunable hyperspectral detector pixel with the potential advantages of reduced hardware complexity and increased dynamic control on the detection parameters in the context of existing hyperspectral detection systems. We discuss the concept, experiments, and simulation of devices along with the different obstacles to be overcome before this technology can mature into a commercial application. (C) 2011 American Institute of Physics. [doi:10.1063/1.3599878]
