Tunable Fabry-Perot filter

Figure 16.23 (a) Quasi-static strain measured with the tunable Fabry—Perot filter (TFPF)-demodulated FBG sensor signal (b) strain wave signals measured with the Mach-Zehnder interferometer (MZI)-demodulated FBG sensor compared with that measured by the PZT sensor [47]. 

Ebermann, M., et al., 2012. Widely tunable Fabry-Perot filter based MWIR and LWIR microspectrometers. In Proc. SPIE 8374. Next-Generation Spectroscopic Technologies V,... 

Receiving equipment for aircraft astrophysical investigations in the far infrared has been developed and flown in 1974-1975 on board the AN-30 aircraft. Four types of infrared and submillimeter detectors mainly of photoresistor type are used in the wavelength region from 10 mkm to 1 mm. Thermal background at the detectors is limited by cooled bandpass filters and by optimal matching of the detectors with the telescope optics. The spectral filters used are combinations of quasiresonance metal mesh filters of different structure and Q-factor from 2 to 7 with the Yamada cut-off powder filters. A tunable Fabry-Perot interferometer, a polarimeter for linear polarization measurements and an aircraft 25 cm-telescope are briefly described. 

Lay out a tunable Fabry-Perot optical filter in a multiproject wafer process as shown in Figure 4.24. The top Bragg mirror should be composed of a stack of dielectric films and should be flat to within a fraction of a wavelength of light that will be filtered. 

Tunable filters in the form of AOTF devices, liquid crystal tunable filter (LCTF) and also tunable cavity Fabry-Perot etalon (FPE) devices have been considered in non-moving part instrument designs for many years. Today, the AOTF and the LCTF devices are used in the NIR spectral region.9,10 Originally, designs were also proposed for mid-IR AOTF devices, but these have not become available, mainly because of fabrication issues (cost and material purity). Tunable FPE devices, which are really just variable cavity interference filters, have been developed for the telecommunications industry. While these have been primarily used in the NIR, in most cases they can be fabricated to work also in the mid-IR, the latter being only an issue of material/substrate selection. 

Interference filters are used in photometers and spectrometers as fixed wavelength or tunable wavelength filters. An interference filter, equivalent to a Fabry-Perot etalon. 

Fabry-Perot tunable filter driven by piezo actuator... 

D. Bonaccini, L. Casini, P. Stefanini. Fabry-Perot tunable filter for the visible and near IR using nematic liquid crystals. In Current Developments in Optical Engineering IV, Robert E. Fischer and Warren J. Smith, eds. SPIE—The International Society for Optical Engineering, San Diego, CA, 1990, 1334 221-230. 

Fabry-Perot etalon devices based on materials sensitive to electric fields have been studied as tuneable optical filters. Gan et al. [165] presented in their work a hybrid organic/inorganic sol-gel material based on 3-methacryloxypropyl trimethoxysilane as precursor and TCBD (15% mol) as NLO chromophore that was covalently incorporated into the silica network. They demonstrated an optical filter having large tunability and high finesse. The EO sol-gel film was corona poled with 5 kV/cm at 170°C for 30 min. 

Fabry-Perot Liquid-Crystal Tunable Filter... 

There are two types of spectrometers using optical filters. The first type is equipped with a number of optical filters transmitting NIR light of different wavelengths, which are used sequentially to transmit spectroscopic data. The other type applies wavelength-tunable Alters such as a liquid crystal tunable filter (LCTF) or a Fabry-Perot interferometer. 

The distance between the mirrors can be adjusted with a MEMS actuator to enable a tunable interferometer. When the distance between the mirrors is adjusted to 2/2, the light passes through the interferometer while light with other wavelengths is blocked. The Fabry-Perot interferometer acts as a narrow bandpass filter for light, with the bandpass is dependent on the finesse of the optical cavity. 

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