Mid-wavelength infrared (MWIR) filters are optical components that select a narrow wavelength region of a much broader light spectrum. They can be integrated in systems devoted to a great number of applications and areas, which include, thermal monitoring, gas sensing, aerospacial or medical, among others.
The conventional way of manufacturing MWIR filters is by multilayer deposition, either by evaporation or by sputtering. The resulting filters are one-dimensional structures consisting of a stack of layers of different materials that, by constructive and destructive interferences, block most of the infrared spectrum while allowing the transmission of a narrow band of it.
In contrast to this, Mapsi Photonics manufactures all-silicon filters which, in addition to being suitable for conventional applications, are particularly interesting in harsh environments, such as those involving high temperatures and/or high pressures. Moreover, the fact that we use only silicon, which is transparent from 1 µm to 10 µm, approximately, allows us to have very good optical specifications (see Fig.1-left) and, at the same time, to maintain highly competitive prices throughout the MWIR.
Mapsi filters have proven to be suitable for the selective detection of gases whose spectra are close together or partialy overlapping. For instance, the filter depicted in figure 1-right is narrow enough to fit in the P-branch of CO thus, avoiding cross detection with N2O. Other examples are found in the discrimination between CO2 and N2O, which is especially interesting in medical applications, and in NO2 and water vapor, which is important in the monitoring of polluting gases in industrial processes.
| Gas | Bandwidth |
|---|---|
| Methane/ethanol @ 3.5 µm | 55 ± 15 nm |
| SWIR @ 3.9 µm | 55 ± 15 nm |
| Formaldehyde @ 3.6 µm | 55 ± 15 nm |
| CO2 @ 4.3 µm | 45 ± 15 nm |
| CO @ 4.7 µm | 45 ± 10 nm |
| NO @ 5.3 µm | 65 ± 20 nm |
| FIR @ 10.0 µm | 150 ± 30 nm |
| CO2 @ 10.6 µm | 150 ± 30 nm |
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