Arrays of narrow bandpass filters fabricated by combinatorial etching technique

The basic mechanism and fabrication processes of the combinatorial etching technique have been introduced. It is a high-efficiency technique for the integration of narrow bandpass filters (NBPFs). A filter array integrated with 2^N NBPFs can be fabricated with only N times of etching processes, and the technique can be applied in different wavelength regions. The experimental results of the array integrated with 32 filters in the visible-NIR and the array integrated with 16 filters in the MIR have been demonstrated. The pass-bands of the former NBPFs distribute linearly in the range of 774.7-814.2 nm. All the filters' full widths at half maximum (FWHM) are very narrow and less than 1.5 nm, corresponding to δλ/λ of each filter less than 0.2%. The narrowest FWHM of the integrated filters comes to 0.8 nm with δλ/λ of 0.1% at the wavelength of 794.3 nm. The transmittances of the pass-bands are between 21.2% and 32.4%. Most of them are near 30%.