Optical Filters for Narrow Band Light Adaptation on Imaging Devices

The imagiology using Narrow Band Light (NBL) is widely employed in detection of mucosa's premature changes of gastrointestinal tract, while taking advantage of light spectral features by enhancing the vascular structures without the application of any type of dye. NBL uses two specific spectral bands centered in blue (415 nm) and green (540 nm). Despite their greater advantages, this technique is not available on intra-corporal imagiology devices yet. Thus, this paper presents a low-cost method to adapt such devices without the need to develop specific and expensive LEDs (Light-Emitting Diodes) centered at 415 nm and 540 nm. The method combines optical filters with commercial LEDs to provide transmitted light with the desired peaks at 415 nm and 540 nm. Two optical filters were designed and fabricated, using 7 thin-films layers of SiO ₂ and TiO ₂ deposited by RF sputtering. The measurements showed that the transmitted light through the filters presented relative transmittance peaks located at 414 nm and 542 nm wavelengths with relative transmittances of 31% and 62% and FWHM (Full-Width-Half-Maximum) of 17 nm and 29 nm, respectively. The measurements also showed significant relative transmittances located at NBL central wavelengths of 415 and 540 nm with 30% and 60%.