This article describes the fabrication of MgF₂ and MgO thin-film-based optical filters and compares the optical transmission of the filters over UV. The MgF₂ thin-films were deposited by use of an e-beam technique and their optical properties were characterised by ellipsometry. The effect of substrate temperature on the optical properties was studied. The MgF₂ optimum refractive indices were obtained with a substrate temperature between 200 °C and 300 °C. Optical simulations were performed to compare the performance of MgF₂ and MgO in the fabrication of near-UV narrow bandpass optical filters. While MgO-based optical filters result in a higher transmittance peak intensity, especially at 350 nm, the MgF₂ optical filters are narrower, present lower values of FWHM, a mean value of 20 nm. This feature could be especially relevant for specific applications on fluorescent optical sensors. Finally, a Fabry-Perot based on a MgF₂/TiO₂ optical filter was deposited, using an e-beam technique for the MgF₂ thin-films and RF-sputtering technique for the TiO₂ thin-films. The MgF₂/TiO₂ optical filter peak transmittance is approximately 70% close to 400 nm, as expected. The results are discussed with focus on applications in fluorescent optical sensors for peaks at 350, 370, 380 and 400 nm, respectively.

Minimally invasive medical devices can greatly benefit from Narrow Band Imaging (NBI) diagnostic capabilities, as different wavelengths allow penetration of distinct layers of the gastrointestinal tract mucosa, improving diagnostic accuracy and targeting different pathologies. An important performance parameter is the light intensity at a given power consumption of the medical device. A method to increase the illumination intensity in the NBI diagnostic technique was developed and applied to minimally invasive medical devices (e.g., endoscopic capsules), without increasing the size and power consumption of such instruments. Endoscopic capsules are generally equipped with light-emitting diodes (LEDs) operating in the RGB (red, green, and blue) visible light spectrum. A polydimethylsiloxane (PDMS) µ-lens was designed for a maximum light intensity at the target area of interest when placed on top of the LEDs. The PDMS µ-lens was fabricated using a low-cost hanging droplet method. Experiments reveal an increased illumination intensity by a factor of 1.21 for both the blue and green LEDs and 1.18 for the red LED. These promising results can increase the resolution of NBI in endoscopic capsules, which can contribute to early gastric lesions diagnosis.