Fabrication of Graphene Optical Devices for Endoscope Calibration

Abstract

Endoscopic devices used in the clinical examination of pathologies such as glottic tumors can record real-time images of the vocal cords during vibration. Quantitative analysis of the glottic surface requires the metric system to obtain the absolute dimensions of the larynx in a series of acquired images. However, so far, there is no effectively automated and stable calibration method for clinical use. Therefore, most metrics used by professionals are invasive and subjective. Thus, this study reports the microfabrication of a diffractive optical element (DOE) that could potentially quantify cancer cells from the glottic surface of patients. It has been observed that the image of the glottis seen through an endoscope is shaped by its geometric properties and by the shading of color and brightness. Therefore, tumor location and size can be quantified by overlaying the DOE metric with light spots on images that include the glottic region. DOE was developed from processes used in the fabrication of integrated circuits and MEMS, already quite mature. To obtain high-quality images from optical reconstruction of the glottis, the use of graphene monolayers grown by chemical vapor deposition (CVD) on copper (Cu) foil was investigated. This was transferred to a glass substrate by wet method (Fishing method) and the etching steps of the Cu substrate were carried out. In this method, polymethylmethacrylate (PMMA) was used as the supporting polymer through the spinner. Two lithographs were made under the glass substrate with different approaches (using a Karl Suss MJB3 mask aligner system with a maximum resolution of 1 µm). The first, which preceded the thin-film transfer, aimed to delineate the graphene transfer area using an aluminum (Al) deposition technique by sputtering. The second lithography, linked to oxygen Ashing plasma corrosion, made it possible to study the modulation of a microrelief containing parallel and serpentine patterns, of amplitude and phase, spaced from 1 to 10 μm. An optical system containing an EOD and a Fourier lens was attached to the endoscope end to project a laser line parallel to the vocal cords. Image processing methods automatically identify pixels in the image data that belong to the projected laser line. Thus, the detection of the diffractive pattern was based on segmentation of endoscopic images centered on Sobel filtering and on the method with active boundary regions of the watershed. These use successively robust temporal and spatial characteristics of the laser lines projected onto the endoscopic image sequence. In short, the combination of laser projection device and image processing allows calibration of endoscopic images and can provide quantitative metric data for tumors on the surface of the vocal cords. Therefore, the proposed calibration method can be considered a powerful tool to aid in the prognosis of laryngeal pathologies. Figure 1