Zemax-based optimized design of hydrogel fiber lens

Abstract

In the optical fiber sensor, the signal light output from the silica fiber is transmitted to the detector, which usually needs to be coupled through the lens focusing. However, this often destroys the compactness and flexibility of the optical fiber sensor system structure. Therefore, this article proposes a hydrogel fiber optic lens solution, that is, a method that can directly focus the signal light output from the silica fiber to the photodetector. Its bottom-up photochemical fixation method determines its flexible characteristics and can meet individual needs. In this article, according to the size of the image distance, that is, the distance from the silica fiber to the detector (image distance), and the size of the focus point on the detector (focal point), the curvature radius of the polyethylene glycol diacrylate (PEGDA)-based hydrogel fiber lens and the distance from its apex to the silica fiber end face (object distance) are optimized. Through simulation, it finds that, with the decrease in the curvature radius, the focus point of the hydrogel fiber lens would appear at a shorter image distance and the change in the object distance length would not significantly affect the position of the focus point of the lens. The focus point of the lens focusing on the central bright spot decrease with the decrease in the curvature radius, which is consistent with the variation trend of the Airy spot in the simulation. This simulation confirms that a smaller curvature radius could be able to improve the focusing effect of the hydrogel fiber lens.