Study of CNTs deposition in capillary fiber optics tip structures

Incorporating nanometric structures in optical fibers allows for a vast number of possibilities in designing small and robust sensors and thermal devices. We demonstrate the deposition of carbon nanotubes (CNTs) onto a capillary hollow fiber (CF). By means of an uncomplicated deposition technique based on laser light, we show that CNTs are effectively deposited on the tip of a CF. In order to couple light into the silica tube of the CF, we designed and fabricated a multimodal interference (MMI) device that generates a ring-shaped intensity pattern. Once the MMI device is constructed, a CF segment of 50–$100\mu m$ is spliced after the multimodal section. Afterward, the fiber device is immersed in a liquid solution that contains CNTs, and laser light is launched to promote CNTs deposition. We tested different optical powers and irradiation times to study the effect of experimental parameters on the deposition features. Our results indicate that for optical powers higher than 34 mW, depositions that cover the fiber end face of the CF can be obtained. Higher powers and longer irradiation times produce thicker layers of CNTs material. Moreover, we demonstrate that deposition may occur not only in the end face of the CF but also in the outer surfaces of the fiber. Finally, numerical simulations have shown that these devices can be used as fiber optic microheaters and thermal traps in bio-related applications.