Nanograting-Enhanced Optical Fibers for Visible and Infrared Light Collection at Large Input Angles

Nanoprinted microstructure-assisted light incoupling into high-numerical aperture multimode fibers

The coupling of light into optical fibers is limited by the numerical aperture (NA). Here, we show that large-area polymer axial-symmetric microstructures printed on silica multimode fibers improve their incoupling performance by two to three orders of magnitude beyond the numerical aperture limit. A ray-optical mathematical model describing the impact of the grating-assisted light coupling complements the experimental investigation. This study clearly demonstrates the improvement of incoupling performance by nanoprinting microstructures on fibers, opening new horizons, to the best of our knowledge, for multimode fiber applications in life sciences, quantum technologies, and "lab-on-fiber" devices.

Investigations on Grating-Enhanced Waveguides for Wide-Angle Light Couplings

As a universal physical scheme, effective light couplings to waveguides favor numerous applications. However, the low coupling efficiency at wide angles prohibits this fundamental functionality and thus lowers the performance levels of photonic systems. As previously found, the transmission gratings patterned on waveguide facets could significantly improve the large-angle-inputted efficiency to the order of 10-1. Here, we continue this study with a focus on a common scenario, i.e., a grating-modified waveguide excited by the Gaussian beam. A simplified 2D theoretical model is firstly introduced, proving that the efficiency lineshape could be well flattened by elaborately arranged diffractive gratings. For demonstration, subsequent explorations for proper grating geometries were conducted, and four structural configurations were selected for later full-wave numerical simulations. The last comparison studies showcase that the analytical method approximates the finite element method-based modelings. Both methods highlight grating-empowered coupling efficiencies, being 2.5 bigger than the counterparts of the previously reported seven-ring structure. All in all, our research provides instructions to simulate grating effects on the waveguide's light-gathering abilities. Together with algorithm-designed coupling structures, it would be of great interest to further benefit real applications, such as bioanalytical instrumentation and quantum photon probes.

Special Issue “Novel Specialty Optical Fibers and Applications”: An Overview

Novel specialty optical fibers refer to optical fibers that have been engineered in terms of design, material and structure, and have been post-processed for novel functionalities and applications [...]