Improving wide-angle light-coupling efficiency by air-cladding fibers under near-plane wave excitation

Optical fiber plays a fundamental role in widespread optic systems, while the low coupling efficiency imposes a large optical loss and thus narrows its applied scope. Here a high-NA air-cladding fiber is introduced and further characterized using near plane waves. At three wavelengths of 650 nm, 1000 nm, and 1550 nm, the self-made high-NA fiber displays significantly enhanced coupling efficiency. Particularly within the angle interval of 20-80 degrees, the other two types of fibers (NA = 0.13 and 0.22) fail to operate (i.e., no light can be collected), whereas the coupling coefficients of the microstructured fiber are distributed at a percentage level. In summary, the systematic characterization showcases that the NA of the fiber should be given high priority to compose a high-coupling optical system.