Characterizing Single Mode Lensed Fibers

Author: Tyler Frisch and Sarah Usher Monday, December 22, 2025
Lensed single-mode optical fibers can be used to enhance coupling efficiency in certain specific optical systems, including photonic integrated circuits (PICs), solid-state quantum light sources, high-speed detectors, endomicroscopic imaging, and other sensing applications such as optical probes used for optical coherence tomography (OCT). In space-constrained systems, a common approach is to butt-couple a cleaved optical fiber directly to a component. However, when the component is smaller than the core of the optical fiber (typically ~9 µm), a core size mismatch can lead to significant signal loss. Additionally, if the component is not in direct contact with the fiber, coupling efficiency is further reduced due to the divergent nature of the light exiting the fiber and the longitudinal offset between the component and the fiber. Lensing the optical fiber addresses both issues by enabling focused spot sizes as small as 2 µm at a working distance laterally offset from the fiber tip. These smaller spot sizes and increased working distances (Figure 1) also greatly benefit high-speed detection where a smaller sensing area leads to faster response times.

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