Characterization challenges and trends in specialty optical fibers

Optical fiber technology — both in telecommunications and specialty applications — has advanced significantly in recent years. Telecom fibers, once standardized for long-distance transmission, now also incorporate multi-core designs and antiresonant hollow-core structures to achieve higher capacity and lower latency. Specialty fibers for high power light delivery have evolved toward highly customized architectures, including non-circular geometries, multi-clad and multicore structures, and hollow-core designs for high-power laser delivery and sensing. These innovations enable new functionalities but introduce major challenges for metrology. Off-the-shelf measurement solutions often fail to meet the accuracy requirements for complex preforms and fibers, making advanced characterization indispensable. Techniques such as two-dimensional refractive index reconstruction, laser-based tube metrology, and micro-computed tomography are increasingly required to ensure precise qualification. In addition to geometric and optical characterization, resistance to high-energy radiation — both UV-induced solarization and gamma irradiation — must be evaluated for applications in harsh environments. Achieving the necessary accuracy often demands in-house development of hardware, software, and processes, complemented by collaborations with external partners. This paper reviews key trends in fiber design, outlines metrology challenges, and presents strategies for accurate characterization across all manufacturing stages.