The ranked leader in this dataset holds 32 of the 981 records in scope, with the fifth-placed assignee at 17 and the tenth at 10. That is a top 5 combining for 11.9% of all records — meaningful but not dominant, since the remainder is spread across a long tail of universities, utility research institutes and smaller filers. No single company controls the field outright, which matters for freedom-to-operate assessments: clearance work needs to check the long tail, not just the largest holders.

Filings grew from 26 records in 2021 to 32 in 2024, a 23% increase, after an earlier peak of 43 in 2020. The apparent drop in 2025 and 2026 numbers is a publication-lag artifact — patent applications typically publish roughly 18 months after filing, so the most recent one to two years in any trend chart are always undercounted. Treat 2024 as the last year with a reasonably complete count, and expect the 2025–2026 figures to revise upward as more records publish.

General measuring and recording (IPC class G01D) is the largest single category at 25.1% of the 981 records, ahead of material analysis (G01N, 16.6%), temperature measurement (G01K, 16.5%) and length/dimension measurement (G01B, 16.2%). Vibration (G01H), pressure (G01L), electrical measurement (G01R) and optical elements (G02B) each account for a further 9–14% of records. Because records often carry multiple IPC tags, this shows signal-conditioning circuitry is claimed across nearly every physical quantity fiber optic sensors measure rather than concentrated in one niche.

China is by far the largest receiving office in this dataset at 385 tracked records, more than double the United States at 141. Europe (EPO), South Korea and Japan each sit in the 75–95 range, and WIPO/PCT filings total 59. A filing strategy focused only on the US and Europe would miss the majority of the documented activity — clearance and freedom-to-operate work should prioritise Chinese-language prior art first.

CN214959461U, filed by Zhejiang Wanli University, claims a two-stage amplification circuit: an avalanche-photodiode-based photoelectric conversion stage feeding a first amplifier, coupled through a capacitor to a second amplifier that proportionally re-amplifies the voltage signal for downstream processing. It is a utility model, which in China carries a narrower and faster-granted scope than an invention patent, so its practical blocking effect is limited to designs matching that specific two-stage, capacitor-coupled topology. A workable alternative circuit — a different coupling method or a single-stage design with digital gain correction — would likely sit outside its literal claim scope.