This landscape covers 17,404 published records where pulse amplitude modulation, coherent detection, or decision feedback equalization claims intersect with physical-layer concerns like chromatic dispersion, forward error correction, baud rate, receiver sensitivity, transmitter linearity, or timing recovery. Most of these records classify under H04L (digital information transmission) and H04B (transmission, general), which together cover more than half of all records, meaning the bulk of the art sits at the signal-processing layer rather than in optics-specific classifications. A smaller but meaningful share touches multiplexing (H04J), coding (H03M) and wireless-adjacent (H04W) claims, reflecting how techniques originally built for wireline and wireless systems get re-claimed for optical short-reach interconnect.

The ranking covers 100 companies counted by record, and it is a genuine long tail: the leading assignee holds 1,140 records, well ahead of tenth place at 282, yet the top 10 combined still account for only 30.0% of all 17,404 records in scope. That means no single company or small group controls the claim space, and freedom-to-operate work needs to look well beyond the leading few names. Filing activity among even the most active recent filers has also slowed sharply, with year-over-year drops in the -80% to -100% range for several leading assignees in the latest tracked year.

Filing peaked in 2020 at 921 records and declined to 450 by 2024, a -45% move from the 816 filed in 2021 — this is the clearest complete-year trend the dataset supports. Records from 2025 and 2026 are still incomplete because patent publication typically lags filing by around 18 months, so those most recent years understate actual filing activity and should not be read as a further decline. The honest read is that filing volume pulled back meaningfully after 2021, not that the technology area is being abandoned, since dense existing claim coverage reduces the need for continued high-volume filing.