1. Rationale for the need for very high-speed fiber optic communications

The industrial development of lithium niobate modulators was made possible by the emergence of internet networks in the 1990s. The need for very high-speed digital communications systems to connect cities, countries, and continents had become critical. The basic building block of these networks is, of course, single-mode optical fiber with low propagation losses. By the 1980s, its development had enabled its deployment in transoceanic links. The transmission speeds in the O band (1,310 nm) were then low (140 Mbit/s). They used the Synchronous Digital Hierarchy (SDH) transmission protocol, which was in use at the time, but were limited by the direct modulation mode of the lasers and the use of low-performance optoelectronic line repeaters.

Subsequently, fiber connections will evolve toward the wavelength window centered on the C and L bands around 1,550 nm, which...