The objective to induce reproducible, efficient, and stable second‐order nonlinear optical properties (SONL) in an isotropic material remains a challenge in photonics. Thermal poling allows inducing SONL properties in glasses by the formation of an axial symmetry because of the implementation of a static electric field within the glassy matrix. A description of the main poling mechanisms is proposed. Depending on the glass compositions and the poling conditions, an effort is made to correlate poling mechanisms and the strength of the implemented static electric field. A review of the main technological improvements done to develop poled‐silica‐based electro‐optical modulators as well as the SONL efficiencies obtained for different glass compositions is reported and analyzed.

Molecular and ionic species of nitrogen oxides have been injected, formed, and then trapped within a borosilicate glass during a thermal poling process. This original observation denotes a new aspect of poling mechanisms for ionic glasses. For each poled borosilicate glasses studied, compositional, structural, and second harmonic generation profiles of their subanodic polarized layers have been characterized. A description of the space charge implementation process, involving interactions between charged and chemically active species formed both within plasma discharges at the glass/electrode interface and within the polarized glass matrix, is proposed.