<title>Charge dynamics and distributions in thermally poled silica fiber</title>

Abstract

Silica glass plays a key role in photonic systems because of its excellent optical properties, such as low loss, low fabrication cost and high photo-refractive damage threshold. Unfortunately, silica, being centrosymmetric, has no intrinsic linear electro-optic (LEO) coefficient or second-order nonlinearity (SON). However, thermal poling has been demonstrated to produce a LEO coefficient and SON of approximately 1 pm/V in silica glass and fiber. It is necessary to understand the mechanism of thermal poling in order to achieve a larger, stable and reliable LEO effect. A series of thermal poling experiments on silicate fiber was carried out. The in situ measurements of the total LEO coefficients (the sum of the poling field induced LEO coefficient and the thermal poling induced residual LEO coefficient) suggest movement of charges. Thermal poling induced residual LEO coefficients are measured in situ during prolonged negative thermal poling. Both the shielding field and the ionization field are frozen-in at room temperature and lead to LEO effect. The time evolution of the residual LEO coefficients shows that the competition between the shielding and ionization fields is a linear process. Using this new understanding, a specialty optical fiber was developed for the production of thermally poled optical fiber devices.