Frequency-doubling by modal phase matching in poled optical fibres

Photoinduced self-organization in optical fiber: some answered and unanswered questions

“…Still, however, light was needed, in particular from an argon laser again, to induce the permanent x2• Also, this scheme had the disadvantage that the interaction was not phase matched, since the x2 was not periodic. However, phase matching has been achieved by looking at wavelengths where the mode effective indices at the fundamental and harmonic are equal [72] , but also by poling the fiber in a periodic way, for example by launching the exciting light in two modes of the fiber that beat with the right period [66], or poling with periodic electrodes [73].…”