Absolute measurement of the second-order nonlinearity profile in poled silica

Thermal Poling of Optical Fibers: A Numerical History

This review gives a perspective of the thermal poling technique throughout its chronological evolution, starting in the early 1990s when the first observation of the permanent creation of a second order non-linearity inside a bulk piece of glass was reported. We then discuss a number of significant developments in this field, focusing particular attention on working principles, numerical analysis and theoretical advances in thermal poling of optical fibers, and conclude with the most recent studies and publications by the authors. Our latest works show how in principle, optical fibers of any geometry (conventional step-index, solid core microstructured, etc) and of any length can be poled, thus creating an advanced technological platform for the realization of all-fiber quadratic non-linear photonics.

Investigating the effectiveness of thermally poling optical fibers with various internal electrode configurations

Twin-hole fibers were thermally poled with different internal electrode configurations, including having only one anode wire in the hole, two anode wires in the two holes, one cathode wire, and two cathode wires in the holes, in comparison to the conventional one anode wire and one cathode wire combination. Second harmonic microscopy was utilized to visually reveal the spatial distribution and to measure the magnitude of the induced second-order optical nonlinearity within the poled fibers. It was found that both one- and two-anode configurations resulted in strong nonlinearity comparable with the conventional case but the two-anode configuration was more reproducible than the one-anode case; for the one-cathode-wire and two-cathode-wire configuration, strong nonlinearity in a ring shape concentric with the fiber outer surface was induced as if the cathode metal wire were in the center of the twin-hole fiber rather than substantially offset. These new results provide strong support for the proposed model of a "self-adjustment" mechanism and point the way to simplified and more repeatable experimental techniques.

Measurement of depletion region width in poled silica

The width of the depletion region in fused-silica samples thermally poled during various periods of time is investigated experimentally with four previously reported characterization techniques in an attempt to unify their findings. Although all measurements give a similar width of the depletion region, it is shown that the determination of the profile of chi(2) is also required for a good estimate of the nonlinearity induced by poling.

Nondestructive method for characterization of the second-order nonlinear profile and charge distribution in thermally poled fused silica

Noncollinear frequency conversion of two femtosecond pulses is used to characterize the nonlinear profile induced in thermally poled fused silica. This technique permits one to deduce the nonlinear profile and the charge distribution induced by the poling treatment. These data and the current that passes through the sample during the poling are consistent with the occurrence of a built-in electric field associated with the diffusion of two ionic species.

Noncollinear Maker's fringe measurements of second-order nonlinear optical layers

A novel technique for characterizing thin-film second-order nonlinearities with submicrometer resolution for the film's depth is proposed. This method is substantially a variation of the classic one-beam Maker's fringe technique and uses the second harmonic generated by two noncollinear fundamental beams. Compared with that for the one-beam case, this configuration reduces the coherence length of the process, thus increasing the resolution for the nonlinear depth measurements. The technique has been implemented on thermally poled silica samples, revealing the initial growth of the nonlinear region.