Who needs a cathode?
Creating a second-order nonlinearity by charging glass fiber with two anodes

Abstract

We report that it is possible to create a fiber electret by having both internal electrodes of a twin-hole fiber at the same anodic potential, i.e., without the use of a contacted cathode electrode. We find that a stronger and more temperature-stable charge distribution results when the fiber core is subjected to an external field near zero. Negative charges from the air surrounding the fiber are sufficient for the recording of an electric field across the core of the fiber that is twice stronger than when one anode and one cathode electrode are used. The enhancement in stability and in the strength of the effective chi((2)) induced are a significant step towards the wider use of fibers with a second order optical nonlinearity.

Who needs contacts? Optical fiber poling by induction

“…Since the first reports of the thermal poling of silica fibers almost 25 years ago now, a number of more recent efforts have focused on exploring alternative electrode configurations [1,2] in order to gain both a deeper understanding and to develop more robust methods of device fabrication. In particular, the observation [1] that two internal fiber electrodes at the same positive potential generate a more efficient and stable second order nonlinearity than the conventional positive-negative configuration is at first glance highly counter-intuitive, as the electric field gradient at the midpoint between the two anodes (close to where the poled light guiding core is located) is very small.…”

“…In particular, the observation [1] that two internal fiber electrodes at the same positive potential generate a more efficient and stable second order nonlinearity than the conventional positive-negative configuration is at first glance highly counter-intuitive, as the electric field gradient at the midpoint between the two anodes (close to where the poled light guiding core is located) is very small. However, Margulis et al [1] proposed an "avalanche-like" positive feedback mechanism to explain this poling behaviour, as positive ions migrating away from the anodes immediately lead to a rapid increase in glass resistivity, thus leading to an increase in potential difference at the midpoint. Even more charge movement and larger potential difference between the anodes and fiber midpoint then begins to accumulate until the poling process is completed.…”

Optical fiber poling by induction: analysis by 2D numerical modeling

“…When the sample is cooled down whilst the voltage is still applied, an electric field is frozen into the depleted region and an effective nonlinear susceptibility ( ) is induced into the sample due to a process of third order nonlinear optical rectification. The early issues mainly related to the high risk of breakdown between the two electrodes (typically separated by a few tens of microns) were addressed by Margulis et al [6], who demonstrated that it is possible to induce a value of ( ) higher than the one obtained in the conventional case[5] by means of a poling configuration in which the two embedded electrodes are both connected to the same positive potential of the anode. The method for "charging" optical fibers has been recently further developed by De Lucia et al [7], who discovered that it is possible to create a space charge region using electrostatic induction between an external inductor and the floating electrodes embedded inside a fused silica twin-hole fiber.…”

“…When the sample is cooled down whilst the voltage is still applied, an electric field is frozen into the depleted region and an effective nonlinear susceptibility ( ) is induced into the sample due to a process of third order nonlinear optical rectification. The early issues mainly related to the high risk of breakdown between the two electrodes (typically separated by a few tens of microns) were addressed by Margulis et al [6], who demonstrated that it is possible to induce a value of ( ) higher than the one obtained in the conventional case…”

“…enclosed by a v ced adjacent to charges up the f y distributed N ion of 1 ppm a pm of H3O + ions e fiber at t = 0 s vely charged, no s at ground pote n considering t al. [6], an externa inside fibers wo unded surface, rocess. Furtherm ield-dependent H for longer polin t rate injection e-glass boundar eriod and then g geometry, the s require a field d so necessary to ount ion recom that mapping th ntal geometry ca ry conditions and ribe the dynam e the fiber when ductor (as show m (Na + ) is the ment results in vity near the fl twin-hole fiber ging oxygen s es) have very low on that gives ris trode-cladding s to recombine o g continues for creases but oth g. H3O + ), which b arges.…”