| Poling techniques can be used to break the intrinsic inversion symmetry of glasses, therefore realizing materials with second-order nonlinear properties. To date, the nonlinear interactions in devices based on poled glasses have remained too weak for practical applications because of widely accepted fundamental material and process limitations. This thesis develops an approach that overcomes these limitations and demonstrates artificial silica glass structures that mimic nonlinear crystals and provide a versatile, inexpensive and widely available alternative to natural nonlinear crystals. The approach involves sub-dividing the poled glass into a multitude of glass layers deposited by standard microfabrication techniques. The experimental investigations show that doping of glass layers can be used as an effective tool to control the migration of charges that are responsible for the induced nonlinearity during the poling process. Multilayered silica structures with phosphorus, boron and germanium doping are investigated. A 14-fold improvement is achieved in the second harmonic generated (SHG) in a corona poled multilayered structure with a 2.4 mum-thick stack of phosphorus-doped and undoped silica layers compared to bulk silica glass poled under identical conditions. Furthermore, more than two orders of magnitude enhancement in the SHG is obtained in a thermally poled structure with a 3 mum-thick multilayered stack consisting of sub-100 nm-thick alternating germanium-doped and undoped silica layers. These anomalously large SHG results give a strong indication that the multilayered approach is the key to overcoming the existing challenges of poled glass devices. The high degree of control over the poling-induced nonlinearity that is offered by the multilayered design may therefore lead to practical implementations of efficient active devices in silica glass, including monolithic integration of second-order nonlinear functions directly within silica-based optical chips, and the realization of second-order nonlinear fibers. |
