# Progressive Poling of Large Area, High r\({}_{33}\) Electro-Optic Polymer SEO100c
## 1 Introduction  
Electro-Optic (EO) waveguide modulators are essential in optical communications to convert electrical signals to optical signals. EO modulators produce cleaner modulated signals and provide faster modulation rates than direct modulation options [1]. The majority of commercial EO modulators utilize lithium niobate which has a maximum r\({}_{33}\) tensor of 30.8 pm/V [2] limiting the reduction in \(V_{\pi}\) (on-off voltage) for most modest laser power. To achieve devices with a low \(V_{\pi}\), commercial lithium niobate devices must increase the interaction length (L) of the electro-optic effect. This results a figure of merit \(V_{\pi}\)-L being vital describe optimization of device size and \(V_{\pi}\). Alternative to lithium niobate are electro optic polymers, which consist of a polymer matrix, commonly polycarbonate or PMMA, and nonlinear EO chromophore molecules [3]. EO polymers with r\({}_{33}\) values in excess of 100 pm/V have been reported [4, 5] allowing low voltage designs since the tensor is inversely proportional to the modulator on-off voltage. This high r\({}_{33}\) value also allows for low \(V_{\pi}\)-L values to be achievable. For EO polymers to obtain an r\({}_{33}\), the chromophores must first be aligned through a poling process [6]. Poling involves heating the EO polymer structure to its glass transition temperature while applying a strong electric field across the EO polymer. Various methods of efficient poling to reach maximum r\({}_{33}\) while avoiding dielectric breakdown have been demonstrated including corona poling [7], and contact poling [6]. Corona poling is not used due to the need for voltages in excess of 3 kV, and non-uniform poling of EO-Layers [7]. Utilizing the contact poling method/process involves electrodes surrounding the EO-polymer to distribute an electric field. Contact poling can be used to pole a single film of EO polymer or full device stacks. The highest r\({}_{33}\)'s reported have been for single films of EO-polymers maximizing the static field within the active layer by eliminating the clad resistive layers. Single films of the EO-polymer can be directly sandwiched between two electrodes to get a strong electric field across the polymer layer and provide efficient poling. Single EO-Polymer films can be poled and their r\({}_{33}\) can be measured using the teng-man measurementtechnique [8]. However, this is not practical for waveguide devices as the electrodes would quickly attenuate any optical power. Using a full device stack of a cladding-core-cladding waveguide structure between the polling electrodes allows the waveguides to be fully fabricated and then poled. A major advantage of contact poling is that a device can be poled multiple times under various conditions and can be re-poled if the chromophore alignment relaxes. Relaxation of chromophore alignment can impact the lifespan of an EO polymer device [9; 10]. The contact poling method results in the electric field being distributed between the cladding and core layers, requiring a higher applied voltage to get equivalent poling results. This higher voltage introduces additional risks to the poling process as the high voltage may cause arcing between electrodes or cause a dielectric break down in any of the device layers. A preferred method to ensure maximization of r\({}_{33}\) for a wave-guiding device structure is to pole utilizing the mid-process poling technique [6]. Mid-process poling is performed after the core layer has been fabricated, allowing poling to be carried out on a partial stack of cladding-core layers, reducing the required applied voltage, and maximizing r\({}_{33}\). The electrode size is also a significant factor in the poling process. Electrode size and position for an EO-Modulator are often constrained by the RF operational design frequency. Electrodes are patterned over the modulating part of the waveguide structure to pole the necessary section of the waveguide. Having the electrode over only the waveguide reduces the risk of dielectric breakdown.