# Progressive Poling of Large Area, High r\({}_{33}\) Electro-Optic Polymer SEO100c
## 5 r\({}_{33}\) Measurement Setup  
The r\({}_{33}\) values of the poled devices were measured. A Mach-Zehnder interferometer (MZI) was constructed with optical fiber and the device was inserted into one leg of the MZI, the testing setup is shown in Figure 4. A 100 mW diode laser at 1545 nm was used for testing of the device. This power was split with 90% of the power to the device leg (to overcome waveguide losses and coupling losses) and 10% of the power within the reference leg. For the device leg, a polarization controller was inserted before the splitter, to ensure the light launched into the device was TM polarized. TM light was used because the fabrication process placed the electrodes above and below the waveguides. The polarization of the light is important as the r\({}_{33}\) only effects the index of refraction in the direction the EO-polymer was poled. In order for this effect to be observed the light must be TM polarized. The TM polarized light was coupled into the single mode waveguide with a 6 \(\upmu\)m PM fiber mounted on a three-axis XYZ micrometer stage. The output of the device was collected by a 9 \(\upmu\)m PM fiber mounted on an identical three-axis XYZ stage. The reference leg first passed through a variable attenuator to allow for the power to be matched to that of the device leg. The variable attenuator can cause a change in polarization that must be corrected through a second polarization controller to match the device leg's polarization. Both legs were then recombined in a 50/50 combiner and went to  
Figure 3: Poling temperature (green) and current (blue) for a waveguide stack poled at 400 V, 500 V, 600 V, and 700 V.  
an optical power meter connected to an oscilloscope. A function generator was used to apply a triangular wave to the device. This signal was monitored on the oscilloscope as the optical power modulation was observed.  
Data was collected for frequencies of 40 Hz, 100 Hz, 500 Hz, and 1k Hz using the oscilloscope. Figure 5 shows an example modulation to measure \(V_{\pi}\). \(V_{\pi}\) was measured for each set of data and r\({}_{33}\) values were calculated using Equation (2) [16].  
\[V_{core}=\frac{\lambda d}{n^{3}\text{r}_{33}L\Gamma} \tag{2}\]  
where \(\lambda\) is the wavelength (1545 nm), \(d\) is the thickness of the core layer (2.7 \(\upmu\)m), \(n\) is the index of refraction of the core (1.65) [6; 13] and \(\Gamma\) is the overlap integral is 1 for vertically sandwiched electrodes because the entirety of the waveguide is covered by the uniform electric field. \(V_{core}\) is the percentage of \(V_{\pi}\) applied across the core layer, found to be 21% of the total field as described in Equation (1). \(L\) is the modulation length over which the voltage is applied which varied from 1.73 to 3.63 cm. \(V_{\pi}\) is the change in voltage applied to the device required to change from maximum to minimum optical power. As previously described, \(V_{\pi}\) was measured directly. From that measurement, r\({}_{33}\) could be calculated using Equation (2). It is important to note that because only the electric field in the EO-polymer will contribute to the modulation, the voltage across the 2.7 \(\upmu\)m of the core layer was found using Equation (1) and the resistivities of NOA 73 and SEO 100c. The poling, measurement, and calculation processes were repeated for multiple devices at various poling voltages ranging from 50 to 800 V.  
Figure 4: The testing setup to measure the r\({}_{33}\) of a poled polymer waveguide.  
Figure 5: \(V_{\pi}\) measurement of the EO-waveguide from a MZI configuration showing a \(V_{\pi}\) of 2.1 V. The top (yellow) wave form is the applied triangle wave, and the bottom (green) waveform is the optical modulation response.