We investigate optimal twin-hole poling optical fiber configurations, including distances between core and each electrode, and poling voltage based on the two-dimensional charge dynamics model. We propose a poled fiber with optimized .(2) as well as single-polarization property. Small distance between core and anode -guarantees the poled fiber with large .(2) in fiber core and large polarization-dependent loss. A maximum .(2) in the core region either outside or inside nonlinear layer can be realized by appropriately selecting edge-to-edge distance between core and cathode. The maximum .(2) in the core region can be even larger by increasing the poling voltage.