2-D photonic crystals (2-D PCs) are expected to enable ultrasmall and highly functional photonic devices to be developed. However, 2-D PCs have a large polarization dependency, which can be an important issue depending on the type of application. To address this matter, we propose a method to realize a polarization diversity operation in a PC. Initially, an ultrasmall PC polarization converter that utilizes 45 degrees tilted airholes is considered. A polarization-independent add-drop filter using this polarization converter is then described, and the operation is experimentally demonstrated.