This application describes, among others, wafer designs, testing systems and techniques for wafer-level optical testing by coupling probe light to/from the top of the wafer. A wafer level test system uses an optical probe to search for and align with an optical alignment loop. The test system uses a located alignment loop as a reference point to locate other devices on the wafer. The test system tests the operation of selected devices disposed on the wafer. The alignment loop is also used as a reference device for an adjacent device of unknown performance.