The Unidirectional Integrated Tap Photodiode (UTPD) integrates the functionality of an optical coupler and a photodiode for optical network\'s power detection. The unidirectional feature allows the PD responds power from input port only. It can be applied for channel power monitoring in DWDM system, in-line optical network switching protection monitoring (OLP), re-configurable optical add/drop multiplexer (OADM), and gain/attenuation monitoring in EDFA, etc.