Integrated-optic waveguide devices become more and more complicated to realize high functionality. Numerical simulations are prerequisite for the design of waveguide devices. Planar lightwave circuits (PLCs) provide various important functionalities for optical wavelength division multiplexing (WDM), time division multiplexing (TOM), code division multiplexing (CDM) systems and fiber-to-the-home (FTTH) access networks. This paper reviews the recent progress and future prospects of waveguide device design and its application to FTTH access networks and photonic signal processing applications.