The increasing demand for Internet traffic is the motivation for a large-capacity and flexible network. Photonic networks utilizing wavelength division multiplexing (WDM) are expected to meet these requirements. Silica-glass-based planar lightwave circuit (PLC) technologies provide various optical devices for such photonic networks. This paper reviews silica-based PLC devices including arrayed-waveguide gratings (AWG), thermo-optic switches (TOSW), and hybrid-integrated PLC devices with optical semiconductor devices. A PLC is an optical integrated circuit that employs silica glass, which is a stable optical fiber material. Thus the PLC has characteristics that include low-loss, compactness, low-cost, suitability for mass-production, and good reliability. The AWG multiplexer is a key component in dense optical WDM networks, since it is capable of multi/demultiplexing N optical signals of different wavelengths. This is because the multiplexer employs the same system as a grating-based spectrometer. We recently reported a 400-ch AWG multiplexer, which is the largest number of channels yet achieved. An optical switch is required to eliminate the bottleneck in conventional electronic switching systems and the PLC-TOSW is a promising candidate because of its excellent characteristics and reliability. We have already reported 16x16 and 1 x 32 TOSW modules. We can construct a larger-scale photonic switching system with more than 100 ports using these modules. Furthermore we developed hybrid-integration technologies in which optical semiconductor devices can be assembled on a PLC substrate. Using hybrid integration, we can realize a high-speed wavelength channel selector and an optical transceiver for optical access systems.