The present invention provides an integrated optical device comprising a metaloxide-based optical planar waveguide amplifier monolithically integrated on a common substrate with at least one additional planar waveguide selected from a group comprising: a planar waveguide signal-processing circuit arranged to process an optical communications signal; and a planar waveguide pump-signal coupling circuit arranged to couple or decouple a pump wavelength to or from the amplifier; wherein the amplifier has a metal-oxide-based core comprising an optically-transmissive metal oxide material doped with a gain medium and is arranged to amplify an optical communication signal when optically pumped with a source of pump radiation. The amplifier can have a core composed of aluminium oxide doped with erbium and/or ytterbium. The signal processing circuit may comprise a multiplexer, demultiplexer, channel gain equalizer, N×M optical switch matrix, an optical modulator, or an add-drop multiplexer. The pump-signal coupling circuit may comprise an asymmetric Mach-Zehnder interferometer.