a plurality of input waveguides, each comprising an input slab portion and an input rib portion;

an output waveguide, comprising an output slab portion and output rib portion; and

a wavelength multiplexer element, coupled to each input waveguide and the output waveguide, the wavelength multiplexer element comprising a slab waveguide which includes a grating configured to multiplex signals of differing wavelengths, received from the input waveguides, into a multiplexed signal, and provide the multiplexed signal to the output waveguide,

wherein the input rib portion(s) of one or more of the input waveguides are tapered so as to decrease in width in a direction towards the slab waveguide of the wavelength multiplexer element,

wherein the input slab portions of the input waveguides and/or the output slab portion of the output waveguide have a height which is substantially equal to a height of the slab waveguide in the wavelength multiplexer element, and

wherein the wavelength multiplexer element is an echelle grating multiplexer element.