A device that allows multiple wavelengths to be combined and separated in a DWDM system. An array of planar waveguides diffracts light at angles that depend on the wavelength. The central element is an array of narrow, curved waveguides that run parallel to each other between a pair of mixing regions. The waveguides differ in length by an increment that is much larger than the wavelength. The input signal enters the first mixing region and is coupled into the waveguides to pass into the second mixing region.