Techniques are described for forming an arrayed waveguide grating. In one example, an arrayed waveguide grating comprises a waveguide array coupled to the output of a parallel mode converter and a concave reflective diffraction grating coupled to the output of the waveguide array, wherein the waveguide array comprises a first waveguide and a second waveguide, wherein the first waveguide of the waveguide array has a different length from the second waveguide of the waveguide array. The waveguide array has a first dispersion having a first sign and a first magnitude, wherein the concave reflective diffraction grating has a second dispersion having a second sign and a second magnitude, wherein the second sign is opposite the first sign.