Integrated chirped-grating spectrometer-on-a-chip

A method of forming a spectral sensor comprising:

• providing a semiconductor substrate;
• forming a detector array on the semiconductor substrate;
• forming a planar waveguide on the semiconductor substrate;
• forming a transversely chirped input grating comprising grating lines that are tilted with respect to each other, such that a period of the transversely chirped input grating varies along the grating lines of the transversely chirped input grating, to couple incident light into the planar waveguide, wherein the transversely chirped input grating provides a spatially and spectrally selective coupling of incident light into the planar waveguide;
• forming a propagation region to filter out light that is not coupled into the planar waveguide;
• forming a restriction mechanism that restricts a range of angles of incidence of light impinging onto the chirped input grating;
• forming a transversely output grating comprising grating lines that are tilted with respect to each other, such that a period of the transversely chirped output grating varies along the grating lines of the transversely chirped output grating and differently than the transversely chirped input grating, that couples the light from the planar waveguide to the detector array;
• and
• forming an electrical circuit to readout output signals from the detector array.