Planar waveguide spectrograph

A multi-channel spectrograph for receiving a plurality of optical input signals, and for detecting the optical energy of each input signal in a range of wavelengths, the spectrograph comprising:

• a plurality of planar waveguides, each waveguide having a plurality of side edges extending between upper and lower faces, the side edges of each planar waveguide including a curved edge having an inwardly concave shape, an input edge, and a straight output edge, the curved edge including a dispersive portion having a reflective diffraction grating formed thereon, the grating comprising a plurality of lines and having a variable line spacing, the line spacing and the positions of the input and output edges being selected such that when one of the optical input signals is introduced into the waveguide at the input edge, the input signal travels through the waveguide and strikes the grating, and the grating focuses the optical energy in the input signal at a focal spot at the output edge, the waveguides being stacked parallel to one another such that their output edges are positioned in a plane and said dispersive portion of the curved edge is fabricated integrally on the plurality of planar waveguides after they are stacked;
• and
• a detector array comprising a two-dimensional array of photodetectors positioned along a plurality of adjacent and parallel straight lines, the array being positioned such that the photodetectors of each line are positioned at the respective focal spots of one of the waveguides, such that the optical energy detected by each photodetector corresponds to the optical energy in a corresponding portion of the range of wavelengths of one of the input signals.