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A planar spectrograph design is described that features a flat-field output and operates over a remarkably broad range of wavelengths. The grating facet positions are described by an iterative algorithm that ensures that light will arrive in phase at the focal point. There are no aberrations of any order at the design wavelength and aberrations near the design wavelength are simultaneously minimized. The peak intensity of the output varies less than 3 dB over a wavelength range of 1.46 to 1.64 μm. The spectrograph may be used as a demultiplexer in photonics systems using wavelength division multiplexing. The design easily accommodates hybrid integration of a linear detector array at the output.