The GLV generates contrast by re-distributing light between fixed diffraction orders. Imaging is achieved using a conjugate lens pair and a spatial filter (aperture) located at the transform plane between the lenses. With the GLV located one focal length away from the Fourier transform lens (FTL), rays exiting the device from a common angle are brought to a common focus in the transform plane. Rays exiting the GLV normally (0th-order) are focused on axis while other orders (e.g. ±1st-order) are focused off-axis. The aperture selects which orders are allowed to reconstruct the image by passing through the inverse Fourier transform lens (FTL-1). Typically GLV-based systems use either the 0th-order or one or both of the ±1st-order beams to generate images.
