In detection and sensing, light is transmitted through layers or structures that vary laterally, such as with a constant gradient or a step-like gradient. After transmission, a position of a transmitted portion of the light or of output photons can be used to determine wavelength change or to obtain other photon energy information. The light can be received, for example, from a stimulus-wavelength converter such as an optical fiber sensor or another optical sensor. A component that propagates the light from the converter to a transmission structure can spread the light across the transmission structure's entry surface. At the exit surface of the transmission structure, photosensor components can sense or detect transmitted light or output photons, such as with a photosensor array or a position sensor. A photosensed quantity can be compared, such as with another photosensed quantity or with a calibration quantity. A differential quantity can be obtained using photosensed quantities.