Optical device with phase correction

An optical element for introducing a predetermined phase delay into incident electromagnetic radiation, the optical element comprising:

• a first layer and a second layer arranged in a propagation path of a portion of the electromagnetic radiation,
• wherein the first layer comprises a transmission region configured to introduce a first phase delay into the portion of electromagnetic radiation propagating therethrough,
• wherein the second layer comprises a metasurface configured to introduce a second phase delay into the portion of electromagnetic radiation propagating therethrough, and
• wherein the first layer comprises:
• a plurality of transmission regions having constant, alternating thicknesses and arranged in respective propagation paths of respective portions of the electromagnetic radiation to introduce respective first phase delays into said respective portions,
• wherein respective lateral extents of the transmission regions are greater than a wavelength of the respective portion of incident electromagnetic radiation propagating therethrough.