Abstract: A display device (500) includes an expander device (EPE1) to form output light (OUT1) by diffractively expanding input light (IN1) that includes input light beams (B0P1, B0P2) representing an input image (IMG0). The output light (OUT1) includes output light beams (B3P1, B3P2) representing the input image (IMG0). The expander device (EPE1) includes: a waveguide plate (SUB1), a diffractive in-coupling element (DOE1) to couple the input light (IN1) into the waveguide plate (SUB1), a diffractive out-coupling element (DOE3) to form the output light (OUT1) by diffracting guided light (B1, B2) out of the waveguide plate (SUB1). The out-coupling element (DOE3) includes buried diffractive ridges (PR1) and complementing regions (FIL2) between the ridges (PR1), the buried diffractive ridges (PR1) have a first refractive index (n1), the complementing regions (FIL2) have a second different refractive index (n2). A slant angle (?S) of the ridges (PR1) is in a range of 20° to 70°.

Abstract: A display apparatus includes an optical engine and a stack of expander devices. The optical engine forms input light which comprises a plurality of input light beams representing an input image. The stack of expander devices forms output light by diffractively expanding the input light. The output light includes a plurality of output light beams representing the input image. The stack includes a first expander device and a second expander device. The grating period of each diffractive element of the first expander device is equal to the grating period of a corresponding diffractive element of the second expander device.