A holographic storage optical system includes a storage medium, a recording unit, an imaging unit and a servo unit. The recording unit comprises a movable Fourier lens, by which the positions and irradiation angles of a signal light spot and a reference light spot are adjusted. The servo unit comprises a calibration lens for adjusting the positions of a servo light spot in the horizontal and vertical directions so that the servo light spot is located at an optimal position relative to signal light beam and reference light beam. The beam calibrating method comprises (1) before recording a data hologram, burning a calibration hologram at a calibration holographic positioning mark on an optical track of a storage medium; (2) before reproducing the data hologram, using the calibration hologram to optimize the signal-to-noise ratio of the hologram reproduced by adjusting the calibration lens and the Fourier lens.

A method of forming a security device includes: a holographic image layer, diffusion element, and barrier layer. A region of the barrier layer includes a heat-transformable material. The method further includes selectively applying heat at a plurality of positions within the region of the barrier layer, in accordance with a predetermined pattern, so as to modify the heat-transformable material such that the region of the barrier layer is selectively rendered passable to the diffusible substance at each of the plurality of positions, thereby permitting diffusion of the diffusible substance between the regions of the diffusion element and the holographic image layer such that, at a plurality of positions within the region of the holographic image layer and corresponding to the predetermined pattern, the volume hologram is dimensionally modified so as to become viewable in a second observable colour, different from the first observable colour.

A diffractive optical element according to the invention includes a holographic element configured to deflect incident light, a first substrate provided on one surface side of the holographic element, a first dielectric film provided between the first substrate and the holographic element, a second dielectric film provided on another surface side of the holographic element, and a third dielectric film provided on a side surface side of the holographic element.

A diffractive optical element according to the invention includes a holographic element configured to deflect incident light, a first substrate provided on one surface side of the holographic element, a first dielectric film provided between the first substrate and the holographic element, a second dielectric film provided on another surface side of the holographic element, and a third dielectric film provided on a side surface side of the holographic element.

A holographic skew mirror has a reflective axis, or skew axis, that can be tilted with respect to its surface normal. Tilting the skew axis in two dimensions with respect to the surface normal expands the holographic skew mirror's possible field of view, e.g., to 60 or more. These additional angles can be accessed using an out-of-plane writing geometry with matched total internal grazing extension rotation (TIGER) prisms.

A holographic skew mirror has a reflective axis, or skew axis, that can be tilted with respect to its surface normal. Tilting the skew axis in two dimensions with respect to the surface normal expands the holographic skew mirror's possible field of view, e.g., to 60 or more. These additional angles can be accessed using an out-of-plane writing geometry with matched total internal grazing extension rotation (TIGER) prisms.

Provided is a display medium configured to allow for intended drawing. The display medium includes a first recording layer capable of performing recording with a first laser beam having a first peak wavelength and a second recording layer capable of performing recording with a second laser beam having a second peak wavelength. The first recording layer and the second recording layer employ different recording methods.