Digital Holographic Optics
In the realm of optics, a hologram seems at first glance to be the most analog type of element, after the conventional smooth surface refractive lens.
Holography, in its original form, is truly an analog phenomenon and an analog optical element, in its design (the use of analytic techniques) and in its recording (the use of conventional optics) as well as in its internal form (an analogous modulation of refractive indices).
This said, the holograms used in industry today (including HOEs) can be classified as digital elements because of the many improvements to their original nature. These improvements are digital in nature and are as follows:
- the wavefront to be recorded in the hologram calculated by a digital computer rather than produced by real analog optical elements;
- the recording of holograms (Bragg gratings) by the use of digital phase masks;
- the recording of HOEs by the use of digital CGHs (beam splitting, beam shaping etc.);
- the recording of pixelated holograms (for display or optical processing applications); and
- the recording of HOEs into photoresist (rather than analog holographic emulsions) to produce surface-relief elements, and then replicating them on wafers, similar to digital lithography.
Other than for traditional 3D display holograms, which were every kid's (and also most grown-ups') favorite eye candy, today industrial holography is increasingly becoming a digital process, for the integration of complex optical functionality in ...