Uses of volume holographic optical elements

Several uses that have been developed or proposed for volume holographic optical elements (HOEs) are reviewed. Volume HOEs possess several unique properties that distinguish them from conventional optical elements. These properties include (1) wavelength and angle selectivity, (2) imaging functions relatively independent of surface shape, (3) ability to impart spectral notches that are deep (>5 OD) and steep-sided, (4) high, negative V-number dispersion, and (5) ability to share a single aperture between multiple elements. Several applications that make use of these unique features of volume HOEs have been developed or proposed. Holographic head-up display (HUD) combiners provide high display reflectance simultaneously with high visual transmittance. Curved, highly off-axis holographic HUD combiners provide built-in aberration correction, enabling high image quality over wide fields-of-view in systems having very restricted installation geometries. Notch filters have found use in protection against laser damage for sensors and eyes, attenuation of atmospheric emission lines in remote sensing, and range extension of Raman spectroscopy instruments to lower wavenumber shifts. Rotating HOEs have been used as laser scanners for barcode readers and higher resolution imaging equipment. Holographic gratings are used in multiplexers/ demultiplexers and other monochromator devices to provide both focusing and wavelength separation. Holographic optical interconnects may provide parallel VLSI electronic circuit connections with large fan-out and negligible propagation delay.