Edge-lit volume holograms recorded by free space exposure: diffraction by 2^ndHarmonics in Bayfol HX film

Abstract

Miniaturization of optical components, specifically the reduction in thickness created by using planar optical devices, makes light manipulation by diffraction more and more attractive. Optical gratings based on volume Holographic Optical Elements (vHOEs) have the advantage over surface gratings as they reconstruct only a single diffraction order and hence provide high diffraction efficiencies, selectivity and remain fully transparent in the off-Bragg condition.Guiding light inside an optically transparent medium by total internal reflection (TIR) is common and useful in thin planar optical devices. vHOEs offer unique ways to create selective in-and out-coupling of TIR light. As such vHOEs typically have to be recorded in an edge-lit configuration as the necessary high diffraction angles could not be generated by two free-space beams outside the medium. To record such an edge-lit vHOE, bulky recording blocks or liquid baths are used in complex and hard to align recording setups.We present in this paper our findings to use instant-developing photopolymer film (Bayfol ® HX) to generate 2 nd harmonics in the index profile of phase gratings while using free-space recording setups. Those 2 nd harmonic components enable the vHOE to diffract at such large angles that they replay in an edge-lit configuration. We will discuss in this paper selected materials and beneficial recording parameters to tune the diffraction efficiency towards 2 nd harmonic replay. By this -in reported specific cases -the cumbersome and complex edge-lit recording can be substituted by easy-to-use free-space setups. This process significantly simplifies master recordings for vHOEs with edge-lit functionalities which later can be used in contact copy schemes for mass replication.

Second harmonics HOE recording in Bayfol HX

“…18 With that we were able to compare theoretical predictions with experimental results. In the current paper we focus on two experimental use cases and elaborate on the beneficial application of this concept.…”

Roadmap on holography

“…The intrinsic mechanical moduli can-within certain limitations-be tuned to meet individual customer requirements [68]. Further insights from our modelling of the recording mechanism in Bayfol ® HX film are described in [69,70] dealing with the generation of 2nd harmonic gratings and forcing those to achieve a high index modulation n2 by tuning the recording conditions and/or the photopolymer formulation. Some useful applications of this feature are proposed in the given [69,70], too.…”

“…Further insights from our modelling of the recording mechanism in Bayfol ® HX film are described in [69,70] dealing with the generation of 2nd harmonic gratings and forcing those to achieve a high index modulation n2 by tuning the recording conditions and/or the photopolymer formulation. Some useful applications of this feature are proposed in the given [69,70], too. Wavelength multiplexing is essential to a recording material to be able to generate full colour volume image or display holograms.…”

Multilayer volume holographic gratings from BayFol HX: light and neutron optical characteristics

“…1 The latter has been characterized extensively and applied for light optical purposes. [18][19][20][21][22][23][24][25][26][27][28][29][30] Applications of DOEs for other fields such as cold atom trapping or in astronomy were envisaged, too. [31][32][33][34]…”