Abstract
Diffractive optical elements (DOEs) have been in development for many years and are an exciting technology with the capability to re-direct light, using diffraction rather than refraction. Holographic Optical Elements (HOEs) are a subset of diffractive optical elements for which the photonic structure is created holographically, i.e., by recording a specific interference pattern in a suitable, photosensitive optical material. Volume HOEs are of particular interest for some applications because of their very high diffraction efficiency and single diffracted order; however, high dispersion and angular wavelength selectivity still present significant challenges. This paper explores a method for producing a compound DOE useful for situations where elements designed for two separate target wavelengths can be advantageously combined to achieve a highly efficient HOE with reduced dispersion. A photopolymer material consisting of two independently sensitized laminated layers is prepared and used in sequential holographic recording at two different wavelengths. The photonic structures recorded are investigated through examination of their diffraction peaks and comparison with the structure predicted by modeling. Finally, the device is illuminated with an expanded diverging beam at both target wavelengths and with white light, and a strong diffracted beam is observed.
Highlights
Diffractive Optical Elements (DOEs) are photonics structures that focus and redirect light, using diffraction rather than refraction
This paper explores a method for producing a compound element useful for situations where elements that are designed for two separate target wavelengths can be advantageously combined to achieve a highly efficient Holographic Optical Elements (HOEs)
The stack envisaged consists of two off-axis lens elements, one designed for a blue target wavelength, and one designed for a green, both having a focal point of 5 cm from the plane of the photopolymer element
Summary
Diffractive Optical Elements (DOEs) are photonics structures that focus and redirect light, using diffraction rather than refraction. ‘Volume’ or ‘thick’ Diffractive Optical Elements utilize Bragg diffraction and can very efficiently transfer energy from the incident beam into a diffracted beam [1]. DOEs have the potential to replace optical components in a range of applications and have the advantages of being low cost, lightweight and in most cases, much thinner than their refractive counterparts. DOEs can replace standard optical components (e.g., lenses and mirrors) in some applications. Introduces wavelength and angular selectivity, which can be restrictive if the element/grating is thick [1]
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