Broadband and Efficient Diffraction

Abstract

Abstract:Surface topography dictates the deterministic functionality of diffraction by a surface. In order to maximize the efficiency with which a diffractive optical component, such as a grating or a diffractive lens, directs light into a chosen order of diffraction, it is necessary that it be "blazed". The efficiency of most diffractive optical components reported so far varies with the wavelength, and blazing is achieved only at a specific nominal energy, the blaze wavelength. The existence of spurious light in undesirable orders represents a severe limitation that prevents using diffractive components in broadband systems. Here we experimentally demonstrate that broadband blazing over almost one octave can be achieved by combining advanced optical design strategies and artificial dielectric materials that offer dispersion chromatism much stronger than those of conventional bulk materials. The possibility of maintaining an efficient funneling of the energy into a specific order over a broad spectral range may empower advanced research to achieve greater control over the propagation of light, leading to more compact, efficient and versatile optical components.The basic principles for tailoring the electromagnetic field of free-space optical waves and the physics of reflection, refraction and diffraction on which it is based, have been well understood for a very long time. However, until relatively recently the whole of optical technology has been limited by the very reasonable constraint that optical systems can only be designed to be made from materials that are actually available. This paradigm is presently challenged with the introduction of electromagnetic metamaterials [1], which are artificially engineered structures that have effective dielectric or magnetic constitutive parameters not attainable with naturally occurring materials. Here we study graded metamaterial films composed of mesoscopic holes and pillars etched in a semiconductor substrate. Under illumination by an incident light whose wavelength is slightly larger than the indentation dimensions, the film implements unusually strong chromatic dispersions of the effective refractive-indices. We suggest that the fusion of low-cost lithographic techniques with this new 2 design strategy will play a central role in devising diffractive optical components that remain blazed over a broad range of energies. Our first generation device, fabricated with fully standard semiconductor processes in a GaAs wafer, offers an efficient funnelling of the incident energy into a single diffraction orders over almost an octave.The common way to achieve perfect blazing into a specific diffraction order is to imprint the incident electromagnetic field with a gradual phase variation that varies by exactly 2π from one side of a diffractive zone to the other. Echelette profiles with triangular grooves are common examples which have been manufactured for the last century [2]. The 2π-phase jump is in general achieved at a single energy, the blaze wavelength. Illuminated at...

Metalenses at visible wavelengths: past, present, perspectives

“…With this extra degree of freedom, it is possible to exploit the highly chromatic behavior of semiconductor structures with dimensions only slightly smaller than the wavelength to make the product nearly independent of wavelength. The idea initiated in the context of broadband subwavelength phase‐plate gratings was tested in for metalenses composed of a careful combination of micropillars and microholes. The device has been characterized in the thermal infrared (band III) and blazing over nearly one octave was observed experimentally.…”

Binary blazed reflection grating for UV/VIS/NIR/SWIR spectral range

“…In consequence, one has to look for alternative approaches. Binary gratings where the blazing functionality is achieved via sub-wavelength features have been demonstrated to be a promising alternative 6,7,8 . Moreover, by a dedicated design of the sub-wavelength features' sizes the spectral response can be either broadened or it can be tuned in order to emphasize particular spectral regions of interest.…”

All-dielectric subwavelength metasurface focusing lens

“…Similar dielectric diffractive structures have been used for designing physically thin versions of various optical components, including blazed gratings [11][12][13][14][15][16][17][18], waveguide couplers [19][20][21], and computer generated holograms [22][23][24]. Flat lenses based on diffractive structures have also been proposed [17,25,26] and demonstrated [9,25].…”