Abstract
Axicon lenses are versatile optical elements that can convert Gaussian beams to Bessel-like beams. In this letter, we demonstrate that axicons operating with high efficiencies and at large angles can be produced using high-contrast, multilayer gratings made from silicon. Efficient beam deflection of incident monochromatic light is enabled by higher-order optical modes in the silicon structure. Compared to diffractive devices made from low-contrast materials such as silicon dioxide, our multilayer devices have a relatively low spatial profile, reducing shadowing effects and enabling high efficiencies at large deflection angles. In addition, the feature sizes of these structures are relatively large, making the fabrication of near-infrared devices accessible with conventional optical lithography. Experimental lenses with deflection angles as large as 40° display field profiles that agree well with theory. Our concept can be used to design optical elements that produce higher-order Bessel-like beams, and the combination of high-contrast materials with multilayer architectures will more generally enable new classes of diffractive photonic structures.
Highlights
Axicon lenses have broad utility due to their ability to produce Bessel-like beams, which focus light along a line, suppress diffraction, and are self-healing.[1,2] These unique properties have made axicons useful in many applications in biological imaging, such as optical coherence tomography[3,4] and light-sheet microscopy,[5] where the linear focusing and robustness of Bessel-like beams to scattering enable improvements in resolution and depth of field
When the grating periods are near the operation wavelength and the deflection angles are large, the device efficiencies decrease due to shadowing effects incurred by the physical topology of these grating structures.[13,14,15]
We show that high-contrast, multilayer gratings made from silicon [Fig. 1(e)] can be used to produce high-performance axicon lenses
Summary
Axicon lenses have broad utility due to their ability to produce Bessel-like beams, which focus light along a line, suppress diffraction, and are self-healing.[1,2] These unique properties have made axicons useful in many applications in biological imaging, such as optical coherence tomography[3,4] and light-sheet microscopy,[5] where the linear focusing and robustness of Bessel-like beams to scattering enable improvements in resolution and depth of field. These devices generally contain relatively large feature sizes and operate with high efficiencies at small deflection angles.
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