Abstract
Planar lenses such as metalenses and diffractive lenses exhibit severe field-dependent aberrations when imaging extended objects with high numerical aperture. This problem can be overcome by stacking at least two of such devices on top of each other. In this work, we present such stacked imaging systems, namely doublets and triplets of diffractive optical elements. They are fabricated by femtosecond direct laser writing in one single step without the need for alignment in sizes of below 200 µm in diameter and 100 µm in height. The lenses allow for efficient sub µm resolution imaging at visible wavelengths combined with a full field-of-view of up to 60°. As additional benefit, our approach dramatically reduces the writing times of 3D printed lens systems to below 15 minutes.
Highlights
We present 3D printed stacked diffractive imaging systems which combine the aforementioned advantages with nearly aberration-free imaging for a given wavelength, allowing for high resolution imaging over an extended field of view
Flat diffractive lenses were first conceived by Augustin-Jean Fresnel [12] and evolved into elaborate schemes [13,14,15,16] that culminated in wafer level optics [17,18] as well as in metalenses [19,20,21,22,23,24]
At an angle of 55° which corresponds to the marginal ray angle when focusing with a numerical aperture of 0.82, a mean efficiency of 25.6% was measured
Summary
We present 3D printed stacked diffractive imaging systems which combine the aforementioned advantages with nearly aberration-free (aplanatic) imaging for a given wavelength, allowing for high resolution imaging over an extended field of view. Our stacked diffractive optical elements can be realized with a simple one-step fabrication process and a high miniaturization of the overall device. Field dependent monochromatic aberrations such as astigmatism, coma, and field curvature can be corrected by bending a diffractive lens [26,27,28] or by combining multiple elements as was suggested theoretically by Bobrov [29] and later by Buralli [30]. Arbabi et al presented a miniature metasurface camera consisting of two separated flat lenses which shows corrected imaging performance over a field of view of 70° in the near infrared [31]. Groever et al presented a similar metalens working in the visible regime [32]
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