演示多色衍射镜头可调焦距外文翻译资料

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Demonstration of a multi-color diffractive lens

with adjustable focal length

N. BREGENZER , 1 T. Ouml; TTL ,2 M. ZOBERNIG , 1 M. BAWART, 1,2

S. BERNET, 1,* AND M. RITSCH-MARTE1

1Institutefor Biomedical Physics, Medical University of Innsbruck, Muuml;llerstr. 44, 6020 Innsbruck, Austria

2Diffratec Optics OG, Sonnenstr. 14, 6020 Innsbruck, Austria

* stefan.bernet@i-med.ac.at

Abstract: A pair of combined diffractive optical elements (DOEs) realizes a so-called moireacute; lens, with an optical power which can be tuned by a mutual rotation of the two DOEs around their central optical axis. Earlier demonstrated moireacute; lenses still suffered from chromatic aberrations. Here we experimentally investigate a multi-color version of such a lens, realized by a pair of multi-order DOEs. These DOEs have a deeper surface structure which modulates the phase of the transmitted light wave by several multiples of 2n. The corresponding multi-order moireacute; lenses all have the same focal length at a fixed set of harmonic wavelengths within the white light spectrum. The experiments demonstrate that multi-order moireacute; lenses have significantly reduced chromatic aberrations. We investigate the performance of the lens for narrow band and white light imaging applications.

copy; 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Tunable lenses consisting of a pair of adjacent optical elements have been known for more than 50 years. Alvarez-Lohmann lenses named after their two independent inventors [1–4] are translated with respect to each other in order to control the optical power. Later, rotational versions of these lenses (sometimes also called moireacute; lenses, due to their underlying operation principle), have been investigated first numerically [5], and later experimentally [6–9]. They consist of two adjacent diffractive optical elements (DOEs), which are rotated with respect to each other around their central optical axis in order to change the optical power. Moireacute; lenses are interesting for laser machining applications, since they are suited for high laser powers, they provide diffraction limited focusing, they introduce no undesired Petzval field curvature and no barrel or pincushion field distortions, and they keep the focus exactly on the optical axis during optical power variation. The same principle is now also employed for designing tunable lenses with nanostructured optical meta-materials [10,11].

The currently demonstrated diffractive tunable lenses are, however, strongly dispersive. On the one hand, this feature can be advantageously used to control the dispersion in optical setups using a hybrid system consisting of a tunable refractive lens and a subsequent tunable diffractive lens [12]. However, on the other hand strong dispersion is usually not desired for imaging applications with broadband light, although chromatic errors may be reduced by computational post-processing [13]. Thus there is a high interest in designing achromatic tunable lenses. One recent approach is based on 'metalenses', which correspond to nano-structured meta surfaces. There it was shown that achromatic behavior can be achieved by polarization control of the incident light [14]. Furthermore, tunable meta lenses based on the Alvarez principle have been demonstrated, which showed a considerably reduced chromatic error as compared to static meta lenses [15].

For the case of achromatic diffractive moireacute; lenses, suggested in the following, numerical studies have already been performed, which demonstrate their feasibility. One approach suggested by [16] shows that full diffraction efficiency over the whole visible light range can be achieved

using multi-layer diffractive structures, consisting of combinations of materials with different refraction indices. However, in this case the focal length is still wavelength-dependent. Another approach suggests to employ multi-order diffractive optical elements [17]. This principle has already been demonstrated for static diffractive 'harmonic lenses', which were shown to have the same optical power, and the same (in principle unlimited) diffraction efficiency at a set of harmonic wavelengths [18–21]. More recently, methods have been developed to design s

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