The growing importance of diffractive and meta-lenses in modern optical systems makes it vital to investigate and understand their capabilities. They play an important role in various applications like imaging systems, laser-beam shaping, bio/medical-optics, etc. We propose methods for the modeling of diffractive and meta-lenses based on the concept of the fast-physical-optics approach. A diffractive or meta-lens can be modeled as a series of structures functioning locally (e.g. local gratings) on a base interface. Each local structure introduces a certain local phase modulation, and by putting all of them together, the lens functionality can be achieved. In our approach, the rigorous Fourier modal method (FMM), also known as the rigorous coupled wave analysis (RCWA), is applied for the analysis of the local micro-/nanostructures, with all vectorial effects and possible higher-order effects taken into consideration; then the phase modulations can be collected for the lens function modeling. In this manner, a multi-scale simulation of optical systems with diffractive/meta-lenses becomes feasible and efficient in practice.
Optical components consisting of hybrid elements (reflective, refractive and diffractive elements) are widely used in modern optical applications. Diffractive lenses as an example play an important role in imaging systems, laser-beam shaping, integration systems in optical communications, etc. Recently, due to the advances in modern fabrication technologies, meta-lenses also start to draw attention. We propose methods for the modeling and design of diffractive and meta-lenses based on the concept of the fast-physical-optics approach. A diffractive or meta-lens can be modeled as a series of structures functioning locally (e.g. local gratings) on a base interface. Each local structure introduces a certain local phase modulation, and by putting all of them together, the lens functionality can be achieved. In our approach, the rigorous Fourier modal method (FMM) is applied for the analysis of the local micro-/nanostructures, with all vectorial effects and possible higher-order effects taken into consideration; then the phase modulations can be collected for the lens function modeling. In this manner, a multi-scale simulation becomes feasible and efficient in most cases. The design of diffractive/meta-lenses follows an inverse concept—starting with a functional description of the whole lens, and then searching for suitable local structures which realize the desired phase modulation with high efficiency. Depending on the working diffraction order of the local structures, either a diffractive or a meta-lens can be constructed.
We discuss the implications of the modeling and the design of diffractive and refractive freeform surfaces in nonparaxial regions of the fields to shape the profile of a laser beam in its far field, its focus or any other region. The fast physical optics approach employed enables the inclusion of freeform surfaces and diffractive beam shaping elements in the modeling. The design of beam shaping elements follows an inverse physical optics approach. We will discuss the pros and cons of refractive and diffractive solutions together with examples.
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