Scalar Diffraction Analysis Of Dispersion In Low-Index Thin Flat Lenses

TL;DR

This paper investigates the dispersion properties of low-index thin flat lenses using scalar diffraction and FDTD methods, comparing results with analytical formulas and experimental data to assess accuracy across different numerical apertures.

Contribution

It introduces a comparative analysis of scalar diffraction, FDTD, and analytical models for low-index thin lenses, highlighting the accuracy limits of the analytical formula at various NAs.

Findings

Analytical formula is accurate for NA up to 0.2.

FDTD results agree with experimental data.

Error remains around 8% for larger NAs.

Abstract

We analyze the dispersion property of low-index thin lenses by using scalar diffraction and finite difference time domain (FDTD) methods. We compare the dispersion results obtained by using these methods with reported experimental results, and the well-known analytical formula for focal length (f) of diffractive lenses as a function of wavelength ({\lambda}),f({\lambda})=(f_0 {\lambda}_0)/{\lambda},where f_0 is the designed focal length for wavelength {\lambda}_0. We show that when the analytical formula is applied to thin flat lenses with low-refractive index, the results are accurate for small numerical aperture (NA) up to 0.2. For larger NA, the error between the analytical approximation and the FDTD analysis remains around 8% over a wide range of NA.