Simulation of relief-type diffractive lenses in ZEMAX using parametric modelling and scalar diffraction

et al. 2022

The polychromatic integral diffraction efficiency (PIDE) metric is generally used to select the most suitable materials for multilayer diffractive optical elements (MLDOEs). However, this method is based on the thin element approximation, which yields inaccurate results in the case of thick diffractive elements such as MLDOEs. We propose a new material selection approach, to the best of our knowledge, based on three metrics: transmission, total internal reflection, and the optical component’s total thickness. This approach, called “geometric optics material selection method” (GO-MSM), is tested in mid-wave and long-wave infrared bands. Finite-difference time-domain is used to study the optical performance (Strehl ratio) of the “optimal” MLDOE combinations obtained with the PIDE metric and the GO-MSM. Only the proposed method can provide MLDOE designs that perform. This study also shows that an MLDOE gap filled with a low index material (air) strongly degrades the image quality.

Section: Limits Of the Pide Methodsmentioning

confidence: 99%

Multilayer diffractive optical element material selection method based on transmission, total internal reflection, and thickness

Laborde¹,

Loicq²,

et al. 2022

“…In this section, two alternatives to TEA are described. Our ray model, inspired by [18,19], examined in this paper is a scalar model based on the calculation of OPL using ray-tracing. FDTD is an electromagnetic calculation providing exact vectorial fields and serves as a reference solution for the comparison of the ray and TEA models.…”

Section: Alternative Phase Models: Ray Model and Fdtdmentioning

confidence: 99%

“…This approach is not new and was developed in [18] under the name "zone decomposition" modeling for the design of hybrid optical systems. It is further implemented in [19] and coupled with diffraction calculation to estimate the modulation transfer function of relief-type DOEs. We aim to examine the reliability and accuracy of the ray model compared with TEA in the case of MLDOEs.…”

Section: Introductionmentioning

confidence: 99%

“…The outputs of each of the three methods (TEA, ray model, and FDTD) are the MLDOE phase and amplitude patterns in the near field. Consequently, a Fourier optics propagator based on the angular spectrum method is used to generate optical fields and evaluation metrics in the far field, at the detector plane (similarly to [19]). Both MWIR and LWIR wave bands are investigated.…”

Section: Introductionmentioning

confidence: 99%

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Hybrid ray-tracing/Fourier optics method to analyze multilayer diffractive optical elements

Laborde¹,

Loicq

et al. 2022

The performance (paraxial phase delay) of conventional diffractive optical elements is generally analyzed using the analytical scalar theory of diffraction, based on thin-element approximation (TEA). However, the high thickness of multilayer diffractive optical elements (MLDOEs) means that TEA yields inaccurate results. To address this, we tested a method based on ray-tracing simulations in mid-wave and long-wave infrared wave bands and for multiple f -numbers, together with the effect of MLDOE phase delay on a collimated on-axis beam with an angular spectrum method. Thus, we accurately generate optical figures of merit (point spread function along the optical axis, Strehl ratio at the “best” focal plane, and chromatic focal shift) and, by using a finite-difference time-domain method as a reference solution, demonstrate it as a valuable tool to describe and quantify the longitudinal chromatic aberration of MLDOEs.

“…Finally, ray-tracing and Fourier optics have been combined to estimate MLDOE's optical performance at the focal plane [12] and provide a material selection method [13]. This concept is not new and has been used for the modeling and design of hybrid optical systems [14,15]. The optical performance of many MLDOE examples has been accurately retrieved using the finite-difference time-domain (FDTD) method [12,13].…”

Section: Introductionmentioning

confidence: 99%

Thickness optimization algorithm to improve multilayer diffractive optical elements performance

Laborde¹,

Loicq

et al. 2023

The diffractive zone thicknesses of conventional diffractive optical elements (DOEs) are generally obtained using the thin element approximation (TEA). However, the TEA yields inaccurate results in the case of thick multilayer DOEs (MLDOEs). The extended scalar theory (EST) is an alternative thickness optimization method that depends on the diffractive order and the optimization wavelength. We developed an algorithm to research suitable EST input parameters. It combines ray-tracing and Fourier optics to provide a performance estimate for each EST parameter pair. The resulting “best” MLDOE designs for three different material combinations are analyzed using rigorous finite-difference time-domain. Compared to the TEA, the proposed algorithm can provide performing zone thicknesses.