Fourier Optics for the Analysis of Distributed Absorbers Under THz Focusing Systems

Abstract

An analytical spectral model able to accurately and efficiently characterize absorbers distributed in the focal plane of focusing THz systems is presented. The model is obtained by using a Fourier optics representation of the electromagnetic field in the focal plane in conjunction with a recently developed equivalent network representation for the interaction of plane waves with distributed absorbers. The model is validated by comparisons with numerical full-wave simulations. Finally, the model is used to design a few architectures based on lens-coupled Kinetic Inductance Detectors (KIDs), which show high absorption efficiency over a large bandwidth.

Reception Power Pattern of Distributed Absorbers in Focal Plane Arrays: A Fourier Optics Analysis

“…In [25] an analytical method, based on a Fourier Optics (FO) approach, for calculating the power absorbed by a resistive linear strip mesh in the focal plane of an optical system, was presented. The FO method can be used to derive in a simple way a spectral wave expansion of the direct field focused on the focal plane.…”

“…Other proposed approaches for deriving the spectrum resort to asymptotic procedures which make use of numerical evaluations of the Physical Optics (PO) field as in [34]. In [25], the spectral plane wave expansion derived by using FO was linked to a periodic spectral field representation in the surrounding of the absorbers (via a Floquet mode expansion [35]). In this section, the extension of the analysis to generic planar periodic absorbing geometries, and slightly offbroadside incidence, is presented.…”

“…It is based on a Fourier Optics (FO), [24], spectral field representation. The power received by a periodic absorber is evaluated by using a Floquet mode based equivalent circuit model similar to the one introduced in [25], whose generators are obtained by expanding the direct fields in terms of plane waves coming from the quasi-optical system (reflector in Fig. 1).…”

“…1). In particular, the methodology in [25] is extended to skew incidence, and to any type of periodic absorber. The analysis of reflector systems in reception has also been used for characterizing antenna feeds [26], [27].…”

Analysis of absorber based imaging systems with distributed incoherent sources

“…As shown in [4], the power received by a periodic absorber can be evaluated by using a Floquet mode born circuit model, whose generators are obtained by expanding the direct fields in terms of plane waves coming from the quasi-optical system. Here the methodology in [4] is extended to a more general type of periodic mesh absorbers and squint incidences. Using this approach, we can derive the point source angular response of bare absorbers under a focusing system (i.e.…”