Coherent Fourier Optics Model for the Synthesis of Large Format Lens-Based Focal Plane Arrays

Abstract

Future sub-millimetre imagers are being developed with large focal plane arrays (FPAs) of lenses to increase the field of view (FoV) and the imaging speed. A full-wave electromagnetic analysis of such arrays is numerically cumbersome and timeconsuming. This paper presents a spectral technique based on Fourier Optics combined with Geometrical Optics for analysing, in reception, lens based FPAs with wide FoVs. The technique provides a numerically efficient methodology to derive the Plane Wave Spectrum (PWS) of a secondary Quasi Optical component. This PWS is used to calculate the power received by an antenna or absorber placed at the focal region of a lens. The method is applied to maximize the scanning performance of imagers with monolithically integrated lens feeds without employing an optimization algorithm. The derived PWS can be directly used to define the lens and feed properties. The synthesized FPA achieved scan losses much lower than the ones predicted by standard formulas for horn based FPAs. In particular, a FPA with scan loss below while scanning up to ± .° (~± beam-widths) is presented with directivity of complying with the needs for future sub-millimetre imagers. The technique is validated via a Physical Optics code with excellent agreement.

Antenna-coupled MKIDs for an Integral Field Unit at 7.8 THz

“…The characterization of the sensitivity and the optical efficiency of the pixels [19], as well as the measurement of their complex beam patterns [20], is ongoing. Furthermore, we are currently evaluating the performance with an equivalent reflector quasioptical system using the formalism described in [21]. #%& ) and the spill-over efficiency (" '( #%& ).…”

A Fourier Optics Tool to Derive the Plane Wave Spectrum of Quasi-Optical Systems [EM Programmer's Notebook]

“…The electric PWS in (1a) can be expressed as a function of the electric field scattered by the QO component and evaluated over the FO sphere [27]:…”

“…In a ray picture scenario, far from the focus point (or caustics), one can asymptotically evaluate the PO radiation integral to derive a GO representation of the EM fields. The spreading factor is then computed using this method as described in [27] and [29]:…”

“…By using reciprocity, the electric field, 𝐸 ⃗ 𝑄𝑂 , that the antennacoupled QO system would radiate to (𝑅 𝐹𝐹 , 𝜃 𝐹𝐹 , 𝜙 𝐹𝐹 ) position, at a far distance from the QO component, is evaluated as [27]: In order to construct the pattern in Rx, one needs to illuminate the QO component by a set of incident fields with different skew angles: 𝜃 𝐹𝐹 ∈ [0, 𝜃 𝑅𝑥 ] , 𝜙 𝐹𝐹 ∈ [0,2𝜋] , where 𝜃 𝑅𝑥 represents the maximum elevation angle in the observation grid. By using (12), the GUI plots and exports both the amplitude and phase of the radiative pattern ("Export" button in Fig.…”

“…This PWS can be used as an optimization goal for achieving field matching, and therefore maximizing the aperture efficiency for a certain angular direction. Moreover, the tool can evaluate directly the radiation performance of the entire user-defined QO antenna over a frequency band, similarly to [27]. Particularly, the power delivered to the load of the antenna feed, the aperture efficiency, the directivity, and gain patterns of the whole QO system are estimated.…”