Design and experimental investigation of a planar metamaterial Silicon based lenslet

TL;DR

This paper presents the design and initial performance analysis of a planar, lithographically fabricable metamaterial silicon lenslet for cosmic microwave background experiments, offering efficient, scalable, and anti-reflection coating-free optical coupling.

Contribution

It introduces a novel phase-engineered metamaterial flat-lenslet that is compatible with large-format detector arrays and simplifies fabrication without anti-reflection coatings.

Findings

Preliminary measured performance shows promising optical properties.

Design inherently matches free space, eliminating anti-reflection coatings.

Compatible with large-scale, multiplexed detector arrays.

Abstract

The next generations of ground-based cosmic microwave background experiments will require polarisation sensitive, multichroic pixels of large focal planes comprising several thousand detectors operating at the photon noise limit. One approach to achieve this goal is to couple light from the telescope to a polarisation sensitive antenna structure connected to a superconducting diplexer network where the desired frequency bands are filtered before being fed to individual ultra-sensitive detectors such as Transition Edge Sensors. Traditionally, arrays constituted of horn antennas, planar phased antennas or anti-reflection coated micro-lenses have been placed in front of planar antenna structures to achieve the gain required to couple efficiently to the telescope optics. In this paper are presented the design concept and a preliminary analysis of the measured performances of a phase-engineered metamaterial flat-lenslet. The flat lens design is inherently matched to free space, avoiding the necessity of an anti-reflection coating layer. It can be fabricated lithographically, making scaling to large format arrays relatively simple. Furthermore, this technology is compatible with the fabrication process required for the production of large-format lumped element kinetic inductance detector arrays which have already demonstrated the required sensitivity along with multiplexing ratios of order 1000 detectors/channel.