**Abstract**

Infrared optical detection devices such as photodetectors, solar cells, cameras, and microbolometers are becoming smaller in size with a tiny active area in the range of a few micrometers or even nanometers. That comes at the expense of a smaller aperture area of the device, and in turn inefficient collection of infrared energy. Therefore, infrared plasmonic optical antennas are becoming essential to efficiently collect optical energy from free space and concentrate it down to the device's tiny area. However, it is desirable to develop plasmonic antennas with a broad bandwidth, polarization insensitivity, wide field-of-view, and reasonable plasmonic losses. That ensures collection of most incident infrared radiation and enhancement of power absorption efficiency. In this chapter, some types of plasmonic antennas are explored with an emphasis on innovative type of optical antenna called Bundt Optenna. We investigate Bundt Optenna design and optimization. This antenna has a novel shape that looks like a Bundt baking pan and it is made of gold. Several Bundt unit cells can be arranged in a periodic array that is placed on top of a thin-film infrared absorbing layer. The Bundt Optenna utilizes surface plasmons to squeeze both electric and magnetic fields of infrared radiation down to a 50 nm wide area, thus enhancing absorption efficiency within an underneath thin-film layer. The Optenna demonstrates polarization insensitivity and ultra-broad bandwidth with a large fractional bandwidth within the near, short-wave, and mid-wave infrared bands. It also shows a remarkable enhanced power absorption efficiency and a wide field-of-view.

**Keywords:** nanophotonics, optical antenna, surface plasmonics, infrared detection, infrared absorption enhancement
