Optical rectenna

Figure 1. Spectral irradiance of wavelengths in the solar spectrum. The red shaded area shows the irradiance at sea level. There is less irradiance at sea level due to absorption of light by the atmosphere.

An optical rectenna is a rectenna (rectifying antenna) that works with visible or infrared light.[1] A rectenna is a circuit containing an antenna and a diode, which turns electromagnetic waves into direct current electricity. While rectennas have long been used for radio waves or microwaves, an optical rectenna would operate the same way but with infrared or visible light, turning it into electricity.

While traditional (radio- and microwave) rectennas are fundamentally similar to optical rectennas, it is vastly more challenging in practice to make an optical rectenna. One challenge is that light has such a high frequency—hundreds of terahertz for visible light—that only a few types of specialized diodes can switch quickly enough to rectify it. Another challenge is that antennas tend to be a similar size to a wavelength, so a very tiny optical antenna requires a challenging nanotechnology fabrication process. A third challenge is that, being very small, an optical antenna typically absorbs very little power, and therefore tend to produce a tiny voltage in the diode, which leads to low diode nonlinearity and hence low efficiency. Due to these and other challenges, optical rectennas have so far been restricted to laboratory demonstrations, typically with intense focused laser light producing a tiny but measurable amount of power.

Nevertheless, it is hoped that arrays of optical rectennas could eventually be an efficient means of converting sunlight into electric power, producing solar power more efficiently than conventional solar cells. The idea was first proposed by Robert L. Bailey in 1972.[2] As of 2012, only a few optical rectenna devices have been built, demonstrating only that energy conversion is possible.[3] It is unknown if they will ever be as cost-effective or efficient as conventional photovoltaic cells.

The term nantenna (nano-antenna) is sometimes used to refer to either an optical rectenna, or an optical antenna by itself. [4] In 2008 it was reported that Idaho National Laboratories designed an optical antenna to absorb wavelengths in the range of 3–15 μm.[5] These wavelengths correspond to photon energies of 0.4 eV down to 0.08 eV. Based on antenna theory, an optical antenna can absorb any wavelength of light efficiently provided that the size of the antenna is optimized for that specific wavelength. Ideally, antennas would be used to absorb light at wavelengths between 0.4 and 1.6 μm because these wavelengths have higher energy than far-infrared (longer wavelengths) and make up about 85% of the solar radiation spectrum[6] (see Figure 1).

  1. ^ Moddel, Garret; Grover, Sachit (2013). Garret Moddel; Sachit Grover (eds.). Rectenna Solar Cells. Springer. ISBN 978-1-4614-3716-1.
  2. ^ Corkish, R; M.A Green; T Puzzer (December 2002). "Solar energy collection by antennas". Solar Energy. 73 (6): 395–401. Bibcode:2002SoEn...73..395C. doi:10.1016/S0038-092X(03)00033-1. hdl:1959.4/40066. ISSN 0038-092X. S2CID 122707077.
  3. ^ "M254 Arts & Engineering/Science Research". www.mat.ucsb.edu. Retrieved 2023-11-06.
  4. ^ Awad, Ehab (21 August 2019). "Nano-plasmonic Bundt Optenna for broadband polarization-insensitive and enhanced infrared detection". Scientific Reports. 9 (1): 12197. Bibcode:2019NatSR...912197A. doi:10.1038/s41598-019-48648-6. ISSN 2045-2322. PMC 6704059. PMID 31434970.
  5. ^ Dale K. Kotter; Steven D. Novack; W. Dennis Slafer; Patrick Pinhero (August 2008). Solar Nantenna Electromagnetic Collectors (PDF). 2nd International Conference on Energy Sustainability. INL/CON-08-13925. Archived from the original (PDF) on 11 August 2016. Retrieved 12 June 2016.
  6. ^ Berland, B. (2009-04-13). "Photovoltaic Technologies Beyond the Horizon: Optical Rectenna Solar Cell" (PDF). National Renewable Energy Laboratory.