Plasmonics is an innovative concept in nanophotonics that combines the properties of both electronics and photonics by confining the light energy to a nanometer-scale oscillating field of free electrons/surface plasmon. This article discusses the importance and applications of plasmonics in photonics.
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The Importance of Plasmonics
Plasmonics is an innovative concept in nanophotonics that combines the properties of both electronics and photonics by confining the light energy to a nanometer-scale oscillating field of free electrons/surface plasmon.
Surface plasmon polaritons are primarily highly confined electromagnetic waves that can be used to develop miniaturized optical devices to address the size mismatch issues between large diffraction-limited photonic devices and nanoscale electronics.
The amplification, routing, processing, and generation of optical signals at the nanoscale can play a crucial role in medical, optical communications, biophotonics, chemistry, energy harvesting, and sensing applications.
The manifestation of surface plasmons as confined oscillations enables the development of state-of-the-sensors, ultra-compact optical detectors, and optical nanoantennas. Surface plasmons facilitate both controlling and guiding light at the nanoscale and resonant characteristics of nanostructures.
Resonant nanostructures offer the strength required in light-matter interaction, including significant improvement of electromagnetic fields and their high localization and large optical cross-sections of scattering and absorption processes.
Metamaterials and plasmonics can advance several photonic designs, including light concentrators, hyper- and super-lenses, optical nanoresonators, and subwavelength guides, with exceptional capabilities.
Underlying Processes of Plasmonics Applications
Plasmonic applications rely on the optical processes that occur in nanostructures incorporating materials with free-career oscillations and negative permittivity. These processes involve the coupling of collective oscillation of electrons/plasmons and light at the metal-dielectric interface.
The plasmon properties, such as their localization and resonance frequency, can be manipulated by engineering the composition, shape, and size of nanostructures. The tuning of plasmonic nanostructure properties can enable the development of plasmonics applications by allowing the control of light-matter interactions at the nanoscale.
Plasmonic nanostructures, specifically the structures supporting localized surface plasmon resonance (LSPR), possess strong electromagnetic fields. LSPR leads to significant enhancement of local electromagnetic fields, which improves the functionality of different applications, such as spectroscopy and sensing.
For instance, surface-enhanced Raman spectroscopy (SERS) can be used to substantially enhance the Raman signal through the interaction between plasmons, incident light, and molecules adsorbed on the plasmonic nanostructure surface. SERS plays a critical role in imaging, biosensing, and analytical chemistry.
Scattering and interference of waves in plasmonic nanostructures can be exploited for improved performance in various applications. The scattering and interference rely on different optical processes, including plasmon hybridization and Fano resonance.
Plasmon hybridization involves coupling between plasmons in multiple nanostructures, while Fano resonance emerges due to interference between a broad background continuum and discrete resonance.
In photonics, these processes can be utilized to improve the performance of several applications, including plasmon-induced hot electron generation in catalysis and photocatalysis, plasmon-mediated energy transfer in nanoscale devices, and plasmon-enhanced light harvesting in photovoltaics.
Applications of Plasmonics in Photonics
Plasmonic processes can play a critical role in the operation of light sources and lasers by improving energy transfer efficiency and light-matter interactions and increasing light extraction. For instance, plasmonic nanostructures can improve incident light absorption, leading to higher energy transfer efficiency and enhanced laser performance.
Plasmonic nanoparticles can increase the light absorption in thin-film solar cells and enhance laser light absorption and improve feedback in solid-state laser materials. Similarly, plasmon-induced resonance energy transfer (PIRET) is a process that involves the transfer of energy from a plasmonic nanostructure to an adjacent chromophore/molecule, leading to enhanced emission or other photophysical processes.
Thus, the PIRET process can be utilized to increase the light-emitting diode (LED) efficiency and improve the fluorescence-based sensor performance. Surface plasmon resonance (SPR) is primarily a phenomenon that involves interaction between collective oscillations of electrons and light in a thin metal film, leading to robust scattering/absorption of light at specific wavelengths. This process can be employed to create plasmonic resonators/waveguides and to improve the selectivity and sensitivity of optical biosensors.
Additionally, plasmonic nanostructures can be utilized to improve the light extraction from LEDs or other light sources by enhancing the amount of light coupled out of the LED device into the surrounding environment. This process can increase the brightness and efficiency of LEDs and enable the utilization of lightweight, flexible, and low-cost organic-LED displays.
Photonic integrated circuits (PIC) designs depend on mature nanofabrication processes and optimized and readily available photonic components, such as couplers, splitters, and gratings.
Although hybrid plasmonic elements can improve the PIC functionalities, such as enhanced nonlinearities, nanoscale optical volumes, and wavelength-scale polarization rotation, most PIC-compatible designs utilize single plasmonic elements, with more complex PICs requiring completely new designs.
In a study recently published in the journal Nature Communications, researchers demonstrated a modular approach to post-process silicon-on-insulator (SOI) waveguides into hybrid plasmonic integrated circuits. These circuits consisted of a nanofocusser and a plasmonic rotator, which generated the second harmonic frequency of the incoming light.
Researchers evaluated the performance of every component on the SOI waveguide. Experimental results displayed intensity enhancements of over 200 in 100 nm2 inferred mode area at 1320 nm pump wavelength, which showed that the modular approach to plasmonic circuitry could facilitate its use in practical applications.
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References and Further Readings
Stockman, M. I., Kneipp, K., Bozhevolnyi, S. I., Saha, S., Dutta, A., Ndukaife, J., Kinsey, N., Reddy, H., Guler, U., Shalaev, V. M., Boltasseva, A., Gholipour, B., Krishnamoorthy, H. N. S., MacDonald, K. F., Soci, C., Zheludev, N. I., Savinov, V., Singh, R., Gross, P. et al. (2017). Roadmap on plasmonics. Journal of Optics, 20, 4. https://doi.org/10.1088/2040-8986/aaa114
Babicheva, V. E. (2023). Optical Processes behind Plasmonic Applications. Nanomaterials, 13(7). https://doi.org/10.3390/nano13071270
Tuniz, A., Bickerton, O., Diaz, F. J., Käsebier, T., Kley, E., Kroker, S., Palomba, S., de Sterke, C. M. (2020). Modular nonlinear hybrid plasmonic circuit. Nature Communications, 11(1), 1-8. https://doi.org/10.1038/s41467-020-16190-