Dielectric Nanophotonics

Photonic crystal lasers on paper substrates. (Credit: KAIST)

Arseniy Kuznetsov of the Data Storage Institute in Singapore focuses his research in the field of dielectric nanophotonics, which studies the behavior and use of light in nanoscale projects. Among other things, his team is working on developing a new concept of low-loss dielectric nanoantennas. The concept can be used in several industries, including creating improved medical devices, applying it in virtual reality and augmented reality, and developing holographic displays.

Kuznetsov received Britain's IET AF Harvey Prize for his research in this field. According to Sir John O'Reilly, chair of the IET's selection committee for the prize, Kuznetsov's research may lead to explosive growth in this field, creating new products based on nanophotonics. Kuznetsov says the award demonstrates the success of his research in the past several years, as well as the field's promising future.

To effectively control light, its electric and magnetic components must be controlled simultaneously and independently. Yet, there is a problem: the magnetic response of natural materials at optical frequencies is often weak, and photonic devices mainly work with the electric part of the optical wave. Dielectric nanophotonics aims to solve this problem because it allows controlling both electric and magnetic resonances.

How does it work? According to Kuznetsov, most structures with a magnetic response contain metal elements and have high losses at optical frequencies. This naturally limits their performance. Plasmonic nanoantennas are structures based on metals — gold, aluminum, silver, and copper. They are almost ideal for working in the radiofrequency band, but are not good at controlling light on a nanoscale.

These limitations affect applications such as sensing, which is used in both biology and medicine. Almost every biochemical laboratory has devices based on surface plasmon resonance that can be used to monitor a chemical reaction on a nanoscale. The plasmon sensors overheat due to losses, which limits the use of sensing. For example, it is difficult to apply it to small concentrations of temperature-sensitive proteins.

Dielectric nanoantennas can solve this problem. Dielectric nanoantennas are structures based on materials with low losses such as silicon or gallium arsenide. Such materials react to both the electric and the magnetic parts of the wave. In addition, depending on the shape of the particle, responses can be varied, which gives much greater flexibility in controlling light.

In collaboration with the Data Storage Institute, the Metamaterials Laboratory at ITMO University (St. Petersburg, Russia) also conducts research on the optical properties of dielectric silicon metasurfaces that can conduct light in 2D on a potential optical chip. Other research focuses on detection of hot spots in the magnetic fields of dielectric structures. This research will make it possible to more effectively detect substances that are sensitive to the magnetic field at optical frequencies. Current projects involve research on luminescence amplification, nonlinear dielectric antennas, and hybrid nanoantennas and metasurfaces.

The next challenge in the field of dielectric nanophotonics will be creating tunable structures, the ability to dynamically control the optical properties of each nanoparticle separately. These developments will enable the creation of a display that will show 3D images. Future research in dielectric nanophotonics will allow the development of tunable flat optics, reducing the thickness of existing lenses to just a few hyperfine layers with dynamically controllable optical properties.

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Photonic Nanocavities

Photonic crystal resonator laser and refractive index sensor operating on paper substrates. (Credit: KAIST)

Researchers have developed a semiconductor photonic nanocavity laser that can operate on a paper substrate. Prof. Yong-Hoon Cho and his team in the Department of Physics at KAIST (Daejeon, Korea) hope that this novel method, which involves transferring nanosized photonic crystal particles onto a paper substrate with high absorptiveness, will enable the diagnoses of various diseases by using low-cost semiconductor sensors.

Photonic crystals, which utilize light as a medium to provide high bandwidths, can transfer large amounts of information. Compared with their electronic counterparts, photonic crystals also consume less energy to operate.

Normally, semiconductor photonic particles require substrates, which play only a passive role in the assembly and endurance of individual, functional photonic components. These substrates, however, are bulky and environmentally hazardous because they are made up of non-biodegradable materials.

The research team overcame these two shortcomings by replacing a semiconductor substrate with standard paper. The substrate's mass was reduced considerably, and because paper is made from trees, it degrades. Paper can be easily and cheaply acquired, which drastically reduces the unit cost of semiconductors. In addition, paper possesses superior mechanical characteristics. It is flexible and can be repeatedly folded and unfolded without tearing. These are traits that researchers have long sought for existing flexible substrates.

The team used a microsized stamp to detach photonic crystal nanobeam cavities selectively from their original substrate and transfer them onto a new paper substrate. Using this technique, the team removed nanophotonic crystals that had been patterned (using a process of selectively etching circuits onto a substrate) onto a semiconductor substrate with a high degree of integration and realigned them as desired on a paper substrate.

In this research, the nanophotonic crystals that the team combined with paper were 0.5 μm in width, 6 μm in length, and 0.3 μm in height — about one-hundredth of the width of a single hair (0.1 mm).

The team also transferred their photonic crystals onto paper with a fluid channel, which proved that it could be used as a refractive index sensor. Since photonic crystal particles have high sensitivity, they are highly suitable for applications such as sensors. Current commercial pregnancy diagnosis kits use paper with high absorptiveness.

Cho says that by using paper substrates, this technology can greatly contribute to the rising field of producing environmentally friendly photonic particles and that combining inexpensive paper and high-performance photonic crystal sensors enables them to keep costs low while designing technologies with high performance.

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This article was compiled by Sherrie Trigg, Editor and Director of Medical Content for Medical Design Briefs.