Nanophotonics concerns the light-matter interactions between species on the nanometer length scale and light. Nanophotonics is an interesting field for study because there are many unique phenomena that occur when the wavelength of the incident light is nearly equivalent to the size of the structure, opening up new possibilities for the control and manipulation of the properties of light.
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One growth area in nanophotonics is the development of on-chip nanophotonic devices or photonic integrated circuits.1 Photonics is the light-based equivalent of electronics and many researchers and engineers have been working on ways to create logic devices and circuits that use photons rather than electrons, as is done in traditional electronics.
The advantage light-based devices are that they offer faster communication speeds and reduced thermal load on components. Some optical devices also have the unusual property that heating can be used to intentionally control the device's behavior.2
Another advantage of photonic devices is that such devices can be miniaturized to very small scales. The ability to create complete ‘lab on a chip’ devices is very important for sensor technologies as, with the right nanofabrication methods, it is possible to create compact nanophotonic devices that can be used for applications such as detection and quantification of specific chemical species or the presence of biomarkers for particular diseases.3
The use of plasmonic resonances in nanoscale structures often helps to enhance the detected signal levels and boost the sensitivity of such sensors.
Miniaturization
One recent innovation in nanophotonics devices is the development of ‘on-a-chip’ optical phase modulators that work in the visible region of the electromagnetic spectrum.4 A benchtop laser system relies on several different kinds of optical components to work, from mirrors to control the beam pointing to more complex devices such as optical parametric amplifiers that can be used for frequency conversions of the incident laser beam.
As many optical applications, whether in spectroscopy or metrology, need a variety of optical hardware components, the challenge is to find a way to replicate them on the length scale of a single chip. Optical phase modulators are highly important optical components as they can be used to modulate the phase of a beam.
Phase modulation is found in a number of optics applications, including fiber-optic communication, interferometer-based sensor devices and gyroscopes. While there has been good success in creating nanophotonic devices that operate in the infrared region of the electromagnetic spectrum, creating photonic phase modulators that operate in the visible has been more challenging.5
Nanophotonics
Researchers at Columbia University have been developing micrometer-scale phase modulators with very low power consumption.4 Typically electro-optic modulators, which often use an electrical current to drive a polarization change in a particular material, have demanding power consumption and large footprints. The new advancement in making robust and efficient chip-sized devices will open a wealth of possibilities for integrating phase modulators in small-scale technologies.
Many current technologies that operate on the nanoscale for photonics applications are based on waveguides and the propagation of light through them. While waveguides work very well for many applications, there are some limitations to large-scale on-chip integration with such technology.
The team’s advancement came in developing strongly over-coupled micro-resonators to form a micro-ring resonator that could be used to control the phase of the incident light. The key to achieving this was finding ways to minimize optical scattering losses within the device and using an optical design that enhanced the resonator-waveguide coupling strength.
The micro-rings that formed the part of the resonator were nanofabricated from silicon nitride and a platinum micro-heater was used as a way of controlling the device. Electron beam lithography provided the spatial resolution and precision required to create the components on the nanoscale required for this particular application.
Laser Innovation
The team at Columbia University and their collaborators have also been working to develop visible laser technologies that produce narrow-band light for quantum information applications. It has been challenging to find ways to reduce the cost of lab-based visible laser systems, but integrated photonic devices are starting to produce results and beam outputs that mean they could offer a competitive lower-cost alternative.
One of the advantages of the new miniature laser was the high degree of tunability. The team was able to demonstrate the laser could generate wavelengths from the near-UV to the near-IR at extremely high repetition rates.
While many high-power laser applications will still need large, dedicated laser facilities to house the equipment and bulky laser systems, nanophotonics advances are now starting to offer more, chip-sized, cost-effective alternatives making it easier than ever to integrate the advantages of laser beam outputs into small and affordable devices. With their low power consumption and small footprint, nanophotonics-based laser systems are likely to become a staple of portable sensor and spectrometry instrumentation.
References and Further Reading
Karabchevsky, A., Katiyi, A., Ang, A. S., & Hazan, A. (2020). On-chip nanophotonics and future challenges. Nanophotonics, 9(12), 3733–3753. https://doi.org/10.1515/nanoph-2020-0204
Li, L., Tamanuki, T., & Baba, T. (2022). All-optic control using a photo-thermal heater in Si photonics. Optics Express, 30(23), 41874–41883. https://doi.org/10.1364/OE.469977
Estevez, M. C., Alvarez, M., & Lechuga, L. M. (2012). Integrated optical devices for lab‐on‐a‐chip biosensing applications. Laser Photonics Review, 6, 463–487. https://doi.org/10.1002/lpor.201100025
Liang, G., Huang, H., Mohanty, A., Shin, M. C., Ji, X., Carter, M. J., Shrestha, S., Lipson, M., & Yu, N. (2021). Robust, efficient, micrometre-scale phase modulators at visible wavelengths. Nature Photonics, 15(12), 908–913. https://doi.org/10.1038/s41566-021-00891-y
Guo, Q., Li, C., Deng, B., Yuan, S., Guinea, F., & Xia, F. (2017). Infrared Nanophotonics Based on Graphene Plasmonics. ACS Photonics, 4(12), 2989–2999. https://doi.org/10.1021/acsphotonics.7b00547
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