Recent Advancements in Meta Waveguide Manufacturing and Applications
Waveguides are a type of device which are used frequently in broadcasting, radar installations, and several other types of communication systems. They are hollow metallic tubes or pipes that do not contain end surfaces. They come in several types as Rectangular, Circular, Elliptical, Corrugated. These are used to transfer energy in the form of electromagnetic waves from one place to another in the microwave region with minimal loss of energy. Waveguides are usually used in high-power applications. The use of microwave radar systems and the energy transmission from the transmitter to antennas can be given as examples of such use cases. A waveguide with two dielectric materials with the one having a higher refractive index is surrounded by the other is called a dielectric waveguide. An optical fiber is a very common example of dielectric waveguides. Usually, waveguides are built using metals that have low bulk resistivity such as copper, silver, aluminium, brass. With the recent advancements, the need for even lower lossy waveguides and waveguides that can go further into the smaller microwave spectrum has increased. Lithographic methods, Electro-forming, Dip-brazing, Electronic-discharge-machining, are some of the waveguide manufacturing methods that are used frequently.
Nanofabrication is the design and manufacture of devices with dimensions that span in the nanometer range. Nanofabrication can be divided into three categories as etching, lithography, and thin films. The ever-growing development in nanofabrication has opened new ventures for us to explore and build complex optical structures in chips that we previously could not. As we know the precise controlling of electromagnetic waves in waveguides is necessary. This holds special value when it comes to integrated optics and nano-photonics, as light waves are used for information transfer in these devices. These optical-based communication devices have shown promising results when it comes to communication applications with faster and broader data transfer by overcoming the usual limitations of electrical wires. On the other hand, some of the recent advancements in photonic integrated circuits have shown that some of the limitations of the traditional optical waveguides could also be overcome.
Traditional optical waveguide structures could sometimes result in limited functionalities and the demand for better versatile photonic systems, which can be achieved in a more compact, configurable & multifunctional manner, has been increasing for the past few years. Together with nanofabrication, optical metasurfaces, and metamaterials, these challenges could be tackled according to some of the research work done in the last year. Optical metasurfaces and metamaterials are generally composed of artificial structures with feature sizes much smaller than the light wavelength. Variants of these devices have also shown far better manipulation of features of electromagnetic waves such as the polarization, phase, amplitude, etc. Other devices which have been created combining these technologies have also shown promising results in applications in other optical subfields as well. By tuning the scattering properties of such devices, antenna combinations can also be designed on top of dielectric waveguides to act as directional couplers. Furthermore, Fano antennas, wavelength-selective demultiplexers can also be realized through a combination of devices that can be manufactured using the above technologies.
Another interesting method of designing Metamaterial waveguides is the use of Deep Learning. Both generative and discriminative type algorithms and neural networks are used to come up with the most optimal design structure for nanostructured integrated photonics such as wavelength spitters. In most cases, the combinations and the possible device structures that could be tested before finalizing are a huge number, and testing these can be a tedious, unnecessarily resource and time-consuming task. All of these issues can be addressed by the use of conventional type deep learning methods and other advanced types of neural networks. Many types of research have been done in the past two years to explore the new avenues of using deep learning in such nanostructured photonics and chip design.
Compared to conventional waveguides comprising of subwavelength structures, meta-waveguides have the ability to outperform these conventional devices in many areas such as performing numerous functionalities with meta-structures, guiding and confining light in better ways. Nanofabrication, optical metasurfaces, and metamaterials have also influenced many other categories of devices that are not addressed in this article. On the other hand, many new manufacturing methods and advancements in other fields such as manufacturing, deep learning has helped to boost the recent studies and the design & build of complex and more versatile nanostructured devices for general applications.
This article was based on the findings of Meng, Y., Chen, Y., Lu, L. et al. Optical meta-waveguides for integrated photonics and beyond. Light Sci Appl 10, 235 (2021). https://doi.org/10.1038/s41377-021-00655-x.