Concept and history of development

The development of the concept started practically in 2014, when we started to work on the design and characterization of microwave-optical systems, while in the last 3-4 years our activity has been much more intensive due to the development of a prototype within the MIT TRIO national project FV30427 together with RF SPIN and then the cooperation with foreign research institutes within the European projects COST CA16220 (http://euimwp.eu/) and CA19111 (http://www.newfocus-cost.eu/). The most time-consuming part was the development and experimental testing of the beamforming phased array antenna, which was carried out in the optical domain.

Research and experimental challenges

The main challenge has been the transmission of millimeter waves in particular, where the size of connectors, antennas, etc. decreases with decreasing radiation wavelength, which places considerable demands on the implementation itself. Another aspect of millimetre wave transmission is the losses, the effect of dispersion during propagation in the optical fibre and the sensitivity of the optical signal phasing for the antenna array. All of these formed a set of challenges that had to be addressed in an expedient manner.

The development of the prototype resulted in the experimental verification of a number of unique results, which have been published in several papers in prestigious scientific journals, and also demonstrated for the first time various concepts for the use of optical infrastructure for millimeter band radio signal transmission, particularly for 5G networks. The topicality of the subject is evidenced by the fact that these recently published articles are also widely cited by other international research teams.

Practical applications

With the introduction of 5G networks and other wireless technologies, the opportunities for the use of RF over fibre technology are opening up significantly. As both the implementation of higher frequency bands in 5G and the beginning of standardization of 6G networks can be expected in the near future, it is the convergence of RF and optical technologies that will play an important role for their final implementation.

It is clear that to achieve sufficient capacity for high-definition video transmission, virtual reality, etc., the use of up to sub-THz bands will be essential, and without optics, this will definitely not be possible. In this direction, it will then be possible to apply the concepts that we have also experimentally verified and apply them in higher frequency bands, possibly with respect to the requirements of a specific application.

There are many areas for the use of RF over fibre technology in industry. In the simplest case, it is preferably used as a replacement for metallic lines, where cable transmission over coaxial lines would exhibit unacceptable attenuation or could be interfered with, thus limiting its usefulness. If we use RF over fibre technology, we are able to transmit the signal in its original form over units of up to tens of kilometres with minimal loss, which is used e.g. in the aerospace industry.