# Hollow-Core Optical Fibers for Telecommunications and Data Transmission
## 14 Conclusions  
The emergence and ongoing improvements of hollow-core fibers, in particular NANFs, have opened up new prospects for a major technical change in the communications and IT sectors, primarily via a reduction in latency, the extension of optical bandwidth, the elimination of optical nonlinear effects, and an expected decrease in fiber attenuation.  
The review of the features and parameters of two main types of HCFs suitable for telecom networks, data transmission and similar applications, HC-PBGF and NANF, and their comparison to conventional (solid-core) single-mode fibers has identified both advantages and shortcomings of HCFs in these applications. NANFs are definitely superior to HC-PBGFs due to a simpler design, wide bandwidth, low dispersion and low attenuation, and are already competitive with SMFs, except for cost and splicing.  
We have looked at several possible applications of HCFs, analyzing the advantages of these (in their current forms) over alternative, existing technologies--or the lack of them. The most prospective are high-speed trading (currently the prime use of HCFs), DWDM networks, data centers, and radio sites with feeder cables exposed to temperature swings.  
Hollow-core fibers are not yet ready for wide deployment, primarily due to low-volume and costly manufacturing. The following can be carried out to improve this situation:  
* Development of more efficient and consistent manufacturing process;
* Standardization of fibers;
* Development of inexpensive and simple to use dedicated fusion splicing machines;
* Development of compatible optical amplifiers.  
Funding acquisition, research of the subject, collection of information (most), writing of complete draft except for Section 8, drawings, data curation--K.B. Collection of additional information, writing of Section 8, review and final editing of draft--T.O. All authors have read and agreed to the published version of the manuscript.  
The work of [PERSON] in 2022 was funded by the Polish Ministry of Education and Science (MEiN) through support for research at National Institute of Telecommunications, Project No. 12.30.007.2 \"Review of advanced designs of optical fibers, cables and networks reducing latency in optical transmission, including hollow core fibers\". Work of both authors in 2023 was financed from Project No. 12.30.003.3 \"Research on photonic structures for metrology, sensing and fiber optic communications\".  
Not applicable (study not involving humans or animals).  
Not applicable (study not involving humans).  
This review paper was based on already existing, publicly available data. The only new data created were drawings and Section 10.5. A complete set of the digital files present in the literature used (and some extra, collected, but not used) and drawings (.ppt and png files) is stored at National Institute of Telecommunications, Warsaw. Person responsible: [PERSON].  
The support of the management of the National Institute of Telecommunications, Warsaw, for the writing of the draft in 2023 by [PERSON] and [PERSON] is acknowledged.  
The authors declare no conflict of interest.