Abstract
With the growing interest in hollow-core antiresonant fibers (HC-ARF), attributed to the development of their fabrication technology, the appearance of more sophisticated structures is understandable. One of the recently advancing concepts is that of dual hollow-core antiresonant fibers, which have the potential to be used as optical fiber couplers. In the following paper, a design of a dual hollow-core antiresonant fiber (DHC-ARF) acting as a polarization fiber coupler is presented. The structure is based on a highly birefringent hollow-core fiber design, which is proven to be a promising solution for the purpose of propagation of polarized signals. The design of an optimized DHC-ARF with asymmetrical cores is proposed, together with analysis of its essential coupling parameters, such as the extinction ratio, coupling length ratio, and coupling strength. The latter two for the x- and y-polarized signals were ~2 and 1, respectively, while the optical losses were below 0.3 dB/cm in the 1500–1700 nm transmission band.
Highlights
Over twenty years have passed since Cregan et al presented the first hollow-core optical fiber (HCF)with a microstructured cladding [1]
Remarkable optical features of HCFs [2,3,4] have resulted in their extensive experimental use, for example in telecommunications [5,6,7], gas and liquid spectroscopy [8,9,10,11,12,13], supercontinuum generation [14,15], high power optical beam delivery [16,17,18], transmission in the spectral regions unavailable for conventional fibers [19,20,21,22], biomedical applications [23,24], and many others
One of the reasons for this is the lack of HCF-integrated optical devices, such as optical fiber couplers (OFCs) based on a structure with two closely spaced fiber cores
Summary
Over twenty years have passed since Cregan et al presented the first hollow-core optical fiber (HCF). All of the above, combined with a great modification and design flexibility of HC-ARFs, have resulted in researchers presenting numerous different structures based on two most known HC-ARF cladding types—the single-ring [34,35] and Kagomé [36,37] types This flexibility can be considered one of the factors which have encouraged researchers to pursue the idea of a dual hollow-core antiresonant fiber (DHC-ARF). The width (or diameter) of this channel was found to be even more important for the coupling efficiency of DHC-ARFs than the distance between the cores This strongly influences the coupling of signals with different polarizations, suggesting the possibility of creating polarization OFCs. A single-ring cladding DHC-ARF was presented one year later [41], confirming many of the theoretical findings from the previous works. The presented approach may help in the process of potential future fabrication of such fibers, but it provides some additional insight into the matter of light guidance in HC-ARFs, which is still waiting to be fully described
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