A Simple overview on Hollow Core Fiber

Hollow core fibers (HCFs) are a form of fiber with an air core surrounding by dielectric layer cladding components that restrict light [1]. In comparison to the embodiment of traditional fiber, it can direct light at a very rapid propagation speed through hollow regions and has a number of unique properties such as reduced nonlinearity, lower material absorption, and a higher damage threshold [2-5]. Various designs of HCFs have caught the interest of researchers all around the world due to their exceptional features and design flexibility [2]. HCFs have several uses, such as laser sources [3], ultrashort pulse delivery [6], optical fiber communication [7,8], terahertz guiding [9], and so on. Hollow-core photonic bandgap fibers (HC-PBGFs) are implemented by having a periodic refractive index in the cladding that guides light using the photonic bandgap effect [1], and hollow-core photonic bandgap fibers (HC-PBGFs) are implemented by having a periodic refractive index in the cladding that guides light using the photonic bandgap effect. Hollow-core antiresonant fibers (HC-ARFs), on the other hand, guide light by observing antiresonant reflection and wavenumber mismatch in the core and cladding regions [4]. The cladding geometry of HC-ARFs is relatively simple, resulting in very low loss, low group velocity dispersion (GVD), decreased nonlinearity, and so on [5].

Antiresonant fibers (ARFs) mainly focus on the cladding elements responsible for confining light in the core by applying antiresonant reflection through it [10]. The cladding geometry maintains a gap between neighboring cladding antiresonant tubes (ARTs) that leads to attenuating the resonance happening in the nodes [4].

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Furthermore, several studies have been conducted using nested cladding tubes to reduce light leakage by augmenting anti-resonant reflection [4,5,10,11]. Aside from that, various studies on various cladding configurations have been reported, such as single-ring (SR) ART elements [12], double-ring (DR) ART elements [13], nested ring elements [4, 5, 14], elliptical shape ART elements [15], ice-cream cone shape ART elements [16], conjoined tube elements [7, 17–19], and so on. Pryamikov et al. [12] presented and manufactured an ARF based on the SR platform with six ARTs and demonstrated a reduced loss in the mid-IR region with broad bandwidth. Furthermore, as compared to circular tube architectures, elliptical capillary structures showed a loss of less than one order of magnitude [15]. In addition, Poletti et al. proposed a layered nodeless ARF with six ART that outperformed SR-ARFs and PBGFs in terms of fiber performance [4].

Multilayer based ARFs have a new research focus that aims to improve confinement loss (CL) and bending loss (BL) performance. For example, a conjoined tube fiber (CTF) structure with six tubes was reported to have a 2 dB/km loss at 1.512 m and a higher BL of 1 dB/km for telecommunication applications [7]. Adding a silica layer in the radial direction greatly lowered the CL [6, 18, 19, 20]. With state-of-the-art manufacturing, however, CTFs must be improved and updated to present a revolutionary design with amazing low losses and single mode (SM) performance, which will accelerate the advancement of ARFs in optical fiber communication systems.

REFERENCES

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