Page 51 - Market Analysis Report of Optical Communications Field in China & Global market 2025

Low-loss fusion splicing between G.657 fibers and
antiresonant hollow-core fibers
Ruowei Yu,1,#,* Tiantian Yue,1,# Zhihui Dong,1 Xi Zhang,1 Lin Wang,1 Wei Sun,1 Zuowei He,1 Guocai Tian,1 Zhenhua Liu1
1 Jiangsu Hengtong Optical Fiber Technology Co. Ltd., Suzhou, China
#These authors contributed equally to this work.
The development of advanced communication networks has met
a growing demand for interconnecting bend-insensitive G.657
fibers and antiresonant hollow-core fibers (AR-HCFs) with low
latency and nonlinearity. However, the large mode-field mismatch
between these fibers leads to high connection loss, limiting the
application of AR-HCFs in the last mile of access networks and
short-reach interconnects. This paper proposes and demonstrates
an efficient solution based on the fiber thermal diffusion technique. in Fig. 1(a), during this process, the core diameter expands,
By controlling the thermal diffusion process to G.657 fibers, we
successfully expanded the mode-field diameter at 1550 nm from
9.6 μm to 20.2 μm, significantly improving the mode-field match
with AR-HCFs. Experimental results show that the coupling loss
between the optimized thermally diffused G.657 fiber and the AR-
HCF was dramatically reduced from 2.6 dB to 0.6 dB. Ultimately,
we achieved low splicing losses of 0.7 dB for a single G.657 fiber/
AR-HCF joint and 1.5 dB for a G.657 fiber/AR-HCF/G.657 fiber
chain. This research provides a unique perspective for integrating
hollow-core fibers into existing optical access networks.
Key word: G.657 fiber, antiresonant hollow-core fiber, fusion
splicing, thermal diffusion, mode-field matching, low-loss
interconnection
1. Introduction
Bend-insensitive G.657 single-mode fibers have become
a key medium in fiber-to-the-home networks due to their
excellent cabling performance in confined spaces [1].
Meanwhile, antiresonant hollow-core fibers (AR-HCFs),
with their near-vacuum light speed, ultra-low nonlinearity,
and ultra-low loss, are promising transmission media for
future high-speed communication systems [2, 3]. Integrating
AR-HCFs into the edge of access networks holds great
potential for significantly enhancing network speed and
reducing latency. However, a challenge lies in establishing
low-loss and highly reliable optical interfaces between G.657
fibers and AR-HCFs. Due to the larger mode-field area of
AR-HCFs compared to conventional single-mode fibers, the
coupling losses exceeding more than 2 dB in direct splicing
[4]. To date, no reliable solution for the low-loss splicing
between G.657 fibers and AR-HCFs has been reported.
This paper presents the first demonstration utilizing the
fiber thermal diffusion technique to tailor the mode-field
characteristics of G.657 fibers, successfully achieving low-
loss fusion splicing with AR-HCFs.
2. Method and analysis
The thermal diffusion technique of optical fibers is a post-
processing technique that involves heating a doped fiber
at high temperatures (typically>1200°C), causing dopants
to diffuse thermally, thereby altering the refractive index
profile and the mode-field characteristics [5]. As illustrated
and the mode-field diameter (MFD) of the fundamental
mode increases [6]. This MFD enlargement effectively
facilitates matching with waveguides possessing larger
mode fields.
Coupling loss between dissimilar optical waveguides is
primarily caused by the mode-field mismatch and can be
estimated by the overlap integral of the two mode fields [7].
As shown in Fig. 1(b), by expanding and optimizing the
mode-field characteristics of the G.657 fiber via thermal
diffusion to closely resemble those of the AR-HCF, the
coupling efficiency can be significantly enhanced, and the
coupling loss substantially reduced.
Fig. 1. Schematics of (a) the thermally diffused optical fiber and (b)
the mode-field matching coupling between the diffused G.657 fiber
and the AR-HCF.
3. Experiments and results
3.1 Characterization of fibers
The G.657A2 fiber and the AR-HCF used in this study
were both developed by Hengtong. Fig. 2 shows the end-
face images of the two fibers at the same scale, presenting
their significant structural differences. Table 1 lists the key
parameters of the two fibers.
Fig. 2. End-face images of the experimental fibers at the same scale:
(a) the G.657A2 fiber and (b) the AR-HCF.
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