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1990 Vol. 48,No. 8 /15 April 2023 / Optics Letters Letter
Highly sensitive gas pressure sensor based on the
hollow core Bragg fiber and harmonic Vernier effect
Yu Wang,1,2 Yaxi Yan,3Weihao Yuan,3,∗Zhenggang Lian,4Daru Chen,1Alan Pak
Tao Lau,3Changyuan Yu,2AND Chao Lu2
1Hangzhou Institute of advanced studies, Zhejiang Normal University, Hangzhou, China
2Photonics Research Institute, Department of Electronic and Information Engineering, Hong Kong Polytechnic University, Hong Kong, China
3Photonics Research Institute, Department of Electrical Engineering, Hong Kong Polytechnic University, Hong Kong, China
4Yangtze Optical Electronics Co., Ltd. (YOEC), Fifth Hi-Tech Avenue, East Lake Hi-Tech Develop Zone, Wuhan, China
*weihao.yuan@connect.polyu.hk
Received 1 March 2023; accepted 16 March 2023; posted 20 March 2023; published 3 April 2023
A highly sensitive inline gas pressure sensor based on the
hollow core Bragg fiber (HCBF) and harmonic Vernier
effect (VE) is proposed and experimentally demonstrated.
By sandwiching a segment of HCBF between the lead-in
single-mode fiber (SMF) and the hollow core fiber (HCF),
a cascaded Fabry–Perot interferometer is produced. The
lengths of the HCBF and HCF are precisely optimized and
controlled to generate the VE, achieving a high sensitiv-
ity of the sensor. Meanwhile, a digital signal processing
(DSP) algorithm is proposed to research the mechanism
of the VE envelope, thus providing an effective way to
improve the sensor’s dynamic range based on calibrating
the order of the dip. Theoretical simulations are investi-
gated and matched well with the experimental results. The
proposed sensor exhibits a maximum gas pressure sensitiv-
ity of 150.02 nm/MPa with a low temperature cross talk of
0.00235 MPa/◦C. All these advantages highlight the sensor’s
enormous potential for gas pressure monitoring under var-
ious extreme conditions. © 2023 Optica Publishing Group
https://doi.org/10.1364/OL.488930
Gas pressure monitoring is of great importance in various
industrial fields, such as downhole mining, gas transportation,
and environment monitoring [1]. Over the past decades, opti-
cal fiber sensors have attracted widespread attention due to
their unique advantages compared with their electronic coun-
terparts [2]. These properties include compact size, lightweight,
high-temperature tolerance, cost-effective production, and good
resistance to chemical corrosion and electromagnetic interfer-
ence. Diverse kinds of optical fiber sensors have been proposed
based on different configurations, including fiber Bragg grat-
ings (FBGs), long-period gratings (LPGs), antiresonant fibers
(ARFs), and interferometers [3,4]. However, all-silica fiber
structures commonly have low-pressure sensitivity because of
the material’s inherent properties. For example, pure-silica pres-
sure sensors based on FBG, LPG, Mach–Zehnder interferometer
(MZI), and ARF present low sensitivity of the order of 0.01
nm/MPa, 1.68 nm/MPa, −3.74 nm/MPa, and −9.6 pm/MPa,
respectively [5–8].
Pressure sensors based on the Fabry–Perot interferometer
have been widely researched due to their simple structure, easy-
to-operate reflective configuration, and the potential for high
sensitivity [9]. Different optimization schemes based on FPI
have been proposed to enhance pressure sensitivity. One way
is to immobilize the fiber tip with various diaphragms, the
Young’s modulus of which are much lower compared with silica
[10]. However, the durability, stability, and mechanical strength
are much poorer than all-silica structures, limiting their prac-
tical applications, especially in high-temperature and chemical
corrosion environments.
Another effective method is based on the Vernier effect (VE),
formed by a pair of FPIs. The free spectral range (FSR) of
one is typically almost an integer multiple of the other [11,12].
By monitoring the VE-related envelope, the sensitivity can be
amplified significantly. However, most researchers focused on
the magnification factor calculated by the free spectral range
(FSR) to evaluate the sensitivity of the envelope rather than an
in-depth analysis of the envelope’s mechanism and properties
[13,14]. It is noted that adjacent fringes will be mistaken and lead
to ambiguity when the envelope shifts more than one FSR with
changing pressure. Generally, a higher sensitivity with a fixed
FSR will result in a lower dynamic range. Therefore, a trade-
off should be made between sensitivity and dynamic range in
works where the envelope is not analyzed deeply. For example,
Yang et al. reported a cascaded FP sensor based on the harmonic
VE, showing a high sensitivity of 80.8 nm/MPa with a limited
dynamic range of 0.1 MPa [13].
In this paper, we designed and successfully achieved a highly
sensitive gas pressure sensor based on the VE with a sim-
plified all-fiber structure. The probe comprises a hollow-core
Bragg fiber (HCBF) and hollow-core fiber (HCF) with precise
lengths. A digital signal processing (DSP) method is conducted
to investigate the mechanism of the harmonic VE in-depth. The
theoretical analysis matches well with the experimental results,
showing a high gas pressure sensitivity of 150.02 nm/MPa and
low temperature cross talk of 0.00235 MPa/◦C. Meanwhile,
a method to determine the order of the dip is theoretically
researched and experimentally demonstrated, thus significantly
improving the dynamic range of the sensor while ensuring high
0146-9592/23/081990-04 Journal ©2023 Optica Publishing Group
