1 © 2018 IOP Publishing Ltd Printed in the UK
1. Introduction
The ber optic inline Mach–Zehnder interferometer (MZI)
has attracted a wide range of interest for its ultra-compact
structure and capability of performing many sensing func-
tions. It has been used for the measurement of refractive index
(RI) [1], vibration [2], micro-displacement [3], etc. In recent
years, several ber optic RI sensors based on inline interfer-
ometers have been developed, including the inline Michelson
interferometer based on an abrupt-tapered single mode ber
(SMF) [4], the inline Fabry–Pérot (FP) interferometer based
on a microhole [5], and inline MZIs based on a thinned SMF
[6], a photonics crystal ber (PCF) [7], a microstructure ber
Bragg grating [8], a femtosecond pulse microfabricated SMF
[1] or a tapered PCF [9]. Magnetic uid (MF) is one kind of
material whose RI can be demodulated by a magnetic eld [10].
MF-based ber optic magnetic eld sensors can be realized
by using RI-sensitive inline interferometers. In 2012, Zu etal
reported an inline MZI-based magnetic eld sensor by using
PCF with a sensitivity of 2.367 pm Oe
−1
[11]. Layeghi etal
reported a at tapered ber-based inline MZI for the measure-
ment of magnetic eld with a sensitivity of −7.17 pm Oe
−1
[12]. However, such inline interferometer-based ber optic
sensors either require high-cost specialty bers or specic
fabrication equipment, such as femtosecond lasers and ber
optic taper machines.
Fiber optic inline interferometer fabrication using chem-
ical solutions is cheaper and much simpler than the afore-
mentioned techniques. In 2007, Zhang et al proposed a
microgap multicavity FP biosensor by the wet etching [14]. In
Measurement Science and Technology
Fiber optic refractive index and magnetic
eld sensors based on microhole-induced
inline Mach–Zehnder interferometers
FeifeiChen
1
, YiJiang
1
, LiuchaoZhang
1
, LanJiang
2
and SumeiWang
2
1
School of Opto-Electronics, Beijing Institute of Technology, No. 5 Zhongguancun South Street, Haidian
District, Beijing 100081, People’s Republic of China
2
Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute
ofTechnology, Beijing 100081, People’s Republic of China
E-mail: bitjy@bit.edu.cn
Received 20 May 2017, revised 27 September 2017
Accepted for publication 2 October 2017
Published 26 February 2018
Abstract
A compact microhole-induced ber optic inline Mach–Zehnder interferometer (MZI) is
demonstrated for measurements of refractive index (RI) and magnetic eld. Inline MZIs with
different etched diameters, different interaction lengths and different sizes of microholes are
fabricated and assessed. The optical transmission spectra of the inline MZIs immersed into
a series of liquids are characterized and analysed. Experimental results show that liquid RI
sensitivity as high as 539.8436 nm RIU
−1
in the RI range of 1.3352–1.4113 RIU is achieved
and also exhibits good linearity with a correlation coefcient >93%. An inline MZI is also
fabricated to be a magnetic eld sensor by using magnetic uid material. The experimental
results show that this magnetic eld sensor has a high sensitivity of −275.6 pm Oe
−1
. The
inline MZI-based ber optic sensors possess many advantages, such as small size, simple
fabrication, high sensitivity and good linearity, which has a wide application potential in
chemical, biological and environmental sensing elds.
Keywords: ber optic sensor, magnetic eld measurement, refractive index measurement,
interferometry
(Some guresmay appear in colour only in the online journal)
F Chen etal
Printed in the UK
045103
MSTCEP
© 2018 IOP Publishing Ltd
29
Meas. Sci. Technol.
MST
10.1088/1361-6501/aa902c
Paper
4
Measurement Science and Technology
IOP
2018
1361-6501
1361-6501/18/045103+6$33.00
https://doi.org/10.1088/1361-6501/aa902c
Meas. Sci. Technol. 29 (2018) 045103 (6pp)
