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All-optical Mach–Zehnder interferometric NH3 gas sensor based on graphene microfiber hybrid

Sensors and Actuators B 194 (2014) 142–148

Contents lists available at ScienceDirect

All-optical Mach–Zehnder interferometric NH3 gas sensor based on graphene microfiber hybrid

All-optical Mach–Zehnder interferometric NH3 gas sensor based on graphene microfiber hybrid

Sensors and Actuators B:

Chemical

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /s n

b

All-optical Mach–Zehnder interferometric NH 3gas sensor based on graphene/microfiber hybrid waveguide

All-optical Mach–Zehnder interferometric NH3 gas sensor based on graphene microfiber hybrid

Baicheng Yao a ,Yu Wu a ,c ,∗,Yang Cheng a ,Anqi Zhang a ,Yuan Gong a ,Yun-Jiang Rao a ,∗∗,Zegao Wang b ,Yuanfu Chen b

a

Key Laboratory of Optical Fiber Sensing and Communications (Education Ministry of China),University of Electronic Science and Technology of China,Chengdu 610054,PR China b

State Key Laboratory of Electronic Thin Films and Integrated Devices,University of Electronic Science and Technology of China,Chengdu 610054,PR China c

Department of Electronic Engineering,City University of Hong Kong,Kowloon,Hong Kong,China

a r t i c l e

i n f o

Article history:

Received 2September 2013Received in revised form 19December 2013

Accepted 21December 2013

Available online 30 December 2013

Keywords:

Optical fiber sensors Graphene Microfiber

NH 3gas sensor

M–Z interferometer

a b s t r a c t

In this paper,we report an all-optical NH 3gas sensor based on graphene/microfiber hybrid waveguide (GMHW).The study on the sensing mechanism shows that as the adsorption of NH 3modifies the con-ductivity of graphene and thus the effective refractive index of the GMHW,and the transmitting light along the GMHW is very sensitive to NH 3gas concentration.The wavelength shift induced by the NH 3absorption is spectrally demodulated by using a microfiber-based Mach–Zehnder interferometer (MZI).A high sensitivity of ∼6pm/ppm is obtained for the NH 3adsorption measurement.The resolution of such a sensor is ∼0.3ppm,mainly limited by the resolution of the optical spectrum analyzer used.The work of this paper may open a window for the development of novel GMHW-based gas sensors with high sensitivity,small footprint,easy fabrication and low cost.

© 2013 Elsevier B.V. All rights reserved.

1.Introduction

Graphene,a monolayer of carbon atoms,has attracted world-wide interests for its special electronic and photonic properties [1,2].In recent years,researches indicate that graphene has great potential for sensing applications due to its high carrier mobility [3,4].Currently,most of the graphene-based gas sensors employ the voltage or current effect of graphene [5,6],such as utiliz-ing pristine graphene for sensing polar gases (NH 3,NO 2),doping metal elements for sensing non-polar gases (H 2)and optimiz-ing the molecular structure of graphene for specific gas detection [7–11].As all the electric gas sensors are active,a graphene-based passive optical gas sensor is needed for a number of practical appli-cations where the immunity of the sensor to electro-magnetic interference is essential.Based on the optical intensity attenu-ation effect of graphene,the concentration of chemical gas can be measured [12].However,the sensitivity and accuracy of the

∗Corresponding author at:Key Laboratory of Optical Fiber Sensing and Com-munications (Education Ministry of China),University of Electronic Science and Technology of China,Chengdu 610054,PR China.Tel.:+86186********∗∗Corresponding author.

E-mail addresses:wuyuzju@http://doc.docsou.com (Y.Wu),yjrao@http://doc.docsou.com (Y.-J.Rao).

intensity-based sensors are limited by the sensing principle,while optical interferometric detection would offer much higher sensi-tivity [13,14].

In this paper,a highly sensitive optical interferometric NH 3sen-sor based on graphene/microfiber hybrid waveguide (GMHW)has been theoretically analyzed and experimentally demonstrated.For this hybrid structure,a microfiber [15]is used to launch and collect transmission light from the graphene waveguide [16],and light can propagate along the surface of graphene several millimeters.The GMHW integrated in a Mach–Zehnder interferometer (MZI)can detect the gas concentration variation via measuring the spectral fringe shift in the interference spectrum.

2.Structure and fabrication

The GMHW-based gas sensor is shown in Fig.1,schematically.In Fig.1(a),broadband light is launched into and collected from a MZI with one arm where the GMHW is integrated.In front of the MZI,a polarization controller (PC)is adopted to optimize the polarization state of the lunched light.In the MZI,through a 3dB coupler,the transmission light is divided into 2interfering arms.In arm A,a single mode fiber (SMF)is drawn into a microfiber with the diameter of ∼1␮m and the waist length of ∼15cm.Part of the microfiber is attached onto the graphene film.As shown in

0925-4005/$–see front matter © 2013 Elsevier B.V. All rights reserved.http://doc.docsou.com/10.1016/j.snb.2013.12.085

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