Magnetron Sputtering Coated Optical Fiber Probe

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 23, NO. 2, MARCH/APRIL 2017

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Magnetron Sputtering Coated Optical Fiber Probe Designs for Surface Plasmon Resonance Sensor Rashmi A. Minz, Sudipta Sarkar Pal, Aditi Chopra, Shivam Bargujar, Randhir Bhatnagar, R. K. Sinha, Member, IEEE, and Samir K. Mondal

Abstract—In this paper, we have reported the design of the surface plasmon resonance probes prepared from partially etched polymer optical probe and specially tapered single-mode fiber tip probe which are gold coated in magnetron-sputtering unit. The coating parameters and conditions are discussed in details to achieve sensitive surface plasmon resonance probes. The sensor probes work in transmission modes. The gold-coated etched in-line polymer fiber probe demonstrates high sensitivity, ∼2459 nm/RIU and working range includes visible to infrared wavelength. The fiber tip probe with very small interaction area demonstrates sensitivity, ∼166 nm/RIU. The in-line fiber probe could be used for large volume sample and the pointed fiber tip could be used for small volume samples.

Usually, such matching occurs when the nano material structure is excited with evanescent waves involving TM mode. SPR arises as a result of coupling between the incident light propagation constant Kd , and surface Plasmon’s propagation constant, KSP , of the conducting film at a resonance angle for kretchman configuration or resonance wavelength for waveguides such as optical fiber. The surface Plasmon propagation constant can be expressed by 1/2  εm εs 2π (1) KSP = λ εm + εs

Index Terms—Evanescent wave (EW), magnetron sputtering (MS), refractive index (R.I), surface plasmon resonance (SPR).

where εm the real is part of the metal dielectric constant and εs is the dielectric constant of the sensing layer. The light propagation constant Kd is the lateral component of the wave vector of the incident light in the dielectric medium and is given by

I. INTRODUCTION URFACE plasmon resonance (SPR) phenomenon has emerged as an attractive spectroscopic analytical technique used in chemistry, physics, and bio-science advanced research [1]–[3].The Plasmonic based sensor is a promising field of research since the inception of the Surface Plasmon. The SPR is associated with collective oscillation of free electrons at the surface of metal-dielectric nano-structure under certain conditions [4]. Depending upon the nature of nano-material structure, the Plasmonic sensors are categorized into localized SPR (LSPR) sensor [5] and SPR sensor [6]. An LSPR usually needs monolayer coating of nano-particles on the source of evanescent wave where scattering from nano-particles contributes in the LSPR [7]–[9]. In case of SPR it is propagating surface wave which is supported at the interface between a bulk metal film and a dielectric [10]. The resonance is a result of the interaction between electromagnetic vectors in the incident light and free electrons available on the surface of specific Plasmonic coating [11]. The excitation of surface Plasmon requires phase matching between the natural oscillation frequencies of the electron clouds present in the metal and the electromagnetic wave [12].

S

Manuscript received May 27, 2016; revised August 12, 2016; accepted September 21, 2016. R. A. Minz is with the Academy of Scientific and Innovative Research Central Scientific Instruments Organisation, Chandigarh 160 030, India (e-mail: [email protected]). S. S. Pal, A. Chopra, S. Bargujar, R. Bhatnagar, R. K. Sinha, and S. K. Mondal are with the Department of Advanced Materials and Sensors, Central Scientific Instruments Organisation, Chandigarh 160 030, India (e-mail: sudipta.sarkar12@gmail; [email protected]; shivam.bargujar102@ gmail.com; [email protected]; [email protected]; samirmondal01@ gmail.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSTQE.2016.2613859

Kd =

2π √ εd sin θ λ

(2)

where ‘θ’ is the incident angle through the light coupling medium such as prism, waveguide or optical fiber. εd is the dielectric constant of the dielectric medium, λ is the wavelength of the incident light. Momentum matching and energy conservation condition, KSP = Kd determines the value of θ as  ⎤1/2 ⎡ −1 ⎣

θ = sin

εm εs ε m +ε s

εd

⎦

(3)

The angle can be related to the critical angle θcr for total internal reflection. As the propagation constant of the surface Plasmon and the incident light matches to each other at the dielectric-metal interface, the SPR occurs leading to sharp dip in the intensity of the transmitted light due to energy transfer. Field intensity of Surface Plasmon wave (SPW) decays exponentially away from the interface. Any perturbation of refractive index within the SPW zone brings characteristic change in the SPR spectra. However, optimization of light confining structure is one of the key topics in this area [13], [14].The optical fiber based SPR sensor structure is becoming a popular [15] option due to the fact that optical fiber is immune from several factors such as electromagnetic interference. It is also easier to generate evanescent wave, necessary for exciting surface Plasmon, in optical fiber. This can also be considered as miniaturisation of the sensor probe compared to bulky Kretchman configuration used in bio sensing applications [16]–[18].The fiber optic SPR sensor has different Plasmonic response and sensitivity depending upon the design parameters such as tapering [19] or bending

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IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 23, NO. 2, MARCH/APRIL 2017

[20] of the fiber, and coating materials including the thickness. It is to be mentioned that the multimode fiber is preferred for in-line fiber based SPR probe due to lower value of critical angle given by   ncl θcr = sin−1 (4) nc where ncl and nc are refractive index of cladding and core respectively. The low angle allows more light to response the Plasmonic resonance [21]. It should also be mentioned that the light incident angle θ at the fiber core-cladding boundary should be equal to the critical angle to generate evanescent wave which satisfies the boundary conditions for SPR. In this work we have reported gold coated chemically etched in-line multimode polymer optical fiber and specially tapered pointed single-mode optical fiber tip based SPR sensors probes. The coating is done using Magnetron sputtering technique in a customized Magnetron sputtering unit. The in-line-fiber sensor can be used for large volume of sample sensing while pointed tip can be used for small volume of sample sensing. The work has been presented below in the order of SPR probes fabrication, sensing experiments, Results and discussions and finally the conclusion.

Fig. 1.

AFM images characterizing the thickness of the gold coating film.

TABLE I SHOWS RELATION BETWEEN NUMBER OF ROTATIONS AND SENSITIVITY Sl. No. 1 2 3 4 5 6

Deposition Time (Rotation)

Sensitivity (nm/RIU)

3 4 5 6 7 8

612.97 997.66 1352.75 2232.23 2253.06 2458.88

II. SPR PROBE PREPARATION A. In-Line Fiber Probe Preparation The Plastic clad silica multimode optical fiber 400EMT (low OH content) of diameter 400 μm is used in our experiment. The sensing region is prepared by burning the Tefzel jacket (buffer) by flame (hobby and torch method) and is cleaned with acetone to remove the cladding in the desired sensing region. The exposed fiber core is etched in 48% HF in order to reduce the core diameter to ∼150 μm. The etched polymer fiber can generate more evanescent wave enhancing SPR with the metallic film. The MS unit has been modified to accommodate optical fiber with rotational option for uniform coating around the etched part. The deposition pressure for the sputtering unit chamber is maintained at 2.1 × 10 −2 Torr. Before gold coating, the sample is given thin chromium coating which helps adhering gold film. The chromium is coated at 21.6 W and gold coating is done at power of 4 W. no. of Rotations are varied while keeping all other parameters fixed. The sensing length of the fiber is kept ∼ 1.5 cm as sensing length beyond this doesn’t show any improvement [22], [23].To standardize the coating thickness with rotation, we have primarily chosen a planer structure placed on rotating platform. The coated film is characterized using AFM which is shown in Fig. 1. The details about rotations of samples and sensitivity can be found in Table I.

tapered optical fiber tip based SPR probe is ideal one [24]. A novel optical fiber tip is proposed for the pointed fiber tip SPR probe. The tip is prepared from photosensitive single-mode optical fiber of diameter 125 μm by chemical etching guided by capillary action [25]. The tapered optical fiber tip with cavity and a protruded pointed probe is further coated with thin film of chromium and gold in the same sputtering unit. In this case the tip is oriented towards the target so that rotation of the sample is not required. The sputtering condition is similar to etched polymer fiber coating. However, instead of rotation the fiber tip is exposed 10 s for chromium coating followed by 3 min for gold coating inside the chamber. This is equivalent to coating thickness of ∼ 40 nm. Fig. 2 is the SEM image of a typical chromium-gold coated pointed fiber tip used in our experiment. The thickly coated optical fiber tip contains a protruded antenna like structure within the cavity. The unique optical fiber tip enhances the evanescent wave significantly at the tip end due to the tapered structure which enhances SPR response. It is to be mentioned that similar type of fiber tip has been reported for attenuation based sensor [26]. However, the design we have considered takes the advantage of novel tip, the Magnetron sputtering coating and its SPR response. III. SENSING EXPERIMENTATION

B. Pointed Fiber Tip Based Probe Preparation

A. In-Line Fiber SPR Sensor Probe Experimentation

The in-line optical fiber sensor as SPR probe in transmission mode with large interaction area works for large volume of samples. However, there are many instances where one has to measure very small volume of sample. For such experiments,

Fig. 3 is the schematic of the experimental setup used in the sensing experimentation. SPR condition and resolution depend upon the properties of optical system and the transuding medium [27]. For the wavelength interrogation of optical fiber

MINZ et al.: MAGNETRON SPUTTERING COATED OPTICAL FIBER PROBE DESIGNS FOR SURFACE PLASMON RESONANCE SENSOR

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A reference spectrum and dark spectrum need to be recorded. The reference spectrum is acquired with bare fiber probe; the dark spectrum is obtained by blocking the light path in front of the tungsten halogen light source. The sample spectrum is recorded with the metallic film coated fiber for different solutions. The measured sample transmission Spectra M (λ)of the fiber sensor probe is obtained by the following equation M (λ) =

Fig. 2. (a) SEM image of gold coated optical fiber tip. (b) Side view of the zoomed tip. (c) Top view of FESEM image of a similar protruded uncoated tip, scale bar 10 μm.

(λs − λd ) × 100 ( λr − λd )

(5)

where λs , λd and λr represent sample wavelength, dark signal and Reference Wavelength respectively. The data obtained is recorded using Spectra suite software. The scan average value is set at 50 times in order to get better SPR curve and high signal to noise ratio. The data is further processed using origin software for the analysis. IV. RESULT AND DISCUSSION A. In-Line-Fiber SPR Probe Results

Fig. 3. Schematic of the experimental setup (a) for in-line sensor probe (b) pointed tip fiber probe. The fiber tip is placed vertically in a stable translation stage to move it in the samples on the thin cover slip which is placed on the opening path to the spectrometer.

probe a white light source is coupled to the fiber and spectrometer records the intensity of the transmitted light. Tungsten halogen lamp HL2000FHSA and USB4000 spectrophotometer from ocean optics have been used in our experiment. SMA connectors with universal fiber terminator connect the fiber with light source and spectrometer. The glycerol samples are prepared with water solution and the refractive indexes of solutions are checked in AtagoRx-7000i refractometer. The optical fiber sensor probe is inserted into a flow cell where glycerol and distilled water solutions ranging from RI 1.338 to 1.398 were successively fed into the sensing region. For different concentration of glycerol the recorded refractive index values obtained are 1.338, 1.343, 1.351, 1.356, 1.360, 1.370, 1.374, 1.376, 1.390 and 1.398 for concentration of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50% respectively. The spectrometer acquires data using the following principle.

As the white light source is coupled with the probe input, the etched part of the fiber with coating interacts with the entire spectra of the Tungsten source. It interacts strongly over certain wavelength domain which matches criteria for surface Plasmon supported by the dielectric and metal structure. The characteristics of light-matter interaction are reflected in the transmission spectra obtained in the spectrometer. The transmission spectra experiences loss over the wavelength range due to transfer of energy to surface Plasmon causing a dip in the spectra. The surface Plasmon propagating on the surface of the optical fiber is perturbed due to change in medium of the fiber’s surroundings resulting in shift of the position of the dip. This change in position of the dip is used for sensing the refractive index change. The spectral characteristics of SPR response are presented in Fig. 4. for different glycerol and water concentration giving different RI values. The spectra show both the change in intensity and in the position of the dip, namely red shift of the absorbance wavelength with the increase in surrounding RI. It may be pointed out that intensity based pointed optical fiber tip sensor has already been explored [24]. Though change in intensity could be a sensing parameter, in our study we have considered change in dip in the spectra due to SPR as the sensing parameter. Spectrum data processing is same as it is mentioned in Section III since pointed tip sensor also works in the transmission mode. Fig. 4. represents the response of the probe with different coating thickness which is approximately determined by the number of rotations. With the more number of rotations and the increased thickness the SPR curve is shifting from visible to infra red regime. Sensing response of SPR probe, the relative wavelength shift as a function of refractive index, is plotted for different rotation and for various concentrations as mentioned in Section III-A. For the clarity of the figures, we have plotted SPR response for few selective concentrations. However, in Fig. 5. We have considered all the concentrations used in the experiments. As the no of rotation varies from 4 to 7 the sensing

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Fig. 4.

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 23, NO. 2, MARCH/APRIL 2017

Transmission Spectra of Surface Plasmon resonance sensor for varied Rotation with different R.I solution.

response has increased significantly. One rotation is equivalent to 36 s. For the 8th rotation we have achieved sensitivity of ∼2459 nm/RIU, although the sensitivity is nearly saturated for thickness corresponding to 6 rotations, ∼2232 nm/RIU. The overall range of shifting is from ∼520 nm to ∼850 nm. The probe has been tested for concentrations starting from 5% to 50% and the sensitivity results are plotted in Fig. 5.The results demonstrate the near linear sensitivity response of the sensor probe. Table I indicates the quantitive relations among the number of rotations and the sensitivity. Fig. 6 shows the trend of shifting of the dip towards near-infra red region. From rotation 2 to rotation 7, the coating thickness increases in step of ∼(5 to 6) nm to the thickness ∼40 nm. It is to be noted that increasing the thickness of gold coating leads to shift of the dip from visible to near Infra region [28] and the resonance curve becomes more sensitive leading to increase in sensitivity [29], [30] of the probe. It can also be mentioned that gold thin film of thickness 45 nm to 50 nm corresponds to the best surface Plasmon response [31]. B. Pointed Fiber Tip SPR Probe Results The experimental arrangement for pointed fiber tip based sensor is similar to the in-line fiber SPR probe experimentation

in transmission mode. In this arrangement, the tip is vertically placed on the spectrometer entrance with cover slip [24]. The samples are placed on the cover slip such that the tip enters into the sample. The spectrometer scan the transmission spectrum transmitted through the fiber tip. Enhanced evanescent waves at the tip interact with the sample through surface Plasmon which has been used in other type of applications [32], [33] as well. As the probe is dipped into solution of liquid like water, acetone and methanol, we observe a dip in the transmitted light. In this experiment we have avoided glycerol like solution due to its sticky nature. The transmission spectra of the pointed gold coated optical fiber probe are presented inFig. 7. The dips for acetone, water and methanol are observed at 864 nm, 859 nm and 860 nm respectively. It is to be mentioned that water (1.33) and methanol (1.329) have nearly same value of refractive index which may be the reason the position of dips are nearly same. However, methanol experiences higher transmission loss. Considering the refractive index of the acetone, 1.36, and the shift compared to the water, the sensitivity of the tip obtained is 166.4 nm/RIU for ∼40 nm coating thickness. The sensitivity is less due to lesser area of interaction. However, such fiber tip sensor probe has the advantage of sensing small volume samples. In this case we

MINZ et al.: MAGNETRON SPUTTERING COATED OPTICAL FIBER PROBE DESIGNS FOR SURFACE PLASMON RESONANCE SENSOR

Fig. 5.

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Sensitivity characteristic of the SPR response for different rotations (R).

Fig. 6. Response curve of SPR for different rotations for glycerol concentration 50%.

Fig. 7. Transmission spectra of gold coated pointed plasmonic fiber tip in presence of various chemicals.

V. CONCLUSION have presented proof of the concept with coating thickness ∼45 nm which results in near saturated SPR response as observed in-line sensor probe. However, a detail study can be done separately.

In conclusion, we have reported Magnetron sputtering based gold coating to develop sensitive SPR based sensor. A partially etched polymer fiber and a pointed optical fiber tip are considered for SPR sensor probes. The sensor probes are gold coated

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IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 23, NO. 2, MARCH/APRIL 2017

using customized Magnetron sputtering unit with an option of sample rotation. The response of the probe significantly depends upon the coating thickness which is varied with the rotation of the samples during sputtering. The in-line polymer fiber sensor with coating thickness ∼40 nm shows high sensitivity, ∼2459 nm/RIU. In case of specially pointed fiber tip with coating thickness ∼40 nm, we observe sensitivity ∼166 nm/RIU. The in-line fiber probe can be used for large sample volume detection whereas the pointed fiber probe could be useful for small volume of sample, ∼μl, sensing. ACKNOWLEDGMENT The authors would like to acknowledge the staff members of Advanced Materials and Sensors division for their support during the work. The authors would also like to acknowledge Dr. A. Deep and S. Bhardwaj for helping with FESEM characterization. REFERENCES [1] S. Srivastava and B. Gupta, “Fiber optic plasmonic Sensors: Past, present and future,” Open Opt. J., vol. 7, no. 1902, pp. 58–83, 2013. [2] P. K. Jain, X. Huang, I. H. El-Sayed, and M. A. El-Sayed, “Noble metals on the nanoscale: Optical and photothermal properties and some applications in imaging, sensing, biology, and medicine,” Acc. Chem. Res., vol. 41, no. 12, pp. 1578–1586, 2008. [3] P. Singh, “SPR biosensors: Historical perspectives and current challenges,” Sensors Actuators, B Chem., vol. 229, pp. 110–130, 2016. [4] A. G. Brolo, “Plasmonics for future biosensors,” Nat. Photon., vol. 6, pp. 709–713, 2012. [5] K. A. Willets, R. Van Duyne, and R. P. Van Duyne, “Localized surface plasmon resonance spectroscopy and sensing,” Annu. Rev. Phys. Chem., vol. 58, no. 1, pp. 267–297, 2007. [6] M. E. Stewart et al., “Nanostructured plasmonic sensors,” Chem. Rev., vol. 108, no. 2, pp. 494–521, 2008. [7] E. Hutter and J. H. Fendler, “Exploitation of localized surface plasmon resonance,” Adv. Mater., vol. 16, no. 19, pp. 1685–1706, 2004. [8] A. K. Sharma and B. D. Gupta, “Fiber optic sensor based on surface plasmon resonance with nanoparticle films,” Photon. Nanostruct., Fundam. Appl., vol. 3, no. 1, pp. 30–37, 2005. [9] R. A. Minz, S. S. Pal, R. K. Sinha, and S. K. Mondal, “Plasmonic coating on chemically treated optical fiber probe in the presence of evanescent Wave: a novel approach for designing sensitive plasmonic sensor,” Plasmonics, vol. 11, no. 2, pp. 653–658, 2016. [10] J. Homola, S. S. Yee, and G. Gauglitz, “Surface plasmon resonance sensors: review,” Sensors Actuators, B Chem., vol. 54, no. 1, pp. 3–15, 1999. [11] A. V. Zayats, I. I. Smolyaninov, and A. A. Maradudin, “Nano-optics of surface plasmon polaritons,” Phys. Rep., vol. 408, nos. 3/4, pp. 131–314, 2005. [12] Y. Yuan and L. Ding, “Theoretical investigation for excitation light and fluorescence signal of fiber optical sensor using tapered fiber tip,” Opt. Express, vol. 19, no. 22, pp. 21515–21523, 2011. [13] B. D. Gupta and R. K. Verma, “Surface plasmon Resonance-Based fiber optic Sensors: Principle, probe designs, and some applications,” J. Sensors, vol. 2009, pp. 979761-1–979761-12, 2009. [14] L. Yin et al., “Subwavelength focusing and guiding of surface plasmons,” Nano Lett., vol. 5, no. 7, pp. 1399–1402, 2005. [15] A. K. Sharma, R. Jha, and B. D. Gupta, “Fiber-optic sensors based on surface plasmon resonance: A comprehensive review,” IEEE Sensors, vol. 7, no. 8, pp. 1118–1129, 2007. [16] Y. Shevchenko, N. U. Ahamad, A. Ianoul, and J. Albert, “In situ monitoring of the formation of nanoscale polyelectrolyte coatings on optical fibers using surface plasmon resonances,” Opt. Express, vol. 18, no. 19, pp. 20409–20421, 2010. [17] J. Satija, N. S. Punjabi, V. V. R. Sai, and S. Mukherji, “Optimal design for U-bent fiber-optic LSPR sensor probes,” Plasmonics, vol. 9, no. 2, pp. 251–260, 2014.

[18] A. Leung, P. M. Shankar, and R. Mutharasan, “A review of fiber-optic biosensors,” Sensors Actuators, B Chem., vol. 125, no. 2, pp. 688–703, 2007. [19] S. Kumar, G. Sharma, and V. Singh, “Sensitivity of tapered optical fiber surface plasmon resonance sensors,” Opt. Fiber Technol., vol. 20, no. 4, pp. 333–335, 2014. [20] M. Napiorkowski and W. Urbanczyk, “Effect of bending on surface plasmon resonance spectrum in microstructured optical fibers,” Opt. Express, vol. 21, no. 19, pp. 22762–22772, 2013. [21] N. Cennamo, D. Massarotti, R. Galatus, L. Conte, and L. Zeni, “Performance comparison of two sensors based on surface plasmon resonance in a plastic optical fiber,” Sensors (Basel), vol. 13, no. 1, pp. 721–735, 2013. [22] P. Hlubina, M. Kadulova, D. Ciprian, and J. Sobota, “Reflection-based fibre-optic refractive index sensor using surface plasmon resonance,” J. Eur. Opt. Soc. Rapid Publ., vol. 9, 2014, Art. no. 14033. [23] Y. S. Dwivedi, A. K. Sharma, and B. D. Gupta, “Influence of design parameters on the performance of a surface plasmon sensor based fiber optic sensor,” Plasmonics, vol. 3, no. 2, pp. 79–86, 2008. [24] Y.-H. Tai and P.-K. Wei, “Sensitive liquid refractive index sensors using tapered optical fiber tips,” Opt. Lett., vol. 35, no. 7, pp. 944–946, 2010. [25] S. S. Pal, S. K. Mondal, P. P. Bajpai, and P. Kapur, “Optical fiber tip for field-enhanced second harmonic generation,” Opt. Lett., vol. 37, no. 19, pp. 4017–4019, 2012. [26] O. Esteban, N. D´ıaz-Herrera, M.-C. Navarrete, and A. Gonz´alez-Cano, “Surface plasmon resonance sensors based on uniform-waist tapered fibers in a reflective configuration,” Appl. Opt., vol. 45, no. 28, pp. 7294–7298, 2006. [27] M. Piliarik and J. Homola, “Surface plasmon resonance (SPR) sensors: approaching their limits?,” Opt. Express, vol. 17, no. 19, pp. 16505–16517, 2009. [28] W. Knoll, “Influence of metal film thickness on the sensitivity of surface plasmon resonance biosensors,” Appl. Spectrosc., vol. 59, no. 5, pp. 661– 667, 2005. [29] Y. Yuan, L. Ding, and Z. Guo, “Numerical investigation for SPR-based optical fiber sensor,” Sensors Actuators B Chem., vol. 157, no. 1, pp. 240– 245, 2011. [30] H. Moayyed, I. T. Leite, L. Coelho, J. L. Santos, and D. Viegas, “Theoretical study of phase-interrogated surface plasmon resonance based on optical fiber sensors with metallic and oxide layers,” Plasmonics, vol. 10, no. 4, pp. 979–987, 2015. [31] A. A. Rifat et al., “Highly sensitive multi-core flat fiber surface plasmon resonance refractive index sensor,” Opt. Express, vol. 24, no. 3, pp. 2485– 2495, 2016. [32] Y. Chang, Y. Chen, and H. Kuo, “Nanofiber optic sensor based on the excitation of surface plasmon wave near fiber tip,” Biomed. Opt. Express, vol. 11, no. 2006, pp. 014032–014035, 2006. [33] P. Uebel, S. T. Bauerschmidt, M. A. Schmidt, and P. S. J. Russell, “A goldnanotip optical fiber for plasmon-enhanced near-field detection,” Appl. Phys. Lett., vol. 103, no. 2, pp. 2–6, 2013.

Rashmi A. Minz received the B.Tech. (Hons.) degree in electronics and instrumentation from Dr. M.G.R University Chennai, Chennai, India, the M.Tech. degree with distinction in advanced instrumentation engineering from Academy of Scientific and Innovative Research, Central Scientific and Instruments Organisation (CSIO), Chandigarh, India, in 2014. She is currently working toward the Ph.D. degree in Photonics group at CSIO. She is currently a Trainee Scientist at CSIO. She is a member of SPIE. Her current research interests include plasmonic sensors, optical biosensors, and near field instruments designing.

MINZ et al.: MAGNETRON SPUTTERING COATED OPTICAL FIBER PROBE DESIGNS FOR SURFACE PLASMON RESONANCE SENSOR

Sudipta Sarkar Pal received the B.Sc. degree from Bethune College, Kolkata, India, the M.Sc. degree from Calcutta University, Kolkata, the Ph.D. degree from Saha Institute of Nuclear Physics, Kolkata, in 2006. She was a Visiting Research Fellow at Max-Planck-Institut f¨ur Metallforschung, Stuttgart, Germany, a Postdoctoral Fellow at Katholieke Universiteit Leuven, Leuven, Belgium (2006–2008), a Visiting Scientist at Materials Science Division, Indira Gandhi Centre for Atomic Research , Kalpakkam, India (2008–2009), a Guest Lecturer in the Department of Nanoscience and Nanotechnology, Panjab University, Chandigarh, India (2009–2010), and a Fellow Scientist at Central Scientific Instruments Organisation (CSIR-CSIO), Chandigarh (2010–June 2012). She is currently a Senior Scientist in Advanced Materials and Sensors CSIO, Chandigarh. Her ongoing research interests include the field of nanophotonics and plasmonics.

Aditi Chopra received the B.Tech. degree in biomedical engineering and the M.Tech. degree in nanoscience and technology from Punjab Technical University, Jalandhar, India, in 2010 and 2014, respectively. She is currently working as a Senior Project Fellow in Central Scientific Instruments Organisation, Chandigarh, India. Her research interests include nanomaterials and nanomedicine.

Shivam Bargujar received the B.E. degree in mechanical engineering from Chandigarh College of Engineering and Technology, Chandigarh, India, in 2014. He is currently working as a Project Fellow in Central Scientific Instruments Organisation, Chandigarh. His research interests include mechanical designing and its applications.

Randhir Bhatnagar received the M.Tech. degree in opto electronics from Indian Institute of Technology Delhi, New Delhi, India. He is currently a Chief Scientist and the Head of the Department of Advanced Materials and Sensors Divison, Central Scientific Instruments Organisation, Chandigarh, India. He is specialized in the design of optoelectronics system and instrumentation. His research interests include gas sensing, plasmonic sensor, and PH sensing.

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R. K. Sinha received the M.Sc. degree in physics from the Indian Institute of Technology (IIT), Kharagpur, India, in 1984, and the Ph.D. degree in the area of fiber optics and optical communication technology from IIT Delhi, New Delhi, India, in 1990. He had held various research and academic positions at the Indian Institute of Science, Bangalore, India, during 1991, Birla Institute of Technology and Science (BITS), Pilani, India, during 1992–1994, REC (now NIT), Hamirpur, India, during 1994–1998, and Delhi College of Engineering-DCE (now Delhi Technological University-DTU), University of Delhi during December 31, 1998 to July 1, 2015. He is a Fulbright Scholar and received the Fulbright-Nehru Fellowship to acquire first-hand knowledge of Higher Education Systems and Practices of USA covering over a dozen U.S. universities and higher educational institutions as an International Educational Administrator in 2013. His research interests include photonic crystal fiber sensors, metamaterials, and plasmonics. He received The Institution of Electronics and Telecommunication Engineers (IETE) Biman-Behari Sen Memorial Award for outstanding research in the area of Telecom Grade Optical Fibers and Optoelectronic Devices Optics in 2012, the Emerging Optoelectronics Technology Award [(CEOT-IETE, India)], 2006 for outstanding research work in the area of Nano-photonics, the S. K. Mitra Memorial Award for Best Research Paper in IETE Technical Review 2002 on Nanostructure Electron Waveguides and Devices, and his coauthored research paper won several Best Research Paper Awards which include Swarna Jayanti Puraskar (Gold Medal) from the National Academy of Sciences in the area of Nano-scale Optical Devices for the year 2001, Reliance Technology Awards 2010, SPIE 2014 best research presentation award and OSI-2014 second best poster presentation award. He is a Fellow of SPIE—The International Society of Optical Engineering, a Fellow of the IETE, and a Fellow of Optical Society of India, a member of The Optical Society (OSA, USA), a member of The Photonics Society of IEEE. He is currently the Director of CSIR—Central Scientific Instruments Organisation, Chandigarh, India, with effect from July 2, 2015.

Samir K. Mondal received the M.Sc. degree in physics and the Ph.D. degree in fiber and integrated optics from the University of Calcutta, Kolkata, India. He has postdoctoral research experience from the University of California, Irvine, CA, USA and the University of Minnesota, Minneapolis, MN, USA. Later on he joined the Tyndall National Institute, Cork, Ireland as a Research Scientist. He has research collaborations with research teams from France, China, and Russia. He is currently working as a Principal Scientist in the Department of Advanced Material and Sensors, CSIR-CSIO (Central Scientific and Instruments Organisation), Chandigarh, India. His research interests include optical nanoantenna and nanophotonics, optical nano-tweezer, near field optics, surface plasmon sensor and optical coherence tomography imaging. Besides serving as an Associate Editor Member in couple international journals, he regularly reviews manuscripts from reputed journals in the area of photonics and optics.