Recent Advances in Mid-IR Optical Fibres for Chemical and Biological Sensing in the 2-15 µm Spectral Range

Animesh Jha*, Xin Jiang, Joris Lousteau, Billy Richards,

The Institute for Materials Research, Houldsworth Building, University of Leeds, Clarendon Road, LS2 9JT, UK.

Hongxia Li, William N Macpherson, Henry T Bookey, James S Barton and Ajoy Kar,

Department of Physics, Heriot-Watt University, Edinburgh, EH14 4AS, UK

Yuen H Tsang and David J Binks Photon Physics Group, School of Physics and Astronomy, University of Manchester, Manchester,

M13 9PL UK

ABSTRACT

The invited paper explains the transmission properties of a range of near-, mid-, and far-IR optical fibres for their applications in chemical and biological sensing. Methods for the fabrication of single and multiple-core mid-IR fibres are discussed in view of controlling the thermal and viscosity properties for fibre drawing. In particular, the need for removing impurity bands in the 5000 to 1000 cm-1 range is explained. The importance of engineering multi-core fibres is also discussed for simultaneous measurements of Raman, IR and surface plasmon enhanced modes together with say, temperature using a mid-IR transmitting tellurite fibre e.g. in a chemical process. The paper explains the principles and advantages of evanescent wave coupling of light at the resonant frequency bands for chemical sensing using a fibre evanescent wave spectroscopic sensor having a GeTeSe chalcogenide fibre. Using fibre based techniques, measurements for Cr6+ ions in solution and As3+ and As5+ in solids have been characterized at visible and mid-IR regions, respectively. In this paper we also explain the importance of using mid-IR fibres for engineering novel laser and broadband sources for chemical sensing.

Keywords: IR fibres, Chemical and biological sensing

1. INTRODUCTION Steady development via research in silica optical fibres over the last 3 decades has led to many applications in optical communication and fibre based sensing and instrumentation, some of which will be highlighted in this paper. However for targeting beyond 2 µm in mid-IR (2-10 µm) and far-IR (>20 µm), the total optical attenuation of silicates, phosphates and borates is the major limiting factor. These materials have strong multiphonon absorption, which increases exponentially with increasing wavelength [1]. The spectral region between 2 and 12 µm is characterized as the fundamental molecular vibration regions of functional and skeletal groups, stretching and deformation bands. Beyond 10 µm the weaker molecular finger printing region begins. The intensities of absorption bands for the fundamental vibrations are between 3 and 5 orders of magnitude stronger than their harmonics in the near-IR and visible and finger prints in the far-IR. It is for this reason due to large signal-to-noise ratio alone the mid-IR chemical spectroscopy and imaging is so relevant for chemicals, pharmaceuticals, and environment industry for monitoring and sensing.

* Corresponding author’s e-mail: a.jha@leeds.ac.uk

Invited Paper

Photonics North 2009, edited by Réal Vallée, Proc. of SPIE Vol. 7386, 73860V© 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.840477

Proc. of SPIE Vol. 7386 73860V-1

2. MID-IR FIBRE OPTIC MATERIALS Finding materials for optical fibres, which are as good as silica/silicate fibres in the visible/near-IR, is a major challenge; and in this respect we have systematically investigated 4 different types of glass-forming systems which enable access to spectroscopic measurements in the 2 to 20 µm region. These are heavy-metal oxide (HMO) glasses (e.g. tellurium oxide (TeO2) and germanium oxide (GeO2) glasses) which are structurally modified with the additions of constituent oxides such as ZnO, BaO, Ga2O3, Bi2O3, PbO and WO2/WO3 so that the multiphonon absorption edges in these compositions, either shift to longer wavelengths or they are not as steep as in the unmodified compositions. Such an approach for compositional modification in heavy metal oxides can potentially provide spectroscopic access in the 2 and 7 µm at low power penalty for engineering direct absorption and evanescent wave field chemical sensors for spectroscopic analysis. Fibres derived from HMO glasses are durable and exhibit much reduced sensitivity to atmospheric changes in temperature and moisture, which has been the main cause for the lack of interest in heavy metal fluoride glasses and fibres, developed more than 20 years ago [1]. Besides extended transmission beyond 2 µm, heavy-metal oxide glasses are also Raman active [2] and exhibit large optical nonlinearity [3] for parametric processes in mid-IR and large solubilities for rare-earth oxides [4] some of which have quantum-mechanically efficient optical transitions in the mid-IR (1.8 to 3 µm), so that novel laser and broadband light sources can be engineered for chemical spectroscopy.

Besides HMO glass fibres, there are other categories of fibres based chalcogenide elements (S, Se, Te) and their compounds with the elements in groups IIIA (Ga, In), IVB (Si, Ge, Sn), and VB (As, Sb). These elements yield predominantly three different types chalcogenide glasses: sulphide, selenide and telluride glasses [5-7], which have been known in the literature for at least 4 decades. However many of the constituents in these glasses are strongly photosensitive due to the presence of the lone-pair of electrons in the chalcogen elements and with Pb which contribute to photo-darkening, and therefore loss-contributing factors in the fibre structure at larger intensities of photon. Engineering fibres, which are robust at and above room temperatures and remain transparent at high optical intensity is a formidable barrier in engineering such fibres. Our research focuses in providing solutions by engineering fibres based on sulphide and selenide compounds which exhibit extended transmission in mid-IR up to 11-12 and 16-18 µm, respectively, and can remain stable above room temperatures (150-200oC) for many hundreds of hours without any significant deterioration in the structural properties, measured by thermogravimetric analysis. The extended transmission wavelengths in four different types of bulk glasses, namely germanate (GeO2), tellurite (TeO2), sulphide and selenide glasses are at around 5 µm, 5.5-6 µm, 9-11 µm, and 16-18 µm, respectively. Significant impurity bands, namely O-H, S-H, Se-H, sulphate (SO4), nitrates, carbonates and oxides can be present in the glass and contribute to strong absorption in mid-IR. In our previous work we identified several impurity bands and how these were reduced via enhanced chemical reaction, e.g. the

2222 223..2 SOHClGeSSClHOGe ++=++− reaction which occurs during melting [8]. The reduction in the

absorption intensity bands yields clearer spectra for chemical analysis and monitoring, see figures 1a and 1b. Similar techniques for impurity reduction in tellurite glasses have been applied to achieve loss in the range of 1.5 to 3 dB m-1; with higher value of losses being at shorter wavelengths. The lower loss in tellurite has enabled a number of new applications, discussed below, for these fibres as temperature sensors, fibre Bragg grating [9], Raman frequency generation [2] and for mid-IR fibre lasers. Concerning selenide glasses, the purification of raw materials has been proven to be an effective method to produce a clear spectroscopic window, as shown in figure 2a and 2b. The process of purification was implemented in a customized vacuum drying system, where small lump of elemental Se, Te and Ge were then placed in individual quartz ampoules and the Se ampoule was heated at 230 oC for 4 hours for removing the oxidized SeO2 layer on the surface. The Te was heated in a similar manner but at a higher temperature at 600oC. The heating of germanium (Ge) at 450 oC was only used to remove the surface water at which GeO2 could not be removed due to its high melting and boiling points above 1500oC. A liquid nitrogen trap was attached for condensing the vaporized impurities and collecting them in the bottle, before letting the clean gas out into the atmosphere. Figure 2b compares the infrared absorption spectra of the GeTeSe glasses before and after purification. For fibre sensor engineering, the length requirements differ significantly and may vary from sub meter length for portable devices to several meters for remote measurements[10], for which 1-3 dB m-1 loss, although not ideal, however it is acceptable. Longer than ten to hundreds of meters of fibres are required for sensors area network, for which the overall loss has to be less than 0.1 dB m-1 in the mid-IR region; e.g. in the near-IR silica fibre methane gas sensor networks [11]. For network applications, both structural robustness and environmental durability are essential requirements in specifying the sensor design.

Proc. of SPIE Vol. 7386 73860V-2

3. FIBRE OR WAVEGUIDE DESIGN FOR EVANESCENT WAVE SENSING Optical fibres guide light based on the principle of total internal reflection between a denser medium with refractive index n1 and the surrounding rarer medium n2, such that from the Snell’s law,

2211 sinsin. θθ nn = (1)

which at a critical angle

⎟⎟⎠

⎞⎜⎜⎝

⎛= −

1

21sinnn

cθ (2)

For total internal reflection, the condition θ > θc saves the energy of propagating electric field inside the denser core glass. However each time a propagating wave suffers reflection, a fraction of energy is leaked out via refraction into the cladding region, and the depth, β to which the electric field of propagating evanescent wave penetrates is given by equation 3:

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

po d

zItI exp.)( (3)

where z is a distance in the vicinity of core-clad interface. The penetration depth β is then expressed as [12]:

2

2

21 )()(sin2

nn

dm

p

−

=

θπ

λ (4)

From eq.4, with increasing launch angle θ, the proportion of evanescent field decays inversely to the sinθ. In a similar manner as the refractive index difference, given by the n2/n1 ratio, increases for a given θ the penetration depth of electric field decreases. In table 1, we have compared the penetration depth of the evanescent field for different glasses and mid-IR crystals in contact with aqueous medium, from which it is evident that the mid-IR transmitting glasses offer greater opportunity for probing at larger penetration of evanescent field in the adjoining aqueous medium. A priori knowledge of these geometrical parameters is therefore essential for engineering evanescent waveguiding region and launch condition at a given wavelength.

The guided optics for evanescent waves also allows us to determine the polarisation states of the evanescent wave from the Fresnel equation for the TE and TM polarisation states of the incident electric field (e.g. a laser beam). The distinction of two polarisation states is particularly advantageous in determining the chirality of molecules; e.g. lipids, DNA and liquid-crystal structures [13]. Finally, for enhanced signal-to-noise ratio, multiple reflections in the evanescently coupled medium is particularly advantageous, if the concentrations of species for detection is small, or the extinction coefficient α is small. For multiple reflection, α represents the total extinction coefficient , and R has two

main components, first one due to the Fresnel reflectivity, which is due to the term: 2

2

2

)()(⎥⎦

⎤⎢⎣

⎡+−

m

m

nnnn and secondly due to the

extinction coefficient of the medium itself (αo), which is given by the Lambert-Beer’s law type equation :

( )opo dII α.exp. −= (5)

The sum of two components can be then expressed as: N

edR ).1( α−= (6)

where N is the number of reflections. Here n2 and nm are the cladding glass and evanescent wave medium refractive indices. It is evident from the multiple reflection equation 6 that along the length of waveguide region, the intensity of coupled electric field will decay rapidly if the value of αo is large. Also it is important to note that the intensity modulation [14] will arise due to multiple reflections and interference along the attenuation path, which will be damped by the medium.

Proc. of SPIE Vol. 7386 73860V-3

4. FABRICATION AND CHARACTERISATION OF FIBRES The fabrication of single and multiple core fibres was carried out via preform fabrication using melting and high-temperature (above glass transition temperature, Tg) and pressure extrusion for engineering a core-clad glass with refractive index n1 for core and n2 for cladding [15,16]. The fabrication of fibres also requires matching the coefficient of thermal expansion of core and cladding, such that the overall structure has a compressive stress by allowing cladding to have a lower expansion coefficient than the core [1]. Together with the matched expansion coefficients and refractive

indices for required numerical aperture, ( 22

21 nnNA −= ), the fibre drawing condition also necessitates the viscosities

of core and cladding glasses are sufficiently close to each other such that the inhomogeneous flow due to differential viscous drag is kept to a minimum for reducing the propensity for forming structural defects at the core-clad interface. The structures of fibres drawn with multiple cores are shown in figure 3b. In figure 3a, we show the absorption peaks and the background loss spectra for bulk germanate (inset) and GeS2 glasses and find that there are unobscured transmission windows in both types of glasses for accessing various molecular vibrations. The OH- absorption at around 3.2 μm has been reduced to less than 10 dB/m from over 1000 dB/m. The peak before 4.5μm is due to the residual carbonates present from the raw materials, Na2CO3 which can be reduced by chlorine-oxygen reactive atmosphere processing of the glass. The background loss in dB m-1 for the fitted line is

001.0305.0exp.105.9 9 +⎟⎠⎞

⎜⎝⎛−−

λx (7)

Wavelength regions between 2 and 2.7 μm and 3.5 and 3.8 μm remain unobscured for chemical analysis. In GeS2 glass, the impurity IR vibration bands are present at 2530-2500 cm-1, 1490-1410 cm-1 for carbonates, 3430cm-1, 1470cm-1 for sulphate, 2580-2450 cm-1 for S-H, 1800-1700 cm-1, 1520-1280 cm-1 for nitrates, and at 2100-1950 cm-1 for Ge-H [17]. In figure 3c, we compare the propagation of broadband light in each core and compare it with a reference.

5. APPLICATIONS OF MID-IR FIBRES AND BULK GLASSES 5.1 Near-IR Fibre Fabry Perot Interferometry

One of the first applications for mid-IR fibres is in temperature sensing using a Fabry-Perot interferometer. We used a broadband erbium doped amplified spontaneous emission source with centre wavelength at 1530 nm by connecting it through a 2x2 single mode fibre coupler. Because of the refractive index difference between single mode silica and tellurite fibres, the two-fibre spliced junction functions like a mirror, which partially reflects the source light and the remaining enters the FP interferometer, as shown in figure 4a. The observed interferogram is shown in figure 4b, in which the phase shift is evident with a change in temperature. The phase (ϕ) of interference fringes is given by:

ln1.4λπϕ = (8)

and the free spectral range (Δλ) is equal to ln

mean

1

2

2λ . Here n1 is the refractive index of the core of tellurite fibre, λm is the

mean wavelength, and l is the fibre Fabry Perot length. The shift in the fringe is caused by the temperature dependence of refractive index and the thermal expansion coefficient, and is physically depicted as the temperature coefficient of phase change

dTdϕ , which is expressed in terms of n1, αl and βT (= dn1/dT), where βT is the temperature coefficient of

refractive index. We measured the phase sensitivity of FP in the temperature range of 280 to 320 K, which is shown in figure 4c. From the derived value of

dTdϕ , the value of dn1/dT for tellurite glass is equal to –16.4x10-6 K-1.

5.2 Mid-IR Rare-earth ion doped Fibre lasers

One of the most important applications of mid-IR fibre lasers is in chemical sensing and imaging by targeting the molecular vibrations and finger printing regions of infrared spectra. Efficient lasing transitions, capable of yielding 5 to

Proc. of SPIE Vol. 7386 73860V-4

100 mW power, can potentially generate many applications. An example of Tm-doped tellurite fibre laser operating in the region of 1900-1995 nm range is discussed here. Tm-doped silica fibres pumped with 800 nm source has been very well known in the literature for very large output powers 10-100 of Watts [18,19]. However the 800 nm diode laser is not convenient for pumping fibre based system for engineering compact design, as it is commercially not available in fibre pigtailed geometry. As an example of fibre based pumping scheme, we have chosen the 1080 nm Yb-fibre laser to pump Tm-doped tellurite fibres with 0.5 wt% Tm2O3 co-doped with 2.5 wt% Yb2O3 in the core. The fibre length was less than 20 cm. The lasing threshold was 400 mW and the slope efficiency was ~10%, yielding ~80 mW power at 1953 nm, as shown in figure 5. This is quite a significant achievement since tellurium oxide glasses offer 20 to 50 times larger solubility of rare-earth oxides than in conventional silicates, which allows us to shorten the cavity length for tuneable lasers by at least an order of magnitude. Compact fibre IR lasers can be combined with near IR plasmonics for opening opportunities for nonlinear processes for new wavelengths generations in near IR via coherent anti-stoke Raman spectroscopy (CARS), surface enhanced and resonant Raman (SERS and SERRS) spectroscopy, white light supercontinuum; all of which can be achieved in a strongly nonlinear and Raman-active medium such tellurite, germanate, and chalcogenide fibres. Such approaches for frequency conversion may allow us to extend the region of laser operation in the mid-IR which will complement the emerging room temperature quantum cascade lasers operating in the 5 to 12 μm region. Availability of new wavelengths in mid-IR, which are not possible via direct rare-earth doped fibres and quantum cascade laser techniques, together with existing wavelengths in near-IR will open new opportunities for resonant Raman imaging, IR-mapping, SERS and SERRS for biological and chemical speciation, and tracking photo-induced chemical changes in biology, which are relevant to human physiology [13].

5.3 Fibre evanescent wave spectroscopic (FEWS) sensors

Optical fibre sensing for analyzing the presence of hazardous chemical wastes and pollutants is becoming an important issue for industrial wastes from drug and food manufacturing and petro-chemical processes. The determination of concentration of toxic and hazardous materials in products is critical for reducing the risks of exposure. For determining concentration in the ppm to sub-ppm range, it is important to perform measurement in the mid-infrared (IR) spectrum where the molecules have large fundamental vibration bands which are 104-106 times larger than their weaker harmonics in the visible and near-IR regions. Although silica based near-IR fibre sensors have been widely used, for mid-IR the chalcogenide materials with extended transmission is essential for accessing the fundamental molecular bands and their finger prints [20-22]. There are various types of fibre sensors, but most of them are based on spectroscopic analyses [20,21]. Fibre evanescent wave spectroscopic (FEWS) sensors were intensively studied recently [23,24]. As reported, chalcogenide glasses have IR transmission up to 20-25 μm, where a majority of molecular species have strong vibrational signatures. These IR vibrations are utilized for chemical analysis for the determination of impurities and crystallisation behaviour during drug synthesis, oil, gas and chemicals manufacturing processes, in which challenges in maintaining product quality is essential [25-28]. Figure 6a shows the experimental setup of a FEWS sensor [29]. The sensor element consists of a 40 cm long Ge-Te-Se fibre coupled with a Bruker Vertex 70 FTIR spectrometer which is equipped with a mercury-cadmium-telluride (MCT) detector. The sensing length is about 3 cm. The IR beam was coupled into this fibre through a parabola mirror, which was not found to be ideal for launching light in such a large diameter fibre with refractive index more than 3. For improving launching of light into the fibre each end was mounted on a 3-dimension stage to allow accurate position for maximizing the coupling light. The output power at the other end of the fibre was focused through another parabolic mirror to the MCT detector. All the free space optics were reflective rather than in transmission to avoid possible materials absorption in the IR range. Figure 6b and 6c present the measured FEWS absorption spectra of acetone solutions (5-70 vol.%) and vitamin E and C solutions (680 and 500 ppm). The observed absorption peaks are consistent to the Sigma library of FTIR spectra [30] and hence these characteristic peaks can be used for real-time identification of corresponding chemical species. Further improvement on the sensor sensitivity may be focused on extending the fibre sensing length and coating the fibre with a cladding layer to avoid the loss of optical signal.

6. HEAVY METAL ANALYSIS We have characterised As3+/As5+ in arsenic-laden sludges and iron complexes, and in Cr6+ bearing aqueous solutions at mid-IR wavelengths and UV-visible wavelengths, respectively in figures 7a and 7b. These ions are known as the

Proc. of SPIE Vol. 7386 73860V-5

carcinogens in human beings, which can cause widespread damage to internal organs on prolonged exposure. The concentration limits at which these two elements cause cancer in human beings is not well understood, which is why it is essential to carry out both qualitative and quantitative analyses of say, Cr-ion and As-ion species. In figure 7a for the first time we report the capabilities of FTIR technique in the speciation analysis of As-ions. The arsenic-laden sludges were obtained from the water treatment plant in W Bengal in India, where there is endemic arsenic poisoning, affecting hundreds of thousands to millions people. Arsenic in its trivalent state is known to be carcinogen and it is for this reason, the characterisation of speciation of arsenic in drinking water source is essential. In figure 7b, we have measured the spectra of Cr6+ ions present in water, which unlike arsenic is present in the industrial waste water stream, particularly emerging from chromium chemicals, foundries waste sites, leather tanneries, and chromium plating industrial sites. We thus prove the capabilities of fibre optic tools for spectroscopic applications for analysis of complex elements.

7. CONCLUSIONS In this paper various mid-IR fibres have been discussed together with their fabrication. The mid-IR fibre technology is still under research and development and is opening new opportunities for chemical analysis, laser and broadband source engineering. Research in future will focus on improving fibres for lower losses for engineering nonlinear optical devices and chemical and physical sensors.

Acknowledgements: The authors acknowledge the financial support (GR/T19889/01) and (EP/C515226/1) from the EPSRC, BP Chemicals (UK), and GlaxoSmithKline (UK).

REFERENCES

[1] P. France, [Fluoride Glass Optical Fibres], Blackie Press, London, Chap 2 (1990). [2] R. Stegman et al: Optics Letters, 28, 1126-1128 (2003). [3] S. Shen et al: J Am. Ceram. Soc. 85, 1391-1395 (2002). [4] A. Jha, S. Shen and M Naftaly, Phys Rev B (62), 6215-6227 (2000). [5] M.P. Fontana, B Rosi, Z Ivanova, and N Kirov, Phil Mag B, 56, 507-514 (1987). [6] J. Nishi, T. Yamashita, and T. Yamagishi, Appl. Optics, 28, 5122-5127 (1989). [7] A.R. Hilton, C.E. Jones, and M. Brau, Phys. Chem. Glasses 7, 105 (1966). [8] X. Liu, A. Jha and V. Tikhomirov, J Mater. Res., 12, 2864-2874 (2000). [9] J. S. Sanghera and I.D. Aggarwal, J Non-Cryst. Solids, 256 & 257, 6-16 (1999). [10] B. Culshaw, G. Stewart, F. Dong, C. Tandy and D. Moodie, Sensors & Actuators B, 51, 25-37 (1998). [11] C. Vigano, J.M. Ruysschaert and E. Goormahtigh, Talanta, 65, 1132-1142 (2005). [12] P Prasad, Biophotonics [13] J. Lousteau, H.T. Bookey, X. Jiang, C. Hill, A. Kar, and A. Jha: ICTON 2007 (Rome) 4-6th July 2007 (accepted) [14] S. Shen, A. Jha, E. Zhang, S.J. Wilson, C R Chimie, 5 (12), 921-938 (2002) [15] G. Socrates, [Infrared and Raman Characteristic Group Frequencies, Tables and Charts], 3rd Edition, John Wiley & Sons, 277, 286-292 (2001). [16] S.D. Jackson, A. Sabella, A. Hemming, S. Bennetts, and D. Lancaster, Optics Letters, 23, 241-243 (2007). [17] J. Wu, Z. Yao, J. Zong and S. Jiang, Optics Letters, 32, 638-640 (2007). [18] F. Neubrech et al, Appl. Phys. Lettl, 89, 253104 (2006) [19] Y. Menke, M. Ferraris, C. Corbari and J. Fage-Patterson, J Non-Cryst. solids, 345 & 346, 361-365 (2004). [20] H. J. Arditty, J. P. Dakin and R. T. Kersten, eds., Optical fiber sensors, Springer-Verlag, Berlin (1989) [21] M. Saito and K. Kikuchi, Opt. Rev., 4, 527-538 (1997) [22] K. Newby, W. M. Reichert, J. D. Andrade and R. R. Benner, Appl. Opt., 23, 1812-1815 (1984) [23] F.S. Ligler and Chris A.Rove Taitt, Optical biosensors: present and future, Amsterdam, Elsevier, Oxford (2002) [24] S. Simhony, E. M. Kosower and A. katzir, Appl. Phys. Lett. 49, 253-254 (1986) [25] A. Messica, A. Greenstein and A. Katzir, Appl. Opt., 35, 2274-2284 (1996) [26] J. Heo, M. Rodrigues, S. J. Saggese and G. H. Sigel, Appl. Opt., 30, 3944-3951 (1991) [27] J. S. Sanghera, F. H. Hung, L. E. Busse, P. C. Pureza and I. D. Aggarwal, J. Am. Ceram. Soc., 78, 2198-2202 (1995)

Proc. of SPIE Vol. 7386 73860V-6

[28] J. Keirsse, C. Boussard-Pledel, O. Loreal, O. Sire, B. Bureau, P. Leroyer, B. Turlin and J. Lucas, Vib. Spectrosc., 32, 23-32 (2003) [29] X.Jiang and A. Jha, OFS-20 (Edinburgh), 5-9th September 2009 (accepted) [30] R.J. Keller, [The sigma library of FT-IR spectra], eds 1, Sigma Chemical Company, INC. St. Louis, Missouri (1986)

Figure 1: A comparison of FTIR spectra for tellurite (TZN), GeAsSeTe, and GeS2 glasses

3000 4000 5000 6000 7000 8000 9000 100000

1

2

3

4

5

6

A(c

m-1)

Wavelength(nm)

77GeS2-13Ga2S3-8CsI-2Sb2S3

77GeS2-13Ga

2S

3-8CsI-2As

2S

3

75GeS2-13Ga2S3-6CsI-6SnS 75GeS

2-13Ga

2S

3-10CsI-2Sb

2S

3

800 1200 1600 2000 2400 2800 3200 3600 40000

1

2

3

4

5

6

Abs

orpt

ion,

cm

-1

Wavenumber, cm-1

TZN GeTeSeAs

Proc. of SPIE Vol. 7386 73860V-7

Figure 2: a) Experimental setup for the purification of starting chemicals for selenide glasses; b) FTIR spectra of 20Ge-10Te-70Se glasses before (blue) and after (red) the purification of starting chemicals. The upper figure shows the

magnified spectra with marked impurity bonds marked.

Figure 3: a) A comparison of background loss in chalcogenide and germanate glass for mid-IR transmission, b) a triple core TeO2 fibre cross-section, c) loss spectra

4 6 8 10 12 14 16 18 20 22 24

0

5

10

15

2020Ge-10Te-70Se

Wavelength [μm]

4 6 8 10 12 14 16 18 20 22 24

0.0

0.5

1.0

1.5

2.0

2.5

before purification after purification

Combination of Ge-O, Se-O and Te-O bonds

Te-OGe-O

CO/CO2

Se-H

O-H

Abso

rptio

n co

effic

ient

[cm

-1]

3000 4000 5000 6000 7000 8000 90000.0

5.0x104

1.0x105

1.5x105

2.0x105

2.5x105

2 .5 3.0 3 .5 4 .0 4.5 5 .0-10

0102030405060708090

100110120

Loss

[dB

/m]

W aveleng th [μm ]

56G eO2-22PbO -9N a

2O -4G a

2O

3-9PbF

2

F itting curve

Back

grou

nd L

oss(

dB/k

m)

Wavelength(nm)

77GeS2-15Ga2S3-4CsI-4Sb2S3

a c

b

Proc. of SPIE Vol. 7386 73860V-8

osqpsuq

UPLGS2E b CSA!fX

!PLe COfl

eu

Figure 4: (a) Fibre Fabry Perot interferometer, (b) Phase shift in interferogram with temperature, and (c) phase shift as function of T(K).

Figure 5: Slope efficiencies of lasing at 1953 nm in a Tm-doped tellurite fibre pumped at 1080 nm. Fibre lengths are specified for two output couplers at 10% and 2% slope efficiencies.

(a)

(b)

(c)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.10.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07 L = 16.1 cm, 50% R output coupler Slope = 10% L = 14.7 cm, 90% R output coupler Slope = 2%

Lase

r out

put p

ower

(W)

Absorbed pump power (W)

Proc. of SPIE Vol. 7386 73860V-9

Figure 6: a) Experimental setup of a FWES sensor using GeTeSe fibres; b) FEWS absorption spectra of acetone solutions in the concentration range of 5-70 vol.%; c) FEWS absorption spectra of vitamin E (680 ppm) and vitamin C (500 ppm) solutions

Figure 7: a) FTIR and UV-visible analysis of As5+, As3+ ions and b) Cr6+ ions, respectively in sludge and leather waste solutions.

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

0

2

4

6

Abso

rban

ce

Abs

orba

nce

Wavelength [μm]

Acetone solution [vol.%] 5% 10% 30% 70%

5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.30

2

4

6 Acetone solution [vol.%] 5% 10% 30% 70%

(a)

(b)

3.0 3.5 4.0 4.5 5.0 5.5 6.0

0.0

0.5

1.0

1.5

2.0

Abs

orba

nce

Wavelength [μm]

Vitamin E capsule136 mg/capsule in 200 g water: 680 ppm

Multi-Vitamins tabletVitamin C 20 mg in 40 g water: 500 ppm

(c)

400 600 800 1000 1200 1400 1600 1800 20000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Frac

tiona

l tra

nsm

itten

ce

Wavenumbers, cm-1

B(SL5) D(SD1) E(NaAsO

2)As3+

As5+

400 600 800 1000 1200 1400 1600 1800 20000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Frac

tiona

l tra

nsm

itten

ce

Wavenumbers, cm-1

B(SL5) D(SD1) E(NaAsO

2)As3+

As5+

-1

0

1

2

3

4

5

6

7

3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0

C r-2 5C r-5 0C r-7 5C r-1 0 0B L C -2 LB L C -1 0 L

Wavelength, nm-1

0

1

2

3

4

5

6

7

3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0

C r-2 5C r-5 0C r-7 5C r-1 0 0B L C -2 LB L C -1 0 L

Wavelength, nm

Proc. of SPIE Vol. 7386 73860V-10

Table 1: Comparison of penetration (dp) at 5 µm for various mid-IR materials

Materials r. index, n2, Critical Angle, θc θl = θc+5o dp, µm

Silica 1.5 59.1 64.1 2.94

Germanate 1.8 47.6 52.6 2.71

Tellurite 2.0 41.7 46.7 2.69

GeS2 2.5 32.1 37.1 2.78

ZnSe 2.4 33.7 38.7 2.76

GeAsSeTe 3.35 23.4 28.4 3.04

Ge 4.0 19.4 24.4 3.23

Proc. of SPIE Vol. 7386 73860V-11