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Enhanced supercontinuum generation in tapered tellurite suspended core fiber
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Enhanced supercontinuum generation in tapered tellurite suspended core fiber J. Picot-Clemente a, C. Strutynski a, F. Amrani a, F. Désévédavy a, J-C Jules a, G. Gadret a, D. Deng b, T. Cheng b, K. Nagasaka b, Y. Ohishi b, B. Kibler a,n, F. Smektala a a b
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne Franche-Comté, 21078 Dijon, France Research Center for Advanced Photon Technology, Toyota Technological Institute, Nagoya 468-8511, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 12 May 2015 Received in revised form 5 June 2015 Accepted 6 June 2015
We demonstrate 400-THz (0.6–3.3 mm) bandwidth infrared supercontinuum generation in a 10 cm-long tapered tellurite suspended core fiber pumped by nJ-level 200-fs pulses from an optical parametric oscillator. The increased nonlinearity and dispersion engineering extended by the moderate reduction of the fiber core size are exploited for supercontinuum optimization on both frequency edges (i.e., 155-THz overall gain), while keeping efficient power coupling into the untapered fiber input. The remaining limitation of supercontinuum bandwidth is related to the presence of the high absorption beyond 3 mm whereas spectral broadening is expected to fully cover the glass transmission window (0.5–4.5 mm). & 2015 Elsevier B.V. All rights reserved.
Keywords: Nonlinear optics Supercontinuum generation Microstructured fibers
1. Introduction Development of fiber-based supercontinuum (SC) light sources spanning the mid-infrared molecular fingerprint region is currently undergoing a dramatic increase, particularly stimulated by high-demanding applications such as biomolecular and environmental sensing. This can be largely attributed to the development of novel and high-quality mid-infrared (mid-IR) materials devoted to fiber optics. In the last several years mid-IR SC sources were implemented on alternative non-silica glass fibers and waveguides, such as fluoride, tellurite or chalcogenide glasses, since they represent an attractive solution thanks to their wide transparency and high nonlinearity [1]. For fluoride and tellurite fibers, the wavelength coverage in the mid-IR can reach 4.5 mm [2, 3], whereas for chalcogenide fibers and waveguides it can be extended until 8 mm [4, 5]. Recently, larger SC spectra up to 13 mm were also reported in multimode fibers [6], however such observations are restricted to the use of ultrashort amplifier laser chains and remain close to experimental configurations of SC generation in bulk media [7–11]. From a general point of view, it still remains very challenging to confirm such dramatic spectral broadenings that almost cover the entire glass transmission window, in particular when considering quasi-single-mode fibers and pump lasers at moderate energy levels for compact SC sources. Several detrimental effects related to the wavelength dependence n
Corresponding author. E-mail address: [email protected] (B. Kibler).
of the fiber attenuation usually arise such as extra water (OH) pollution or other absorption mechanisms [12–17]. To improve the spectral range of SC light and dispose of possible limitations of both fiber and pump laser, various methods were already demonstrated for engineered SC generation in silica fibers based on the fine control of nonlinear propagation dynamics. Enhanced blue- and red-expansion of the SC bandwidth can be achieved through extra dispersion engineering of photonic crystal fibers (PCFs) along the fiber axis, i.e. tapered PCFs, the fabrication of microwires, and the cascaded fiber approach [18– 21]. As a result, SC generation in silica fibers is now well-established and it usually covers the full transmission window of the material. The underlying mechanisms of spectral broadening in those methods are related to the tailoring of soliton dynamics (in anomalous dispersion) and associated dispersive waves (in normal dispersion) but also their mutual interactions. In most cases the SC bandwidth is fully driven by interactions such as the soliton trapping of dispersive waves, which modifies the short-wavelength edge (i.e., dispersive waves) as a function of the long-wavelength edge (i.e., solitons) in a way that satisfies group-velocity matching. In some sense, such techniques were recently applied to SC generation in soft-glass fibers but this remains restricted to chalcogenides microwires or waveguides, and near-IR studies of tapered tellurite PCFs [22–26]. More recently, tailoring SC generation was also investigated through accurate control of a novel fiber core design with high birefringence (i.e., an elongated core on a thin filament of glass) [27]. In this paper, we exploit both increased nonlinearity and dispersion engineering extended by the
http://dx.doi.org/10.1016/j.optcom.2015.06.014 0030-4018/& 2015 Elsevier B.V. All rights reserved.
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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extra reduction of an initial suspended core microstructured tellurite fiber for SC optimization on both frequency edges, i.e. visible and mid-IR. We demonstrate a 155-THz increase of the full SC bandwidth by using a moderate tapering ratio over a short fiber segment by means of a commercial glass processing platform.
2. Simulations 2.1. Group-velocity matching First we performed numerical simulations of the nonlinear pulse propagation in tapered tellurite suspended core fibers to evaluate the impact of the tapering process on both soliton and group-velocity matching dynamics. Detailed studies were already reported to optimize taper profiles for enhanced soliton self-frequency shift and blue-shifted dispersive waves [28–33]. Here the goal is to take advantage of such existing tools without going into details of wave interactions. Our simulations used a well-known generalized nonlinear Schrödinger equation that has successfully described the SC generation process over a wide parameter range [34]. The longitudinal variation of the fiber core diameter as a function of propagation distance is accurately taken into account through its effect on the fiber dispersion and nonlinearity. The fiber dispersion requires particular care because the group velocity varies greatly over the supercontinuum bandwidth (as seen in Fig. 1), our accurate modeling includes the full dispersion profile. In particular, for the fundamental guided mode we calculated the wavelength dependence of both the mode effective refractive index and the effective mode area by means of a commercial software using a fully vectorial finite-element model. Such calculations were repeated for various core diameters (in the range 1– 4 mm) of our suspended core fiber structure used in our experiments (see Fig. 4). The value of the fiber parameters were then modeled locally along the taper profile through a lookup table. Our model also takes into account the measured losses of a singlematerial fiber made from our low-OH tellurite TeO2–ZnO–Na2O (TZN) glass composition including some fluoride ions (i.e., with typical background losses of 1 dB/m up to 3 mm, and below 10 dB/m in the range 3–4 mm, see Ref. [35] and Fig. 3(a)). It also includes Kerr effect (nonlinear Kerr coefficient is deduced from numerical calculation of effective area, and with nonlinear refractive index n2 ¼3.8 10–19 m2/W [36]), self-steepening term with dispersion of the nonlinearity and the Raman response
function for our TZN glass adapted from Ref. [37]. Fig. 1 reports the beneficial impact of moderate tapering on SC generation in our typical tellurite suspended core fiber design used in Ref. [35] and shown in Section 3, in particular we consider an initial 3.6-μm suspended-core fiber pumped by 200-fs pulses at 1730 nm with 12 kW peak power (i.e., similar parameters to Refs. [12,35] and used in the experiments that follow). Such a fiber exhibits a zero dispersion wavelength (ZDW) close to 1.6 mm; our pumping regime then occurs in the anomalous dispersion regime with input conditions corresponding to a high soliton order (N 420) [34]. The resulting SC generation is found to be sensitive to input noise, which leads to significant shot-to-shot fluctuations in the SC bandwidth and a low average SC coherence as well. Detailed studies of the noise properties of supercontinuum spectra generated at different power levels in uniform and tapered photonic crystal fibers can be found in Ref. [38]. Here the input pulse shot noise was modeled by adding a noise seed of one photon per mode with random phase on each frequency discretization bin [34]. Consequently, we performed an averaging over 20 simulations with different input noise imposed on the initial 200-fs pulse, thus creating typically smooth SC spectra similar to average spectral measurements. A 10-cm long fiber segment was chosen due to experimental restrictions on both the overall tapered section 7 cm (see Section 3) and the maximum pump power coupled into the uniform fiber (i.e. spectral broadening almost saturates for longer propagation). Our taper design to enhance SC generation through group-velocity matching is here based on a long downtapering section (as proposed in Refs. [31,32]) and a moderate reduction of the fiber core size (i.e., reduction ratio of 1/3) to save the suspended core structure (see taper profile shown in Fig. 1(a)). Fig. 1(b,c) show the numerical results of simulated SC spectra at three main positions along the taper and the corresponding groupindex curves for the fundamental guided mode in order to highlight the major stages of nonlinear dynamics. The first stage (blue lines) corresponds to the input uniform fiber section wherein the SC spectrum extends in the infrared from 1 mm to 3 mm (for the –20 dB bandwidth) similarly to our previous studies [12,35]. The shortest wavelength generated (i.e., a DW) is determined by the maximum soliton shift towards the infrared. The group-index matching between both spectral components is confirmed when transferring the corresponding wavelengths on the group-index curve of the tested fiber section, we clearly join the point on either edge by a straight line. We checked that further propagation does not significantly extend the spectral broadening,
Fig. 1. (a) Taper suspended core profile: initial and final core diameters are 3.6 mm, and the core waist diameter is 1.3 mm. Dashed lines indicate three major stages of nonlinear dynamics studied in the following subfigures (i.e., (1) end of the uniform fiber input, (2) middle of the first transition region, and (3) taper waist). (b) Group-index curves of the fundamental guided mode at the corresponding positions along the taper. Dashed horizontal lines confirm the group-velocity matching between the most redshifted soliton and related dispersive wave observed during spectral broadening along the taper profile as shown in subfigure (c). (c) Numerical results of SC generation recorded at the different positions denoted in (a) along the taper (S: most-red shifted soliton, DW: related dispersive waves).
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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so that a change in the fiber structure is strongly required to tailor SC generation. The second stage is associated with a long downtapering section, in particular the transient SC evolution at the middle of this stage is represented with red lines in Fig. 1. The increased nonlinearity and dispersion engineering extended by the reduction of the fiber core size allows to overcome the natural saturation of the Raman soliton-self frequency shift. Note that the group-velocity matching is still satisfied in the transition region, thus developing SC in the blue edge of the spectrum. The SC spectrum now extends in the infrared from 0.7 mm to 3.5 mm (for the –20 dB bandwidth). Finally the third main stage is played by the taper waist section (green lines), in particular the apparition of a second zero group-velocity dispersion in the wavelength range of the most red-shifted solitons (see inflection point of the group index curve close to 3.3 mm) stimulates new transfer of energy to DWs in the mid-IR, so that the SC spectrum covers the entire glass transmission window (0.5–4.5 mm). After propagation in the second transition and the output uniform section, no significant change of the SC spectrum was noticed. 2.2. Influence of taper profiles In this subsection, we present the numerical analysis of the influence of the taper profile on the resulting output SC spectrum and its –20-dB bandwidth. Fig. 2(a–d) reports the effect of varying uniform, transition and waist lengths without changing the maximum core reduction. We observe that such variations mainly influence the mid-IR SC edge. By varying both down-tapering and up-tapering sections, compared to our first design, we generally decrease all soliton red-shifts and the subsequent energy transfer to mid-IR DWs. The second set of numerical simulations depicted in Fig. 2(e,f) focus on the effect of the core reduction ratio compared to Fig. 2(a). For a smaller waist, the second zero dispersion is then located at shorter wavelengths, which recoils the most redshifted solitons and then limits DW spreading below 4 mm. However the overall SC spectrum is more compact and flat, it exhibits a higher power spectral density. When considering a larger waist, the second ZDW is located far from the most red-shifted solitons, which prevents from efficient energy transfer towards mid-IR DWs. It is worth mentioning that our analysis reveals that our taper design based on a long down-tapering section are at the origin of the largest SC bandwidth as suggested in Refs. [31,32]. The long down-tapering section optimizes the group-velocity matching dynamics and SC extension while the short up-tapering section only provides easier output coupling for experimental
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convenience. 2.3. Influence of fiber losses Another parameter that significantly affects SC generation is related to the detrimental fiber attenuation in particular close to well-known OH absorption peaks and additional confinement loss due to tapering post-processing as well. Experimental measurements of tapering-induced losses were carried out by using an initial six-hole microstructured fiber with a larger core diameter. When applying a similar core reduction ratio, extra-losses were recorded in the wavelength range 1–4 mm (as shown later in Fig. 4). This confirms that possible extra losses compared to the bulk or the single-material fiber are only introduced during the drawing or the tapering post-processing of the suspended core microstructured fiber. Such issues were already noticed in our last study, in particular for wavelengths above 3 mm [35]. The numerical simulations presented above were again performed by introducing high extra losses for wavelengths above 2.8 mm, which corresponds to the beginning of the mid-IR loss bump revealed by measurements in the single-material fiber as shown in Fig. 3(a). Fiber losses were extrapolated for uniform and tapered suspended-core fibers based on a single measurement at 1.55 μm. The resulting output spectra are plotted in Fig. 3(b) and compared to previous simulations from Fig. 1. We first observe a small decrease of soliton-self-frequency shift occurring in both the input uniform section and the down-tapering section. But the main impact of these extra losses appears in the taper waist through complete absorption of mid-IR dispersive waves above 3.5 mm.
3. Experiments 3.1. Fiber fabrication and tapering procedure The fiber preform was elaborated from the glass composition of 75TeO2–15ZnO–5ZnF2–5Na2O with a reduced amount of Na2CO3, as known to contain hydroxyl impurities. The glass rods were fabricated by the conventional melt-quenching technique, starting from the raw materials: Tellurium oxide (FOX-Chemicals, 99.999%), Zinc oxide (FOX-Chemicals, 99.999%), Sodium carbonate (FOX-Chemicals, 99.9999%) and Zinc fluoride (Alfa Aesar, 99.995%). The mixed batches were melted in a platinum crucible covered with a lid of the same inert metal at 850 °C, during 2 h. In order to avoid the tellurium oxide reduction, the glass synthesis was
Fig. 2. Numerical results of output SC spectrum (left plot) for different taper profiles (right plot). Li ¼ 1-5 denote the lengths corresponding to uniform-input, down-tapering, waist, up-tapering and uniform-output sections, respectively. (a) Same parameters than Fig. 1 with L1–5 ¼17.5, 55, 5, 5, and 17.5 mm; waist ¼ 1.3 mm, (b) L1–5 ¼17.5, 5, 55, 5, and 17.5 mm; waist ¼ 1.3 mm, (c) L1–5 ¼ 17.5, 5, 5, 55, and 17.5 mm; waist ¼1.3 mm, (d) L1–5 ¼ 17, 22, 22, 22, 17; waist ¼ 1.3 mm, (e) L1–5 ¼ 17.5, 55, 5, 5, and 17.5; waist ¼ 1.1 mm, (f) L1–5 ¼17.5, 55, 5, 5, and 17.5; waist ¼ 1.7 mm. Dashed red lines reveal the –20-dB bandwidth of output SC spectra. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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Fig. 3. (a) Optical losses measured for a single-material fiber made from our low-OH TZN glass composition (dotted lines), then extrapolated for the suspended-core microstructured fiber (dashed line) and tapered suspended-core fiber (solid line) by using single measurements at 1.55 μm. We also consider extra losses above 3 mm based on previous studies [35]. (b) Numerical results of SC generation recorded at the different positions along the taper as denoted in Fig. 1(a) by taking into updated optical losses (solid line) and compared to previous results from Fig. 1 (dotted line).
performed under an oxygen gas flow (3 L/min, [H2O] o0.5 ppm vol) in a furnace mounted on a water-free glove box (under dry air [H2O]o1 ppm vol). This system allows the stirring of the melts in an OH-free atmosphere, and glass oxidation and homogenization without contamination from hydroxyl compounds. The hot liquid mixes were quenched into a brass mold preheated at 220 °C and subsequently annealed at the vitreous transition temperature Tg for 8 h and finally slowly cooled down to room temperature. Next we drew our three-hole-suspended-core fiber after mechanical drilling of glass rods for the preform manufacturing [12, 35]. Various parameters such as furnace temperature, preform pressure, translation speed and drawing speed were controlled to obtain the following fiber shown in Fig. 4(a), with an outer diameter of 190 μm and a central solid core diameter of 3.6 μm, held to the clad through three surrounding holes by means of three thin struts. It exhibits a ZDW close to 1.6 μm from simulations of fiber modal properties (see Fig.1(b)). Finally, we fabricated short tapers from our fiber using a well-known post-processing technique based on the VYTRAN Glass Processing Workstation (GPX-3400 series) device. This glass processing platform performs fusion splicing and tapering of specialty fibers and the system consists of a filament heater, precision stages with multi-axis control, and a microscopic high resolution CCD imaging system. For the present study we investigated suspended-core fiber tapers that exhibit smooth and fast transition regions from the full fiber diameter to the small waist and back again (transitions are about 55 and 5 mm,
respectively). The 5-mm-long taper waist has an outer diameter of 65 μm and a core diameter of 1.3 μm, as shown in Fig. 4. For such waist diameters, there was no collapsed holes. The tapering process was not performed under protected atmosphere. The corresponding dispersion curve then exhibits two ZDWs at 1.2 μm and 3.3 μm (see Fig.1(b)). As above-mentioned, we tried to evaluate optical losses induced by the post-processing of our microstructured fiber, namely the tapering process, over the full transmission window of the tellurite glass. To this end we carried out tapering-induced loss measurements in a six-hole microstructured fiber with a large core diameter of 15 mm to facilitate the critical light coupling (see inset of Fig. 4(c)). When increasing the core reduction ratio, we clearly note the continuous growth of different combinations of bonded OH groups that manifest themselves between 2.8 and 4 mm in Fig. 4(c). This potentially reveals that the tapering process may stimulate preliminary OH contamination surrounding the suspended core through temperature elevation and core reduction. By contrast background losses, between 1 and 3 mm, are not impacted, excluding a strong increase obtained for the higher core reduction, thus preventing any conclusion here. However, such preliminary results about tapering-induced loss confirm the idea that extra-losses beyond 3 mm due to post-processing or fiber core size can be detrimental for mid-IR SC generation, as suggested in the previous section. Further experimental investigations are still required in particular for smaller core fibers.
Fig. 4. (a) Fiber cross section images captured at different positions along the taper by means of a scanning electron microscope. Note that the suspended-core structure was maintained throughout the length of the taper. (b) Profiles of core diameter and outer fiber diameter along our short taper based on measurements from cross-section images. (c) Additional optical losses induced by similar fiber tapering relative to an initial six-hole fiber with a 15-mm suspended core (inset: fiber cross section image). Measurements correspond to different taper waists with following core diameters: 10 mm (blue curve), 7 mm (yellow curve), 6.25 mm (red curve) and 5.5 mm (green curve). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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Fig. 5. SC generation in our (a) 10-cm-long uniform suspended core fiber and (b) 10-cm-long tapered suspended core fiber by injecting 200-fs pulses at 1730 nm with 12-kW peak power. SC enhancement is obtained on both frequency edges and highlighted in green.
3.2. SC generation The experimental set-up for SC generation consists in an optical parametric oscillator (OPO) pumped by a Ti:Sapphire laser. The OPO delivers 200-fs pulses, tunable from 1.7 to 2.6 μm, at a repetition rate of 80 MHz with maximum average power close to 450 mW. Our fibers were cleaved by means of a scalpel blade and quality of the interfaces was carefully checked under microscope before mounting the sample onto a 3-axis holder. Light coupling into the fiber under test was obtained by means of an aspheric zinc selenide (ZnSe) focus lens. Output supercontinua were collected through a 0.5-m-long multimode fluoride (InF3) fiber with high transmission over the 0.3–5.5 μm spectral range. It is then analyzed by means of two optical spectrum analyzers (OSAs) covering 350–1200 nm and 1200–2400 nm, respectively, as well as by a FTIR spectrometer in the range of 2.4–5 μm. Maximum coupling efficiency into our 3.6-μm suspended-core fiber was estimated to be about 40%. Experimental SC spectra obtained in both uniform and tapered fibers for maximal input power at a pump wavelength of 1730 nm are reported in Fig. 5. We clearly observe the enhancement of SC generation on both frequency edges in our suspended core fiber by using our tapering design shown in Fig. 4(a). On the visible (mid-IR) frequency edge,
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the spectral bandwidth is increased by 135 (20) THz, thus offering a 400- THz (0.6–3.3 mm) bandwidth infrared SC source. However, we note that the remaining limitation of SC bandwidth is still related to the presence of the high absorption beyond 3 mm. Indeed, the increased nonlinearity and dispersion engineering allow to overcome the natural saturation of the Raman soliton-self frequency shift from the uniform fiber, so that the SC spectrum reaches 3.3 mm (the position of the second ZDW at taper waist). But the expected observation of energy transfer from most redshifted solitons to DWs in the mid-IR is completely annihilated by extra losses beyond 3 mm, as previously shown in simulations from Fig. 3. Next we complete our analysis by comparing experiments to numerical simulations for various input powers and pump wavelengths in Figs. 6 and 7, in particular, to assess that the numerical results fit quite well the dynamics observed in the experiments and confirm that the spectral broadening is mainly limited by the extra losses. Fig. 6 confirms the good agreement about between spectral signatures of the soliton dynamics related to SC generation such as the power-dependent Raman soliton self-frequency shift and associated DW generation. Moreover, we show that the increase of the pump wavelength moderately impacts the resulting SC bandwidth (see Fig. 7), such pumping farther from the uniform fiber ZDW mainly modifies the phase-matching of four wave mixing and then the subsequent shape of the SC spectrum.
4. Conclusion In summary, we report here the experimental generation of 400-THz (0.6–3.3 mm) bandwidth infrared supercontinuum generation in a 10 cm-long tapered tellurite suspended core fiber. Our moderate tapering procedure based on a commercial glass processing platform allowed the development of short tapers of suspended core fiber to benefit from additional increased nonlinearity and dispersion engineering. This is here exploited to optimize SC generation bandwidth through underlying solitons-DWs interactions and related group-velocity matching. Moreover, we show that the impact of designed taper profile on SC bandwidth remains limited for our pumping configuration. On the other hand we clearly demonstrate that spectral broadening cannot fully cover
Fig. 6. SC generation in our 10-cm-long tapered suspended core fiber for three different input peak powers: 12, 4 and 2.7 kW (from top to bottom) at 1730 nm. Recorded spectra during our experiment (a) compared to corresponding numerical simulations (b).
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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Fig. 7. SC generation in our 10-cm-long tapered suspended core fiber for three different input pump wavelengths: 1730, 1750 and 1800 nm (from top to bottom). Recorded spectra during our experiment (a) compared to corresponding numerical simulations (b).
the initial glass transmission window due to the presence of the high absorption beyond 3 mm in the suspended core fiber taper. Our preliminary studies suggest that extra losses are strongly dependent on the core size and post-processing technique. Further work will be devoted to overcome this very challenging limitation.
Acknowledgments We acknowledge the financial support from the JSPS-CNRS Bilateral French-Japanese Program. This project has been performed in cooperation with the Labex ACTION program (Contract ANR-11-LABX-0001-01). J. Picot-Clemente acknowledges the support of the Conseil Regional de Bourgogne through his grant “Jeune ” scheme, he also thanks Karol Tarnowski for comments and advice on numerical simulations of fiber modal properties.
References [1] Y. Yu, X. Gai, T. Wang, P. Ma, R. Wang, Z. Yang, D.-Y. Choi, S. Madden, B. LutherDavies, “Mid-infrared supercontinuum generation in chalcogenides”, Opt. Mater. Express 3 (2013) 1075–1086. [2] C. Xia, M. Kumar, O.P. Kulkarni, M.N. Islam, F.L. Terry Jr., M.J. Freeman, M. Poulain, G. Mazé, “Midinfrared supercontinuum generation to 4.5 mm in ZBLAN fluoride fibers by nanosecond diode pumping,”, Opt. Lett. 31 (2006) 2553–2555. [3] P. Domachuk, N.A. Wolchover, M. Cronin-Golomb, A. Wang, A.K. George, C.M. B. Cordeiro, J.C. Knight, F.G. Omenetto, “Over 4000 nm bandwidth of mid-IR supercontinuum generation in sub-centimeter segments of highly nonlinear tellurite PCFs”, Opt. Express 16 (2008) 7161–7168. [4] Y. Yu, X. Gai, P. Ma, D.-Y. Choi, Z. Yang, R. Wang, S. Debbarma, S.J. Madden, B. Luther-Davies, “A broadband, quasi-continuous, mid-infrared supercontinuum generated in a chalcogenide glass waveguide”, Laser Photonics Rev. 8 (2014) 792–798. [5] U. Møller, Y. Yu, I. Kubat, C.R. Petersen, X. Gai, L. Brilland, D. Méchin, C. Caillaud, J. Troles, B. Luther-Davies, O. Bang, “Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber”, Opt. Express 23 (2015) 3282–3291. [6] C. Rosenberg Petersen, U. Møller, I. Kubat, B. Zhou, S. Dupont, J. Ramsay, T. Benson, S. Sujecki, N. Abdel-Moneim, Z. Tang, D. Furniss, A. Seddon, O. Bang, “Mid-infrared supercontinuum covering the 1.4–13.3 μm molecular fingerprint region using ultra-high NA chalcogenide step-index fibre”, Nat. Photon 8 (2014) 830–834. [7] G. Qin, X. Yan, C. Kito, M. Liao, C. Chaudhari, T. Suzuki, Y. Ohishi, “Ultrabroadband supercontinuum generation from ultraviolet to 6.28 μm in a fluoride fiber”, Appl. Phys. Lett. 95 (2009) 161103.
[8] M. Liao, W. Gao, T. Cheng, Z. Duan, X. Xue, H. Kawashima, T. Suzuki, Y. Ohishi, “Ultrabroad supercontinuum generation through filamentation in tellurite glass”, Laser Phys. Lett. 10 (2013) 036002. [9] M. Liao, W. Gao, T. Cheng, X. Xue, Z. Duan, D. Deng, H. Kawashima, T. Suzuki, Y. Ohishi, “Five-octave-spanning supercontinuum generation in fluoride glass,”, Appl. Phys. Express 6 (2013) 032503. [10] D.D. Hudson, M. Baudisch, D. Werdehausen, B.J. Eggleton, J. Biegert, “1.9 octave supercontinuum generation in a As2S3 step-index fiber driven by mid-IR OPCPA”, Opt. Lett. 39 (2014) 5752–5755. [11] F. Théberge, N. Thiré, J.-F. Daigle, P. Mathieu, B.E. Schmidt, Y. Messaddeq, R. Vallée, F. Légaré, “Multioctave infrared supercontinuum generation in largecore As2S3 fibers”, Opt. Lett. 39 (2014) 6474–6477. [12] I. Savelii, O. Mouawad, J. Fatome, B. Kibler, F. Désévédavy, G. Gadret, J.-C. Jules, P.-Y. Bony, H. Kawashima, W. Gao, T. Kohoutek, T. Suzuki, Y. Ohishi, F. Smektala, “Mid-infrared 2000-nm bandwidth supercontinuum generation in suspended-core microstructured Sulfide and Tellurite optical fibers”, Opt. Express 20 (2012) 27083–27093. [13] C. Agger, C. Petersen, S. Dupont, H. Steffensen, J.K. Lyngsø, C.L. Thomsen, J. Thøgersen, S.R. Keiding, O. Bang, “Supercontinuum generation in ZBLAN fibers – detailed comparison between measurement and simulation”, J. Opt. Soc. Am. B 29 (2012) 635–645. [14] X. Gai, D.-Y. Choi, S. Madden, Z. Yang, R. Wang, B. Luther-Davies, “Supercontinuum generation in the mid-infrared from a dispersion-engineered As2S3 glass rib waveguide”, Opt. Lett. 37 (2012) 3870–3872. [15] O. Mouawad, J. Picot-Clémente, F. Amrani, C. Strutynski, J. Fatome, B. Kibler, F. Désévédavy, G. Gadret, J.-C. Jules, D. Deng, Y. Ohishi, F. Smektala, “Multioctave midinfrared supercontinuum generation in suspended-core chalcogenide fibers”, Opt. Lett. 39 (2014) 2684–2687. [16] O. Mouawad, F. Amrani, B. Kibler, J. Picot-Clémente, C. Strutynski, J. Fatome, F. Désévédavy, G. Gadret, J.-C. Jules, O. Heintz, E. Lesniewska, F. Smektala, “Impact of optical and structural aging in As2S3 microstructured optical fibers on mid-infrared supercontinuum generation”, Opt. Express 22 (2014) 23912–23919. [17] A. Al-kadry, M. El Amraoui, Y. Messaddeq, M. Rochette, “Two octaves midinfrared supercontinuum generation in As2Se3 microwires”, Opt. Express 22 (2014) 31131–31137. [18] T.A. Birks, W.J. Wadsworth, P. St. J. Russell, “Supercontinuum generation in tapered fibers”, Opt. Lett. 25 (2000) 1415–1417. [19] M.A. Foster, J.M. Dudley, B. Kibler, Q. Cao, D. Lee, R. Trebino, A.L. Gaeta, “Nonlinear pulse propagation and supercontinuum generation in photonic nanowires: experiment and simulation”, Appl. Phys. B 81 (2005) 363–367. [20] J. Fatome, B. Kibler, M. El-Amraoui, J.C. Jules, G. Gadret, F. Desevedavy, F. Smektala, “Mid-infrared extension of supercontinuum in a chalcogenide suspended core fibre through soliton gas pumping,”, Electron. Lett. 47 (2011) 398–400. [21] J.M. Dudley, J.R. Taylor, Supercontinuum Generation in Optical Fibers, Cambridge University, 2010. [22] A. Marandi, C.W. Rudy, V.G. Plotnichenko, E.M. Dianov, K.L. Vodopyanov, R. L. Byer, “Mid-infrared supercontinuum generation in tapered chalcogenide fiber for producing octave-spanning frequency comb around 3 μm”, Opt. Express 20 (2012) 24218–24225. [23] D.D. Hudson, E.C. Mägi, A.C. Judge, S.A. Dekker, B.J. Eggleton, “Highly nonlinear chalcogenide glass micro/nanofiber devices: Design, theory, and octave-
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spanning spectral generation”, Opt. Commun. 285 (2012) 4660–4669. [24] C.W. Rudy, A. Marandi, K.L. Vodopyanov, R.L. Byer, “Octave-spanning supercontinuum generation in in situ tapered As2S3 fiber pumped by a thuliumdoped fiber laser”, Opt. Lett. 38 (2013) 2865–2868. [25] N. Granzow, M.A. Schmidt, W. Chang, L. Wang, Q. Coulombier, J. Troles, P. Toupin, I. Hartl, K.F. Lee, M.E. Fermann, L. Wondraczek, P. St.J. Russell, “Midinfrared supercontinuum generation in As2S3-silica “nano-spike” step-index waveguide”, Opt. Express 21 (2013) 10969–10977. [26] M. Liao, X. Yan, W. Gao, Z. Duan, G. Qin, T. Suzuki, Y. Ohishi, “Five-order SRSs and supercontinuum generation from a tapered tellurite microstructured fiber with longitudinally varying dispersion”, Opt. Express 19 (2011) 15389–15396. [27] M. Belal, L. Xu, P. Horak, L. Shen, X. Feng, M. Ettabib, D.J. Richardson, P. Petropoulos, J.H.V. Price, “Mid-infrared supercontinuum generation in suspended core tellurite microstructured optical fibers”, Opt. Lett. 40 (2015) 2237–2240. [28] A.C. Judge, O. Bang, B.J. Eggleton, B.T. Kuhlmey, E.C. Mägi, R. Pant, C. Martijn de Sterke, “Optimization of the soliton self-frequency shift in a tapered photonic crystal fiber”, J. Opt. Soc. Am. B 26 (2009) 2064–2071. [29] J.C. Travers, “Blue extension of optical fibre supercontinuum generation”, J. Opt. 12 (2010) 113001. [30] S. Pricking, H. Giessen, “Tailoring the soliton and supercontinuum dynamics by engineering the profile of tapered fibers”, Opt. Express 18 (2010) 20151–20163. [31] S.T. Sørensen, A. Judge, C.L. Thomsen, O. Bang, Optimum tapers for increasing the power in the blue-edge of a supercontinuum-group-acceleration
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matching, Opt. Lett. 36 (2011) 816–818. [32] S.T. Sørensen, U. Møller, C. Larsen, P.M. Moselund, C. Jakobsen, J. Johansen, T. V. Andersen, C.L. Thomsen, O. Bang, “Deep-blue supercontinnum sources with optimum taper profiles–verification of GAM”, Opt. Express 20 (2012) 10635–10645. [33] I. Kubat, C.S. Agger, P.M. Moselund, O. Bang, “Mid-infrared supercontinuum generation to 4.5 um in uniform and tapered ZBLAN step-index fibers by direct pumping at 1064 or 1550 nm”, J. Opt. Soc. Am. B 30 (2013) 2743–2757. [34] J.M. Dudley, G. Genty, S. Coen, “Supercontinuum generation in photonic crystal fiber”, Rev. Mod. Phys. 78 (2006) 1135–1184. [35] U. Møller, S.T. Sørensen, C. Jacobsen, J. Johansen, P.M. Moselund, C.L. Thomsen, O. Bang, “Power dependence of supercontinuum noise in uniform and tapered PCFs”, Opt. Express 20 (2012) 2851–2857. [36] I. Savelii, F. Désévédavy, J.-C. Jules, G. Gadret, J. Fatome, B. Kibler, H. Kawashima, Y. Ohishi, F. Smektala, “Management of OH absorption in tellurite optical fibers and related supercontinuum generation”, Opt. Mater. 35 (2013) 1595–1599. [37] A. Lin, A. Zhang, E.J. Bushong, J. Toulouse, “Solid-core tellurite glass fiber for infrared and nonlinear applications”, Opt. Express 17 (2009) 16716–16721. [38] M.D. O’Donnell, K. Richardson, R. Stolen, C. Rivero, T. Cardinal, M. Couzi, D. Furniss, A.B. Seddon, “Raman gain of selected tellurite glasses for IR fibre lasers calculated from spontaneous scattering spectra”, Opt. Mater. 30 (2008) 946–951.
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Contents lists available at ScienceDirect
Optics Communications journal homepage: www.elsevier.com/locate/optcom
Enhanced supercontinuum generation in tapered tellurite suspended core fiber J. Picot-Clemente a, C. Strutynski a, F. Amrani a, F. Désévédavy a, J-C Jules a, G. Gadret a, D. Deng b, T. Cheng b, K. Nagasaka b, Y. Ohishi b, B. Kibler a,n, F. Smektala a a b
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne Franche-Comté, 21078 Dijon, France Research Center for Advanced Photon Technology, Toyota Technological Institute, Nagoya 468-8511, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 12 May 2015 Received in revised form 5 June 2015 Accepted 6 June 2015
We demonstrate 400-THz (0.6–3.3 mm) bandwidth infrared supercontinuum generation in a 10 cm-long tapered tellurite suspended core fiber pumped by nJ-level 200-fs pulses from an optical parametric oscillator. The increased nonlinearity and dispersion engineering extended by the moderate reduction of the fiber core size are exploited for supercontinuum optimization on both frequency edges (i.e., 155-THz overall gain), while keeping efficient power coupling into the untapered fiber input. The remaining limitation of supercontinuum bandwidth is related to the presence of the high absorption beyond 3 mm whereas spectral broadening is expected to fully cover the glass transmission window (0.5–4.5 mm). & 2015 Elsevier B.V. All rights reserved.
Keywords: Nonlinear optics Supercontinuum generation Microstructured fibers
1. Introduction Development of fiber-based supercontinuum (SC) light sources spanning the mid-infrared molecular fingerprint region is currently undergoing a dramatic increase, particularly stimulated by high-demanding applications such as biomolecular and environmental sensing. This can be largely attributed to the development of novel and high-quality mid-infrared (mid-IR) materials devoted to fiber optics. In the last several years mid-IR SC sources were implemented on alternative non-silica glass fibers and waveguides, such as fluoride, tellurite or chalcogenide glasses, since they represent an attractive solution thanks to their wide transparency and high nonlinearity [1]. For fluoride and tellurite fibers, the wavelength coverage in the mid-IR can reach 4.5 mm [2, 3], whereas for chalcogenide fibers and waveguides it can be extended until 8 mm [4, 5]. Recently, larger SC spectra up to 13 mm were also reported in multimode fibers [6], however such observations are restricted to the use of ultrashort amplifier laser chains and remain close to experimental configurations of SC generation in bulk media [7–11]. From a general point of view, it still remains very challenging to confirm such dramatic spectral broadenings that almost cover the entire glass transmission window, in particular when considering quasi-single-mode fibers and pump lasers at moderate energy levels for compact SC sources. Several detrimental effects related to the wavelength dependence n
Corresponding author. E-mail address: [email protected] (B. Kibler).
of the fiber attenuation usually arise such as extra water (OH) pollution or other absorption mechanisms [12–17]. To improve the spectral range of SC light and dispose of possible limitations of both fiber and pump laser, various methods were already demonstrated for engineered SC generation in silica fibers based on the fine control of nonlinear propagation dynamics. Enhanced blue- and red-expansion of the SC bandwidth can be achieved through extra dispersion engineering of photonic crystal fibers (PCFs) along the fiber axis, i.e. tapered PCFs, the fabrication of microwires, and the cascaded fiber approach [18– 21]. As a result, SC generation in silica fibers is now well-established and it usually covers the full transmission window of the material. The underlying mechanisms of spectral broadening in those methods are related to the tailoring of soliton dynamics (in anomalous dispersion) and associated dispersive waves (in normal dispersion) but also their mutual interactions. In most cases the SC bandwidth is fully driven by interactions such as the soliton trapping of dispersive waves, which modifies the short-wavelength edge (i.e., dispersive waves) as a function of the long-wavelength edge (i.e., solitons) in a way that satisfies group-velocity matching. In some sense, such techniques were recently applied to SC generation in soft-glass fibers but this remains restricted to chalcogenides microwires or waveguides, and near-IR studies of tapered tellurite PCFs [22–26]. More recently, tailoring SC generation was also investigated through accurate control of a novel fiber core design with high birefringence (i.e., an elongated core on a thin filament of glass) [27]. In this paper, we exploit both increased nonlinearity and dispersion engineering extended by the
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extra reduction of an initial suspended core microstructured tellurite fiber for SC optimization on both frequency edges, i.e. visible and mid-IR. We demonstrate a 155-THz increase of the full SC bandwidth by using a moderate tapering ratio over a short fiber segment by means of a commercial glass processing platform.
2. Simulations 2.1. Group-velocity matching First we performed numerical simulations of the nonlinear pulse propagation in tapered tellurite suspended core fibers to evaluate the impact of the tapering process on both soliton and group-velocity matching dynamics. Detailed studies were already reported to optimize taper profiles for enhanced soliton self-frequency shift and blue-shifted dispersive waves [28–33]. Here the goal is to take advantage of such existing tools without going into details of wave interactions. Our simulations used a well-known generalized nonlinear Schrödinger equation that has successfully described the SC generation process over a wide parameter range [34]. The longitudinal variation of the fiber core diameter as a function of propagation distance is accurately taken into account through its effect on the fiber dispersion and nonlinearity. The fiber dispersion requires particular care because the group velocity varies greatly over the supercontinuum bandwidth (as seen in Fig. 1), our accurate modeling includes the full dispersion profile. In particular, for the fundamental guided mode we calculated the wavelength dependence of both the mode effective refractive index and the effective mode area by means of a commercial software using a fully vectorial finite-element model. Such calculations were repeated for various core diameters (in the range 1– 4 mm) of our suspended core fiber structure used in our experiments (see Fig. 4). The value of the fiber parameters were then modeled locally along the taper profile through a lookup table. Our model also takes into account the measured losses of a singlematerial fiber made from our low-OH tellurite TeO2–ZnO–Na2O (TZN) glass composition including some fluoride ions (i.e., with typical background losses of 1 dB/m up to 3 mm, and below 10 dB/m in the range 3–4 mm, see Ref. [35] and Fig. 3(a)). It also includes Kerr effect (nonlinear Kerr coefficient is deduced from numerical calculation of effective area, and with nonlinear refractive index n2 ¼3.8 10–19 m2/W [36]), self-steepening term with dispersion of the nonlinearity and the Raman response
function for our TZN glass adapted from Ref. [37]. Fig. 1 reports the beneficial impact of moderate tapering on SC generation in our typical tellurite suspended core fiber design used in Ref. [35] and shown in Section 3, in particular we consider an initial 3.6-μm suspended-core fiber pumped by 200-fs pulses at 1730 nm with 12 kW peak power (i.e., similar parameters to Refs. [12,35] and used in the experiments that follow). Such a fiber exhibits a zero dispersion wavelength (ZDW) close to 1.6 mm; our pumping regime then occurs in the anomalous dispersion regime with input conditions corresponding to a high soliton order (N 420) [34]. The resulting SC generation is found to be sensitive to input noise, which leads to significant shot-to-shot fluctuations in the SC bandwidth and a low average SC coherence as well. Detailed studies of the noise properties of supercontinuum spectra generated at different power levels in uniform and tapered photonic crystal fibers can be found in Ref. [38]. Here the input pulse shot noise was modeled by adding a noise seed of one photon per mode with random phase on each frequency discretization bin [34]. Consequently, we performed an averaging over 20 simulations with different input noise imposed on the initial 200-fs pulse, thus creating typically smooth SC spectra similar to average spectral measurements. A 10-cm long fiber segment was chosen due to experimental restrictions on both the overall tapered section 7 cm (see Section 3) and the maximum pump power coupled into the uniform fiber (i.e. spectral broadening almost saturates for longer propagation). Our taper design to enhance SC generation through group-velocity matching is here based on a long downtapering section (as proposed in Refs. [31,32]) and a moderate reduction of the fiber core size (i.e., reduction ratio of 1/3) to save the suspended core structure (see taper profile shown in Fig. 1(a)). Fig. 1(b,c) show the numerical results of simulated SC spectra at three main positions along the taper and the corresponding groupindex curves for the fundamental guided mode in order to highlight the major stages of nonlinear dynamics. The first stage (blue lines) corresponds to the input uniform fiber section wherein the SC spectrum extends in the infrared from 1 mm to 3 mm (for the –20 dB bandwidth) similarly to our previous studies [12,35]. The shortest wavelength generated (i.e., a DW) is determined by the maximum soliton shift towards the infrared. The group-index matching between both spectral components is confirmed when transferring the corresponding wavelengths on the group-index curve of the tested fiber section, we clearly join the point on either edge by a straight line. We checked that further propagation does not significantly extend the spectral broadening,
Fig. 1. (a) Taper suspended core profile: initial and final core diameters are 3.6 mm, and the core waist diameter is 1.3 mm. Dashed lines indicate three major stages of nonlinear dynamics studied in the following subfigures (i.e., (1) end of the uniform fiber input, (2) middle of the first transition region, and (3) taper waist). (b) Group-index curves of the fundamental guided mode at the corresponding positions along the taper. Dashed horizontal lines confirm the group-velocity matching between the most redshifted soliton and related dispersive wave observed during spectral broadening along the taper profile as shown in subfigure (c). (c) Numerical results of SC generation recorded at the different positions denoted in (a) along the taper (S: most-red shifted soliton, DW: related dispersive waves).
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so that a change in the fiber structure is strongly required to tailor SC generation. The second stage is associated with a long downtapering section, in particular the transient SC evolution at the middle of this stage is represented with red lines in Fig. 1. The increased nonlinearity and dispersion engineering extended by the reduction of the fiber core size allows to overcome the natural saturation of the Raman soliton-self frequency shift. Note that the group-velocity matching is still satisfied in the transition region, thus developing SC in the blue edge of the spectrum. The SC spectrum now extends in the infrared from 0.7 mm to 3.5 mm (for the –20 dB bandwidth). Finally the third main stage is played by the taper waist section (green lines), in particular the apparition of a second zero group-velocity dispersion in the wavelength range of the most red-shifted solitons (see inflection point of the group index curve close to 3.3 mm) stimulates new transfer of energy to DWs in the mid-IR, so that the SC spectrum covers the entire glass transmission window (0.5–4.5 mm). After propagation in the second transition and the output uniform section, no significant change of the SC spectrum was noticed. 2.2. Influence of taper profiles In this subsection, we present the numerical analysis of the influence of the taper profile on the resulting output SC spectrum and its –20-dB bandwidth. Fig. 2(a–d) reports the effect of varying uniform, transition and waist lengths without changing the maximum core reduction. We observe that such variations mainly influence the mid-IR SC edge. By varying both down-tapering and up-tapering sections, compared to our first design, we generally decrease all soliton red-shifts and the subsequent energy transfer to mid-IR DWs. The second set of numerical simulations depicted in Fig. 2(e,f) focus on the effect of the core reduction ratio compared to Fig. 2(a). For a smaller waist, the second zero dispersion is then located at shorter wavelengths, which recoils the most redshifted solitons and then limits DW spreading below 4 mm. However the overall SC spectrum is more compact and flat, it exhibits a higher power spectral density. When considering a larger waist, the second ZDW is located far from the most red-shifted solitons, which prevents from efficient energy transfer towards mid-IR DWs. It is worth mentioning that our analysis reveals that our taper design based on a long down-tapering section are at the origin of the largest SC bandwidth as suggested in Refs. [31,32]. The long down-tapering section optimizes the group-velocity matching dynamics and SC extension while the short up-tapering section only provides easier output coupling for experimental
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convenience. 2.3. Influence of fiber losses Another parameter that significantly affects SC generation is related to the detrimental fiber attenuation in particular close to well-known OH absorption peaks and additional confinement loss due to tapering post-processing as well. Experimental measurements of tapering-induced losses were carried out by using an initial six-hole microstructured fiber with a larger core diameter. When applying a similar core reduction ratio, extra-losses were recorded in the wavelength range 1–4 mm (as shown later in Fig. 4). This confirms that possible extra losses compared to the bulk or the single-material fiber are only introduced during the drawing or the tapering post-processing of the suspended core microstructured fiber. Such issues were already noticed in our last study, in particular for wavelengths above 3 mm [35]. The numerical simulations presented above were again performed by introducing high extra losses for wavelengths above 2.8 mm, which corresponds to the beginning of the mid-IR loss bump revealed by measurements in the single-material fiber as shown in Fig. 3(a). Fiber losses were extrapolated for uniform and tapered suspended-core fibers based on a single measurement at 1.55 μm. The resulting output spectra are plotted in Fig. 3(b) and compared to previous simulations from Fig. 1. We first observe a small decrease of soliton-self-frequency shift occurring in both the input uniform section and the down-tapering section. But the main impact of these extra losses appears in the taper waist through complete absorption of mid-IR dispersive waves above 3.5 mm.
3. Experiments 3.1. Fiber fabrication and tapering procedure The fiber preform was elaborated from the glass composition of 75TeO2–15ZnO–5ZnF2–5Na2O with a reduced amount of Na2CO3, as known to contain hydroxyl impurities. The glass rods were fabricated by the conventional melt-quenching technique, starting from the raw materials: Tellurium oxide (FOX-Chemicals, 99.999%), Zinc oxide (FOX-Chemicals, 99.999%), Sodium carbonate (FOX-Chemicals, 99.9999%) and Zinc fluoride (Alfa Aesar, 99.995%). The mixed batches were melted in a platinum crucible covered with a lid of the same inert metal at 850 °C, during 2 h. In order to avoid the tellurium oxide reduction, the glass synthesis was
Fig. 2. Numerical results of output SC spectrum (left plot) for different taper profiles (right plot). Li ¼ 1-5 denote the lengths corresponding to uniform-input, down-tapering, waist, up-tapering and uniform-output sections, respectively. (a) Same parameters than Fig. 1 with L1–5 ¼17.5, 55, 5, 5, and 17.5 mm; waist ¼ 1.3 mm, (b) L1–5 ¼17.5, 5, 55, 5, and 17.5 mm; waist ¼ 1.3 mm, (c) L1–5 ¼ 17.5, 5, 5, 55, and 17.5 mm; waist ¼1.3 mm, (d) L1–5 ¼ 17, 22, 22, 22, 17; waist ¼ 1.3 mm, (e) L1–5 ¼ 17.5, 55, 5, 5, and 17.5; waist ¼ 1.1 mm, (f) L1–5 ¼17.5, 55, 5, 5, and 17.5; waist ¼ 1.7 mm. Dashed red lines reveal the –20-dB bandwidth of output SC spectra. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 3. (a) Optical losses measured for a single-material fiber made from our low-OH TZN glass composition (dotted lines), then extrapolated for the suspended-core microstructured fiber (dashed line) and tapered suspended-core fiber (solid line) by using single measurements at 1.55 μm. We also consider extra losses above 3 mm based on previous studies [35]. (b) Numerical results of SC generation recorded at the different positions along the taper as denoted in Fig. 1(a) by taking into updated optical losses (solid line) and compared to previous results from Fig. 1 (dotted line).
performed under an oxygen gas flow (3 L/min, [H2O] o0.5 ppm vol) in a furnace mounted on a water-free glove box (under dry air [H2O]o1 ppm vol). This system allows the stirring of the melts in an OH-free atmosphere, and glass oxidation and homogenization without contamination from hydroxyl compounds. The hot liquid mixes were quenched into a brass mold preheated at 220 °C and subsequently annealed at the vitreous transition temperature Tg for 8 h and finally slowly cooled down to room temperature. Next we drew our three-hole-suspended-core fiber after mechanical drilling of glass rods for the preform manufacturing [12, 35]. Various parameters such as furnace temperature, preform pressure, translation speed and drawing speed were controlled to obtain the following fiber shown in Fig. 4(a), with an outer diameter of 190 μm and a central solid core diameter of 3.6 μm, held to the clad through three surrounding holes by means of three thin struts. It exhibits a ZDW close to 1.6 μm from simulations of fiber modal properties (see Fig.1(b)). Finally, we fabricated short tapers from our fiber using a well-known post-processing technique based on the VYTRAN Glass Processing Workstation (GPX-3400 series) device. This glass processing platform performs fusion splicing and tapering of specialty fibers and the system consists of a filament heater, precision stages with multi-axis control, and a microscopic high resolution CCD imaging system. For the present study we investigated suspended-core fiber tapers that exhibit smooth and fast transition regions from the full fiber diameter to the small waist and back again (transitions are about 55 and 5 mm,
respectively). The 5-mm-long taper waist has an outer diameter of 65 μm and a core diameter of 1.3 μm, as shown in Fig. 4. For such waist diameters, there was no collapsed holes. The tapering process was not performed under protected atmosphere. The corresponding dispersion curve then exhibits two ZDWs at 1.2 μm and 3.3 μm (see Fig.1(b)). As above-mentioned, we tried to evaluate optical losses induced by the post-processing of our microstructured fiber, namely the tapering process, over the full transmission window of the tellurite glass. To this end we carried out tapering-induced loss measurements in a six-hole microstructured fiber with a large core diameter of 15 mm to facilitate the critical light coupling (see inset of Fig. 4(c)). When increasing the core reduction ratio, we clearly note the continuous growth of different combinations of bonded OH groups that manifest themselves between 2.8 and 4 mm in Fig. 4(c). This potentially reveals that the tapering process may stimulate preliminary OH contamination surrounding the suspended core through temperature elevation and core reduction. By contrast background losses, between 1 and 3 mm, are not impacted, excluding a strong increase obtained for the higher core reduction, thus preventing any conclusion here. However, such preliminary results about tapering-induced loss confirm the idea that extra-losses beyond 3 mm due to post-processing or fiber core size can be detrimental for mid-IR SC generation, as suggested in the previous section. Further experimental investigations are still required in particular for smaller core fibers.
Fig. 4. (a) Fiber cross section images captured at different positions along the taper by means of a scanning electron microscope. Note that the suspended-core structure was maintained throughout the length of the taper. (b) Profiles of core diameter and outer fiber diameter along our short taper based on measurements from cross-section images. (c) Additional optical losses induced by similar fiber tapering relative to an initial six-hole fiber with a 15-mm suspended core (inset: fiber cross section image). Measurements correspond to different taper waists with following core diameters: 10 mm (blue curve), 7 mm (yellow curve), 6.25 mm (red curve) and 5.5 mm (green curve). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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Fig. 5. SC generation in our (a) 10-cm-long uniform suspended core fiber and (b) 10-cm-long tapered suspended core fiber by injecting 200-fs pulses at 1730 nm with 12-kW peak power. SC enhancement is obtained on both frequency edges and highlighted in green.
3.2. SC generation The experimental set-up for SC generation consists in an optical parametric oscillator (OPO) pumped by a Ti:Sapphire laser. The OPO delivers 200-fs pulses, tunable from 1.7 to 2.6 μm, at a repetition rate of 80 MHz with maximum average power close to 450 mW. Our fibers were cleaved by means of a scalpel blade and quality of the interfaces was carefully checked under microscope before mounting the sample onto a 3-axis holder. Light coupling into the fiber under test was obtained by means of an aspheric zinc selenide (ZnSe) focus lens. Output supercontinua were collected through a 0.5-m-long multimode fluoride (InF3) fiber with high transmission over the 0.3–5.5 μm spectral range. It is then analyzed by means of two optical spectrum analyzers (OSAs) covering 350–1200 nm and 1200–2400 nm, respectively, as well as by a FTIR spectrometer in the range of 2.4–5 μm. Maximum coupling efficiency into our 3.6-μm suspended-core fiber was estimated to be about 40%. Experimental SC spectra obtained in both uniform and tapered fibers for maximal input power at a pump wavelength of 1730 nm are reported in Fig. 5. We clearly observe the enhancement of SC generation on both frequency edges in our suspended core fiber by using our tapering design shown in Fig. 4(a). On the visible (mid-IR) frequency edge,
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the spectral bandwidth is increased by 135 (20) THz, thus offering a 400- THz (0.6–3.3 mm) bandwidth infrared SC source. However, we note that the remaining limitation of SC bandwidth is still related to the presence of the high absorption beyond 3 mm. Indeed, the increased nonlinearity and dispersion engineering allow to overcome the natural saturation of the Raman soliton-self frequency shift from the uniform fiber, so that the SC spectrum reaches 3.3 mm (the position of the second ZDW at taper waist). But the expected observation of energy transfer from most redshifted solitons to DWs in the mid-IR is completely annihilated by extra losses beyond 3 mm, as previously shown in simulations from Fig. 3. Next we complete our analysis by comparing experiments to numerical simulations for various input powers and pump wavelengths in Figs. 6 and 7, in particular, to assess that the numerical results fit quite well the dynamics observed in the experiments and confirm that the spectral broadening is mainly limited by the extra losses. Fig. 6 confirms the good agreement about between spectral signatures of the soliton dynamics related to SC generation such as the power-dependent Raman soliton self-frequency shift and associated DW generation. Moreover, we show that the increase of the pump wavelength moderately impacts the resulting SC bandwidth (see Fig. 7), such pumping farther from the uniform fiber ZDW mainly modifies the phase-matching of four wave mixing and then the subsequent shape of the SC spectrum.
4. Conclusion In summary, we report here the experimental generation of 400-THz (0.6–3.3 mm) bandwidth infrared supercontinuum generation in a 10 cm-long tapered tellurite suspended core fiber. Our moderate tapering procedure based on a commercial glass processing platform allowed the development of short tapers of suspended core fiber to benefit from additional increased nonlinearity and dispersion engineering. This is here exploited to optimize SC generation bandwidth through underlying solitons-DWs interactions and related group-velocity matching. Moreover, we show that the impact of designed taper profile on SC bandwidth remains limited for our pumping configuration. On the other hand we clearly demonstrate that spectral broadening cannot fully cover
Fig. 6. SC generation in our 10-cm-long tapered suspended core fiber for three different input peak powers: 12, 4 and 2.7 kW (from top to bottom) at 1730 nm. Recorded spectra during our experiment (a) compared to corresponding numerical simulations (b).
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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Fig. 7. SC generation in our 10-cm-long tapered suspended core fiber for three different input pump wavelengths: 1730, 1750 and 1800 nm (from top to bottom). Recorded spectra during our experiment (a) compared to corresponding numerical simulations (b).
the initial glass transmission window due to the presence of the high absorption beyond 3 mm in the suspended core fiber taper. Our preliminary studies suggest that extra losses are strongly dependent on the core size and post-processing technique. Further work will be devoted to overcome this very challenging limitation.
Acknowledgments We acknowledge the financial support from the JSPS-CNRS Bilateral French-Japanese Program. This project has been performed in cooperation with the Labex ACTION program (Contract ANR-11-LABX-0001-01). J. Picot-Clemente acknowledges the support of the Conseil Regional de Bourgogne through his grant “Jeune ” scheme, he also thanks Karol Tarnowski for comments and advice on numerical simulations of fiber modal properties.
References [1] Y. Yu, X. Gai, T. Wang, P. Ma, R. Wang, Z. Yang, D.-Y. Choi, S. Madden, B. LutherDavies, “Mid-infrared supercontinuum generation in chalcogenides”, Opt. Mater. Express 3 (2013) 1075–1086. [2] C. Xia, M. Kumar, O.P. Kulkarni, M.N. Islam, F.L. Terry Jr., M.J. Freeman, M. Poulain, G. Mazé, “Midinfrared supercontinuum generation to 4.5 mm in ZBLAN fluoride fibers by nanosecond diode pumping,”, Opt. Lett. 31 (2006) 2553–2555. [3] P. Domachuk, N.A. Wolchover, M. Cronin-Golomb, A. Wang, A.K. George, C.M. B. Cordeiro, J.C. Knight, F.G. Omenetto, “Over 4000 nm bandwidth of mid-IR supercontinuum generation in sub-centimeter segments of highly nonlinear tellurite PCFs”, Opt. Express 16 (2008) 7161–7168. [4] Y. Yu, X. Gai, P. Ma, D.-Y. Choi, Z. Yang, R. Wang, S. Debbarma, S.J. Madden, B. Luther-Davies, “A broadband, quasi-continuous, mid-infrared supercontinuum generated in a chalcogenide glass waveguide”, Laser Photonics Rev. 8 (2014) 792–798. [5] U. Møller, Y. Yu, I. Kubat, C.R. Petersen, X. Gai, L. Brilland, D. Méchin, C. Caillaud, J. Troles, B. Luther-Davies, O. Bang, “Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber”, Opt. Express 23 (2015) 3282–3291. [6] C. Rosenberg Petersen, U. Møller, I. Kubat, B. Zhou, S. Dupont, J. Ramsay, T. Benson, S. Sujecki, N. Abdel-Moneim, Z. Tang, D. Furniss, A. Seddon, O. Bang, “Mid-infrared supercontinuum covering the 1.4–13.3 μm molecular fingerprint region using ultra-high NA chalcogenide step-index fibre”, Nat. Photon 8 (2014) 830–834. [7] G. Qin, X. Yan, C. Kito, M. Liao, C. Chaudhari, T. Suzuki, Y. Ohishi, “Ultrabroadband supercontinuum generation from ultraviolet to 6.28 μm in a fluoride fiber”, Appl. Phys. Lett. 95 (2009) 161103.
[8] M. Liao, W. Gao, T. Cheng, Z. Duan, X. Xue, H. Kawashima, T. Suzuki, Y. Ohishi, “Ultrabroad supercontinuum generation through filamentation in tellurite glass”, Laser Phys. Lett. 10 (2013) 036002. [9] M. Liao, W. Gao, T. Cheng, X. Xue, Z. Duan, D. Deng, H. Kawashima, T. Suzuki, Y. Ohishi, “Five-octave-spanning supercontinuum generation in fluoride glass,”, Appl. Phys. Express 6 (2013) 032503. [10] D.D. Hudson, M. Baudisch, D. Werdehausen, B.J. Eggleton, J. Biegert, “1.9 octave supercontinuum generation in a As2S3 step-index fiber driven by mid-IR OPCPA”, Opt. Lett. 39 (2014) 5752–5755. [11] F. Théberge, N. Thiré, J.-F. Daigle, P. Mathieu, B.E. Schmidt, Y. Messaddeq, R. Vallée, F. Légaré, “Multioctave infrared supercontinuum generation in largecore As2S3 fibers”, Opt. Lett. 39 (2014) 6474–6477. [12] I. Savelii, O. Mouawad, J. Fatome, B. Kibler, F. Désévédavy, G. Gadret, J.-C. Jules, P.-Y. Bony, H. Kawashima, W. Gao, T. Kohoutek, T. Suzuki, Y. Ohishi, F. Smektala, “Mid-infrared 2000-nm bandwidth supercontinuum generation in suspended-core microstructured Sulfide and Tellurite optical fibers”, Opt. Express 20 (2012) 27083–27093. [13] C. Agger, C. Petersen, S. Dupont, H. Steffensen, J.K. Lyngsø, C.L. Thomsen, J. Thøgersen, S.R. Keiding, O. Bang, “Supercontinuum generation in ZBLAN fibers – detailed comparison between measurement and simulation”, J. Opt. Soc. Am. B 29 (2012) 635–645. [14] X. Gai, D.-Y. Choi, S. Madden, Z. Yang, R. Wang, B. Luther-Davies, “Supercontinuum generation in the mid-infrared from a dispersion-engineered As2S3 glass rib waveguide”, Opt. Lett. 37 (2012) 3870–3872. [15] O. Mouawad, J. Picot-Clémente, F. Amrani, C. Strutynski, J. Fatome, B. Kibler, F. Désévédavy, G. Gadret, J.-C. Jules, D. Deng, Y. Ohishi, F. Smektala, “Multioctave midinfrared supercontinuum generation in suspended-core chalcogenide fibers”, Opt. Lett. 39 (2014) 2684–2687. [16] O. Mouawad, F. Amrani, B. Kibler, J. Picot-Clémente, C. Strutynski, J. Fatome, F. Désévédavy, G. Gadret, J.-C. Jules, O. Heintz, E. Lesniewska, F. Smektala, “Impact of optical and structural aging in As2S3 microstructured optical fibers on mid-infrared supercontinuum generation”, Opt. Express 22 (2014) 23912–23919. [17] A. Al-kadry, M. El Amraoui, Y. Messaddeq, M. Rochette, “Two octaves midinfrared supercontinuum generation in As2Se3 microwires”, Opt. Express 22 (2014) 31131–31137. [18] T.A. Birks, W.J. Wadsworth, P. St. J. Russell, “Supercontinuum generation in tapered fibers”, Opt. Lett. 25 (2000) 1415–1417. [19] M.A. Foster, J.M. Dudley, B. Kibler, Q. Cao, D. Lee, R. Trebino, A.L. Gaeta, “Nonlinear pulse propagation and supercontinuum generation in photonic nanowires: experiment and simulation”, Appl. Phys. B 81 (2005) 363–367. [20] J. Fatome, B. Kibler, M. El-Amraoui, J.C. Jules, G. Gadret, F. Desevedavy, F. Smektala, “Mid-infrared extension of supercontinuum in a chalcogenide suspended core fibre through soliton gas pumping,”, Electron. Lett. 47 (2011) 398–400. [21] J.M. Dudley, J.R. Taylor, Supercontinuum Generation in Optical Fibers, Cambridge University, 2010. [22] A. Marandi, C.W. Rudy, V.G. Plotnichenko, E.M. Dianov, K.L. Vodopyanov, R. L. Byer, “Mid-infrared supercontinuum generation in tapered chalcogenide fiber for producing octave-spanning frequency comb around 3 μm”, Opt. Express 20 (2012) 24218–24225. [23] D.D. Hudson, E.C. Mägi, A.C. Judge, S.A. Dekker, B.J. Eggleton, “Highly nonlinear chalcogenide glass micro/nanofiber devices: Design, theory, and octave-
Please cite this article as: J. Picot-Clemente, et al., Optics Communications (2015), http://dx.doi.org/10.1016/j.optcom.2015.06.014i
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
spanning spectral generation”, Opt. Commun. 285 (2012) 4660–4669. [24] C.W. Rudy, A. Marandi, K.L. Vodopyanov, R.L. Byer, “Octave-spanning supercontinuum generation in in situ tapered As2S3 fiber pumped by a thuliumdoped fiber laser”, Opt. Lett. 38 (2013) 2865–2868. [25] N. Granzow, M.A. Schmidt, W. Chang, L. Wang, Q. Coulombier, J. Troles, P. Toupin, I. Hartl, K.F. Lee, M.E. Fermann, L. Wondraczek, P. St.J. Russell, “Midinfrared supercontinuum generation in As2S3-silica “nano-spike” step-index waveguide”, Opt. Express 21 (2013) 10969–10977. [26] M. Liao, X. Yan, W. Gao, Z. Duan, G. Qin, T. Suzuki, Y. Ohishi, “Five-order SRSs and supercontinuum generation from a tapered tellurite microstructured fiber with longitudinally varying dispersion”, Opt. Express 19 (2011) 15389–15396. [27] M. Belal, L. Xu, P. Horak, L. Shen, X. Feng, M. Ettabib, D.J. Richardson, P. Petropoulos, J.H.V. Price, “Mid-infrared supercontinuum generation in suspended core tellurite microstructured optical fibers”, Opt. Lett. 40 (2015) 2237–2240. [28] A.C. Judge, O. Bang, B.J. Eggleton, B.T. Kuhlmey, E.C. Mägi, R. Pant, C. Martijn de Sterke, “Optimization of the soliton self-frequency shift in a tapered photonic crystal fiber”, J. Opt. Soc. Am. B 26 (2009) 2064–2071. [29] J.C. Travers, “Blue extension of optical fibre supercontinuum generation”, J. Opt. 12 (2010) 113001. [30] S. Pricking, H. Giessen, “Tailoring the soliton and supercontinuum dynamics by engineering the profile of tapered fibers”, Opt. Express 18 (2010) 20151–20163. [31] S.T. Sørensen, A. Judge, C.L. Thomsen, O. Bang, Optimum tapers for increasing the power in the blue-edge of a supercontinuum-group-acceleration
7
matching, Opt. Lett. 36 (2011) 816–818. [32] S.T. Sørensen, U. Møller, C. Larsen, P.M. Moselund, C. Jakobsen, J. Johansen, T. V. Andersen, C.L. Thomsen, O. Bang, “Deep-blue supercontinnum sources with optimum taper profiles–verification of GAM”, Opt. Express 20 (2012) 10635–10645. [33] I. Kubat, C.S. Agger, P.M. Moselund, O. Bang, “Mid-infrared supercontinuum generation to 4.5 um in uniform and tapered ZBLAN step-index fibers by direct pumping at 1064 or 1550 nm”, J. Opt. Soc. Am. B 30 (2013) 2743–2757. [34] J.M. Dudley, G. Genty, S. Coen, “Supercontinuum generation in photonic crystal fiber”, Rev. Mod. Phys. 78 (2006) 1135–1184. [35] U. Møller, S.T. Sørensen, C. Jacobsen, J. Johansen, P.M. Moselund, C.L. Thomsen, O. Bang, “Power dependence of supercontinuum noise in uniform and tapered PCFs”, Opt. Express 20 (2012) 2851–2857. [36] I. Savelii, F. Désévédavy, J.-C. Jules, G. Gadret, J. Fatome, B. Kibler, H. Kawashima, Y. Ohishi, F. Smektala, “Management of OH absorption in tellurite optical fibers and related supercontinuum generation”, Opt. Mater. 35 (2013) 1595–1599. [37] A. Lin, A. Zhang, E.J. Bushong, J. Toulouse, “Solid-core tellurite glass fiber for infrared and nonlinear applications”, Opt. Express 17 (2009) 16716–16721. [38] M.D. O’Donnell, K. Richardson, R. Stolen, C. Rivero, T. Cardinal, M. Couzi, D. Furniss, A.B. Seddon, “Raman gain of selected tellurite glasses for IR fibre lasers calculated from spontaneous scattering spectra”, Opt. Mater. 30 (2008) 946–951.
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