Mid-infrared supercontinuum generation in chalcogenide optical fibers

Accepted Manuscript Title: Mid-infrared supercontinuum generation in chalcogenide optical fibers Authors: Duqiang Xin, Pengfei Gao, Guangwei Huo, Xiaohui Li PII: DOI: Reference:

S0030-4026(19)30275-X https://doi.org/10.1016/j.ijleo.2019.02.158 IJLEO 62485

To appear in: Received date: Revised date: Accepted date:

18 December 2018 21 February 2019 27 February 2019

Please cite this article as: Xin D, Gao P, Huo G, Li X, Mid-infrared supercontinuum generation in chalcogenide optical fibers, Optik (2019), https://doi.org/10.1016/j.ijleo.2019.02.158 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Mid-infrared supercontinuum generation in chalcogenide optical fibers Duqiang Xin1, #, Pengfei Gao2, #, Guangwei Huo3, #, Xiaohui Li2, * 1

College of Science, Xijing University, Xi’an 710123, China

Shaanxi Normal University, College of Physics and Information Technology, Xian, Shaanxi, 710119, PR China. 3

School of Mathematics and Physics, Weinan Normal University. #The

authors contribute equally to this work.

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*Corresponding author: [email protected]

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2

Abstract: The spectral characterization of mid-infrared supercontinuum generation

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(SC) is studied in a highly nonlinear suspended-core As2S3 microstructure optical fiber pumped by different laser sources (The pulse duration can be ranged from femtosecond

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to picosecond). Spectra from 1 to 6.5 m are obtained by using picosecond pulse. The

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SC generation has been analyzed with different pumping wavelengths. It has been

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demonstrated that the longer wavelength can be broadened to 7 m. When the pumping wavelength is around 2.3 m (near the zero dispersion wavelength), a flat SC spectrum

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experimental work.

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is obtained. We expect these results will help to design a flat mid-infrared SC in real

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Keywords ： Supercontinuum generation; fs pulsed lasers; nonlinear Schrödinger equation Introduction

Supercontinuum (SC) generation has been extensively studied in visible region, near-

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infrared, mid-infrared (MIR) and even far-infrared region because of its wide application in numerous fields, such as wavelength division multiplexing, optical time division multiplexing in telecommunication, optical metrology, optical coherence tomography, nonlinear microscopy, and ultrashort pulse generation etc [1-10]. High nonlinear coefficient of optical fiber, flat dispersion profile and longer wavelength transparency are highly demanded for the MIR SC generation. Compared

with fluoride glass and telluride glass, chalcogenide glass has broader MIR transmission window and higher nonlinearities [1, 2]. Therefore, it can be used to generate SCs from 2 to 20 μm. Moreover, the chalcogenide glass has great potential application to generate significant SC spectrum and is highly expected for the advanced MIR spectral applications. However, As2S3 glass has a larger refractive index than fluoride or telluride glass. It is a valid method to tailor the dispersion of As2S3 fiber and

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move the zero dispersion wavelengths (ZDW) down to a shorter wavelength by designing the microstructure of As2S3 fiber. The ZDW of As2S3 can be expected to

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move around 2 m [3].

The researches on PCF and soft glass microstructure fiber have further promoted the development of MIR SC and microstructure PCF [11-14]. Many works about the SC

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generation based on microstructure chalcogenide fiber have been reported previously

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[15-23]. The first guiding chalcogenide As2S3 microstructure optical fibers (MOFs)

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with a suspended-core has been proposed [18]. Subsequently, a 1.0-2.6 m SC generation in a 68-cm As2S3 microstructure optical fiber pumped by a 400-fs, 5.6-kW,

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and 1.55-m pump wavelength pulse laser was reported [19]. After that, Hu et al.

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reported a 5-m-long commercially available PCF by 1.05-μm picosecond pulse to generate a 49.8 W supercontinuum spanning from 500 nm to above 1700 nm [20]. Recently, Gao et al. obtained a SC spectrum covering one octave from 1550 to 3300

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nm in a chalcogenide step-index fiber with AsSe2 core and As2S5 cladding [21]. In addition, SC from 1.7 to 7.5 μm range is obtained experimentally in a suspended core

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fiber [22]. In the work [23], SC generation in the 1-10 μm range is demonstrated numerically in specially produced As2Se3 suspended core fiber with pump at 2 μm. However, the relationship between some parameters of the seed lasers (such as center

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wavelength, pulse duration) and the SC generations need still to be further investigated in the dispersion-engineered microstructure chalcogenide fiber. In this paper, spectra characterization of mid-infrared supercontinuum generation (SC) is demonstrated in a highly nonlinear suspended-core As2S3 microstructure optical fiber pumped by different laser sources. The optimization of SC is to be explored in three aspects, i.e. frequency domain, temporal and output characteristics, respectively.

The analytical results show that picosecond pulse can generate better SC spectrum than femtosecond pulse under the same peak power. The pumping wavelength is close to ZDW in abnormal dispersion regime of the fiber and generates a flat and wide SC spectrum. These results are helpful to generate versatile MIR SC spectra. Theoretical analysis model

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The characteristics of ultrashort pulse propagation in highly nonlinear fibers can be defined by generalized nonlinear Schrödinger equation (GNLSE) [4，18，19]

(1)

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  A  i k 1  k A i    A  k k  i (1  )  A( z, T )  R(T ' ) | A（z, T  T '）|2 dT ' z 2 T 0 T  k  2 k!  ,

where A=A(z,T) is the electric field envelope, z is the fiber length, βk is the high-order dispersion coefficients at center frequency ω0, γ=n2ω0/cAeff is the nonlinear coefficient

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and Aeff is the fiber effective area, α is the fiber loss coefficient. R(t)=(1-fR)δ(t)+fRhR(t)

 12   2 2 exp( t /  2 ) sin(t /  1 )  1 2 2

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hR (t ) 

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Raman response to nonlinear polarization.

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is the response function. fR=0.17 represents the fractional contribution of the delayed

(2)

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is the Raman response function, while τ1 and τ2 are two parameters chosen to fit the actual Raman-gain spectrum. Since the materials is As2S3 glass, the Raman period (15.5

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fs) and lifetime (230.5 fs) are used to calculate the Raman response function [24]. We can obtain a wide spectrum by using only several-centimeter-length fiber due to the

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high nonlinear coefficient and the low loss of the reference optical fiber. The transmission loss is ignored. Simulated result and analysis

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The microstructure optical fiber is a suspended core fibers presenting three holes around a solid core in a triangular shape. There are two kinds of dispersions (Waveguide chromatic dispersion and Material chromatic dispersion) in the total dispersions. Since the materials (As2S3) are known. So only the waveguide chromatic dispersion needs to be calculated Sellmeier equation. Based on the analysis, we can derive the total dispersion coefficients.

The dispersion curve of As2S3 MOFs with a core diameter of 2.6 m is shown in Fig. 1 [18, 25]. DW ZDW=2.2 μm

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Dmat

Fig. 1. The dispersion curves of suspended-core As2S3 microstructure optical fiber.

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The black solid curve refers to the material dispersion (Dmat) of the As2S3 fiber. The

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material zero-dispersion wavelength is approximately 4.5 m. The blue solid curve

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refers to the waveguide chromatic dispersion (Dw), which can be calculated by Sellmeier

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equation. And zero-dispersion wavelength is 2.2 m by designing the microstructure of fibers. The refractive index is around 2.43 at 2 mm and can be varied with wavelength, which

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can be derived from the dispersion curve.

The reference optical fiber length is defined as 5 cm with nonlinear coefficient

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γ=2150 W-1km-1 corresponding to 1550 nm. SC is pumped by ultrashort pulses with peak power of around 3.6 kW and pulse widths of 1 ps and 50 fs, respectively. Considering

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an input pulse with hyperbolic-secant profile, the initial incident pulse has the form: T A(0, T )  P0 sec h( ) T0

(3)

In our study, SC generation in the proposed fiber is pumped by the pulsed laser at

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1550, 2100, 2300, and 2500 nm, respectively. The split-step Fourier transform simulation method is used to solve the nonlinear Schrödinger equation. When the pump wavelengths are close to the ZDW, high-order group-velocity dispersion has a significant influence on SC generation. High-order group-velocity dispersion coefficients corresponding to different pumping wavelengths have been calculated.

Table 1 shows different order dispersions at pump wavelength of 2100 and 2300 nm, respectively. TABLE 1. HIGH-ORDER GROUP-VELOCITY DISPERSION COEFFICIENTS CORRESPONDING TO 2100 NM AND 2300 NM, RESPECTIVELY.

βk（psk/km） β2

β3

β4

β5

β6

β7

2100 nm

49.588

1.1898

-2.6×10-3

1.1537×10-5

-6.4166×10-8

4.2869×10-10

2300 nm

-52.247

1.4343

-3.7×10-3

1.817×10-5

-1.1073×10-7

8.1031×10-10

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Wavelength

Laser sources with different pulse widths and center wavelengths are injected into the

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proposed fibers to get different SC generations. The spectral evolution of ultrashort

pulse is shown in Figs. 2(a)-(f) when the pulsed laser wavelength is 2300 nm. Keeping the pulse laser with peak power of 3.6 kW, ultrashort pulse propagates through the fiber

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with pulse width of 1 ps and 50 fs, respectively. Figures 2(a), (c), (e) demonstrate the evolution of picosecond pulse (~1ps) in a 5-cm As2S3 microstructure optical fiber. The

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range of SC spectrum from 1 to 6 m is obtained as shown in Fig. 2(e). Figures 2(b),

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(d), (f) show the evolution of the femtosecond pulse (~50 fs) with the same length As2S3

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microstructure optical fiber. Figure 2(f) shows a broadband SC generation from 1.5 to 4 m. When the pulse widths are 1 ps and 50 fs, the spectral evolution is shown in figs.

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2(a) and (b), respectively. It is mainly related to self-phase modulation for the initial state of the light propagation in optical fiber. It can be seen that the spectrum broadens

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symmetrically as pulse propagates through the fiber. The soliton splitting and soliton self-frequency shift are observed as shown in figs. 2(c) and 2(d). The range of spectra

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is determined by many nonlinear effects such as dispersion wave radiation, four-wave mixing effect and cross-phase modulation, etc. Especially, high-order dispersion in the abnormal dispersion regime of the fiber also contributes the performance of the SC

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generations. The SC spectrum pumped by the picosecond pulse (~1 ps) in a 5-cm referenced fiber is wider than the one pumped by femtosecond pumping pulse (~50 fs). Considering that the pulse energy of picosecond pulse (~1 ps) is higher than femtosecond pulse (~50 fs) at same pump peak power, the SC spectrum pumped by picosecond pulse is wider than the one pumped by femtosecond pulse.

b

c

d

f

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e

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a

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Fig. 2. The spectrograms of ultrashort pulse centered at 2300 nm in the abnormal dispersion regime as it propagates through a 5cm referenced fiber with a peak power of 3.6 kw, the pulse widths of 1 ps (a), (c), (e) and 50 fs (b), (d), (f), respectively.

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Figure 3 shows that the evolution of SC generation pumped by picosecond pulse laser (~1ps) with different center wavelength through a 5-cm reference optical fiber. As

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shown from figs. 3(a) to (d), it can be seen that spectral width becomes increasingly large when the pump wavelength shifts from normal to abnormal dispersion regime.

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Figure 3(a) shows that self-phase modulation is the dominant nonlinear effect that contributes to the spectral width within the pump wavelength of 1550 nm in the normal

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dispersion regime of the fiber.

e

b

f

g

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c

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a

d

h

Fig. 3. The spectral evolution corresponding to different pumping wavelengths (1550 nm, 2100 nm, 2300 nm, and 2500 nm).

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The spectral widths with pump wavelength of 2100 and 2300 nm are shown in Figs. 3(b) and (c), respectively. The pump wavelength of 2100 and 2300 nm locate at near-zero dispersion wavelength (~2.2 m). In this case, a board SC spectrum can be obtained as depicted in Fig. 4. Due to four-wave mixing effect, dispersive wave radiation, cascaded stimulated Raman scattering, and higher-order soliton fission can be obviously observed in Figs. 3(f) and (g). The reason why SC

spectrum extending to 6.5 nm pumped by 2300-nm laser is boarder than the one pumped by 2100 nm is that higher-order soliton fissure in the abnormal dispersion regime of the fiber. While the 2500-nm pulsed laser is kept away from zero-dispersion wavelength (~2.2 m), so flat spectrum can’t be obtained. One reason is that four-wave mixing effect is relatively weak. It is difficult to achieve phase matching in this regime. This fact means that it is superior when the pump

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wavelength is near zero-dispersion wavelength in the abnormal dispersion regime of the fiber.

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Figure 4 shows that output spectral evolution corresponds to different pumping wavelengths through a 5-cm reference optical fiber. As shown in Fig. 4, it can be seen

that the spectrum is broadened to 7 m pumped by 2500-nm pulsed lasers. We can see

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that a versatile SC generation can be obtained by controlling the pumping wavelength

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and the length of nonlinear fibers.

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Wavelength=1550 nm

Wavelength=2100 nm

Wavelength=2300 nm

Wavelength=2500 nm

Fig. 4. The output spectrum corresponding to different pumping wavelengths (1550 nm, 2100 nm, 2300 nm and 2500 nm).

Conclusion In summary, the startling contrast to generate MIR SC by picosecond (~1 ps) and femtosecond laser source (~50 fs) with same peak power in a highly nonlinear As2S3 microstructure optical fiber is demonstrated in this work. Because the average power

of picosecond pulse (~1 ps) is higher than that of femtosecond pulse (~50 fs) at same peak power, it can generate a broad SC spectrum from 1 to 6.5 m based on picosecond laser source (~1ps). The spectral evolution is also studied with different pump wavelengths. The 2300-nm pumped laser source is near-zero dispersion in the abnormal dispersion regime. In this case, four-wave mixing and higher-order soliton fission effect are quite strong. This work is very useful to generate a broader and longer-wavelength

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mid-IR SC in a versatile profile.

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References

[1] Zhao Wei, Xiaohong Hu, Yishan, Wang, Femtosecond-Pulse Fiber Based Amplification Techniques and Their Applications. IEEE Journal of Selected Topics in

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Quantum Electronics, 2014, 20 (5), 3100513.

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[2] Tonglei Cheng, Kenshiro Nagasaka, Tong Hoang Tuan, Xiaojie Xue, Morio Matsumoto, Hiroshige Tezuka, Takenobu Suzuki, and Yasutake Ohishi. Mid-infrared

M

Optics Letters, 41(9):2117-2120, 2016.

A

supercontinuum generation spanning 2.0 to 15.1 μm in a chalcogenide step-index fiber.

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[3] Weiqing Gao, Meisong Liao, Xin Yan, Chihiro Kito, Tomas Kohoutek, Takenobu Suzuki, Mohammed El-Amraoui, Jean-Charles Jules, Grégory Gadret, Frédéric Désévédavy, Frédéric Smektala, and Yasutake Ohishi, “Visible light generation and its

PT

influence on supercontinuum in chalcogenide As2S3 microstructured optical fiber”, Appl. Phys. Express 4, 102601 (2011).

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[4] Xiaohui Li, Yong Gang Wang, Yishan Wang, et al. Wavelength-Switchable and Wavelength-Tunable All-Normal-Dispersion Mode-Locked Yb-Doped Fiber Laser Based on Single-Walled Carbon Nanotube Wall Paper Absorber [J]. IEEE Photonics

A

Journal, 2012, 4(1):234-241. [5] Wei, C.; Zhu, X.; Norwood, R. A.; Song, F.; Peyghambarian, N., Numerical investigation on high power mid-infrared supercontinuum fiber lasers pumped at 3 m. Opt Express 2013, 21 (24), 29488-29504. [6] Weiqing Gao, Zhongchao Duan, Koji Asano, Tonglei Cheng, Dinghuan Deng, Morio Matsumoto, Takashi Misumi, Takenobu Suzuki, and Yasutake Ohishi, Mid-

infrared supercontinuum generation in a four-hole As2S5 chalcogenide microstructured optical fiber. Appl. Phys. B 116, 847 (2014). [7] Xiaohui Li, Yonggang Wang, Yishan Wang, et al. All-normal-dispersion passively mode-locked Yb-doped fiber ring laser based on a graphene oxide saturable absorber. Laser Physics Letters, 2013, 10(7):075108. [8] Xiaohui Li, Yulong Tang, Zhiyu Yan, et al. Broadband Saturable Absorption of

Selected Topics in Quantum Electronics, 2014, 20(5):441-447.

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Graphene Oxide Thin Film and Its Application in Pulsed Fiber Lasers. IEEE Journal of

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[9] Yixuan Guo, Xiaohui Li, Penglai Guo, et al. Supercontinuum generation in an Er-

doped figure-eight passively mode-locked fiber laser. Optics Express, 2018, 26(8):9893. [10] Zhipei Sun, Daniel Popa, Tawfique Hasan, Felice Torrisi, Fengqiu Wang, Edmund

U

J. R. Kelleher, John C.Travers, Valeria Nicolosi, and Andrea C. Ferrari. A Stable,

A

Laser. Nano Research, 3(9):653-660, 2010.

N

Wideband Tunable, Near Transform-Limited, Graphene Mode-Locked, Ultrafast

[11] Xiaohong Hu, Weiqiang Wang, Leiran Wang, et al. Numerical simulation and

M

temporal characterization of dual-pumped microring resonator-based optical frequency

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combs. Photonics Research, 5(3):207 (2017). [12] Liu Lai, Guanshi Qin, Qijun Tian, Weiping Qin Mid-infrared supercontinuum generation in single mode fluoride fiber. Proceedings of SPIE-The International Society

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for Optical Engineering 8330.7:42, (2011) [13] Jinmei Yao, Bin Zhang, KeYin, Linyong Yang, Jing Hou, and Qisheng Lu, Mid-

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infrared supercontinuum generation in step-index As2S3 fibers pumped by a nanosecond shortwave-infrared supercontinuum pump source. Optics Express 24(13) 15093-15100 (2016).

A

[14] Pengfei Gao, Xiaohui Li, Wenfeng Luo, Tong Chai, Xingxing Pang, Defeng Zou, “Numerical study of Mid-infrared Supercontinuum Generation with different wavelength laser source,” Chinese Journal of Lasers, 44(07), 0703018, (2017). [15] Qing Li, Lai Liu, Zhixu Jia, Guanshi Qin, Yasutake Ohishi, and Weiping Qin, "Increased red frequency shift in coherent mid-infrared supercontinuum generation

from tellurite microstructured fibers." Journal of Lightwave Technology, 35(21), 47404746 (2017). [16] Guanshi Qin, Mid-infrared supercontinuum generation in soft glass fibers. Progress in Electromagnetic Research Symposium IEEE, 2016:3176-3176. [17] Ke Yin, Bin Zhang, Jinmei Yao, Linyong Yang, Shengping Chen, and Jing Hou, Highly stable, monolithic, single-mode mid-infrared supercontinuum source based on

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low-loss fusion spliced silica and fluoride fibers. Opt Lett., 1; 41(5): 946-9 (2016).

[18] M. El-Amraoui, J. Fatome, J. C. Jules, B. Kibler, G. Gadret, C. Fortier, F. Smektala,

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I. Skripatchev, C.F. Polacchini, Y. Messaddeq, J. Troles, L. Brilland, M. Szpulak, and

G. Renversez． Strong infrared spectral broadening in low-loss As-S chalcogenide suspended core microstructured optical fibers. Optics Express, 18(5):4547, 2010.

U

[19] M. El-Amraoui, G. Gadret, J. C. Jules, J. Fatome, C. Fortier, F. Désévédavy, I.

N

Skripatchev, Y. Messaddeq, J. Troles, L. Brilland, W. Gao, T. Suzuki, Y. Ohishi, and F.

A

Smektala, Microstructured chalcogenide optical fibers from As2S3 glass: towards new IR broadband sources. Optics Express, 18(25): 26655-26665, 2010.

M

[20] Xiaohong Hu, Wei Zhang, Zhi Yang, Yishan Wang, Wei Zhao, Xiaohui Li, Hushan

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Wang, Cheng Li, and Deyuan Shen, High average power, strictly all-fiber supercontinuum source with good beam quality. Opt. Lett., 36(14), 2659-2661, 2011. [21] Weiqing Gao, Qiang Xu, Xue Li, Wei Zhang, Jigang Hu, Yuan Li, Xiangdong Chen,

PT

ZijunYuan, Meisong Liao, Xia Li, Wanjun Bi, Tonglei Cheng, Takenobu Suzuki and Yasutake Ohishi. Supercontinuum generation in a step-index chalcogenide fiber with

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AsSe2 core and As2S5 cladding. Japanese Journal of Applied Physics, 55(12), 122201, 2016.

[22] U. Møller, Y. Yu, I. Kubat, et. al., "Multi-milliwatt mid-infrared supercontinuum

A

generation in a suspended core chalcogenide fiber," Opt. Express 23, 3282-3291 (2015). [23] E.A. Anashkina, V.S. Shiryaev, M.Y. Koptev, et. al., "Development of As-Se tapered suspended-core fibers for ultra-broadband mid-IR wavelength conversion," Journal of Non-Crystalline Solids, 480, 43-50 (2018). [24] N. Granzow, S. P. Stark, M. A. Schmidt, A. S. Tverjanovich, L. Wondraczek, and P. St. J. Russell, “Supercontinuum generation in chalcogenide silica step-index fibers,”

Opt. Express 19(21) 21003-21010, (2011). [25] E. Coscelli, F. Poli, J. Li, A. Cucinotta, S. Selleri, "Dispersion engineering of highly nonlinear chalcogenide suspended-core fibers," IEEE Photonics Journal 7(3),

A

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PT

ED

M

A

N

U

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2200408 (2015).