OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 21 — Oct. 10, 2011
  • pp: 19955–19966
« Show journal navigation

Soliton-self compression in highly nonlinear chalcogenide photonic nanowires with ultralow pulse energy

Amine Ben Salem, Rim Cherif, and Mourad Zghal  »View Author Affiliations


Optics Express, Vol. 19, Issue 21, pp. 19955-19966 (2011)
http://dx.doi.org/10.1364/OE.19.019955


View Full Text Article

Acrobat PDF (1244 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We design As2Se3 and As2S3 chalcogenide photonic nanowires to optimize the soliton self-compression with short distances and ultralow input pulse energy. We numerically demonstrate the generation of single optical cycle in an As2S3 photonic nanowire: a 5.07 fs compressed pulse is obtained starting from 250 fs input pulse with 50 pJ in 0.84 mm-long As2S3 nanowire. Taking into account the high two photon absorption (TPA) coefficient in the As2Se3 glass, accurate modeling shows the compression of 250 fs down to 25.4 fs in 2.1 mm-long nanowire and with 10 pJ input pulse energy.

© 2011 OSA

1. Introduction

Highly nonlinear optical waveguides have great interest for compact, low power and all optical nonlinear applications. In fact, photonic nanowires with diameters smaller than the wavelength of the guided light attract considerable interest due to their unique optical and nonlinear properties for wide range of applications [1

1. L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature 426(6968), 816–819 (2003). [CrossRef] [PubMed]

]. They are obtained by tapering optical fibers which is the commonly used method for reducing optical fiber dimensions and engineering the waveguide dispersion [2

2. M. A. Foster, A. C. Turner, M. Lipson, and A. L. Gaeta, “Nonlinear optics in photonic nanowires,” Opt. Express 16(2), 1300–1320 (2008). [CrossRef] [PubMed]

4

4. Y. K. Lizé, E. C. Mägi, V. G. Ta’eed, J. A. Bolger, P. Steinvurzel, and B. J. Eggleton, “Microstructured optical fiber photonic wires with subwavelength core diameter,” Opt. Express 12(14), 3209–3217 (2004). [CrossRef] [PubMed]

]. These structures are not only suitable for nanophotonic devices but also enable nonlinear process such as soliton-effect compression and broadband supercontinuum (SC) generation at low input pulse energies [5

5. R. R. Gattass, G. T. Svacha, L. M. Tong, and E. Mazur, “Supercontinuum generation in submicrometer diameter silica fibers,” Opt. Express 14(20), 9408–9414 (2006). [CrossRef] [PubMed]

,6

6. S. G. Leon-Saval, T. A. Birks, W. J. Wadsworth, P. St. J. Russell, and M. W. Mason, “Supercontinuum generation in submicron fibre waveguides,” Opt. Express 12(13), 2864–2869 (2004). [CrossRef] [PubMed]

]. Generation of few-optical cycles directly from oscillators requires special designed cavities with high reflectivity dispersion compensating mirrors, and initial energy in the order of hundreds of µJ. Therefore, the used compression technique consists of using external passive or active dispersion compensation schemes in order to compress the laser pulse initially broadened by self-phase modulation (SPM) in a waveguide. In both techniques, the required dispersion compensation requires complex electronically controlled feedback systems. An impressive method toward the monocycle regime relying on the soliton-effect compression has been used to successfully compress low-energy ps-pulses without additional dispersion compensation schemes [7

7. L. F. Mollenauer, R. H. Stolen, and J. P. Gordon, “Experimental observation of picosecond pulse narrowing and solitons in optical fibers,” Phys. Rev. Lett. 45(13), 1095–1098 (1980). [CrossRef]

,8

8. L. F. Mollenauer, R. H. Stolen, J. P. Gordon, and W. J. Tomlinson, “Extreme picosecond pulse narrowing by means of soliton effect in single-mode optical fibers,” Opt. Lett. 8(5), 289–291 (1983). [CrossRef] [PubMed]

]. This method exploits the property of propagating high-order soliton in the anomalous dispersion regime in optical fibers where efficient compression results from the interplay between the dispersion and the self phase modulation effects. Therefore scaling laws have been developed for the soliton-self compression parameters, for hyperbolic-secant pulses, with numerical and analytical methods [8

8. L. F. Mollenauer, R. H. Stolen, J. P. Gordon, and W. J. Tomlinson, “Extreme picosecond pulse narrowing by means of soliton effect in single-mode optical fibers,” Opt. Lett. 8(5), 289–291 (1983). [CrossRef] [PubMed]

,9

9. C. M. Chen and P. L. Kelley, “Nonlinear pulse compression in optical fibers: scaling laws and numerical analysis,” J. Opt. Soc. Am. B 19(9), 1961–1967 (2002). [CrossRef]

].

The introduction of highly nonlinear photonic nanowires with anomalous group velocity dispersion at visible and near-infrared wavelengths has enormously contributed in the study of soliton-self compression techniques and the generation of few to single optical cycles. Specifically, the broad region of anomalous dispersion regime can be shifted for photonic nanowires and extends into the visible for silica nanowires and into the midinfrared for chalcogenide nanowires. Large anomalous group velocity dispersion region with low third-order dispersion are required to achieve efficient soliton-self compression [2

2. M. A. Foster, A. C. Turner, M. Lipson, and A. L. Gaeta, “Nonlinear optics in photonic nanowires,” Opt. Express 16(2), 1300–1320 (2008). [CrossRef] [PubMed]

,10

10. M. Foster, A. L. Gaeta, Q. Cao, and R. Trebino, “Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires,” Opt. Express 13(18), 6848–6855 (2005). [CrossRef] [PubMed]

]. In the 800 nm region, Foster et al. [10

10. M. Foster, A. L. Gaeta, Q. Cao, and R. Trebino, “Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires,” Opt. Express 13(18), 6848–6855 (2005). [CrossRef] [PubMed]

], experimentally demonstrated soliton-self compression by performing a cross correlation frequency resolved optical grating (XFROG) measurements. They showed the generation of 6.8 fs compressed pulse at low input energy from initial 70 fs in 980 nm core diameter air-silica photonic nanowire. In addition, they theoretically predicted soliton-self compression of 30 fs input pulse to 1.8 fs in 650 μm-long 800 nm-diameter air-silica nanowire.

Most achievements in ultrafast nonlinear optics have been made in photonic nanowires based on silica glass but studies on highly nonlinear glasses have been recently started too. Chalcogenide glasses based on As2S3 and As2Se3 have been the subject of intense investigations due to their high nonlinear coefficient n2 (100-1000 times larger than of silica glass), low linear loss and low to moderate two photon absorption (TPA) coefficient [11

11. J. M. Harbold, F. O. Ilday, F. W. Wise, J. S. Sanghera, V. Q. Nguyen, L. B. Shaw, and I. D. Aggarwal, “Highly nonlinear As-S-Se glasses for all-optical switching,” Opt. Lett. 27(2), 119–121 (2002). [CrossRef] [PubMed]

]. Recent works have showed the generation of SC in such photonic chalcogenide As2S3 and As2Se3 nanowires with ultra low input energy at a pump wavelength of 1550 nm [12

12. D. I. Yeom, E. C. Mägi, M. R. E. Lamont, M. A. F. Roelens, L. Fu, and B. J. Eggleton, “Low-threshold supercontinuum generation in highly nonlinear chalcogenide nanowires,” Opt. Lett. 33(7), 660–662 (2008). [CrossRef] [PubMed]

,13

13. D. D. Hudson, S. A. Dekker, E. C. Mägi, A. C. Judge, S. D. Jackson, E. Li, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Octave spanning supercontinuum in an As2S3 taper using ultralow pump pulse energy,” Opt. Lett. 36(7), 1122–1124 (2011). [CrossRef] [PubMed]

]. However, to our knowledge, soliton self-compression in such highly nonlinear nanowires has not been studied so far.

In this paper, we investigate the linear and the nonlinear properties of As2Se3 and As2S3 chalcogenide photonic nanowires for soliton self-compression. In Section 2, we study the theory and the numerical modeling behind accurate calculation of the optical properties of photonic nanowires including chromatic dispersion, effective mode area and nonlinear coefficient. In addition, the cut-off condition of single mode operation in photonic nanowires is determined. Section 3 shows the results of the optical properties modeling and analyzes the soliton-self compression in chalcogenide photonic nanowire glasses. Aiming to optimize the soliton-effect compression in photonic nanowire, we select the 800 nm core diameter nanowire size for which large region of the anomalous group velocity dispersion and low third-order dispersion are found at pump wavelength of 1550 nm for the air-chalcogenide (As2Se3 and As2S3) photonic nanowires. We show that we can generate less than one optical cycle in 800 nm diameter As2S3 nanowires at very low pulse energy of pJ levels. In fact, pumping the 800 nm air-As2S3 nanowire at λp = 1550 nm with 50 pJ energy allows the compression of a pre-chirped 250 fs down to 5.07 fs. Therefore, soliton-effect compression in the anomalous dispersion regime in the 800 nm diameter As2Se3 nanowire has been studied and shows the possibility of generating 25.4 fs starting from 250 fs with 10 pJ energy at λp = 1550 nm. The effect of TPA has been also studied since As2Se3 presents a high TPA coefficient comparing to As2S3.

2. Theory and numerical analysis

2.1 Mode propagation

Like conventional optical fibers, photonic nanowires experience single-mode (HE11) guiding for V < 2.405.

2.2 Chromatic dispersion

In order to determine the chromatic dispersion of the chalcogenide nanowires, we need to calculate the effective index neff=βλ/(2π) of the fundamental mode HE11. We apply a full vectorial finite element method (FEM) with dense meshes made up of 104~105 elements according to the dimensions of the photonic nanowire. In fact, by dividing the fiber cross-section into curvilinear hybrid edge/nodal elements and applying the finite element procedure, we obtain the following eigenvalue equation [15

15. M. Zghal and R. Cherif, “Impact of small geometrical imperfections on chromatic dispersion and birefringence in photonic crystal fibers,” Opt. Eng. 46(12), 128002 (2007). [CrossRef]

]:
[K] {E}  k02 neff2[M] {E}={0}
(3)
where [K] and [M] are the finite element matrices, {E} is the discretized electric field vector consisting of the edge and nodal variables. Resolving Eq. (1) in the As-S and As-Se wavelength ranges gives the effective index neff of the fundamental mode as a function of the optical wavelength. Thus, the group velocity dispersion (GVD) referred to as chromatic dispersion (Dc) can be determined from the second derivative of the mode effective index as a function of the wavelength. It is given by:
Dc =λcd2neffdλ2
(4)
where c is the velocity of light in vacuum.

2.3 Evanescent field and effective nonlinearity

With their small core dimensions and the large core-cladding refractive-index difference, chalcogenide nanowires exhibit tighter light confinement and higher nonlinear coefficient than standard fibers. However, in nanowires, the optical mode can extend evanescently outside the core boundaries, and then an accurate estimation of the nonlinear coefficient γ is needed. The nonlinear coefficient γ is then defined as [16

16. M. A. Foster, K. D. Moll, and A. L. Gaeta, “Optimal waveguide dimensions for nonlinear interactions,” Opt. Express 12(13), 2880–2887 (2004). [CrossRef] [PubMed]

]:
γ=2πλn2.Sz2d2r(Szd2r)2
(5)
where Sz is the longitudinal component of the Poynting vector, n2 is the nonlinear index and r is the cross sectional position vector. Because of a significant fraction of the optical mode propagates in the air outside the core and n2 of the cladding (air) is negligible compared to that of the core glass, the integrals in the numerator are evaluated only over the glass core region. The integrals in the denominator are evaluated over the total transverse section of the fiber. In addition, to obtain complete information about the power residing in the evanescent field, we evaluate the fractional power ηEF outside the core. It is given by ηEF=1η where η is the fractional power inside the core and it is expressed by:

η=0d/202πSz.rdr.dφ002πSz.rdr.dφ
(6)

2.4 Nonlinear propagation

Considering the optical waveguide properties of the chalcogenide photonic nanowire, the investigation of the nonlinear propagation and the soliton-self compression are based on the resolution of the generalized nonlinear Schrödinger equation (GNLSE). The authors in ref [17

17. T. Brabec and F. Krausz, “Nonlinear optical pulse propagation in the single-cycle regime,” Phys. Rev. Lett. 78(17), 3282–3285 (1997). [CrossRef]

]. attempt to overcome the limitations of the slowly-varying envelope approximation (SVEA) and have demonstrated that the concept of envelope and first-order equation can be used even in the extreme case of single-optical-cycle-regime. The GNLSE is given by [18

18. G. P. Agrawal, Nonlinear Fiber Optics, 4th ed. (Academic Press, 2007).

]:
Az=α2A+m0jm+1βmm!mAtm+j(γ+jα22Aeff)(1+jω0t)                                                              ×(A(z,t)0+R(t')|A(z,tt')|2dt')
(7)
where A(z,t) is the slowly varying envelope, α is the loss coefficient and βm the mth-order dispersion coefficients. α2 is the TPA coefficient of the core glass and ω0 is the pump central frequency. The nonlinear response function R(t) includes the instantaneous and the delayed Raman contributions. It is given by [18

18. G. P. Agrawal, Nonlinear Fiber Optics, 4th ed. (Academic Press, 2007).

]:
R(t)=(1fR)δ(t)+fRhR(t)
(8)
fR is the fractional contribution of the material. The delayed Raman response hR(t) is expressed through the Green’s function of the damped harmonic oscillator [19

19. K. J. Blow and D. Wood, “Theoretical description of transient stimulated Raman scattering in optical fibers,” IEEE J. Quantum Electron. 25(12), 2665–2673 (1989). [CrossRef]

]:
hR(t)=τ1²+τ2²τ1τ2²exp(tτ2)sin(tτ1)
(9)
where the parameters τ1 and τ2 correspond respectively to the inverse of the phonon oscillation frequency and the bandwidth of the Raman gain spectrum.

The resolution of the GNLSE is performed by the symmetrized split step Fourier method. The 4th-order Runge-Kutta algorithm was used in our calculations. To have accurate numerical results, 213 time and frequency discretization points and a longitudinal step size <1 µm were used in our simulations. To start the resolution, we need to set the input pulse shape and duration. We consider the injection of an input soliton order N having an envelope field expression given by [18

18. G. P. Agrawal, Nonlinear Fiber Optics, 4th ed. (Academic Press, 2007).

]:
A(0,t)=P0sech(tT0)exp(iCt22T02)
(10)
where P0 is the peak power and T0 is the input soliton duration defined as TFWHM /1.763. TFWHM is the input pulse full width at half maximum (FWHM) duration. C is the chirp parameter controlling the initial chirp. The soliton order N is defined as [18

18. G. P. Agrawal, Nonlinear Fiber Optics, 4th ed. (Academic Press, 2007).

] N2=LD/LNL=T02γP0/|β2| where LD=T02/|β2| is the dispersion length and LNL=(γP0)1 is the nonlinear length.

3. Numerical results

In this section, we determine the optical properties of air-chalcogenide nanowires which are produced from tapering conventional single mode fibers. We investigate the optical field distribution in air-As2Se3 and air-As2S3 nanowires and determine the cut-off condition for single mode operation in these photonic nanowires. Then, we analyze the soliton-self compression in both As2Se3 and As2S3 air-chalcogenide photonic nanowires. The study is based on the optimization of initial chirp in order to generate efficient soliton-self compression with the lowest input pulse energy.

3.1 Air-As2Se3 nanowires

We have carried out a rigorous calculation of the chromatic dispersion of the different air-As2Se3 photonic nanowires by using the Sellmeier equation of the As2Se3 glass defined as n(λ)=A+Bλ2/(λ2D)+Cλ2where A = −4.5102, B = 12.0582, C = 0.0018 µm−2 and D = 0.0878 µm2 [20

20. R. Cherif, A. Ben-Salem, M. Zghal, P. Besnard, T. Chartier, L. Brilland, and J. Troles, “Highly nonlinear As2Se3-based chalcogenide photonic crystal fiber for midinfrared supercontinuum generation,” Opt. Eng. 49(9), 095002 (2010). [CrossRef]

]. The unit of λ is µm. Figure 1
Fig. 1 Calculated chromatic dispersion of air-As2Se3 nanowires with core diameters ranging from 600 nm to 1000 nm.
depicts the chromatic dispersion as a function of the wavelength of air-As2Se3 nanowires with core diameters ranging from 600 nm to 1000 nm.

As we can see from Fig. 1, increasing the air-As2Se3 nanowire diameter shifts the first zero dispersion wavelength of the nanowire toward midinfrared wavelengths which enlarges the region of the anomalous dispersion regime. As the core diameter is reduced to sub-micron dimensions, the waveguide dispersion becomes dominant over the material dispersion (bulk As2Se3) allowing the overall-GVD to be highly engineered. We find that the 900 nm air-As2Se3 has a zero dispersion wavelength around 1550 nm. The 800 nm air-As2Se3 presents a positive chromatic dispersion value at 1550 nm and low third-order dispersion (β2 = −0.48 ps2.m−1 and β3 = 7.79 × 10−3 ps3.m−1). Consequently, pumping at this wavelength in the anomalous dispersion regime is attractive to simulate soliton-effect compression. Before investigating the nonlinear propagation in such air-As2Se3 nanowires, one should characterize the optical properties of the air-As2Se3 nanowires under investigation.

Figure 2(a)
Fig. 2 (a) Fractional powers inside and outside the core and (b) effective mode area (Aeff) and nonlinear coefficient (γ) of various air-As2Se3 nanowire diameters at λp = 1550 nm.
depicts the calculated fractional powers inside and outside the core as a function of the air-As2Se3 nanowire diameter at 1550 nm. The dominance of the evanescent field begins to appear and exceeds 50% of the total light with nanowire diameters less than 370 nm. The single mode operation is found in nanowires with diameters less than dSM = 448 nm. At this critical diameter, more than 85% of the light is inside the core. For the 800 nm air-As2Se3 nanowire, 98% of the total light propagates inside the core. Figure 2(b) shows the calculated nonlinear coefficient γ of the different air-As2Se3 nanowires and their effective mode area Aeff=|SzdA|2/|Sz|2dA at λp = 1550 nm. We notice that the mode confinement determined by the effective mode area becomes stronger when reducing the core diameter of the air-As2Se3 nanowire. This behavior continues linearly to evolve and shows an optimal nanowire size exhibiting the minimum effective mode area / the highest effective nonlinearity with a core diameter of about 450 nm. After this optimum value, the mode confinement diverges rapidly. This is justified by the fact that the air-As2Se3 nanowire no longer tightly confines the light so that the evanescent field starts to dominate. For the 800 nm air-As2Se3 nanowire, the effective mode area is evaluated to be Aeff = 0.3 µm2. Thus, a very high nonlinear coefficient is exhibited and found to be around 145.3 W−1.m−1 by taking n2 = 1.1 × 10−17 m2.W−1 [21

21. R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B 21(6), 1146–1155 (2004). [CrossRef]

].

After determining the optical properties of air-As2Se3 photonic nanowires, we introduce them in the GNLSE as inputs to investigate the nonlinear propagation in the 800 nm air-As2Se3 nanowire. As we found that the 800 nm air-As2Se3 performs in the anomalous dispersion regime around a pump wavelength of 1550 nm, we select, based on the availability, a femtosecond laser delivering 250 fs FWHM at 1550 nm [10

10. M. Foster, A. L. Gaeta, Q. Cao, and R. Trebino, “Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires,” Opt. Express 13(18), 6848–6855 (2005). [CrossRef] [PubMed]

]. The Raman response parameters of the As2Se3 glass are set to be τ1 = 23fs, τ2 = 164.5fs and fR = 0.148 [22

22. A. Ben-Salem, R. Cherif, and M. Zghal, “Raman response of a highly nonlinear As2Se3-based chalcogenide photonic crystal fiber,” Proc. PIERS, 1256–1260, Marrakesh, Morocco (2011).

]. The coefficient loss α = 1 dB.m−1 [23

23. C. Xiong, E. Magi, F. Luan, A. Tuniz, S. Dekker, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Characterization of picosecond pulse nonlinear propagation in chalcogenide As2S3 fiber,” Appl. Opt. 48(29), 5467–5474 (2009). [CrossRef] [PubMed]

].

Taking into account the high two photon absorption coefficient (α2 = 2.5 × 10−12 m/W [21

21. R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B 21(6), 1146–1155 (2004). [CrossRef]

]) and the high nonlinearity exhibited in As2Se3 glass, we select a very low input pulse energy to characterize the soliton-self compression in the 800 nm air-As2Se3 nanowire. We set the input pulse energy to 10 pJ at a pump wavelength of 1550 nm and inject an input hyperbolic-secant pulse initially chirped with C = −0.3 which is found to optimize the temporal compression. This optimal value of the chirp is determined by carrying out several calculations, at a fixed input pulse energy, in which we vary the initial chirp and register the shortest FWHM duration of the generated compressed pulse Tcomp, as seen in Fig. 3
Fig. 3 Impact of the initial chirp on the compression efficiency.
. We find that positive chirp degrades the temporal compression while negative chirp enhances the soliton-effect compression (C = −0.3 provides maximum temporal compression).

Figure 4(a)
Fig. 4 (a) Temporal and (b) spectral evolution of 250 fs input pulse with 10 pJ input energy in the 800 nm air-As2Se3 nanowire at λp = 1550 nm, with and without TPA.
shows a maximum generated compressed pulse with a duration of 25.4 fs in 2.1 mm nanowire length. The optimal soliton-self compression length is numerically determined from the simulations ensuring that a maximum-compressed and preserved soliton-shape is reached [24

24. A. Ben Salem, R. Cherif, and M. Zghal, “Generation of few optical cycles in air-silica nanowires,” Proc. SPIE 8001, 80011J (2011). [CrossRef]

] without the presence of high pulse intensity fluctuations or peak perturbations. Good agreement is found with the analytical model giving optimal distance proposed in [9

9. C. M. Chen and P. L. Kelley, “Nonlinear pulse compression in optical fibers: scaling laws and numerical analysis,” J. Opt. Soc. Am. B 19(9), 1961–1967 (2002). [CrossRef]

]. This nonlinear interaction corresponds to the injection of a soliton order N = 14.5. We characterize the compression efficiency by the evaluation of two parameters namely the compression factor Fc and the quality factor Qc. The compression factor Fc, defined as the ratio of the FWHM pulse duration at the beginning and the end of the nanowire, is found to be 9.84. The correspondent quality factor Qc=Pcomp/(P0Fc) [10

10. M. Foster, A. L. Gaeta, Q. Cao, and R. Trebino, “Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires,” Opt. Express 13(18), 6848–6855 (2005). [CrossRef] [PubMed]

] which is equal to the peak power of the compressed pulse (Pcomp) normalized to the input peak power (P0) and the compression factor (Fc) is evaluated to be 0.21. Spectral evolution of the initial pre-chirped hyperbolic-secant pulse is depicted in Fig. 4(b).

The supercontinuum is generated with taking into account the effect of TPA (for which we extracted the maximum compressed pulse) and then without TPA and we notice its big effect on the spectral generated bandwidth. In fact, an extra 500 nm bandwidth is generated when one neglects the TPA. Thus, a perfect modeling has to consider the effect of TPA in order to obtain correct results simulating the nonlinear propagation in highly nonlinear air-As2Se3 nanowires. We notice the generation of over 700 nm bandwidth of near infrared SC showing a symmetrical broadening which confirms that self phase modulation is the dominant effect giving such broadening and leading to temporal soliton-self compression.

3.2 Air-As2S3 nanowires

To evaluate the chromatic dispersion in air-As2S3 photonic nanowires, we used the Sellmeier equation of the As2S3 glass defined as n(λ)=1+iAiλ2/(λ2λi2) where A1 = 1.898367, A2 = 1.922297, A3 = 0.87651, A4 = 0.11887, A5 = 0.95699, λ1 = 0.15 µm, λ2 = 0.25µm, λ3 = 0.35µm, λ4 = 0.45µm and λ5 = 27.3861µm [25

25. M. Bass, Handbook of Optics (McGraw Hill, 1997).

]. The unit of λ is µm.

Figure 5
Fig. 5 Calculated chromatic dispersion of air-As2S3 nanowires with core diameters ranging from 600 nm to 1000 nm.
depicts the calculated chromatic dispersion of air-As2S3 nanowires. We notice the similar chromatic dispersion behavior as air-As2Se3 nanowires: when the diameter increases the region of the anomalous dispersion regime shifts toward infrared wavelengths. Air-As2S3 nanowires with diameters ranging from 600 nm to 1000 nm exhibit positive chromatic dispersion around 1550 nm. We found very low GVD and third-order dispersion coefficients (β2 = −1.54 ps2.m−1 and β3 = 5.65 × 10−3 ps3.m−1) for the 800 nm air-As2S3 nanowire. Pumping at this wavelength will excite soliton-self compression in the anomalous dispersion regime in the 800 nm air-As2S3 nanowire. A detailed study of the fundamental mode has been achieved for air-As2S3 nanowires.

Figure 6(a)
Fig. 6 (a) Fractional powers inside and outside the core and (b) effective mode area (Aeff) and nonlinear coefficient (γ) of different air-As2S3 nanowires at λp = 1550 nm.
shows the calculated fractional powers inside and outside the core at a wavelength of 1550 nm as a function of the air-As2S3 nanowire diameter. The evanescent field starts to dominate and exceeds 50% of the total light with nanowire diameters less than 420 nm. With a critical diameter dSM = 533 nm, air-As2S3 nanowires experience fundamental mode propagation. At this diameter, more than 82% of the light propagates inside the core. For the 800 nm air-As2Se3 nanowire, 4% of the light resides in the evanescent field while 96% of the remaining light propagates inside the core. Thus, high nonlinear coefficient is exhibited and evaluated to be around 48.7 W−1.m−1 by taking n2 = 4 × 10−18 m2.W−1 [26

26. D.-P. Wei, T. Galstian, I. Smolnikov, V. Plotnichenko, and A. Zohrabyan, “Spectral broadening of femtosecond pulses in a single-mode As-S glass fiber,” Opt. Express 13(7), 2439–2443 (2005). [CrossRef] [PubMed]

].

In fact, Fig. 6(b) shows the calculated nonlinear coefficient of different air-As2Se3 nanowires and their effective mode area at 1550 nm. Similar behavior of the nonlinear coefficient is depicted for air-As2S3 nanowires as the air-As2Se3 nanowires. The highest effective nonlinearity is exhibited for an optimal nanowire size of 540 nm. We find that the highest effective nonlinearity and the mode confinement depend on the contrast of the core-cladding refractive-index difference. In fact, when the refractive index difference Δn between the core and the air-cladding increases for a certain optical wavelength, the optimal photonic nanowire diameter presenting the highest effective nonlinearity shifts and becomes smaller. This is the case at 1550 nm for As2S3 (Δn = 1.43) and As2Se3 (Δn = 1.83) glasses showing optimal nanowire diameters of 540 nm and 450 nm, respectively. More light confinement with 2% for the 800 nm air-As2Se3 nanowire is found compared to that in the 800 nm air-As2S3 nanowire.

We are now in the process of investigating the nonlinear propagation in the 800 nm air-As2S3 nanowire. As the 800 nm air-As2Se3, we select the femtosecond laser delivering 250 fs FWHM pulse at 1550 nm. We take τ1 = 15.5fs, τ2 = 230.5fs and fR = 0.1 to model the Raman response function of the As2S3 glass and set α = 1 dB.m−1 [23

23. C. Xiong, E. Magi, F. Luan, A. Tuniz, S. Dekker, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Characterization of picosecond pulse nonlinear propagation in chalcogenide As2S3 fiber,” Appl. Opt. 48(29), 5467–5474 (2009). [CrossRef] [PubMed]

]. Because of the high nonlinearity exhibited in the 800 nm air-As2S3 nanowire, a very low input pulse energy of 50 pJ is taken. This corresponds to the excitation of an input soliton order of N = 10.56. In order to optimize the soliton-self compression, the input hyperbolic-secant pulse is chosen initially chirped with C = −0.2 (Similar approach has been performed to determine the optimal chirp value). Figure 7
Fig. 7 Temporal evolution of 250 fs input pulse with 50 pJ input energy in the 800 nm air-As2S3 nanowire at λp = 1550 nm.
shows a maximum compressed pulse with duration of 5.07 fs in 0.84 mm nanowire length. Thus, less than single optical cycle is generated at a pump wavelength of 1550 nm. Good agreement was found with the analytical expression determining the optimal soliton-self compression distance [9

9. C. M. Chen and P. L. Kelley, “Nonlinear pulse compression in optical fibers: scaling laws and numerical analysis,” J. Opt. Soc. Am. B 19(9), 1961–1967 (2002). [CrossRef]

]. A compression factor Fc = 49.3 and a quality factor Qc = 0.28 are achieved.

4. Conclusion

We have performed a numerical study of soliton self-compression in photonic nanowires. Detailed studies of the optical properties have been achieved in chalcogenide photonic nanowires based on As2S3 and As2Se3 glasses. Most attractive optical properties of photonic nanowire are the existence of the evanescent field surrounding the nanowire and the strong radial confinement of the light which make photonic nanowires well suited for an efficient and controlled interaction of guided light with matter and perfect devices for sensing applications [28

28. G. Brambilla, “Optical fibre nanotaper sensors,” Opt. Fiber Technol. 16(6), 331–342 (2010). [CrossRef]

]. Soliton-effect compression has been investigated in chalcogenide photonic nanowires and pulses in the monocycle regime have been generated in As2S3 nanowire while 25.4fs compressed pulse is generated in the As2Se3 with consideration of TPA. Thus, very high compression factors of 49.3 and 9.84 have been achieved starting from 250 fs for chalcogenide (As2S3 and As2Se3) nanowires, respectively. All the compressed pulses are obtained at very low input pulse energy with pJ levels in just few millimeters-long nanowires. The study was based on the adjustment of the initial chirp in order to maximize the compression. In addition, the generation of midinfrared two octaves spanning SC around 1550 nm in only 0.84 mm air-As2S3 nanowire is shown. Chalcogenide photonic nanowires are very promising devices for designing midinfrared light coherent sources with short lengths and low powers. They are suitable waveguides for high soliton-effect compression which opens new horizon toward extreme nonlinear optics and attosecond physics.

Acknowledgments

The work is partially supported by the “Institut Télécom” through the “Futur et Ruptures” PhD thesis of A. Ben-Salem. The authors thank Professor John Dudley from Institut Femto-ST, Université de Franche-Comté, Besançon, France for helpful discussions and collaboration.

References and links

1.

L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature 426(6968), 816–819 (2003). [CrossRef] [PubMed]

2.

M. A. Foster, A. C. Turner, M. Lipson, and A. L. Gaeta, “Nonlinear optics in photonic nanowires,” Opt. Express 16(2), 1300–1320 (2008). [CrossRef] [PubMed]

3.

E. C. Mägi, P. Steinvurzel, and B. J. Eggleton, “Tapered photonic crystal fibers,” Opt. Express 12(5), 776–784 (2004). [CrossRef] [PubMed]

4.

Y. K. Lizé, E. C. Mägi, V. G. Ta’eed, J. A. Bolger, P. Steinvurzel, and B. J. Eggleton, “Microstructured optical fiber photonic wires with subwavelength core diameter,” Opt. Express 12(14), 3209–3217 (2004). [CrossRef] [PubMed]

5.

R. R. Gattass, G. T. Svacha, L. M. Tong, and E. Mazur, “Supercontinuum generation in submicrometer diameter silica fibers,” Opt. Express 14(20), 9408–9414 (2006). [CrossRef] [PubMed]

6.

S. G. Leon-Saval, T. A. Birks, W. J. Wadsworth, P. St. J. Russell, and M. W. Mason, “Supercontinuum generation in submicron fibre waveguides,” Opt. Express 12(13), 2864–2869 (2004). [CrossRef] [PubMed]

7.

L. F. Mollenauer, R. H. Stolen, and J. P. Gordon, “Experimental observation of picosecond pulse narrowing and solitons in optical fibers,” Phys. Rev. Lett. 45(13), 1095–1098 (1980). [CrossRef]

8.

L. F. Mollenauer, R. H. Stolen, J. P. Gordon, and W. J. Tomlinson, “Extreme picosecond pulse narrowing by means of soliton effect in single-mode optical fibers,” Opt. Lett. 8(5), 289–291 (1983). [CrossRef] [PubMed]

9.

C. M. Chen and P. L. Kelley, “Nonlinear pulse compression in optical fibers: scaling laws and numerical analysis,” J. Opt. Soc. Am. B 19(9), 1961–1967 (2002). [CrossRef]

10.

M. Foster, A. L. Gaeta, Q. Cao, and R. Trebino, “Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires,” Opt. Express 13(18), 6848–6855 (2005). [CrossRef] [PubMed]

11.

J. M. Harbold, F. O. Ilday, F. W. Wise, J. S. Sanghera, V. Q. Nguyen, L. B. Shaw, and I. D. Aggarwal, “Highly nonlinear As-S-Se glasses for all-optical switching,” Opt. Lett. 27(2), 119–121 (2002). [CrossRef] [PubMed]

12.

D. I. Yeom, E. C. Mägi, M. R. E. Lamont, M. A. F. Roelens, L. Fu, and B. J. Eggleton, “Low-threshold supercontinuum generation in highly nonlinear chalcogenide nanowires,” Opt. Lett. 33(7), 660–662 (2008). [CrossRef] [PubMed]

13.

D. D. Hudson, S. A. Dekker, E. C. Mägi, A. C. Judge, S. D. Jackson, E. Li, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Octave spanning supercontinuum in an As2S3 taper using ultralow pump pulse energy,” Opt. Lett. 36(7), 1122–1124 (2011). [CrossRef] [PubMed]

14.

L. Tong, J. Lou, and E. Mazur, “Single-mode guiding properties of subwavelength-diameter silica and silicon wire waveguides,” Opt. Express 12(6), 1025–1035 (2004). [CrossRef] [PubMed]

15.

M. Zghal and R. Cherif, “Impact of small geometrical imperfections on chromatic dispersion and birefringence in photonic crystal fibers,” Opt. Eng. 46(12), 128002 (2007). [CrossRef]

16.

M. A. Foster, K. D. Moll, and A. L. Gaeta, “Optimal waveguide dimensions for nonlinear interactions,” Opt. Express 12(13), 2880–2887 (2004). [CrossRef] [PubMed]

17.

T. Brabec and F. Krausz, “Nonlinear optical pulse propagation in the single-cycle regime,” Phys. Rev. Lett. 78(17), 3282–3285 (1997). [CrossRef]

18.

G. P. Agrawal, Nonlinear Fiber Optics, 4th ed. (Academic Press, 2007).

19.

K. J. Blow and D. Wood, “Theoretical description of transient stimulated Raman scattering in optical fibers,” IEEE J. Quantum Electron. 25(12), 2665–2673 (1989). [CrossRef]

20.

R. Cherif, A. Ben-Salem, M. Zghal, P. Besnard, T. Chartier, L. Brilland, and J. Troles, “Highly nonlinear As2Se3-based chalcogenide photonic crystal fiber for midinfrared supercontinuum generation,” Opt. Eng. 49(9), 095002 (2010). [CrossRef]

21.

R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B 21(6), 1146–1155 (2004). [CrossRef]

22.

A. Ben-Salem, R. Cherif, and M. Zghal, “Raman response of a highly nonlinear As2Se3-based chalcogenide photonic crystal fiber,” Proc. PIERS, 1256–1260, Marrakesh, Morocco (2011).

23.

C. Xiong, E. Magi, F. Luan, A. Tuniz, S. Dekker, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Characterization of picosecond pulse nonlinear propagation in chalcogenide As2S3 fiber,” Appl. Opt. 48(29), 5467–5474 (2009). [CrossRef] [PubMed]

24.

A. Ben Salem, R. Cherif, and M. Zghal, “Generation of few optical cycles in air-silica nanowires,” Proc. SPIE 8001, 80011J (2011). [CrossRef]

25.

M. Bass, Handbook of Optics (McGraw Hill, 1997).

26.

D.-P. Wei, T. Galstian, I. Smolnikov, V. Plotnichenko, and A. Zohrabyan, “Spectral broadening of femtosecond pulses in a single-mode As-S glass fiber,” Opt. Express 13(7), 2439–2443 (2005). [CrossRef] [PubMed]

27.

B. Kibler, R. Fischer, P.-A. Lacourt, F. Courvoisier, R. Ferriere, L. Larger, D. N. Neshev, and J. M. Dudley, “Optimised one-step compression of femtosecond fibre laser soliton pulses around 1550 nm to below 30 fs in highly nonlinear fibre,” Electron. Lett. 43(17), 915–916 (2007). [CrossRef]

28.

G. Brambilla, “Optical fibre nanotaper sensors,” Opt. Fiber Technol. 16(6), 331–342 (2010). [CrossRef]

OCIS Codes
(160.4330) Materials : Nonlinear optical materials
(190.4370) Nonlinear optics : Nonlinear optics, fibers
(190.5530) Nonlinear optics : Pulse propagation and temporal solitons
(320.5520) Ultrafast optics : Pulse compression
(320.7140) Ultrafast optics : Ultrafast processes in fibers
(320.6629) Ultrafast optics : Supercontinuum generation

ToC Category:
Nonlinear Optics

History
Original Manuscript: August 10, 2011
Revised Manuscript: September 16, 2011
Manuscript Accepted: September 20, 2011
Published: September 27, 2011

Citation
Amine Ben Salem, Rim Cherif, and Mourad Zghal, "Soliton-self compression in highly nonlinear chalcogenide photonic nanowires with ultralow pulse energy," Opt. Express 19, 19955-19966 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-21-19955


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature426(6968), 816–819 (2003). [CrossRef] [PubMed]
  2. M. A. Foster, A. C. Turner, M. Lipson, and A. L. Gaeta, “Nonlinear optics in photonic nanowires,” Opt. Express16(2), 1300–1320 (2008). [CrossRef] [PubMed]
  3. E. C. Mägi, P. Steinvurzel, and B. J. Eggleton, “Tapered photonic crystal fibers,” Opt. Express12(5), 776–784 (2004). [CrossRef] [PubMed]
  4. Y. K. Lizé, E. C. Mägi, V. G. Ta’eed, J. A. Bolger, P. Steinvurzel, and B. J. Eggleton, “Microstructured optical fiber photonic wires with subwavelength core diameter,” Opt. Express12(14), 3209–3217 (2004). [CrossRef] [PubMed]
  5. R. R. Gattass, G. T. Svacha, L. M. Tong, and E. Mazur, “Supercontinuum generation in submicrometer diameter silica fibers,” Opt. Express14(20), 9408–9414 (2006). [CrossRef] [PubMed]
  6. S. G. Leon-Saval, T. A. Birks, W. J. Wadsworth, P. St. J. Russell, and M. W. Mason, “Supercontinuum generation in submicron fibre waveguides,” Opt. Express12(13), 2864–2869 (2004). [CrossRef] [PubMed]
  7. L. F. Mollenauer, R. H. Stolen, and J. P. Gordon, “Experimental observation of picosecond pulse narrowing and solitons in optical fibers,” Phys. Rev. Lett.45(13), 1095–1098 (1980). [CrossRef]
  8. L. F. Mollenauer, R. H. Stolen, J. P. Gordon, and W. J. Tomlinson, “Extreme picosecond pulse narrowing by means of soliton effect in single-mode optical fibers,” Opt. Lett.8(5), 289–291 (1983). [CrossRef] [PubMed]
  9. C. M. Chen and P. L. Kelley, “Nonlinear pulse compression in optical fibers: scaling laws and numerical analysis,” J. Opt. Soc. Am. B19(9), 1961–1967 (2002). [CrossRef]
  10. M. Foster, A. L. Gaeta, Q. Cao, and R. Trebino, “Soliton-effect compression of supercontinuum to few-cycle durations in photonic nanowires,” Opt. Express13(18), 6848–6855 (2005). [CrossRef] [PubMed]
  11. J. M. Harbold, F. O. Ilday, F. W. Wise, J. S. Sanghera, V. Q. Nguyen, L. B. Shaw, and I. D. Aggarwal, “Highly nonlinear As-S-Se glasses for all-optical switching,” Opt. Lett.27(2), 119–121 (2002). [CrossRef] [PubMed]
  12. D. I. Yeom, E. C. Mägi, M. R. E. Lamont, M. A. F. Roelens, L. Fu, and B. J. Eggleton, “Low-threshold supercontinuum generation in highly nonlinear chalcogenide nanowires,” Opt. Lett.33(7), 660–662 (2008). [CrossRef] [PubMed]
  13. D. D. Hudson, S. A. Dekker, E. C. Mägi, A. C. Judge, S. D. Jackson, E. Li, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Octave spanning supercontinuum in an As2S3 taper using ultralow pump pulse energy,” Opt. Lett.36(7), 1122–1124 (2011). [CrossRef] [PubMed]
  14. L. Tong, J. Lou, and E. Mazur, “Single-mode guiding properties of subwavelength-diameter silica and silicon wire waveguides,” Opt. Express12(6), 1025–1035 (2004). [CrossRef] [PubMed]
  15. M. Zghal and R. Cherif, “Impact of small geometrical imperfections on chromatic dispersion and birefringence in photonic crystal fibers,” Opt. Eng.46(12), 128002 (2007). [CrossRef]
  16. M. A. Foster, K. D. Moll, and A. L. Gaeta, “Optimal waveguide dimensions for nonlinear interactions,” Opt. Express12(13), 2880–2887 (2004). [CrossRef] [PubMed]
  17. T. Brabec and F. Krausz, “Nonlinear optical pulse propagation in the single-cycle regime,” Phys. Rev. Lett.78(17), 3282–3285 (1997). [CrossRef]
  18. G. P. Agrawal, Nonlinear Fiber Optics, 4th ed. (Academic Press, 2007).
  19. K. J. Blow and D. Wood, “Theoretical description of transient stimulated Raman scattering in optical fibers,” IEEE J. Quantum Electron.25(12), 2665–2673 (1989). [CrossRef]
  20. R. Cherif, A. Ben-Salem, M. Zghal, P. Besnard, T. Chartier, L. Brilland, and J. Troles, “Highly nonlinear As2Se3-based chalcogenide photonic crystal fiber for midinfrared supercontinuum generation,” Opt. Eng.49(9), 095002 (2010). [CrossRef]
  21. R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B21(6), 1146–1155 (2004). [CrossRef]
  22. A. Ben-Salem, R. Cherif, and M. Zghal, “Raman response of a highly nonlinear As2Se3-based chalcogenide photonic crystal fiber,” Proc. PIERS, 1256–1260, Marrakesh, Morocco (2011).
  23. C. Xiong, E. Magi, F. Luan, A. Tuniz, S. Dekker, J. S. Sanghera, L. B. Shaw, I. D. Aggarwal, and B. J. Eggleton, “Characterization of picosecond pulse nonlinear propagation in chalcogenide As2S3 fiber,” Appl. Opt.48(29), 5467–5474 (2009). [CrossRef] [PubMed]
  24. A. Ben Salem, R. Cherif, and M. Zghal, “Generation of few optical cycles in air-silica nanowires,” Proc. SPIE8001, 80011J (2011). [CrossRef]
  25. M. Bass, Handbook of Optics (McGraw Hill, 1997).
  26. D.-P. Wei, T. Galstian, I. Smolnikov, V. Plotnichenko, and A. Zohrabyan, “Spectral broadening of femtosecond pulses in a single-mode As-S glass fiber,” Opt. Express13(7), 2439–2443 (2005). [CrossRef] [PubMed]
  27. B. Kibler, R. Fischer, P.-A. Lacourt, F. Courvoisier, R. Ferriere, L. Larger, D. N. Neshev, and J. M. Dudley, “Optimised one-step compression of femtosecond fibre laser soliton pulses around 1550 nm to below 30 fs in highly nonlinear fibre,” Electron. Lett.43(17), 915–916 (2007). [CrossRef]
  28. G. Brambilla, “Optical fibre nanotaper sensors,” Opt. Fiber Technol.16(6), 331–342 (2010). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited