Ultraflat, broadband, and highly coherent supercontinuum generation in all-solid microstructured optical fibers with all-normal dispersion
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摘要
High flatness, wide bandwidth, and high-coherence properties of supercontinuum(SC) generation in fibers are crucial in many applications. It is challenging to achieve SC spectra in a combination of the properties, since special dispersion profiles are required, especially when pump pulses with duration over 100 fs are employed. We propose an all-solid microstructured fiber composed only of hexagonal glass elements. The optimized fiber possesses an ultraflat all-normal dispersion profile, covering a wide wavelength interval of approximately 1.55 μm. An SC spectrum spanning from approximately 1030 to 2030 nm(corresponding to nearly one octave) with flatness<3 dB is numerically generated in the fiber with 200 fs pump pulses at 1.55 μm. The results indicate that the broadband ultraflat SC sources can be all-fiber and miniaturized due to commercially achievable 200-fs fiber lasers. Moreover, the SC pulses feature high coherence and a single pulse in the time domain, which can be compressed to 13.9-fs pulses with high quality even for simple linear chirp compensation. The Fourier-limited pulse duration of the spectrum is 3.19 fs, corresponding to only 0.62 optical cycles.
High flatness, wide bandwidth, and high-coherence properties of supercontinuum(SC) generation in fibers are crucial in many applications. It is challenging to achieve SC spectra in a combination of the properties, since special dispersion profiles are required, especially when pump pulses with duration over 100 fs are employed. We propose an all-solid microstructured fiber composed only of hexagonal glass elements. The optimized fiber possesses an ultraflat all-normal dispersion profile, covering a wide wavelength interval of approximately 1.55 μm. An SC spectrum spanning from approximately 1030 to 2030 nm(corresponding to nearly one octave) with flatness<3 dB is numerically generated in the fiber with 200 fs pump pulses at 1.55 μm. The results indicate that the broadband ultraflat SC sources can be all-fiber and miniaturized due to commercially achievable 200-fs fiber lasers. Moreover, the SC pulses feature high coherence and a single pulse in the time domain, which can be compressed to 13.9-fs pulses with high quality even for simple linear chirp compensation. The Fourier-limited pulse duration of the spectrum is 3.19 fs, corresponding to only 0.62 optical cycles.
High flatness, wide bandwidth, and high-coherence properties of supercontinuum(SC) generation in fibers are crucial in many applications. It is challenging to achieve SC spectra in a combination of the properties, since special dispersion profiles are required, especially when pump pulses with duration over 100 fs are employed. We propose an all-solid microstructured fiber composed only of hexagonal glass elements. The optimized fiber possesses an ultraflat all-normal dispersion profile, covering a wide wavelength interval of approximately 1.55 μm. An SC spectrum spanning from approximately 1030 to 2030 nm(corresponding to nearly one octave) with flatness<3 dB is numerically generated in the fiber with 200 fs pump pulses at 1.55 μm. The results indicate that the broadband ultraflat SC sources can be all-fiber and miniaturized due to commercially achievable 200-fs fiber lasers. Moreover, the SC pulses feature high coherence and a single pulse in the time domain, which can be compressed to 13.9-fs pulses with high quality even for simple linear chirp compensation. The Fourier-limited pulse duration of the spectrum is 3.19 fs, corresponding to only 0.62 optical cycles.
引文
1.J.M.Dudley,G.Genty,and S.Coen,“Supercontinuum generation in photonic crystal fiber,”Rev.Mod.Phys.78,1135-1184(2006).
2.M.Tsuzuki,L.Jin,M.Yamanaka,V.Sonnenchein,H.Tomita,A.Sato,T.Ohara,Y.Sakakibara,E.Omoda,H.Kataura,T.Iguchi,and N.Nishizawa,“Midinfrared optical frequency comb based on difference frequency generation using high repetition rate Er-doped fiber laser with single wall carbon nanotube film,”Photon.Res.4,313-317(2016).
3.M.Klimczak,B.Siwicki,A.Heidt,and R.Buczynski,“Coherent supercontinuum generation in soft glass photonic crystal fibers,”Photon.Res.5,710-727(2017).
4.A.M.Heidt,J.S.Feehan,J.H.V.Price,and T.Feurer,“Limits of coherent supercontinuum generation in normal dispersion fibers,”J.Opt.Soc.Am.B 34,764-775(2017).
5.X.Liu,J.Laegsgaard,R.Iegorov,A.S.Svane,F.O.Ilday,H.Tu,S.A.Boppart,and D.Turchinovich,“Nonlinearity-tailored fiber laser technology for low-noise,ultra-wideband tunable femtosecond ligh generation,”Photon.Res.5,750-761(2017).
6.Z.Zheng,D.Ouyang,J.Zhao,M.Liu,S.Ruan,P.Yan,and J.Wang“Scaling all-fiber mid-infrared supercontinuum up to 10 W-level based on thermal-spliced silica fiber and zblan fiber,”Photon.Res.4135-139(2016).
7.S.Vyas,T.Tanabe,M.Tiwari,and G.Singh,“Chalcogenide photonic crystal fiber for ultraflat mid-infrared supercontinuum generation,”Chin.Opt.Lett.14,123201(2016).
8.B.B.Yan,J.H.Yuan,X.X.Sang,K.R.Wang,and C.X.Yu“Combined nonlinear effects for UV to visible wavelength generation in a photonic crystal fiber,”Chin.Opt.Lett.14,050603(2016).
9.J.C.Knight,“Photonic crystal fibres,”Nature 424,847-851(2003).
10.P.St.J.Russell,“Photonic crystal fibers,”Science 299,358-362(2003).
11.J.C.Knight,T.A.Birks,P.St.J.Russell,and D.M.Atkin,“All-silica single-mode optical fiber with photonic crystal cladding,”Opt.Lett.211547-1549(1996).
12.M.Chemnitz,J.Wei,C.Jain,B.P.Rodrigues,T.Wieduwilt,JKobelke,L.Wondraczek,and M.A.Schmidt,“Octave-spanning supercontinuum generation in hybrid silver metaphosphate/silica step-index fibers,”Opt.Lett.41,3519-3522(2016).
13.M.Liu,B.Zhao,X.Yang,and J.Hou,“Seven-core photonic liquid crystal fibers for simultaneous mode shaping and temperature sensing,”Chin.Opt.Lett.15,060601(2017).
14.P.S.Maji and R.Das,“Designing broadband fiber optic parametric amplifier based on near-zero single ZDW PCF with ultra-flat nature,”Chin.Opt.Lett.15,070606(2017).
15.N.Nishizawa and J.Takayanagi,“Octave spanning high-quality supercontinuum generation in all-fiber system,”J.Opt.Soc.Am.B24,1786-1792(2007).
16.C.Strutynski,P.Froidevaux,F.Desevedavy,J.C.Jules,G.Gadret A.Bendahmane,K.Tarnowski,B.Kibler,and F.Smektala,“Tailoring supercontinuum generation beyond 2μm in step-index tellurite fibers,”Opt.Lett.42,247-250(2017).
17.Z.K.Dong,Y.R.Song,R.Q.Xu,Y.Zheng,J.R.Tian,and K.X.Li“Broadband spectrum generation with compact Yb-doped fiber laser by intra-cavity cascaded Raman scattering,”Chin.Opt.Lett.15071408(2017).
18.A.V.Husakou and J.Herrmann,“Supercontinuum generation o higher-order solitons by fission in photonic crystal fibers,”Phys Rev.Lett.87,203901(2001).
19.A.M.Heidt,“Pulse preserving flat-top supercontinuum generation in all-normal dispersion photonic crystal fibers,”J.Opt.Soc.Am.B 27550-559(2010).
20.S.Demmler,J.Rothhardt,A.M.Heidt,A.Hartung,E.G.Rohwer,HBartelt,J.Limpert,and A.Tunnermann,“Generation of high quality1.3 cycle pulses by active phase control of an octave spanning supercontinuum,”Opt.Express 19,20151-20158(2011).
21.A.Hartung,A.M.Heidt,and H.Bartelt,“Design of all-norma dispersion microstructured optical fibers for pulse-preserving supercontinuum generation,”Opt.Express 19,7742-7749(2011).
22.A.M.Heidt,A.Hartung,G.W.Bosman,P.Krok,E.G.Rohwer,HSchwoerer,and H.Bartelt,“Coherent octave spanning near-infrared and visible supercontinuum generation in all-normal dispersion photonic crystal fibers,”Opt.Express 19,3775-3787(2011).
23.L.Liu,T.L.Cheng,K.Nagasaka,H.T.Tong,G.S.Qin,T.Suzuki,and Y.Ohishi,“Coherent mid-infrared supercontinuum generation in allsolid chalcogenide microstructured fibers with all-normal dispersion,”Opt.Lett.41,392-395(2016).
24.A.M.Heidt,J.Rothhardt,A.Hartung,H.Bartelt,E.G.Rohwer,JLimpert,and A.Tunnermann,“High quality sub-two cycle pulses from compression of supercontinuum generated in all-normal dispersion photonic crystal fiber,”Opt.Express 19,13873-13879(2011).
25.C.L.Huang,M.S.Liao,W.J.Bi,X.Li,L.F.Wang,T.F.Xue,LZhang,D.P.Chen,L.L.Hu,Y.Z.Fang,and W.Q.Gao“Asterisk-shaped microstructured fiber for an octave coherent supercontinuum in a sub-picosecond region,”Opt.Lett.43,486-489(2018)
26.Y.Liu,Y.B.Zhao,J.Lyngso,S.X.You,W.L.Wilson,H.H.Tu,and S.A.Boppart,“Suppressing short-term polarization noise and related spectral decoherence in all-normal dispersion fiber supercontinuum generation,”J.Lightwave Technol.33,1814-1820(2015).
27.J.J.Miret,E.Silvestre,and P.Andres,“Octave-spanning ultraflat supercontinuum with soft-glass photonic crystal fibers,”Opt.Express 17,9197-9203(2009).
28.I.A.Sukhoivanov,S.O.Iakushev,O.V.Shulika,E.Silvestre,and M.V.Andres,“Design of all-normal dispersion microstructured optical fiber on silica platform for generation of pulse-preserving supercontinuum under excitation at 1550 nm,”J.Lightwave Technol.35,3772-3779(2017).
29.S.K.Chatterjee,S.N.Khan,and P.R.Chaudhuri,“Designing a twooctave spanning flat-top supercontinuum source by control of nonlinear dynamics through multi-order dispersion engineering in binary multi-clad microstructured fiber,”J.Opt.Soc.Am.B 32,1499-1509(2015).
30.M.Diouf,A.Ben Salem,R.Cherif,H.Saghaei,and A.Wague,“Superflat coherent supercontinuum source in As38.8Se61.2chalcogenide photonic crystal fiber with all-normal dispersion engineering at a very low input energy,”Appl.Opt.56,163-169(2017).
31.T.Martynkien,D.Pysz,R.Stepien,and R.Buczynski,“All-solid microstructured fiber with flat normal chromatic dispersion,”Opt.Lett.39,2342-2345(2014).
32.M.Klimczak,B.Siwicki,P.Skibinski,D.Pysz,R.Stepien,A.Heidt,C.Radzewicz,and R.Buczynski,“Coherent supercontinuum generation up to 2.3μm in all-solid soft-glass photonic crystal fibers with flat all-normal dispersion,”Opt.Express 22,18824-18832(2014).
33.K.Tarnowski,T.Martynkien,P.Mergo,K.Poturaj,A.Anuszkiewicz,P.Bejot,F.Billard,O.Faucher,B.Kibler,and W.Urbanczyk,“Polarized all-normal dispersion supercontinuum reaching 2.5μm generated in a birefringent microstructured silica fiber,”Opt.Express 25,27452-27463(2017).
34.K.Tarnowski,T.Martynkien,P.Mergo,K.Poturaj,G.Sobon,and W.Urbanczyk,“Coherent supercontinuum generation up to 2.2μm in an all-normal dispersion microstructured silica fiber,”Opt.Express 24,30523-30536(2016).
35.F.Li,Q.Li,J.H.Yuan,and P.K.A.Wai,“Highly coherent supercontinuum generation with picosecond pulses by using self-similar compression,”Opt.Express 22,27339-27354(2014).
36.G.P.Agrawal,Nonlinear Fiber Optics(Academic,2007).
37.N.L.Boling,A.J.Glass,and A.Owyoung,“Empirical relationships for predicting non-linear refractive-index changes in optical solids,”IEEEJ.Quantum Electron.14,601-608(1978).
38.M.Feng,A.K.Mairaj,D.W.Hewak,and T.M.Monro,“Nonsilica glasses for holey fibers,”J.Lightwave Technol.23,2046-2054(2005).
39.O.Humbach,H.Fabian,U.Grzesik,U.Haken,and W.Heitmann,“Analysis of OH absorption bands in synthetic silica,”J.Non-Cryst.Solids 203,19-26(1996).
40.V.L.Kalashnikov,E.Sorokin,and I.T.Sorokina,“Raman effects in the infrared supercontinuum generation in soft-glass PCFs,”Appl.Phys.B 87,37-44(2007).
41.C.Finot,B.Kibler,L.Provost,and S.Wabnitz,“Beneficial impact of wave-breaking for coherent continuum formation in normally dispersive nonlinear fibers,”J.Opt.Soc.Am.B 25,1938-1948(2008).
42.A.M.Heidt,A.Hartung,and H.Bartelt,“Generation of ultrashort and coherent supercontinuum light pulses in all-normal dispersion fibers,”in The Supercontinuum Laser Source,R.R.Alfano,ed.(Springer,2016),pp.247-280.
43.M.H.Frosz,“Validation of input-noise model for simulations of supercontinuum generation and rogue waves,”Opt.Express 18,14778-14787(2010).
44.F.Krausz and M.Ivanov,“Attosecond physics,”Rev.Mod.Phys.81,163-234(2009).
45.M.Miranda,T.Fordell,C.Arnold,A.L’Huillier,and H.Crespo,“Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges,”Opt.Express 20,688-697(2012).
46.Y.Liu,H.Tu,and S.A.Boppart,“Wave-breaking-extended fiber supercontinuum generation for high compression ratio transformlimited pulse compression,”Opt.Lett.37,2172-2174(2012).
2.M.Tsuzuki,L.Jin,M.Yamanaka,V.Sonnenchein,H.Tomita,A.Sato,T.Ohara,Y.Sakakibara,E.Omoda,H.Kataura,T.Iguchi,and N.Nishizawa,“Midinfrared optical frequency comb based on difference frequency generation using high repetition rate Er-doped fiber laser with single wall carbon nanotube film,”Photon.Res.4,313-317(2016).
3.M.Klimczak,B.Siwicki,A.Heidt,and R.Buczynski,“Coherent supercontinuum generation in soft glass photonic crystal fibers,”Photon.Res.5,710-727(2017).
4.A.M.Heidt,J.S.Feehan,J.H.V.Price,and T.Feurer,“Limits of coherent supercontinuum generation in normal dispersion fibers,”J.Opt.Soc.Am.B 34,764-775(2017).
5.X.Liu,J.Laegsgaard,R.Iegorov,A.S.Svane,F.O.Ilday,H.Tu,S.A.Boppart,and D.Turchinovich,“Nonlinearity-tailored fiber laser technology for low-noise,ultra-wideband tunable femtosecond ligh generation,”Photon.Res.5,750-761(2017).
6.Z.Zheng,D.Ouyang,J.Zhao,M.Liu,S.Ruan,P.Yan,and J.Wang“Scaling all-fiber mid-infrared supercontinuum up to 10 W-level based on thermal-spliced silica fiber and zblan fiber,”Photon.Res.4135-139(2016).
7.S.Vyas,T.Tanabe,M.Tiwari,and G.Singh,“Chalcogenide photonic crystal fiber for ultraflat mid-infrared supercontinuum generation,”Chin.Opt.Lett.14,123201(2016).
8.B.B.Yan,J.H.Yuan,X.X.Sang,K.R.Wang,and C.X.Yu“Combined nonlinear effects for UV to visible wavelength generation in a photonic crystal fiber,”Chin.Opt.Lett.14,050603(2016).
9.J.C.Knight,“Photonic crystal fibres,”Nature 424,847-851(2003).
10.P.St.J.Russell,“Photonic crystal fibers,”Science 299,358-362(2003).
11.J.C.Knight,T.A.Birks,P.St.J.Russell,and D.M.Atkin,“All-silica single-mode optical fiber with photonic crystal cladding,”Opt.Lett.211547-1549(1996).
12.M.Chemnitz,J.Wei,C.Jain,B.P.Rodrigues,T.Wieduwilt,JKobelke,L.Wondraczek,and M.A.Schmidt,“Octave-spanning supercontinuum generation in hybrid silver metaphosphate/silica step-index fibers,”Opt.Lett.41,3519-3522(2016).
13.M.Liu,B.Zhao,X.Yang,and J.Hou,“Seven-core photonic liquid crystal fibers for simultaneous mode shaping and temperature sensing,”Chin.Opt.Lett.15,060601(2017).
14.P.S.Maji and R.Das,“Designing broadband fiber optic parametric amplifier based on near-zero single ZDW PCF with ultra-flat nature,”Chin.Opt.Lett.15,070606(2017).
15.N.Nishizawa and J.Takayanagi,“Octave spanning high-quality supercontinuum generation in all-fiber system,”J.Opt.Soc.Am.B24,1786-1792(2007).
16.C.Strutynski,P.Froidevaux,F.Desevedavy,J.C.Jules,G.Gadret A.Bendahmane,K.Tarnowski,B.Kibler,and F.Smektala,“Tailoring supercontinuum generation beyond 2μm in step-index tellurite fibers,”Opt.Lett.42,247-250(2017).
17.Z.K.Dong,Y.R.Song,R.Q.Xu,Y.Zheng,J.R.Tian,and K.X.Li“Broadband spectrum generation with compact Yb-doped fiber laser by intra-cavity cascaded Raman scattering,”Chin.Opt.Lett.15071408(2017).
18.A.V.Husakou and J.Herrmann,“Supercontinuum generation o higher-order solitons by fission in photonic crystal fibers,”Phys Rev.Lett.87,203901(2001).
19.A.M.Heidt,“Pulse preserving flat-top supercontinuum generation in all-normal dispersion photonic crystal fibers,”J.Opt.Soc.Am.B 27550-559(2010).
20.S.Demmler,J.Rothhardt,A.M.Heidt,A.Hartung,E.G.Rohwer,HBartelt,J.Limpert,and A.Tunnermann,“Generation of high quality1.3 cycle pulses by active phase control of an octave spanning supercontinuum,”Opt.Express 19,20151-20158(2011).
21.A.Hartung,A.M.Heidt,and H.Bartelt,“Design of all-norma dispersion microstructured optical fibers for pulse-preserving supercontinuum generation,”Opt.Express 19,7742-7749(2011).
22.A.M.Heidt,A.Hartung,G.W.Bosman,P.Krok,E.G.Rohwer,HSchwoerer,and H.Bartelt,“Coherent octave spanning near-infrared and visible supercontinuum generation in all-normal dispersion photonic crystal fibers,”Opt.Express 19,3775-3787(2011).
23.L.Liu,T.L.Cheng,K.Nagasaka,H.T.Tong,G.S.Qin,T.Suzuki,and Y.Ohishi,“Coherent mid-infrared supercontinuum generation in allsolid chalcogenide microstructured fibers with all-normal dispersion,”Opt.Lett.41,392-395(2016).
24.A.M.Heidt,J.Rothhardt,A.Hartung,H.Bartelt,E.G.Rohwer,JLimpert,and A.Tunnermann,“High quality sub-two cycle pulses from compression of supercontinuum generated in all-normal dispersion photonic crystal fiber,”Opt.Express 19,13873-13879(2011).
25.C.L.Huang,M.S.Liao,W.J.Bi,X.Li,L.F.Wang,T.F.Xue,LZhang,D.P.Chen,L.L.Hu,Y.Z.Fang,and W.Q.Gao“Asterisk-shaped microstructured fiber for an octave coherent supercontinuum in a sub-picosecond region,”Opt.Lett.43,486-489(2018)
26.Y.Liu,Y.B.Zhao,J.Lyngso,S.X.You,W.L.Wilson,H.H.Tu,and S.A.Boppart,“Suppressing short-term polarization noise and related spectral decoherence in all-normal dispersion fiber supercontinuum generation,”J.Lightwave Technol.33,1814-1820(2015).
27.J.J.Miret,E.Silvestre,and P.Andres,“Octave-spanning ultraflat supercontinuum with soft-glass photonic crystal fibers,”Opt.Express 17,9197-9203(2009).
28.I.A.Sukhoivanov,S.O.Iakushev,O.V.Shulika,E.Silvestre,and M.V.Andres,“Design of all-normal dispersion microstructured optical fiber on silica platform for generation of pulse-preserving supercontinuum under excitation at 1550 nm,”J.Lightwave Technol.35,3772-3779(2017).
29.S.K.Chatterjee,S.N.Khan,and P.R.Chaudhuri,“Designing a twooctave spanning flat-top supercontinuum source by control of nonlinear dynamics through multi-order dispersion engineering in binary multi-clad microstructured fiber,”J.Opt.Soc.Am.B 32,1499-1509(2015).
30.M.Diouf,A.Ben Salem,R.Cherif,H.Saghaei,and A.Wague,“Superflat coherent supercontinuum source in As38.8Se61.2chalcogenide photonic crystal fiber with all-normal dispersion engineering at a very low input energy,”Appl.Opt.56,163-169(2017).
31.T.Martynkien,D.Pysz,R.Stepien,and R.Buczynski,“All-solid microstructured fiber with flat normal chromatic dispersion,”Opt.Lett.39,2342-2345(2014).
32.M.Klimczak,B.Siwicki,P.Skibinski,D.Pysz,R.Stepien,A.Heidt,C.Radzewicz,and R.Buczynski,“Coherent supercontinuum generation up to 2.3μm in all-solid soft-glass photonic crystal fibers with flat all-normal dispersion,”Opt.Express 22,18824-18832(2014).
33.K.Tarnowski,T.Martynkien,P.Mergo,K.Poturaj,A.Anuszkiewicz,P.Bejot,F.Billard,O.Faucher,B.Kibler,and W.Urbanczyk,“Polarized all-normal dispersion supercontinuum reaching 2.5μm generated in a birefringent microstructured silica fiber,”Opt.Express 25,27452-27463(2017).
34.K.Tarnowski,T.Martynkien,P.Mergo,K.Poturaj,G.Sobon,and W.Urbanczyk,“Coherent supercontinuum generation up to 2.2μm in an all-normal dispersion microstructured silica fiber,”Opt.Express 24,30523-30536(2016).
35.F.Li,Q.Li,J.H.Yuan,and P.K.A.Wai,“Highly coherent supercontinuum generation with picosecond pulses by using self-similar compression,”Opt.Express 22,27339-27354(2014).
36.G.P.Agrawal,Nonlinear Fiber Optics(Academic,2007).
37.N.L.Boling,A.J.Glass,and A.Owyoung,“Empirical relationships for predicting non-linear refractive-index changes in optical solids,”IEEEJ.Quantum Electron.14,601-608(1978).
38.M.Feng,A.K.Mairaj,D.W.Hewak,and T.M.Monro,“Nonsilica glasses for holey fibers,”J.Lightwave Technol.23,2046-2054(2005).
39.O.Humbach,H.Fabian,U.Grzesik,U.Haken,and W.Heitmann,“Analysis of OH absorption bands in synthetic silica,”J.Non-Cryst.Solids 203,19-26(1996).
40.V.L.Kalashnikov,E.Sorokin,and I.T.Sorokina,“Raman effects in the infrared supercontinuum generation in soft-glass PCFs,”Appl.Phys.B 87,37-44(2007).
41.C.Finot,B.Kibler,L.Provost,and S.Wabnitz,“Beneficial impact of wave-breaking for coherent continuum formation in normally dispersive nonlinear fibers,”J.Opt.Soc.Am.B 25,1938-1948(2008).
42.A.M.Heidt,A.Hartung,and H.Bartelt,“Generation of ultrashort and coherent supercontinuum light pulses in all-normal dispersion fibers,”in The Supercontinuum Laser Source,R.R.Alfano,ed.(Springer,2016),pp.247-280.
43.M.H.Frosz,“Validation of input-noise model for simulations of supercontinuum generation and rogue waves,”Opt.Express 18,14778-14787(2010).
44.F.Krausz and M.Ivanov,“Attosecond physics,”Rev.Mod.Phys.81,163-234(2009).
45.M.Miranda,T.Fordell,C.Arnold,A.L’Huillier,and H.Crespo,“Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges,”Opt.Express 20,688-697(2012).
46.Y.Liu,H.Tu,and S.A.Boppart,“Wave-breaking-extended fiber supercontinuum generation for high compression ratio transformlimited pulse compression,”Opt.Lett.37,2172-2174(2012).