S P Stark

Max-Planck-Institut für die Physik des Lichts, Erlangen, Bavaria, Germany

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Publications (18)37.77 Total impact

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    ABSTRACT: We investigate how suppressed modes in frequency combs are modified upon frequency doubling and self-phase modulation. We find, both experimentally and by using a simplified model, that these side-modes are amplified relative to the principal comb modes. Whereas frequency doubling increases their relative strength by 6 dB, the growth due to self-phase modulation can be much stronger and generally increases with nonlinear propagation length. Upper limits for this effect are derived in this work. This behavior has implications for high-precision calibration of spectrographs with frequency combs used for example in astronomy. For this application, Fabry-P´erot filter cavities are used to increase the mode spacing to exceed the resolution of the spectrograph. Frequency conversion and/or spectral broadening after non-perfect filtering reamplify the suppressed modes, which can lead to calibration errors.
    Optics Express 05/2013; 21(10):11670. · 3.55 Impact Factor
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    ABSTRACT: We report the formation of an ultrabroad supercontinuum down to 280 nm in the deep UV by pumping sharply tapered (5-30 mm taper lengths) solid-core photonic crystal fibers with 130 fs, 2 nJ pulses at 800 nm. The taper moves the point of soliton fission to a position where the core is narrower, a process that requires normal dispersion at the input face of the fiber. We find that the generation of deep-UV radiation is limited by strong two-photon absorption in the silica.
    Optics Letters 03/2012; 37(5):770-2. · 3.39 Impact Factor
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    ABSTRACT: We explore the use of a highly nonlinear chalcogenide-silica waveguide for supercontinuum generation in the near infrared. The structure was fabricated by a pressure-assisted melt-filling of a silica capillary fiber (1.6 µm bore diameter) with Ga4Ge21Sb10S65 glass. It was designed to have zero group velocity dispersion (for HE11 core mode) at 1550 nm. Pumping a 1 cm length with 60 fs pulses from an erbium-doped fiber laser results in the generation of octave-spanning supercontinuum light for pulse energies of only 60 pJ. Good agreement is obtained between the experimental results and theoretical predictions based on numerical solutions of the generalized nonlinear Schrödinger equation. The pressure-assisted melt-filling approach makes it possible to realize highly nonlinear devices with unusual combinations of materials. For example, we show numerically that a 1 cm long As2S3:silica step-index fiber with a core diameter of 1 µm, pumped by 60 fs pulses at 1550 nm, would generate a broadband supercontinuum out to 4 µm.
    Optics Express 10/2011; 19(21):21003-10. · 3.55 Impact Factor
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    ABSTRACT: We report the use of a specially designed tapered photonic crystal fiber to produce a broadband optical spectrum covering the visible spectral range. The pump source is a frequency doubled Yb fiber laser operating at a repetition rate of 14 GHz and emitting sub-5 pJ pulses. We experimentally determine the optimum core diameter and achieve a 235 nm broad spectrum. Numerical simulations are used to identify the underlying mechanisms and explain spectral features. The high repetition rate makes this system a promising candidate for precision calibration of astronomical spectrographs.
    Optics Express 08/2011; 19(17):15690-5. · 3.55 Impact Factor
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    ABSTRACT: A Yb-fiber based frequency comb spanning more than 150 nm with a multi-GHz mode spacing was set up. Dynamic reamplification of suppressed modes in a nonlinear fiber after the filter cavities was observed and analyzed.
    Lasers and Electro-Optics (CLEO), 2011 Conference on; 06/2011
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    ABSTRACT: We show that solitons undergo a strong blueshift in fibers with a dispersion landscape that varies along the direction of propagation. The experiments are based on a small-core photonic crystal fiber, tapered to have a core diameter that varies continuously along its length, resulting in a zero-dispersion wavelength that moves from 731 nm to 640 nm over the transition. The central wavelength of a soliton translates over 400 nm towards a shorter wavelength. This is accompanied by strong emission of radiation into the UV and IR spectral regions. The experimental results are confirmed by numerical simulation.
    Physical Review Letters 02/2011; 106(8):083903. · 7.73 Impact Factor
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    ABSTRACT: We present a review of our recent research on the use of photonic crystal fibers (PCFs) to manipulate the propagation of ultrashort pulses. The combination of a high nonlinear coefficient and unusual wavelength-dependent group-velocity-dispersion "landscapes", together with the ability to taper the properties along the fiber by thermal post-processing, allows observation of many interesting effects. These include generation of THz trains of equidistant sub-50 fs pulses, highly efficient supercontinuum generation from the UV to the IR, soliton collisions and observation for the first time of a soliton blue-shift, counteracting the Raman-related soliton self-frequency shift.
    Proc SPIE 02/2011;
  • S. Stark, P.S.J. Russell
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    ABSTRACT: Pumping a sharply tapered (5-30 mm taper lengths) solid-core photonic crystal fiber with 130 fs, 2 nJ pulses at 800 nm generates an efficient supercontinuum down to a record-breaking 280 nm in the deep-UV.
    Quantum Electronics Conference & Lasers and Electro-Optics (CLEO/IQEC/PACIFIC RIM), 2011; 01/2011
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    ABSTRACT: We show that solitons undergo a strong blue shift in fibers with a dispersion landscape that varies along the direction of propagation. The experiments are based on a small-core photonic crystal fiber, tapered to have a core diameter that varies continuously along its length, resulting in a zero-dispersion wavelength that moves from 731 nm to 640 nm over the transition. The central wavelength of a soliton translates over 400 nm towards shorter wavelength. This accompanied by strong emission of radiation into the UV and IR spectral region. The experimental results are confirmed by numerical simulation. Comment: 10 pages, 4 figures
    12/2010;
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    ABSTRACT: A small core photonic crystal fiber is used to demonstrate spectral-temporal reshaping of 110 fs laser pulses and the synthesis of THz trains of equidistant sub 50 fs pulses. The mechanisms behind this phenomenon are investigated.
    Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
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    ABSTRACT: We demonstrate analytically and numerically that a subwavelength-core dielectric photonic nanowire embedded in a properly designed photonic crystal fiber cladding shows evidence of a previously unknown kind of nonlinearity (the magnitude of which is strongly dependent on the waveguide parameters) which acts on solitons so as to considerably reduce their Raman self-frequency shift. An explanation of the phenomenon in terms of indirect pulse negative chirping and broadening is given by using the moment method. Our conclusions are supported by detailed numerical simulations.
    Physical Review Letters 08/2010; 105(9):093904. · 7.73 Impact Factor
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    ABSTRACT: We theoretically predict the occurrence of multiple hydrodynamical-like shock phenomena in the propagation of ultrashort intense pulses in a suitably engineered photonic crystal fiber. The shocks are due to the Raman effect, which acts as a nonlocal term favoring their generation in the focusing regime. It is shown that the problem is mapped to shock formation in the presence of a slope and a gravity-like potential. The signature of multiple shocks in cross-correlation frequency-resolved optical gating (XFROG) signals is unveiled.
    Physical Review A 07/2010; 82(1). · 3.04 Impact Factor
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    ABSTRACT: We discuss four-wave mixing and resonant radiation in photonic crystal fibers with three zero dispersion wavelengths. We find a complex phase-matching landscape that allows multiple frequencies to be generated by both continuous waves and solitons.
    Nonlinear Photonics; 06/2010
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    ABSTRACT: In this theoretical study, we show that a simple endlessly single-mode photonic crystal fiber can be designed to yield, not just two, but three zero-dispersion wavelengths. The presence of a third dispersion zero creates a rich phase-matching topology, enabling enhanced control over the spectral locations of the four-wave-mixing and resonant-radiation bands emitted by solitons and short pulses. The greatly enhanced flexibility in the positioning of these bands has applications in wavelength conversion, supercontinuum generation and pair-photon sources for quantum optics.
    Physical Review A 06/2010; · 3.04 Impact Factor
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    ABSTRACT: We report extreme self-compression of sub-μJ 30 fs pulses at 800 nm in Ar-filled hollow-core PCF, resulting in 4% conversion to deep UV light in the fundamental guided mode, pressure-tunable from 220-270 nm.
    05/2010;
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    ABSTRACT: We theoretically predict the occurrence of multiple hydrodynamical-like shock phenomena in the propagation of ultrashort intense pulses in a suitably engineered photonic crystal fiber. The shocks are due to the Raman effect, which acts as a nonlocal term favoring their generation in the focusing regime. It is shown that the problem is mapped to shock formation in the presence of a slope and a gravity-like potential. The signature of multiple shocks in XFROG signals is unveiled.
    04/2010;
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    ABSTRACT: We investigate numerically and experimentally the propagation of visible sub-50 fs pulses in a tapered small core photonic crystal fiber. The fiber has anomalous dispersion between two closely spaced zero dispersion wavelengths at 509 and 640 nm, and the excitation wavelength was varied within this range. We find that the spectral evolution in the low power regime is dominated by higher-order soliton fission, soliton self-frequency shift, and dispersive wave generation. At higher powers, extremely wide spectral broadening of the input pulse occurs within the first few millimeters of fiber. The wavelength conversion into the blue and red spectral ranges is studied as a function of the input power and excitation wavelength. Conversions into the spectral range 300–470 nm at efficiencies as high as 40% are observed when pumping at 523 nm.
    Journal of the Optical Society of America B 01/2010; 27(3). · 2.21 Impact Factor
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    ABSTRACT: Here we study propagation of ultrashort laser pulses in tapered PCFs. A PCF with a core diameter of 1.23 mum and high air-filling fraction was tapered to a core diameter of 590 nm using the flame-brush technique. The group-velocity dispersion (GVD) was measured for both untapered and tapered fibers using white-light interferometry. The tapered fiber has two closely-spaced zero dispersion wavelengths (ZDWs) at 509 nm and 640 nm. The laser source was a commercial non-collinear optical parametric amplifier with tuning range 490-700 nm, repetition rate 250 kHz, pulse energy up to 250 nJ and pulse duration 35 fs. The spectral evolution of the laser pulses strongly depends on the phase-matching conditions, and is driven by the position of the ZDWs relative to the pump wavelength, the peak power as well as the magnitude and the slope of the GVD. The conversion efficiency to the blue (450plusmn20 nm) was measured to be more than 10%. As can be seen, up-conversion to the UV is very efficient.
    01/2009;