Type-I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasers (original) (raw)
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Applied Physics Letters, 2004
We study cascaded quadratic soliton compressors and address the physical mechanisms that limit the compression. A nonlocal model is derived, and the nonlocal response is shown to have an additional oscillatory component in the nonstationary regime when the group-velocity mismatch (GVM) is strong. This inhibits efficient compression. Raman-like perturbations from the cascaded nonlinearity, competing cubic nonlinearities, higher-order dispersion, and soliton energy may also limit compression, and through realistic numerical simulations we point out when each factor becomes important. We find that it is theoretically possible to reach the single-cycle regime by compressing high-energy fs pulses for wavelengths λ = 1.0 − 1.3 µm in a β-barium-borate crystal, and it requires that the system is in the stationary regime, where the phase mismatch is large enough to overcome the detrimental GVM effects. However, the simulations show that reaching single-cycle duration is ultimately inhibited by competing cubic nonlinearities as well as dispersive waves, that only show up when taking higher-order dispersion into account.
Optics Letters, 1997
We demonstrate the use of an aperiodic quasi-phase-matching (QPM) grating to generate second-harmonic pulses that are stretched or compressed relative to input pulses at the fundamental frequency. We frequency doubled an externally chirped erbium-doped fiber laser generating 17-ps (FWHM) pulses at 1560 nm to produce near-transform-limited 110-fs (FWHM) pulses at 780 nm by use of a 5-cm-long lithium niobate crystal poled with a QPM grating chirped from an 18.2-to a 19.8-mm period.
3D-soliton waveguides in lithium niobate for femtosecond light pulses
Journal of Optics A: Pure and Applied Optics, 2006
We show that efficient waveguides can be written by bright spatial solitons in the volume of lithium niobate photorefractive crystals by cw and pulsed laser beams. Using high-repetition-rate femtosecond laser pulses, an efficient formation of soliton waveguides (SWGs) is possible, after accumulating a large number of pulses, because the characteristic photorefractive build-up time is much longer than the pulse period and the efficient two-photon absorption may contribute to the solitonic confinement. These results open the possibility of writing reconfigurable single SWGs and SWG arrays (with any spatial orientation and large range of periods) and optimally guiding the femtosecond pulsed laser beams through them, creating a graded refractive-index profile matched to the spatial beam profile. Our experiments also show a small increase in pulse duration (small dispersion) in these waveguides.
Laser induced soliton waveguides in lithium niobate crystals for guiding femtosecond light pulses
We show that efficient waveguides can be written by bright spatial solitons in lithium niobate photorefractive crystals by c.w. and pulsed laser beams. Using high repetition rate femtosecond laser pulses, an efficient formation of soliton waveguides is possible, after accumulating a large number of pulses, because the photo-excited carrier relaxation time is much longer than the pulse period. These results open the possibility of optimum waveguiding the femtosecond pulsed laser beams, the soliton waveguides creating a graded refractive index profile matched to the spatial beam profile. Our experiments show also very low pulse dispersion in these waveguides.
Frequency doubling of femtosecond erbium-fiber soliton lasers in periodically poled lithium niobate
Optics Letters, 1997
We report efficient frequency doubling of passively mode-locked femtosecond erbium-fiber lasers. Quasiphase-matched second-harmonic generation in periodically poled lithium niobate is used to generate 8.1 mW of 190-fs (FWHM), 90-pJ pulses at 777 nm with a conversion efficiency greater than can be obtained with existing birefringently phase-matched nonlinear materials. A dispersion-compensation-free soliton oscillator generating transform-limited 230-fs (FWHM) pulses at 1554 nm is used as a pump laser.
Formation and interaction of few-cycle solitons in a lithium niobate ridge waveguide are numerically investigated. The solitons are created through a cascaded phase-mismatched second-harmonic generation process, which induces a dominant self-defocusing Kerr-like nonlinearity on the pump pulse. The inherent material self-focusing Kerr nonlinearity is overcome over a wide wavelength range, and self-defocusing solitons are supported from 1100 to 1900 nm, covering the whole communication band. Single cycle self-compressed solitons and supercontinuum generation spanning 1.3 octaves are observed when pumped with femtosecond nanojoule pulses at 1550 nm. The waveguide is not periodically poled, as quasi-phase-matching would lead to detrimental nonlinear effects impeding few-cycle soliton formation.
Scaling laws for soliton pulse compression by cascaded quadratic nonlinearities
Journal of The Optical Society of America, 2007
We present a detailed study of soliton compression of ultra-short pulses based on phase-mismatched second-harmonic generation (\textit{i.e.}, the cascaded quadratic nonlinearity) in bulk quadratic nonlinear media. The single-cycle propagation equations in the temporal domain including higher-order nonlinear terms are presented. The balance between the quadratic (SHG) and the cubic (Kerr) nonlinearity plays a crucial role: we define an effective soliton number -- related to the difference between the SHG and the Kerr soliton numbers -- and show that it has to be larger than unity for successful pulse compression to take place. This requires that the phase mismatch be below a critical level, which is high in a material where the quadratic nonlinearity dominates over the cubic Kerr nonlinearity. Through extensive numerical simulations we find dimensionless scaling laws, expressed through the effective soliton number, which control the behaviour of the compressed pulses. These laws hold in the stationary regime, in which group-velocity mismatch effects are small, and they are similar to the ones observed for fiber soliton compressors. The numerical simulations indicate that clean compressed pulses below two optical cycles can be achieved in a beta\betabeta-barium borate crystal at appropriate wavelengths, even for picosecond input pulses.
Scaling laws for soliton pulse compression by cascaded quadratic nonlinearities: erratum
Journal of the Optical Society of America B, 2010
We present a detailed study of soliton compression of ultrashort pulses based on phase-mismatched secondharmonic generation (SHG) (i.e., the cascaded quadratic nonlinearity) in bulk quadratic nonlinear media. The single-cycle propagation equations in the temporal domain including higher-order nonlinear terms are presented. The balance between the quadratic (SHG) and the cubic (Kerr) nonlinearity plays a crucial role; we define an effective soliton number-related to the difference between the SHG and the Kerr soliton numbersand show that it has to be larger than unity for successful pulse compression to take place. This requires that the phase mismatch be below a critical level, which is high in a material where the quadratic nonlinearity dominates over the cubic Kerr nonlinearity. Through extensive numerical simulations we find dimensionless scaling laws, expressed through the effective soliton number, that control the behavior of the compressed pulses. These laws hold in the stationary regime, in which group-velocity mismatch effects are small, and they are similar to the ones observed for fiber soliton compressors. The numerical simulations indicate that clean compressed pulses below two optical cycles can be achieved in a -barium borate crystal at appropriate wavelengths, even for picosecond input pulses.
Optics Express, 2014
We numerically investigate self-defocusing solitons in a lithium niobate (LN) waveguide designed to have a large refractive index (RI) change. The waveguide evokes strong waveguide dispersion and all-normal dispersion is found in the entire guiding band spanning the near-IR and the beginning of the mid-IR. Meanwhile, a self-defocusing nonlinearity is invoked by the cascaded (phase-mismatched) second-harmonic generation under a quasi-phase-matching pitch. Combining this with the all-normal dispersion, mid-IR solitons can form and the waveguide presents the first all-nonlinear and solitonic device where no linear dispersion (i.e. non-solitonic) regimes exist within the guiding band. Soliton compressions at 2 µm and 3 µm are investigated, with nano-joule single cycle pulse formations and highly coherent octave-spanning supercontinuum generations. With an alternative design on the waveguide dispersion, the soliton spectral tunneling effect is also investigated, with which few-cycle pico-joule pulses at 2 µm are formed by a near-IR pump.
Applied Physics Letters, 2003
We experimentally demonstrate the second harmonic generation (SHG) of infrared femtosecond pulses using a BIBO crystal placed in an external ring cavity, synchronized with an input mode-locked laser at 78 MHz. A frequency doubling efficiency of 53% is achieved which is, to the best of our knowledge, the highest value ever reported for a low energy input beam of 1.4 nJ/pulse. Theoretical analysis of cavity related issues such as design, fundamental mode characteristics and fidelity against misalignments are also presented. The modeling of SHG cavity enables us to estimate the cavity losses and the mode matching visibility. Such synchronized SHG cavities in pulse domain, having higher SHG conversion efficiencies compared to their continuous wave counterparts, may find potential applications in scientific areas such as in photonics, and in quantum optics.