Low-energy Self-defocusing Soliton Compression at Optical Communication Wavelengths in Unpoled Lithium Niobate Ridge Waveguide (original) (raw)
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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.
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.
Physical Review A, 2010
The output pulses of a commercial high-power femtosecond fiber laser or amplifier are typically around 300-500 fs with a wavelength around 1030 nm and 10s of µJ pulse energy. Here we present a numerical study of cascaded quadratic soliton compression of such pulses in LiNbO3 using a type I phase matching configuration. We find that because of competing cubic material nonlinearities compression can only occur in the nonstationary regime, where group-velocity mismatch induced Raman-like nonlocal effects prevent compression to below 100 fs. However, the strong group velocity dispersion implies that the pulses can achieve moderate compression to sub-130 fs duration in available crystal lengths. Most of the pulse energy is conserved because the compression is moderate. The effects of diffraction and spatial walk-off is addressed, and in particular the latter could become an issue when compressing in such long crystals (around 10 cm long). We finally show that the second harmonic contains a short pulse locked to the pump and a long multi-ps red-shifted detrimental component. The latter is caused by the nonlocal effects in the nonstationary regime, but because it is strongly red-shifted to a position that can be predicted, we show that it can be removed using a bandpass filter, leaving a sub-100 fs visible component at λ = 515 nm with excellent pulse quality.
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.
Spatial optical solitons in nonlinearly coupled lithium niobate waveguides
IEEE Photonics Technology Letters, 2000
We numerically investigate a novel type of quadratic spatial solitons in the system of surface and buried planar waveguides obtained via direct-and reverse-proton exchange in -cut lithium niobate, respectively, and coupled by the second-order susceptibility. Through frequency doubling, transverse-electric and transverse-magnetic modes lock into a 1 + 1 solitary wave encompassing orthogonal field components at the two harmonic wavelengths. The phase matching scheme leads to a wavelength-comb filter with adjustable linewidths.
Writing single-mode waveguides in lithium niobate by ultra-low intensity solitons
Applied Surface Science, 2005
Optical waveguides can be conveniently written in photorefractive materials by using spatial solitons. We have generated bright spatial solitons inside lithium niobate which allow single-mode light propagation. Efficient waveguides have been generated with CW light powers as high as few microwatts. According to the soliton formation, waveguides can be formed with different shapes. Due to the slow response time of the lithium niobate, both for soliton formation and relaxation, the soliton waveguide remains memorised for a long time, of the order of months. #
Optics Letters, 1997
We demonstrate that traveling-wave second-harmonic generation produces amplitude-squeezed light at both the fundamental and the harmonic frequencies. Quasi-phase-matched second-harmonic conversion efficiencies approaching 60% were obtained in a 26-mm-long single-mode LiNbO 3 waveguide with pulses from a modelocked laser at 1.53 mm. The amplitude noise of the transmitted fundamental field was measured to be 0.8 dB below the shot-noise level, and the generated 0.765-mm harmonic light was measured to be amplitude squeezed by 0.35 dB. The conversion-efficiency dependence of the observed squeezing at both wavelengths agrees with theoretical predictions. Waveguide losses appear to degrade the squeezing, but the maximum observed squeezing is currently limited only by the available input power.
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.
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.
Optical bright solitons in lithium niobate and their applications
In the present paper we review the physics of soliton formation in lithium niobate by means of photorefractive nonlinearity. Considering the waveguides that such solitonic beams leave in the host material, we summarise some application of such waveguides in terms of integrated photonic circuits.