Hairun Guo - Academia.edu (original) (raw)
Papers by Hairun Guo
A popular crystal for ultrafast cascading experiments is beta-barium-borate (β-BaB 2 O 4 , BBO). ... more A popular crystal for ultrafast cascading experiments is beta-barium-borate (β-BaB 2 O 4 , BBO). It has a decent quadratic nonlinear coefficient, and because the crystal is anisotropic it can be birefringence phase-matched for type I (oo → e) second-harmonic generation (SHG). For femtosecond experiments BBO is popular because of low dispersion and a high damage threshold. The main attractive property of ultrafast cascading is that the induced cascading nonlinearity n I 2,casc can be negative, i.e. generate a self-defocusing Kerr-like nonlinearity. However, the material Kerr nonlinearity n I 2,Kerr is self-focusing and competes with the cascading nonlinearity. Therefore, precise knowledge of its strength is crucial. We perform an experiment measuring the main c 11 tensor component, and together with literature experimental data [1], we propose a c 11 value composed of 14 different data points. 0.85 0.90 0.95 1.00 1.05 1.10 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 k [1/mm] 0.0 12.0 23.8 35.3 46.7 57.7 68.6 79.1 89.4 99.4 109.2 Input Intensity [a.u.] [ m] (a) 80 85 90 95 100 65 70 75 80 85 ( 10 dB) [nm] k [1/mm] Input Output 100 GW/cm 2 200 GW/cm 2 (b) critical point 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 0 5 10 15 E g =6.8 eV Theory (2-band model) Avg. value+Miller's scaling Tan et al. 1993 Hache et al. 1995 DeSalvo et al. 1996 Li et al. 1997 Li et al. 2001 Ganeev et al. 2003 Moses et al. 2007 This work n I 2 Kerr [10 -20 m 2 /W] [ m] E g =6.2 eV , (c) Figure 1. (a) Experimental spectra recorded with 50 fs@1030 nm and 200 GW/cm 2 transform-limited pulses, (b) the spectral bandwidth@-10 dB vs. ∆k. (c) Summary of the experimental data from the literature corresponding to the c11 nonlinear susceptibility coefficient (n I 2,Kerr = 3c11/4n 2 1 ε0c). The data are corrected by us for cascading contributions. The shaded areas "σ" and "2σ" represent one and two standard deviations.
Dispersive waves (DW) are radiated when temporal solitons are perturbed by higher-order dispersio... more Dispersive waves (DW) are radiated when temporal solitons are perturbed by higher-order dispersion (HOD). This is also called optical Cherenkov radiation (OCR). Currently among much efforts of generating optical octavespanning supercontinuum (SCG), OCR has become an efficient nonlinear frequency conversion in the blue edge of SCG and blue-shifting the edge with the soliton self-frequency shift(SSFS) by the Raman effect [1]. Moreover, a sharp switching of SSFS can occur across a normal group velocity dispersion (GVD) region sandwiched in the anomalous GVD regions, known as soliton spectral tunneling (SST) effect . Its mechanism was attributed to the phase-matching (PM) between the soliton and linear DW in the anomalous GVD. Here we argue first that groupvelocity (GV) matching is another necessary condition for such SST effect and present a detailed analysis on the broadband OCR by employing GV-matching in the index-guiding photonic crystal fibers (PCFs). This approach is expected to efficiently generate ultrashort pulses in the near-and mid-IR. Fig. 1 (a) Chromatic dispersion and effective nonlinear coefficient γ versus wavelength (insets are mode field distributions). (b) Phase matching curves between soliton and its radiation wavelengths, ⋆ indicate the critical point (CP). (c) Spectra evolution of 25 fs (FWHM) input soliton (N = 1) at the pump wavelength of 1.40 µm under the dispersion profile (∆ 1 ). (d) and (e) are soliton and OCR pulses by using a lowpass filter cut at 1.68 µm (red line in (c)). (f) The electric field of output pulse by solving the NWEF. (g) Spectrogram of the output pulse.
Quadratic cascading response is evoked during the ultrafast and phase mismatched (cascading limit... more Quadratic cascading response is evoked during the ultrafast and phase mismatched (cascading limit) second harmonic generation (SHG) process, which becomes more and more recognized alongside with typical nonlinear phenomena such as nonlinear phase change, pulse intrinsic self-steepening (SS) and material Raman effects. The mean value (local component) of this cascading response has been widely investigated and known as cascading quadratic nonlinearity (has a soliton number N casc ) which gives rise to a Kerr-like phase change and is tailored by the phase mismatch (∆k) between the fundamental wave (FW) and the second harmonic (SH) . Moreover, the first order of the cascading response is revealed as an effective SS term , which adds to the intrinsic SS and induces shock front on pulses. Then, such SS effects will cause pulse delay when operating with material dispersions. Meanwhile, first order Raman response will also cause pulse delay by continuously red-shifting the pulse spectrum. Hence, there comes a pulse delay competition between the cascading and Raman responses.
ABSTRACT form only given. Optical Cherenkov radiation (OCR) is referred to as dispersive wave (DW... more ABSTRACT form only given. Optical Cherenkov radiation (OCR) is referred to as dispersive wave (DW) generation or non-solitonic radiation originating from soliton propagation perturbed by high order dispersion (HOD). The OCR becomes of particular importance for octave-spanning spectral broadening and blue-shifted supercontinuum generation (SCG) [1]. When the OCR generation lies in the anomalous GVD region and tends to be a soliton state, the phase-matching (PM) condition between linear DWs and the soliton could become a soliton PM condition: β<;sub>s<;/sub>(ω<;sub>s<;/sub>) = β<;sub>s<;/sub>(ω<;sub>r<;/sub>), provided that v<;sub>g<;/sub>(ω<;sub>s<;/sub>) = v<;sub>g<;/sub>(ω<;sub>r<;/sub>). β<;sub>s<;/sub>(ω<;sub>k<;/sub>) ≡ β(ω<;sub>k<;/sub>) + (ω-ω<;sub>k<;/sub>)/v<;sub>g<;/sub>(ω<;sub>k<;/sub>) + q<;sub>k<;/sub> reflects the nondispersive nature of the soliton at the center frequency ω<;sub>k<;/sub> and v<;sub>g<;/sub>(ω<;sub>k<;/sub>) is the group velocity. k = r, s represents the radiation or soliton wave. A sharp spectral switching of the soliton due to the soliton spectral tunneling (SST) effect in the photonic crystal fibers (PCFs) can occur across a normal group velocity dispersion (GVD) region, which is sandwiched in the anomalous GVD regions [2]. This approach shows a new efficient wavelength conversion scheme, and we explore the cascaded OCR to enlarge the span of the wavelength conversion.We show the flexible dispersion profiles with three controlled ZDWs, λ1 <; λ2 <; λ3, as shown in Fig. 1(a), by tuning the pitch - Δ and the relative hole size D = d/Δ in PCFs. λ2 and λ3 shift to longer wavelengths as the increase of D. Three anomalous GVD regions separated normal GVD are formed. Fig. 1(b) shows the predicted PM wavelength versus soliton wavelength when the input pulse has a full width at half-maximum (FWHM) of 50 fs and the soliton number N = 1. The soliton PM condition is satisfied at a so-called critical point (CP), where two radiation bands are degenerate. Two different CPs are chosen to make soliton spectral tunneling in two-segment PCFs.
We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiatio... more We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-IR pulses centering from 2.8-2.92 µm are generated using the single pump wavelengths from 1.25-1.45 µm.
Self-defocusing soliton compression supported by the cascaded phase-mismatched second-harmonic ge... more Self-defocusing soliton compression supported by the cascaded phase-mismatched second-harmonic generation process is numerically demonstrated in unpoled lithium niobate ridge waveguides where nano-joule pulses are operated and quasi-phase-matching is unnecessary. The soliton range is 1100-1800 nm.
ABSTRACT We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave... more ABSTRACT We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-infrared pulses centering from 2.8-2.92 µm are generated using the single pump wavelengths from 1.25-1.45 µm.
Supercontinuum generation (SCG) is most efficient when the solitons can be excited directly at th... more Supercontinuum generation (SCG) is most efficient when the solitons can be excited directly at the pump laser wavelength. Quadratic nonlinear waveguides may induce an effective negative Kerr nonlinearity, so temporal solitons can be directly generated in the normal (positive) dispersion regime overlapping with common ultrafast laser wavelengths. There is no need for waveguide dispersion engineering. Here, we experimentally demonstrate SCG in standard lithium niobate (LN) waveguides without quasi-phase matching (QPM), pumped with femtosecond pulses in the normal dispersion regime. The observed large bandwidths (even octave spanning), together with other experimental data, indicate that negative nonlinearity solitons are indeed excited, which is backed up by numerical simulations. The QPM-free design reduces production complexity, extends the maximum waveguide length, and limits undesired spectral resonances. Finally, nonlinear crystals can be used where QPM is inefficient or impossible, which is important for mid-IR SCG. QPM-free waveguides in mid-IR nonlinear crystals can support negative nonlinearity solitons, as these waveguides have a normal dispersion at the emission wavelengths of mid-IR ultrafast lasers.
We numerically investigate the influence of high-order dispersion (HOD) on temporal and spectral ... more We numerically investigate the influence of high-order dispersion (HOD) on temporal and spectral characteristics of microresonator-based optical frequency combs. Theoretical analysis based on the moment method associated with numerical simulations are utilized to study the comb evolution dynamics, showing that temporal shifts of steady-state intracavity solitons are induced by high-odd-order dispersion rather than high-even-order dispersion. The role of HOD on comb spectral envelopes is also elucidated through analyzing the intracavity dispersive wave generations. We further demonstrate that the spectral envelope of a broadband optical frequency comb can be engineered by using a cavity dispersion profile with multiple zero dispersion wavelengths.
A popular crystal for ultrafast cascading experiments is beta-barium-borate (β-BaB 2 O 4 , BBO). ... more A popular crystal for ultrafast cascading experiments is beta-barium-borate (β-BaB 2 O 4 , BBO). It has a decent quadratic nonlinear coefficient, and because the crystal is anisotropic it can be birefringence phase-matched for type I (oo → e) second-harmonic generation (SHG). For femtosecond experiments BBO is popular because of low dispersion and a high damage threshold. The main attractive property of ultrafast cascading is that the induced cascading nonlinearity n I 2,casc can be negative, i.e. generate a self-defocusing Kerr-like nonlinearity. However, the material Kerr nonlinearity n I 2,Kerr is self-focusing and competes with the cascading nonlinearity. Therefore, precise knowledge of its strength is crucial. We perform an experiment measuring the main c 11 tensor component, and together with literature experimental data [1], we propose a c 11 value composed of 14 different data points. 0.85 0.90 0.95 1.00 1.05 1.10 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 k [1/mm] 0.0 12.0 23.8 35.3 46.7 57.7 68.6 79.1 89.4 99.4 109.2 Input Intensity [a.u.] [ m] (a) 80 85 90 95 100 65 70 75 80 85 ( 10 dB) [nm] k [1/mm] Input Output 100 GW/cm 2 200 GW/cm 2 (b) critical point 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 0 5 10 15 E g =6.8 eV Theory (2-band model) Avg. value+Miller's scaling Tan et al. 1993 Hache et al. 1995 DeSalvo et al. 1996 Li et al. 1997 Li et al. 2001 Ganeev et al. 2003 Moses et al. 2007 This work n I 2 Kerr [10 -20 m 2 /W] [ m] E g =6.2 eV , (c) Figure 1. (a) Experimental spectra recorded with 50 fs@1030 nm and 200 GW/cm 2 transform-limited pulses, (b) the spectral bandwidth@-10 dB vs. ∆k. (c) Summary of the experimental data from the literature corresponding to the c11 nonlinear susceptibility coefficient (n I 2,Kerr = 3c11/4n 2 1 ε0c). The data are corrected by us for cascading contributions. The shaded areas "σ" and "2σ" represent one and two standard deviations.
Dispersive waves (DW) are radiated when temporal solitons are perturbed by higher-order dispersio... more Dispersive waves (DW) are radiated when temporal solitons are perturbed by higher-order dispersion (HOD). This is also called optical Cherenkov radiation (OCR). Currently among much efforts of generating optical octavespanning supercontinuum (SCG), OCR has become an efficient nonlinear frequency conversion in the blue edge of SCG and blue-shifting the edge with the soliton self-frequency shift(SSFS) by the Raman effect [1]. Moreover, a sharp switching of SSFS can occur across a normal group velocity dispersion (GVD) region sandwiched in the anomalous GVD regions, known as soliton spectral tunneling (SST) effect . Its mechanism was attributed to the phase-matching (PM) between the soliton and linear DW in the anomalous GVD. Here we argue first that groupvelocity (GV) matching is another necessary condition for such SST effect and present a detailed analysis on the broadband OCR by employing GV-matching in the index-guiding photonic crystal fibers (PCFs). This approach is expected to efficiently generate ultrashort pulses in the near-and mid-IR. Fig. 1 (a) Chromatic dispersion and effective nonlinear coefficient γ versus wavelength (insets are mode field distributions). (b) Phase matching curves between soliton and its radiation wavelengths, ⋆ indicate the critical point (CP). (c) Spectra evolution of 25 fs (FWHM) input soliton (N = 1) at the pump wavelength of 1.40 µm under the dispersion profile (∆ 1 ). (d) and (e) are soliton and OCR pulses by using a lowpass filter cut at 1.68 µm (red line in (c)). (f) The electric field of output pulse by solving the NWEF. (g) Spectrogram of the output pulse.
Quadratic cascading response is evoked during the ultrafast and phase mismatched (cascading limit... more Quadratic cascading response is evoked during the ultrafast and phase mismatched (cascading limit) second harmonic generation (SHG) process, which becomes more and more recognized alongside with typical nonlinear phenomena such as nonlinear phase change, pulse intrinsic self-steepening (SS) and material Raman effects. The mean value (local component) of this cascading response has been widely investigated and known as cascading quadratic nonlinearity (has a soliton number N casc ) which gives rise to a Kerr-like phase change and is tailored by the phase mismatch (∆k) between the fundamental wave (FW) and the second harmonic (SH) . Moreover, the first order of the cascading response is revealed as an effective SS term , which adds to the intrinsic SS and induces shock front on pulses. Then, such SS effects will cause pulse delay when operating with material dispersions. Meanwhile, first order Raman response will also cause pulse delay by continuously red-shifting the pulse spectrum. Hence, there comes a pulse delay competition between the cascading and Raman responses.
ABSTRACT form only given. Optical Cherenkov radiation (OCR) is referred to as dispersive wave (DW... more ABSTRACT form only given. Optical Cherenkov radiation (OCR) is referred to as dispersive wave (DW) generation or non-solitonic radiation originating from soliton propagation perturbed by high order dispersion (HOD). The OCR becomes of particular importance for octave-spanning spectral broadening and blue-shifted supercontinuum generation (SCG) [1]. When the OCR generation lies in the anomalous GVD region and tends to be a soliton state, the phase-matching (PM) condition between linear DWs and the soliton could become a soliton PM condition: β<;sub>s<;/sub>(ω<;sub>s<;/sub>) = β<;sub>s<;/sub>(ω<;sub>r<;/sub>), provided that v<;sub>g<;/sub>(ω<;sub>s<;/sub>) = v<;sub>g<;/sub>(ω<;sub>r<;/sub>). β<;sub>s<;/sub>(ω<;sub>k<;/sub>) ≡ β(ω<;sub>k<;/sub>) + (ω-ω<;sub>k<;/sub>)/v<;sub>g<;/sub>(ω<;sub>k<;/sub>) + q<;sub>k<;/sub> reflects the nondispersive nature of the soliton at the center frequency ω<;sub>k<;/sub> and v<;sub>g<;/sub>(ω<;sub>k<;/sub>) is the group velocity. k = r, s represents the radiation or soliton wave. A sharp spectral switching of the soliton due to the soliton spectral tunneling (SST) effect in the photonic crystal fibers (PCFs) can occur across a normal group velocity dispersion (GVD) region, which is sandwiched in the anomalous GVD regions [2]. This approach shows a new efficient wavelength conversion scheme, and we explore the cascaded OCR to enlarge the span of the wavelength conversion.We show the flexible dispersion profiles with three controlled ZDWs, λ1 <; λ2 <; λ3, as shown in Fig. 1(a), by tuning the pitch - Δ and the relative hole size D = d/Δ in PCFs. λ2 and λ3 shift to longer wavelengths as the increase of D. Three anomalous GVD regions separated normal GVD are formed. Fig. 1(b) shows the predicted PM wavelength versus soliton wavelength when the input pulse has a full width at half-maximum (FWHM) of 50 fs and the soliton number N = 1. The soliton PM condition is satisfied at a so-called critical point (CP), where two radiation bands are degenerate. Two different CPs are chosen to make soliton spectral tunneling in two-segment PCFs.
We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiatio... more We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-IR pulses centering from 2.8-2.92 µm are generated using the single pump wavelengths from 1.25-1.45 µm.
Self-defocusing soliton compression supported by the cascaded phase-mismatched second-harmonic ge... more Self-defocusing soliton compression supported by the cascaded phase-mismatched second-harmonic generation process is numerically demonstrated in unpoled lithium niobate ridge waveguides where nano-joule pulses are operated and quasi-phase-matching is unnecessary. The soliton range is 1100-1800 nm.
ABSTRACT We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave... more ABSTRACT We experimentally demonstrate efficient mid-infrared pulse generation by dispersive wave radiation in bulk lithium niobate crystal. Femtosecond mid-infrared pulses centering from 2.8-2.92 µm are generated using the single pump wavelengths from 1.25-1.45 µm.
Supercontinuum generation (SCG) is most efficient when the solitons can be excited directly at th... more Supercontinuum generation (SCG) is most efficient when the solitons can be excited directly at the pump laser wavelength. Quadratic nonlinear waveguides may induce an effective negative Kerr nonlinearity, so temporal solitons can be directly generated in the normal (positive) dispersion regime overlapping with common ultrafast laser wavelengths. There is no need for waveguide dispersion engineering. Here, we experimentally demonstrate SCG in standard lithium niobate (LN) waveguides without quasi-phase matching (QPM), pumped with femtosecond pulses in the normal dispersion regime. The observed large bandwidths (even octave spanning), together with other experimental data, indicate that negative nonlinearity solitons are indeed excited, which is backed up by numerical simulations. The QPM-free design reduces production complexity, extends the maximum waveguide length, and limits undesired spectral resonances. Finally, nonlinear crystals can be used where QPM is inefficient or impossible, which is important for mid-IR SCG. QPM-free waveguides in mid-IR nonlinear crystals can support negative nonlinearity solitons, as these waveguides have a normal dispersion at the emission wavelengths of mid-IR ultrafast lasers.
We numerically investigate the influence of high-order dispersion (HOD) on temporal and spectral ... more We numerically investigate the influence of high-order dispersion (HOD) on temporal and spectral characteristics of microresonator-based optical frequency combs. Theoretical analysis based on the moment method associated with numerical simulations are utilized to study the comb evolution dynamics, showing that temporal shifts of steady-state intracavity solitons are induced by high-odd-order dispersion rather than high-even-order dispersion. The role of HOD on comb spectral envelopes is also elucidated through analyzing the intracavity dispersive wave generations. We further demonstrate that the spectral envelope of a broadband optical frequency comb can be engineered by using a cavity dispersion profile with multiple zero dispersion wavelengths.