Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Optics Letters

Spectral phase correlation of coded femtosecond pulses by second-harmonic generation in thick nonlinear crystals

Zheng Zheng, Andrew M. Weiner

Published Jul 1, 2000• 57 citations
Publisher

Abstract

We demonstrate a novel all-optical scheme for measuring the correlation of spectrally phase-coded ultrashort optical waveforms that uses second-harmonic generation (SHG) in long, periodically poled lithium niobate crystals. The SHG yield can be controlled over a range of ~30 dB, depending on the correlation of the applied phase codes. Such a spectral phase correlator has applications for ultrashort-pulse optical code-division multiple-access networking and could serve as a nonlinear optical but classical analog for certain schemes for coherent quantum control of multiphoton processes.

DOI
10.1364/ol.25.000984

Related papers

All-optical recognition of spectrally coded optical pulses using periodically poled lithium niobate second-harmonic waveguides for ultrashort pulse optical code division multiple-access

Zheng Zheng, Andrew M. Weiner, Krishnan R. Parameswaran +2 more

Summary form only given.There been increasing interest in realizing optical signal processing functions in optical communication systems based on nonlinear optical parametric processes. In the proposed ultrashort pulse optical code-division multiple access (CDMA) systems, in order to realize multiplexing and demultiplexing for multichannel operation, a nonlinear element is needed to distinguish between correctly decoded signals and incorrectly decoded multiaccess interference, which have comparable average optical power but carry different spectral information. It had been proposed to realize all-optical recognition of optical phase-coded ultrashort waveforms by using second-harmonic generation in long nonlinear crystals, which could have advantages in contrast ratio, operating power and detection efficiency over other proposed schemes. While high contrast ratios have been demonstrated based on such a scheme using bulk periodically poled lithium niobate (PPLN) crystals, the high efficiency has not yet been demonstrated. We use a simple combination of PPLN SHG waveguides and conventional photodetectors to realize all-optical recognition of spectrally phase coded optical pulses, which shows the potential of much higher conversion efficiency compared to previous bulk experiments, which is crucial for real-time operation with a high signal to noise ratio.

Conference on Lasers and Electro-Optics•Jan 1, 2000•1 citation

Novel optical thresholder based on second harmonic generation in long periodically poled lithium niobate for ultrashort pulse optical code division multiple-access

Zheng Zheng, Andrew M. Weiner

We report a novel yet practical optical thresholding scheme for ultrashort pulse CDMA using second harmonic generation in a long PPLN crystal, with a demonstrated contrast ratio of /spl sim/30 dB and the potential for low power operation.

Optical Fiber Communication Conference•Nov 7, 2002•0 citations

Spectral compression and modulation of second harmonic generation by Fresnel-inspired binary phase shaping

Baihong Li, Yonggang Xu, Haifei Zhu +4 more

The second harmonic generation (SHG) process is investigated theoretically using the quantum mechanics method of coherent control. Based on the extremum conditions for the SHG intensity at the center frequency, a Fresnel-inspired binary phase shaping scheme is proposed for tailoring the fundamental pulse. The SHG spectrum can be compressed into a narrowband signal with lower background by modulating the relative phases between the frequency components within the fundamental pulse, inducing constructive interference at the center frequency and destructive interference elsewhere. Multipeak second harmonic signals can also be obtained by properly modulating various interference pathways. These results have potential applications in high resolution nonlinear spectroscopy, microscopy, and information coding.

Journal of the Optical Society of America B•Oct 1, 2014•5 citations

Generation of squeezed vacuum pulses using cascaded second-order optical nonlinearity of periodically poled lithium niobate in a Sagnac interferometer

Kenichi Hirosawa, Yasuyuki Ito, Hidetake Ushio +2 more

Squeezed vacuum pulses up to $\ensuremath{-}1.7\text{ }\text{dB}$ at telecom-band $(\ensuremath{\sim}1550\text{ }\text{nm})$ is generated with femtosecond laser pulses using cascaded ${\ensuremath{\chi}}^{(2)}$ optical nonlinearity in a periodically poled lithium niobate crystal placed in a Sagnac interferometer. In spite of group velocity mismatch at short laser pulse pumping, sufficient cascaded nonlinear wave mixing is obtainable at the wavelength shifted from the phase matching wavelength for second harmonic generation. The theoretical model prediction agrees well with the experimental results.

Physical Review A•Oct 26, 2009•7 citations

Quantum interference of correlated photons generated by cascaded second-order nonlinearity

Yuhang Luo, Tao Xie, Meimei Wang +2 more

Cascaded second-order nonlinear processes, specifically second-harmonic generation (SHG) and the following spontaneous parametric down-conversion (SPDC) in a periodically poled lithium niobate (PPLN) waveguide represent significant methods for generating correlated photon pairs. To date, studies on the quantum interference characteristics of entangled photon pairs generated via cascaded SHG and type-0 SPDC process have not been reported. To address this issue, we systematically derive the theoretical expression for the coincidence counts of energy-time entangled photon pairs generated by this nonlinear process after passing through an optical fiber interferometer. The theoretical analysis reveals that the two-photon interference process within the interferometer primarily comprises Hong-Ou-Mandel (HOM) interference and N00N state interference. Experimental results subsequently validate these theoretical findings. In our experiments, a 1550.12 nm laser was used to pump the cascaded SHG/SPDC process in a PPLN waveguide, which satisfies the type-0 quasi-phase matching condition and generates broadband correlated photons in the C-band with a full width at half maximum (FWHM) of approximately 17.5 nm. After being split, the correlated photon pairs were directed into a fiber interferometer. A short-term interference visibility of 76.06% was measured, co-determined by the phase-insensitive HOM effect and the phase-sensitive N00N state interference. Upon increasing the measurement accumulation time, the interference visibility reduced to 49.32%, demonstrating the elimination of N00N state interference under longterm averaging, which is consistent with theoretical predictions. This scheme achieves all-fiber-coupled generation of correlated photon pairs, employing standard fiber components in the optical communication band. This approach significantly reduces the complexity of optical coupling links, thereby offering a feasible pathway for the miniaturization and integration of entangled photon sources and quantum interferometers.

International Conference on Optical Communication and Optical Information Processing (OCOIP)•Dec 11, 2025•0 citations

Ultrabroadband generation of multiple concurrent nonlinear coherent interactions in random quadratic media

Luis Mateos, Pablo Molina, Juan Francisco Galisteo‐López +3 more

Triply coincident nonlinear second harmonic interactions continuously tunable in an extremely large spectral range (800–1400 nm) are demonstrated in strontium barium niobate random quadratic crystal. The spectral dependence of the triple process is in agreement with a first order quasi-phase-matching collinear interaction. The analysis of the polarization states of the generated beams reveals mutually coherent interactions between different processes simultaneously contributing to the total intensity. The results constitute a necessary step in the implementation of ultra-broadband entangled photon pairs from randomly poled structures and are relevant to a wide range of applications, for which broadband polarization controlled light is required.

Applied Physics Letters•Sep 2, 2013•5 citations
We demonstrate a novel all-optical scheme for measuring the correlation of spectrally phase-coded ultrashort optical waveforms that uses second-harmonic generation (SHG) in long, periodically poled lithium niobate crystals. The SHG yield can be controlled over a range of ~30 dB, depending on the correlation of the applied phase codes. Such a spectral phase correlator has applications for ultrashort-pulse optical code-division multiple-access networking and could serve as a nonlinear optical but classical analog for certain schemes for coherent quantum control of multiphoton processes.
Summary form only given.There been increasing interest in realizing optical signal processing functions in optical communication systems based on nonlinear optical parametric processes. In the proposed ultrashort pulse optical code-division multiple access (CDMA) systems, in order to realize multiplexing and demultiplexing for multichannel operation, a nonlinear element is needed to distinguish between correctly decoded signals and incorrectly decoded multiaccess interference, which have comparable average optical power but carry different spectral information. It had been proposed to realize all-optical recognition of optical phase-coded ultrashort waveforms by using second-harmonic generation in long nonlinear crystals, which could have advantages in contrast ratio, operating power and detection efficiency over other proposed schemes. While high contrast ratios have been demonstrated based on such a scheme using bulk periodically poled lithium niobate (PPLN) crystals, the high efficiency has not yet been demonstrated. We use a simple combination of PPLN SHG waveguides and conventional photodetectors to realize all-optical recognition of spectrally phase coded optical pulses, which shows the potential of much higher conversion efficiency compared to previous bulk experiments, which is crucial for real-time operation with a high signal to noise ratio.
The second harmonic generation (SHG) process is investigated theoretically using the quantum mechanics method of coherent control. Based on the extremum conditions for the SHG intensity at the center frequency, a Fresnel-inspired binary phase shaping scheme is proposed for tailoring the fundamental pulse. The SHG spectrum can be compressed into a narrowband signal with lower background by modulating the relative phases between the frequency components within the fundamental pulse, inducing constructive interference at the center frequency and destructive interference elsewhere. Multipeak second harmonic signals can also be obtained by properly modulating various interference pathways. These results have potential applications in high resolution nonlinear spectroscopy, microscopy, and information coding.
Squeezed vacuum pulses up to $\ensuremath{-}1.7\text{ }\text{dB}$ at telecom-band $(\ensuremath{\sim}1550\text{ }\text{nm})$ is generated with femtosecond laser pulses using cascaded ${\ensuremath{\chi}}^{(2)}$ optical nonlinearity in a periodically poled lithium niobate crystal placed in a Sagnac interferometer. In spite of group velocity mismatch at short laser pulse pumping, sufficient cascaded nonlinear wave mixing is obtainable at the wavelength shifted from the phase matching wavelength for second harmonic generation. The theoretical model prediction agrees well with the experimental results.
Cascaded second-order nonlinear processes, specifically second-harmonic generation (SHG) and the following spontaneous parametric down-conversion (SPDC) in a periodically poled lithium niobate (PPLN) waveguide represent significant methods for generating correlated photon pairs. To date, studies on the quantum interference characteristics of entangled photon pairs generated via cascaded SHG and type-0 SPDC process have not been reported. To address this issue, we systematically derive the theoretical expression for the coincidence counts of energy-time entangled photon pairs generated by this nonlinear process after passing through an optical fiber interferometer. The theoretical analysis reveals that the two-photon interference process within the interferometer primarily comprises Hong-Ou-Mandel (HOM) interference and N00N state interference. Experimental results subsequently validate these theoretical findings. In our experiments, a 1550.12 nm laser was used to pump the cascaded SHG/SPDC process in a PPLN waveguide, which satisfies the type-0 quasi-phase matching condition and generates broadband correlated photons in the C-band with a full width at half maximum (FWHM) of approximately 17.5 nm. After being split, the correlated photon pairs were directed into a fiber interferometer. A short-term interference visibility of 76.06% was measured, co-determined by the phase-insensitive HOM effect and the phase-sensitive N00N state interference. Upon increasing the measurement accumulation time, the interference visibility reduced to 49.32%, demonstrating the elimination of N00N state interference under longterm averaging, which is consistent with theoretical predictions. This scheme achieves all-fiber-coupled generation of correlated photon pairs, employing standard fiber components in the optical communication band. This approach significantly reduces the complexity of optical coupling links, thereby offering a feasible pathway for the miniaturization and integration of entangled photon sources and quantum interferometers.
Triply coincident nonlinear second harmonic interactions continuously tunable in an extremely large spectral range (800–1400 nm) are demonstrated in strontium barium niobate random quadratic crystal. The spectral dependence of the triple process is in agreement with a first order quasi-phase-matching collinear interaction. The analysis of the polarization states of the generated beams reveals mutually coherent interactions between different processes simultaneously contributing to the total intensity. The results constitute a necessary step in the implementation of ultra-broadband entangled photon pairs from randomly poled structures and are relevant to a wide range of applications, for which broadband polarization controlled light is required.