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Nonlinear Optics|129 Article(s)
Polarization-dependent neutral nitrogen fluorescence induced by long-distance laser filamentation
Yuezheng Wang, Lu Sun, Zhiwenqi An, Zeliang Zhang... and Weiwei Liu|Show fewer author(s)
Femtosecond laser filamentation has attracted significant attention due to its applications in remote sensing of atmospheric pollutants and artificial weather intervention. Nitrogen is the most abundant gas in the atmosphere, and its stimulated ultraviolet emission is remarkably clean, distinctly different from the fluorescence obtained through electron impact or laser breakdown. While numerous experiments and mechanism analyses have been conducted on its characteristic fluorescence excited by laser filamentation, they predominantly focused on short-distance filamentation (less than 1 m). Contrary to previous reports, we find that at long distances (30 m), the fluorescence intensity of neutral nitrogen molecules excited by linearly polarized laser pulses is approximately 7 times that excited by circularly polarized pulses with the same energy. This enhancement is caused by the enhanced tunneling ionization rate, 3.7 times that under circular polarization, and the elongated filament length, 1.85 times that under circular polarization, when using linear polarization. Additionally, after comparing existing theories for N2(C3Πu)) excitation, the dissociation-recombination model is found to be more appropriate for explaining the formation of N2(C3Πu)) excited states during long-distance filamentation. Femtosecond laser filamentation has attracted significant attention due to its applications in remote sensing of atmospheric pollutants and artificial weather intervention. Nitrogen is the most abundant gas in the atmosphere, and its stimulated ultraviolet emission is remarkably clean, distinctly different from the fluorescence obtained through electron impact or laser breakdown. While numerous experiments and mechanism analyses have been conducted on its characteristic fluorescence excited by laser filamentation, they predominantly focused on short-distance filamentation (less than 1 m). Contrary to previous reports, we find that at long distances (30 m), the fluorescence intensity of neutral nitrogen molecules excited by linearly polarized laser pulses is approximately 7 times that excited by circularly polarized pulses with the same energy. This enhancement is caused by the enhanced tunneling ionization rate, 3.7 times that under circular polarization, and the elongated filament length, 1.85 times that under circular polarization, when using linear polarization. Additionally, after comparing existing theories for N2(C3Πu)) excitation, the dissociation-recombination model is found to be more appropriate for explaining the formation of N2(C3Πu)) excited states during long-distance filamentation.
Photonics Research
- Publication Date: May. 30, 2025
- Vol. 13, Issue 6, 1691 (2025)
Towards high-power and ultra-broadband mid-infrared supercontinuum generation using tapered multimode glass rods
Esteban Serrano, Damien Bailleul, Frédéric Désévédavy, Pierre Béjot... and Bertrand Kibler|Show fewer author(s)
Simultaneously increasing the spectral bandwidth and average output power of mid-infrared supercontinuum sources remains a major challenge for their practical application. We particularly address this issue for the long mid-infrared spectral region through experimental developments of short tapered rods made from selenide glass by means of supercontinuum generation in the femtosecond regime. Our simple post-processing of glass rods unlocks potentially higher-power and coherent fiber-based supercontinuum sources beyond the 10-μm waveband. By using a 5-cm-long tapered Ge-Se-Te rod pumped at 6 μm, a supercontinuum spanning from 2 to 15 μm (3–14 μm) with an average output power of 93 mW (170 mW) is obtained for 500-kHz (1-MHz) repetition rate. Additional experiments on other glass families (silica and tellurite) covering distinct spectral regions are also reported to develop and support our analyses. We demonstrate that ultra-broadband spectral broadenings over entire glass transmission windows can be achieved in few-cm-long segments of tapered rods by a fine adjustment of input modal excitation. Numerical simulations are used to confirm the main contribution of the fundamental mode in the ultrafast nonlinear dynamics, as well as the possible preservation of coherence features. Our study opens a new route, to our knowledge, towards the power scaling of high-repetition-rate fiber supercontinuum sources over the full molecular fingerprint region. Simultaneously increasing the spectral bandwidth and average output power of mid-infrared supercontinuum sources remains a major challenge for their practical application. We particularly address this issue for the long mid-infrared spectral region through experimental developments of short tapered rods made from selenide glass by means of supercontinuum generation in the femtosecond regime. Our simple post-processing of glass rods unlocks potentially higher-power and coherent fiber-based supercontinuum sources beyond the 10-μm waveband. By using a 5-cm-long tapered Ge-Se-Te rod pumped at 6 μm, a supercontinuum spanning from 2 to 15 μm (3–14 μm) with an average output power of 93 mW (170 mW) is obtained for 500-kHz (1-MHz) repetition rate. Additional experiments on other glass families (silica and tellurite) covering distinct spectral regions are also reported to develop and support our analyses. We demonstrate that ultra-broadband spectral broadenings over entire glass transmission windows can be achieved in few-cm-long segments of tapered rods by a fine adjustment of input modal excitation. Numerical simulations are used to confirm the main contribution of the fundamental mode in the ultrafast nonlinear dynamics, as well as the possible preservation of coherence features. Our study opens a new route, to our knowledge, towards the power scaling of high-repetition-rate fiber supercontinuum sources over the full molecular fingerprint region.
Photonics Research
- Publication Date: Apr. 21, 2025
- Vol. 13, Issue 5, 1106 (2025)
Integrated optical switches based on Kerr symmetry breaking in microresonators|Editors' Pick
Yaojing Zhang, Shuangyou Zhang, Alekhya Ghosh, Arghadeep Pal... and Pascal Del’Haye|Show fewer author(s)
With the rapid development of the Internet of Things and big data, integrated optical switches are gaining prominence for applications in on-chip optical computing, optical memories, and optical communications. Here, we propose a novel approach for on-chip optical switches by utilizing the nonlinear optical Kerr effect induced spontaneous symmetry breaking (SSB), which leads to two distinct states of counterpropagating light in ring resonators. This technique is based on our first experimental observation of on-chip symmetry breaking in a high-Q (9.4×106) silicon nitride resonator with a measured SSB threshold power of approximately 3.9 mW. We further explore the influence of varying pump powers and frequency detunings on the performance of SSB-induced optical switches. Our work provides insights into the development of new types of photonic data processing devices and provides an innovative approach for the future implementation of on-chip optical memories. With the rapid development of the Internet of Things and big data, integrated optical switches are gaining prominence for applications in on-chip optical computing, optical memories, and optical communications. Here, we propose a novel approach for on-chip optical switches by utilizing the nonlinear optical Kerr effect induced spontaneous symmetry breaking (SSB), which leads to two distinct states of counterpropagating light in ring resonators. This technique is based on our first experimental observation of on-chip symmetry breaking in a high-Q (9.4×106) silicon nitride resonator with a measured SSB threshold power of approximately 3.9 mW. We further explore the influence of varying pump powers and frequency detunings on the performance of SSB-induced optical switches. Our work provides insights into the development of new types of photonic data processing devices and provides an innovative approach for the future implementation of on-chip optical memories.
Photonics Research
- Publication Date: Jan. 17, 2025
- Vol. 13, Issue 2, 360 (2025)
Four-wave mixing in a laser diode gain medium induced by the feedback from a high-Q microring resonator
Daria M. Sokol, Nikita Yu Dmitriev, Dmitry A. Chermoshentsev, Sergey N. Koptyaev... and Artem E. Shitikov|Show fewer author(s)
Laser diodes are widely used and play a crucial role in myriad modern applications including nonlinear optics and photonics. Here, we explore the four-wave mixing effect in a laser diode gain medium induced by the feedback from the high-Q microring resonator. This phenomenon can be observed at a laser frequency scan close to the microresonator eigenfrequency, prior to the transition of the laser diode from a free-running to a self-injection locking regime. The effect opens up the possibility for generation of remarkably low-noise, stable, and adjustable microwave signals. We provide a detailed numerical study of this phenomenon proven with experimental results and demonstrate the generation of the signals in the GHz range. The obtained results reveal the stability of such regime and disclose the parameter ranges enabling to achieve it. Cumulatively, our findings uncover, to our knowledge, a novel laser diode operation regime and pave the way for the creation of new types of chip-scale, low-noise microwave sources, which are highly demanded for diverse applications, including telecommunication, metrology, and sensing. Laser diodes are widely used and play a crucial role in myriad modern applications including nonlinear optics and photonics. Here, we explore the four-wave mixing effect in a laser diode gain medium induced by the feedback from the high-Q microring resonator. This phenomenon can be observed at a laser frequency scan close to the microresonator eigenfrequency, prior to the transition of the laser diode from a free-running to a self-injection locking regime. The effect opens up the possibility for generation of remarkably low-noise, stable, and adjustable microwave signals. We provide a detailed numerical study of this phenomenon proven with experimental results and demonstrate the generation of the signals in the GHz range. The obtained results reveal the stability of such regime and disclose the parameter ranges enabling to achieve it. Cumulatively, our findings uncover, to our knowledge, a novel laser diode operation regime and pave the way for the creation of new types of chip-scale, low-noise microwave sources, which are highly demanded for diverse applications, including telecommunication, metrology, and sensing.
Photonics Research
- Publication Date: Dec. 17, 2024
- Vol. 13, Issue 1, 59 (2025)
Image reconstruction through a nonlinear scattering medium via deep learning
Shuo Yan, Yiwei Sun, Fengchao Ni, Zhanwei Liu... and Xianfeng Chen|Show fewer author(s)
Image reconstruction through the opaque medium has great significance in fields of biophotonics, optical imaging, mesoscopic physics, and optical communications. Previous researches are limited in the simple linear scattering process. Here, we develop a nonlinear speckle decoder network, which can reconstruct the phase information of the fundamental frequency wave via the nonlinear scattering signal. Further, we validate the ability of our model to recover simple and complex structures by using MNIST and CIFAR data sets, respectively. We then show that the model is able to restore the image information through different sets of nonlinear diffusers and reconstruct the image of a kind of completely unseen object category. The proposed method paves the way to nonlinear scattering imaging and information encryption. Image reconstruction through the opaque medium has great significance in fields of biophotonics, optical imaging, mesoscopic physics, and optical communications. Previous researches are limited in the simple linear scattering process. Here, we develop a nonlinear speckle decoder network, which can reconstruct the phase information of the fundamental frequency wave via the nonlinear scattering signal. Further, we validate the ability of our model to recover simple and complex structures by using MNIST and CIFAR data sets, respectively. We then show that the model is able to restore the image information through different sets of nonlinear diffusers and reconstruct the image of a kind of completely unseen object category. The proposed method paves the way to nonlinear scattering imaging and information encryption.
Photonics Research
- Publication Date: Aug. 30, 2024
- Vol. 12, Issue 9, 2047 (2024)
Advancing large-scale thin-film PPLN nonlinear photonics with segmented tunable micro-heaters|Editors' Pick
Xiaoting Li, Haochuan Li, Zhenzheng Wang, Zhaoxi Chen... and Cheng Wang|Show fewer author(s)
Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802% W-1 cm-2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device. The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification. Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802% W-1 cm-2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device. The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification.
Photonics Research
- Publication Date: Aug. 01, 2024
- Vol. 12, Issue 8, 1703 (2024)
High-resolution mid-infrared single-photon upconversion ranging
Shuhong Jiang, Kun Huang, Tingting Yu, Jianan Fang... and Heping Zeng|Show fewer author(s)
Single-photon laser ranging has widespread applications in remote sensing and target recognition. However, highly sensitive light detection and ranging (lidar) has long been restricted in the visible or near-infrared bands. An appealing quest is to extend the operation wavelength into the mid-infrared (MIR) region, which calls for an infrared photon-counting system at high detection sensitivity and precise temporal resolution. Here, we devise and demonstrate an MIR upconversion lidar based on nonlinear asynchronous optical sampling. Specifically, the infrared probe is interrogated in a nonlinear crystal by a train of pump pulses at a slightly different repetition rate, which favors temporal optical scanning at a picosecond timing resolution and a kilohertz refreshing rate over ∼50 ns. Moreover, the cross-correlation upconversion trace is temporally stretched by a factor of 2×104, which can thus be recorded by a low-bandwidth silicon detector. In combination with the time-correlated photon-counting technique, the achieved effective resolution is about two orders of magnitude better than the timing jitter of the detector itself, which facilitates a ranging precision of 4 μm under a low detected flux of 8×10-5 photons per pulse. The presented MIR time-of-flight range finder is featured with single-photon sensitivity and high positioning resolution, which would be particularly useful in infrared sensing and imaging in photon-starved scenarios. Single-photon laser ranging has widespread applications in remote sensing and target recognition. However, highly sensitive light detection and ranging (lidar) has long been restricted in the visible or near-infrared bands. An appealing quest is to extend the operation wavelength into the mid-infrared (MIR) region, which calls for an infrared photon-counting system at high detection sensitivity and precise temporal resolution. Here, we devise and demonstrate an MIR upconversion lidar based on nonlinear asynchronous optical sampling. Specifically, the infrared probe is interrogated in a nonlinear crystal by a train of pump pulses at a slightly different repetition rate, which favors temporal optical scanning at a picosecond timing resolution and a kilohertz refreshing rate over ∼50 ns. Moreover, the cross-correlation upconversion trace is temporally stretched by a factor of 2×104, which can thus be recorded by a low-bandwidth silicon detector. In combination with the time-correlated photon-counting technique, the achieved effective resolution is about two orders of magnitude better than the timing jitter of the detector itself, which facilitates a ranging precision of 4 μm under a low detected flux of 8×10-5 photons per pulse. The presented MIR time-of-flight range finder is featured with single-photon sensitivity and high positioning resolution, which would be particularly useful in infrared sensing and imaging in photon-starved scenarios.
Photonics Research
- Publication Date: May. 31, 2024
- Vol. 12, Issue 6, 1294 (2024)
Nonlinear generation of vector beams by using a compact nonlinear fork grating
Qian Yang, Yangfeifei Yang, Hao Li, Haigang Liu, and Xianfeng Chen
Vectorial beams have attracted great interest due to their broad applications in optical micromanipulation, optical imaging, optical micromachining, and optical communication. Nonlinear frequency conversion is an effective technique to expand the frequency range of the vectorial beams. However, the scheme of existing methods to generate vector beams of the second harmonic (SH) lacks compactness in the experiment. Here, we introduce a new way to realize the generation of vector beams of SH by using a nonlinear fork grating to solve such a problem. We examine the properties of generated SH vector beams by using Stokes parameters, which agree well with theoretical predictions. Then we demonstrate that linearly polarized vector beams with arbitrary topological charge can be achieved by adjusting the optical axis direction of the half-wave plate (HWP). Finally, we measure the nonlinear conversion efficiency of such a method. The proposed method provides a new way to generate vector beams of SH by using a microstructure of nonlinear crystal, which may also be applied in other nonlinear processes and promote all-optical waveband applications of such vector beams. Vectorial beams have attracted great interest due to their broad applications in optical micromanipulation, optical imaging, optical micromachining, and optical communication. Nonlinear frequency conversion is an effective technique to expand the frequency range of the vectorial beams. However, the scheme of existing methods to generate vector beams of the second harmonic (SH) lacks compactness in the experiment. Here, we introduce a new way to realize the generation of vector beams of SH by using a nonlinear fork grating to solve such a problem. We examine the properties of generated SH vector beams by using Stokes parameters, which agree well with theoretical predictions. Then we demonstrate that linearly polarized vector beams with arbitrary topological charge can be achieved by adjusting the optical axis direction of the half-wave plate (HWP). Finally, we measure the nonlinear conversion efficiency of such a method. The proposed method provides a new way to generate vector beams of SH by using a microstructure of nonlinear crystal, which may also be applied in other nonlinear processes and promote all-optical waveband applications of such vector beams.
Photonics Research
- Publication Date: May. 01, 2024
- Vol. 12, Issue 5, 1036 (2024)
Synergic action of linear dispersion, second-order nonlinearity, and third-order nonlinearity in shaping the spectral profile of a femtosecond pulse transporting in a lithium niobate crystal
Lihong Hong, Yuanyuan Liu, and Zhi-Yuan Li
We present a detailed theoretical and numerical analysis on the temporal-spectral-spatial evolution of a high-peak-power femtosecond laser pulse in two sets of systems: a pure lithium niobate (LN) plate and a periodically poled lithium niobate (PPLN) plate. We develop a modified unidimensional pulse propagation model that considers all the prominent linear and nonlinear processes and carried out the simulation process based on an improved split-step Fourier transformation method. We theoretically analyze the synergic action of the linear dispersion effect, the second-order nonlinearity (2nd-NL) second-harmonic generation (SHG) effect, and the third-order nonlinearity (3rd-NL) self-phase modulation (SPM) effect, and clarify the physical mechanism underlying the peculiar and diverse spectral broadening patterns previously reported in LN and PPLN thin plate experiments. Such analysis and discussion provides a deeper insight into the synergetic contribution of these linear and nonlinear effects brought about by the interaction of a femtosecond laser pulse with the LN nonlinear crystal and helps to draw a picture to fully understand these fruitful optical physical processes, phenomena, and laws. We present a detailed theoretical and numerical analysis on the temporal-spectral-spatial evolution of a high-peak-power femtosecond laser pulse in two sets of systems: a pure lithium niobate (LN) plate and a periodically poled lithium niobate (PPLN) plate. We develop a modified unidimensional pulse propagation model that considers all the prominent linear and nonlinear processes and carried out the simulation process based on an improved split-step Fourier transformation method. We theoretically analyze the synergic action of the linear dispersion effect, the second-order nonlinearity (2nd-NL) second-harmonic generation (SHG) effect, and the third-order nonlinearity (3rd-NL) self-phase modulation (SPM) effect, and clarify the physical mechanism underlying the peculiar and diverse spectral broadening patterns previously reported in LN and PPLN thin plate experiments. Such analysis and discussion provides a deeper insight into the synergetic contribution of these linear and nonlinear effects brought about by the interaction of a femtosecond laser pulse with the LN nonlinear crystal and helps to draw a picture to fully understand these fruitful optical physical processes, phenomena, and laws.
Photonics Research
- Publication Date: Apr. 01, 2024
- Vol. 12, Issue 4, 774 (2024)
Tunable polarization holographic gratings obtained by varying the ratio of intensities of the recording beams
Hong Chen, Ziyao Lyu, and Changshun Wang
Polarization holography has been extensively applied in many fields, such as optical science, metrology, and biochemistry, due to its property of polarization modulation. However, the modulated polarization state of diffracted light corresponds strictly to that of incident light one by one. Here, a kind of tunable polarization holographic grating has been designed in terms of Jones matrices, and intensity-based polarization manipulation has been realized experimentally. The proposed tunable polarization holographic grating is recorded on an azobenzene liquid-crystalline film by a pair of coherent light beams with orthogonal polarization states and asymmetrically controlled intensities. It is found that the diffracted light can be actively manipulated from linearly to circularly polarized based on the light intensity of the recording holographic field when the polarization state of incident light keeps constant. Our work could enrich the field of light manipulation and holography. Polarization holography has been extensively applied in many fields, such as optical science, metrology, and biochemistry, due to its property of polarization modulation. However, the modulated polarization state of diffracted light corresponds strictly to that of incident light one by one. Here, a kind of tunable polarization holographic grating has been designed in terms of Jones matrices, and intensity-based polarization manipulation has been realized experimentally. The proposed tunable polarization holographic grating is recorded on an azobenzene liquid-crystalline film by a pair of coherent light beams with orthogonal polarization states and asymmetrically controlled intensities. It is found that the diffracted light can be actively manipulated from linearly to circularly polarized based on the light intensity of the recording holographic field when the polarization state of incident light keeps constant. Our work could enrich the field of light manipulation and holography.
Photonics Research
- Publication Date: Apr. 01, 2024
- Vol. 12, Issue 4, 749 (2024)
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