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Nonlinear Optics|131 Article(s)
Frequency conversion of vortex states by chiral flexural acoustic phonons
Xinglin Zeng, Philip St.J. Russell, and Birgit Stiller
An object or system is said to be chiral if it cannot be superimposed on its mirror reflection. Chirality is ubiquitous in nature, for example, in protein molecules and chiral phonons—acoustic waves carrying angular momentum—which are usually either intrinsically present or magnetically excited in suitable materials. Here, we report the use of intervortex forward Brillouin scattering to optically excite chiral flexural phonons in a twisted photonic crystal fiber, which is itself a chiral material capable of robustly preserving circularly polarized optical vortex states. The phonons induce a spatiotemporal rotating linear birefringence that acts back on the optical vortex modes, coupling them together. We demonstrate intervortex frequency conversion under the mediation of chiral flexural phonons and show that, for the same phonons, backward and forward intervortex conversion occurs at different wavelengths. The results open up, to our knowledge, new perspectives for Brillouin scattering and the chiral flexural phonons offer new opportunities for vortex-related information processing and multi-dimensional vectorial optical sensing. An object or system is said to be chiral if it cannot be superimposed on its mirror reflection. Chirality is ubiquitous in nature, for example, in protein molecules and chiral phonons—acoustic waves carrying angular momentum—which are usually either intrinsically present or magnetically excited in suitable materials. Here, we report the use of intervortex forward Brillouin scattering to optically excite chiral flexural phonons in a twisted photonic crystal fiber, which is itself a chiral material capable of robustly preserving circularly polarized optical vortex states. The phonons induce a spatiotemporal rotating linear birefringence that acts back on the optical vortex modes, coupling them together. We demonstrate intervortex frequency conversion under the mediation of chiral flexural phonons and show that, for the same phonons, backward and forward intervortex conversion occurs at different wavelengths. The results open up, to our knowledge, new perspectives for Brillouin scattering and the chiral flexural phonons offer new opportunities for vortex-related information processing and multi-dimensional vectorial optical sensing.
Photonics Research
- Publication Date: Jul. 01, 2025
- Vol. 13, Issue 7, 1997 (2025)
High-harmonic generation in submicron-thick chirped periodically poled thin-film lithium niobate
Lingzhi Peng, Xiaoni Li, Liqiang Liu, Yuanyuan Liu, Yuanyuan Zhao, Xuanming Duan, Lihong Hong, and Zhiyuan Li
Submicron-thick thin-film lithium niobate (TFLN) has emerged as a promising platform for nonlinear integrated photonics. In this work, we demonstrate the efficient simultaneous generation of broadband 2nd–8th harmonics in chirped periodically poled (CPP) TFLN. This is achieved through the synergistic effects of cascaded χ(2) nonlinear up-conversion and χ(3) self-phase modulation, driven by near-infrared femtosecond pulses with a central wavelength of 2100 nm and a pulse energy of 1.2 μJ. Remarkably, the 7th and 8th harmonics extend into the deep ultraviolet (DUV) region, reaching wavelengths as short as 250 nm. The 3rd–8th harmonic spectra seamlessly connect, forming a broadband supercontinuum spanning from the DUV to the visible range (250–800 nm, -25 dB), with an on-chip conversion efficiency of 19% (0.23 μJ). This achievement is attributed to the CPP-TFLN providing multiple broadband reciprocal lattice vector bands, enabling quasi-phase matching for a series of χ(2) nonlinear processes, including second harmonic generation (SHG), cascaded SHG, and third harmonic generation. Furthermore, we demonstrated the significant role of cascaded χ(2) phase-mismatched nonlinear processes in high-harmonic generation (HHG). Our work unveils the intricate and diverse nonlinear optical interactions in TFLN, offering a clear path toward efficient on-chip HHG and compact coherent white-light sources extending into the DUV. Submicron-thick thin-film lithium niobate (TFLN) has emerged as a promising platform for nonlinear integrated photonics. In this work, we demonstrate the efficient simultaneous generation of broadband 2nd–8th harmonics in chirped periodically poled (CPP) TFLN. This is achieved through the synergistic effects of cascaded χ(2) nonlinear up-conversion and χ(3) self-phase modulation, driven by near-infrared femtosecond pulses with a central wavelength of 2100 nm and a pulse energy of 1.2 μJ. Remarkably, the 7th and 8th harmonics extend into the deep ultraviolet (DUV) region, reaching wavelengths as short as 250 nm. The 3rd–8th harmonic spectra seamlessly connect, forming a broadband supercontinuum spanning from the DUV to the visible range (250–800 nm, -25 dB), with an on-chip conversion efficiency of 19% (0.23 μJ). This achievement is attributed to the CPP-TFLN providing multiple broadband reciprocal lattice vector bands, enabling quasi-phase matching for a series of χ(2) nonlinear processes, including second harmonic generation (SHG), cascaded SHG, and third harmonic generation. Furthermore, we demonstrated the significant role of cascaded χ(2) phase-mismatched nonlinear processes in high-harmonic generation (HHG). Our work unveils the intricate and diverse nonlinear optical interactions in TFLN, offering a clear path toward efficient on-chip HHG and compact coherent white-light sources extending into the DUV.
Photonics Research
- Publication Date: Jul. 01, 2025
- Vol. 13, Issue 7, 1917 (2025)
Polarization-dependent neutral nitrogen fluorescence induced by long-distance laser filamentation
Yuezheng Wang, Lu Sun, Zhiwenqi An, Zeliang Zhang, Zhi Zhang, Nan Zhang, Pengfei Qi, Lie Lin, and Weiwei Liu
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, Grégory Gadret, Pierre Mathey, Frédéric Smektala, and Bertrand Kibler
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, George N. Ghalanos, Toby Bi, Haochen Yan, Hao Zhang, Yongyong Zhuang, Lewis Hill, and Pascal Del’Haye
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, Anatoly V. Masalov, Valery E. Lobanov, Igor A. Bilenko, and Artem E. Shitikov
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, Haigang Liu, and Xianfeng Chen
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, Fei Ma, Ke Zhang, Wenzhao Sun, and Cheng Wang
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, Ben Sun, Yan Liang, Qiang Hao, E. Wu, Ming Yan, and Heping Zeng
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)
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