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Nonlinear Optics|114 Article(s)
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)
Microscopic nonlinear optical activities and ultrafast carrier dynamics in layered AgInP2S6
Zixin Wang, Ningning Dong, Yu Mao, Chenduan Chen, Xin Chen, Chang Xu, Zhouyuan Yan, and Jun Wang
Since the emergence of graphene, transition metal dichalcogenides, and black phosphorus, two-dimensional materials have attracted significant attention and have driven the development of fundamental physics and optoelectronic devices. Metal phosphorus trichalcogenides (MPX3), due to their large bandgap of 1.3–3.5 eV, enable the extension of optoelectronic applications to visible and ultraviolet (UV) wavelengths. Micro-Z/I-scan (μ-Z/I-scan) and micro-pump-probe (μ-pump-probe) setups were used to systematically investigate the third-order nonlinear optical properties and ultrafast carrier dynamics of the representative material AgInP2S6. UV-visible absorption spectra and density functional theory (DFT) calculations revealed a quantum confinement effect, in which the bandgap decreased with increasing thickness. The two-photon absorption (TPA) effect is exhibited under the excitation of both 520 and 1040 nm femtosecond pulses, where the TPA coefficient decreases as the AgInP2S6 thickness increases. In contrast, the TPA saturation intensity exhibits the opposite behavior that the TPA saturation is more likely to occur under visible excitation. After the valence band electrons undergo photon transitions to the conduction band, the non-equilibrium carriers relax through non-radiative and defect-assisted recombination. These findings provide a comprehensive understanding of the optical response process of AgInP2S6 and are a valuable reference for the development of optoelectronic devices. Since the emergence of graphene, transition metal dichalcogenides, and black phosphorus, two-dimensional materials have attracted significant attention and have driven the development of fundamental physics and optoelectronic devices. Metal phosphorus trichalcogenides (MPX3), due to their large bandgap of 1.3–3.5 eV, enable the extension of optoelectronic applications to visible and ultraviolet (UV) wavelengths. Micro-Z/I-scan (μ-Z/I-scan) and micro-pump-probe (μ-pump-probe) setups were used to systematically investigate the third-order nonlinear optical properties and ultrafast carrier dynamics of the representative material AgInP2S6. UV-visible absorption spectra and density functional theory (DFT) calculations revealed a quantum confinement effect, in which the bandgap decreased with increasing thickness. The two-photon absorption (TPA) effect is exhibited under the excitation of both 520 and 1040 nm femtosecond pulses, where the TPA coefficient decreases as the AgInP2S6 thickness increases. In contrast, the TPA saturation intensity exhibits the opposite behavior that the TPA saturation is more likely to occur under visible excitation. After the valence band electrons undergo photon transitions to the conduction band, the non-equilibrium carriers relax through non-radiative and defect-assisted recombination. These findings provide a comprehensive understanding of the optical response process of AgInP2S6 and are a valuable reference for the development of optoelectronic devices.
Photonics Research
- Publication Date: Mar. 21, 2024
- Vol. 12, Issue 4, 691 (2024)
Cnoidal waves and their soliton limits in single mode fiber lasers
Xiao Hu, Tupei Chen, Seongwoo Yoo, and Dingyuan Tang
Cnoidal waves are a type of nonlinear periodic wave solutions of the nonlinear dynamic equations. They are well known in fluid dynamics, but it is not the case in optics. In this paper we show both experimentally and numerically that cnoidal waves could be formed in a fiber laser either in the net normal or net anomalous cavity dispersion regime, especially because, as the pump power is increased, the formed cnoidal waves could eventually evolve into a train of bright (in the net anomalous cavity dispersion regime) or dark (in the net normal cavity dispersion regime) solitons. Numerical simulations of the laser operation based on the extended nonlinear Schrödinger equation (NLSE) have well reproduced the experimental observations. The result not only explains why solitons can still be formed in a fiber laser even without mode locking but also suggests a new effective way of automatic stable periodic pulse train generation in lasers with a nonlinear cavity. Cnoidal waves are a type of nonlinear periodic wave solutions of the nonlinear dynamic equations. They are well known in fluid dynamics, but it is not the case in optics. In this paper we show both experimentally and numerically that cnoidal waves could be formed in a fiber laser either in the net normal or net anomalous cavity dispersion regime, especially because, as the pump power is increased, the formed cnoidal waves could eventually evolve into a train of bright (in the net anomalous cavity dispersion regime) or dark (in the net normal cavity dispersion regime) solitons. Numerical simulations of the laser operation based on the extended nonlinear Schrödinger equation (NLSE) have well reproduced the experimental observations. The result not only explains why solitons can still be formed in a fiber laser even without mode locking but also suggests a new effective way of automatic stable periodic pulse train generation in lasers with a nonlinear cavity.
Photonics Research
- Publication Date: Mar. 01, 2024
- Vol. 12, Issue 3, 543 (2024)
Coherent link between a Ti:sapphire comb and a 1.5 μm laser via nonlinear interaction in photonic crystal fiber
Yuan Yao, Haosen Shi, Guang Yang, Bo Li, Congyu Wang, Hongfu Yu, Longsheng Ma, and Yanyi Jiang
Optical clock networks have distinct advantages for the dissemination of time/frequency, geodesy, and fundamental research. To realize such a network, the telecom band and optical atomic clocks have to be coherently bridged. Since the telecom band and optical atomic clocks reside in a distinct spectral region, second-harmonic generation is usually introduced to bridge the large frequency gap. In this paper, we introduce a new method to coherently link a 1550 nm continuous wave laser with a Ti:sapphire mode-locked laser-based optical frequency comb. By coupling the 1550 nm continuous wave laser light and the Ti:sapphire comb light together into a photonic crystal fiber, nonlinear interaction takes place, and new comblike frequency components related to the 1550 nm laser frequency are generated in the visible region. Consequently, we can detect beat notes between two combs in the visible region with a signal-to-noise ratio of more than 40 dB in a resolution bandwidth of 300 kHz. With this signal, we realize an optical frequency divider for converting the frequency of optical clocks in the visible region to the telecom band at 1.55 μm. An out-of-loop measurement shows that the additional noise and uncertainty induced in optical frequency conversion are 5×10-18 at 1 s averaging time and 2.2×10-19, respectively, which are limited by the uncompensated light path fluctuation but fulfill precision measurement using state-of-the-art optical clocks. Optical clock networks have distinct advantages for the dissemination of time/frequency, geodesy, and fundamental research. To realize such a network, the telecom band and optical atomic clocks have to be coherently bridged. Since the telecom band and optical atomic clocks reside in a distinct spectral region, second-harmonic generation is usually introduced to bridge the large frequency gap. In this paper, we introduce a new method to coherently link a 1550 nm continuous wave laser with a Ti:sapphire mode-locked laser-based optical frequency comb. By coupling the 1550 nm continuous wave laser light and the Ti:sapphire comb light together into a photonic crystal fiber, nonlinear interaction takes place, and new comblike frequency components related to the 1550 nm laser frequency are generated in the visible region. Consequently, we can detect beat notes between two combs in the visible region with a signal-to-noise ratio of more than 40 dB in a resolution bandwidth of 300 kHz. With this signal, we realize an optical frequency divider for converting the frequency of optical clocks in the visible region to the telecom band at 1.55 μm. An out-of-loop measurement shows that the additional noise and uncertainty induced in optical frequency conversion are 5×10-18 at 1 s averaging time and 2.2×10-19, respectively, which are limited by the uncompensated light path fluctuation but fulfill precision measurement using state-of-the-art optical clocks.
Photonics Research
- Publication Date: Feb. 01, 2024
- Vol. 12, Issue 2, 350 (2024)
Hyperbolic resonant radiation of concomitant microcombs induced by cross-phase modulation
Yang Wang, Weiqiang Wang, Zhizhou Lu, Xinyu Wang, Long Huang, Brent E. Little, Sai T. Chu, Wei Zhao, and Wenfu Zhang
A high-quality optical microcavity can enhance optical nonlinear effects by resonant recirculation, which provides a reliable platform for nonlinear optics research. When a soliton microcomb and a probe optical field are coexisting in a micro-resonator, a concomitant microcomb (CMC) induced by cross-phase modulation (XPM) will be formed synchronously. Here, we characterize the CMC comprehensively in a micro-resonator through theory, numerical simulation, and experimental verification. It is found that the CMCs spectra are modulated due to resonant radiation (RR) resulting from the interaction of dispersion and XPM effects. The group velocity dispersion induces symmetric RRs on the CMC, which leads to a symmetric spectral envelope and a dual-peak pulse in frequency and temporal domains, respectively, while the group velocity mismatch breaks the symmetry of RRs and leads to asymmetric spectral and temporal profiles. When the group velocity is linearly varying with frequency, two RR frequencies are hyperbolically distributed about the pump, and the probe light acts as one of the asymptotic lines. Our results enrich the CMC dynamics and guide microcomb design and applications such as spectral extension and dark pulse generation. A high-quality optical microcavity can enhance optical nonlinear effects by resonant recirculation, which provides a reliable platform for nonlinear optics research. When a soliton microcomb and a probe optical field are coexisting in a micro-resonator, a concomitant microcomb (CMC) induced by cross-phase modulation (XPM) will be formed synchronously. Here, we characterize the CMC comprehensively in a micro-resonator through theory, numerical simulation, and experimental verification. It is found that the CMCs spectra are modulated due to resonant radiation (RR) resulting from the interaction of dispersion and XPM effects. The group velocity dispersion induces symmetric RRs on the CMC, which leads to a symmetric spectral envelope and a dual-peak pulse in frequency and temporal domains, respectively, while the group velocity mismatch breaks the symmetry of RRs and leads to asymmetric spectral and temporal profiles. When the group velocity is linearly varying with frequency, two RR frequencies are hyperbolically distributed about the pump, and the probe light acts as one of the asymptotic lines. Our results enrich the CMC dynamics and guide microcomb design and applications such as spectral extension and dark pulse generation.
Photonics Research
- Publication Date: May. 30, 2023
- Vol. 11, Issue 6, 1075 (2023)
Spatiotemporal mode decomposition of ultrashort pulses in linear and nonlinear graded-index multimode fibers|Editors' Pick
Mario Zitelli, Vincent Couderc, Mario Ferraro, Fabio Mangini, Pedro Parra-Rivas, Yifan Sun, and Stefan Wabnitz
We develop a spatiotemporal mode decomposition technique to study the spatial and temporal mode power distribution of ultrashort pulses in long spans of graded-index multimode fiber, for different input laser conditions. We find that the beam mode power content in the dispersive pulse propagation regime can be described by the Bose–Einstein law, as a result of the process of power diffusion from linear and nonlinear mode coupling among nondegenerate mode groups. In the soliton regime, the output mode power distribution approaches the Rayleigh–Jeans law. We develop a spatiotemporal mode decomposition technique to study the spatial and temporal mode power distribution of ultrashort pulses in long spans of graded-index multimode fiber, for different input laser conditions. We find that the beam mode power content in the dispersive pulse propagation regime can be described by the Bose–Einstein law, as a result of the process of power diffusion from linear and nonlinear mode coupling among nondegenerate mode groups. In the soliton regime, the output mode power distribution approaches the Rayleigh–Jeans law.
Photonics Research
- Publication Date: Apr. 25, 2023
- Vol. 11, Issue 5, 750 (2023)
Spatially engineered nonlinearity in resonant metasurfaces|On the Cover
Anna Fedotova, Mohammadreza Younesi, Maximilian Weissflog, Dennis Arslan, Thomas Pertsch, Isabelle Staude, and Frank Setzpfandt
Spatial engineering of the nonlinear susceptibility χ(2) in resonant metasurfaces offers a new degree of freedom in the design of the far-field response of second-harmonic generation (SHG). We demonstrate this by applying electric field poling to lithium niobate (LN) thin films, which inverts the spontaneous polarization and thus the sign of χ(2). Metasurfaces fabricated in periodically poled LN films reveal the distinct influence of the χ(2)-patterning on the spatial distribution of the second harmonic. This work is a first step toward far-field engineering of SHG in metasurfaces with electric field poling. Spatial engineering of the nonlinear susceptibility χ(2) in resonant metasurfaces offers a new degree of freedom in the design of the far-field response of second-harmonic generation (SHG). We demonstrate this by applying electric field poling to lithium niobate (LN) thin films, which inverts the spontaneous polarization and thus the sign of χ(2). Metasurfaces fabricated in periodically poled LN films reveal the distinct influence of the χ(2)-patterning on the spatial distribution of the second harmonic. This work is a first step toward far-field engineering of SHG in metasurfaces with electric field poling.
Photonics Research
- Publication Date: Feb. 01, 2023
- Vol. 11, Issue 2, 252 (2023)
Classical imaging with undetected photons using four-wave mixing in silicon core fibers
M. Huang, D. Wu, H. Ren, L. Shen, T. W. Hawkins, J. Ballato, U. J. Gibson, M. Beresna, R. Slavík, J. E. Sipe, M. Liscidini, and A. C. Peacock
Undetected-photon imaging allows for objects to be imaged in wavelength regions where traditional components are unavailable. Although first demonstrated using quantum sources, recent work has shown that the technique also holds with classical beams. To date, however, all the research in this area has exploited parametric down-conversion processes using bulk nonlinear crystals within free-space systems. Here, we demonstrate undetected-photon-based imaging using light generated via stimulated four-wave mixing within highly nonlinear silicon fiber waveguides. The silicon fibers have been tapered to have a core diameter of ∼915 nm to engineer the dispersion and reduce the insertion losses, allowing for tight mode confinement over extended lengths to achieve practical nonlinear conversion efficiencies (∼-30 dB) with modest pump powers (∼48 mW). Both amplitude and phase images are obtained using classically generated light, confirming the high degree of spatial and phase correlation of our system. The high powers (>10 nW) and long coherence lengths (>4 km) associated with our large fiber-based system result in high contrast and stable images. Undetected-photon imaging allows for objects to be imaged in wavelength regions where traditional components are unavailable. Although first demonstrated using quantum sources, recent work has shown that the technique also holds with classical beams. To date, however, all the research in this area has exploited parametric down-conversion processes using bulk nonlinear crystals within free-space systems. Here, we demonstrate undetected-photon-based imaging using light generated via stimulated four-wave mixing within highly nonlinear silicon fiber waveguides. The silicon fibers have been tapered to have a core diameter of ∼915 nm to engineer the dispersion and reduce the insertion losses, allowing for tight mode confinement over extended lengths to achieve practical nonlinear conversion efficiencies (∼-30 dB) with modest pump powers (∼48 mW). Both amplitude and phase images are obtained using classically generated light, confirming the high degree of spatial and phase correlation of our system. The high powers (>10 nW) and long coherence lengths (>4 km) associated with our large fiber-based system result in high contrast and stable images.
Photonics Research
- Publication Date: Jan. 10, 2023
- Vol. 11, Issue 2, 137 (2023)
Biophotonic rogue waves in red blood cell suspensions|On the Cover
Yu-Xuan Ren, Joshua Lamstein, Chensong Zhang, Claudio Conti, Demetrios N. Christodoulides, and Zhigang Chen
Rogue waves are ubiquitous in nature, appearing in a variety of physical systems ranging from acoustics, microwave cavities, optical fibers, and resonators to plasmas, superfluids, and Bose–Einstein condensates. Unlike nonlinear solitary waves, rogue waves are extreme events that can occur even without nonlinearity by, for example, spontaneous synchronization of waves with different spatial frequencies in a linear system. Here, we report the observation of rogue-wave-like events in human red blood cell (RBC) suspensions under weak light illumination, characterized by an abnormal L-shaped probability distribution. Such biophotonic extreme events arise mostly due to the constructive interference of Mie-scattered waves from the suspended RBCs, whose biconcave shape and mutable orientation give rise to a time-dependent random phase modulation to an incident laser beam. We numerically simulate the beam propagation through the colloidal suspensions with added disorder in both spatial and temporal domains to mimic random scattering due to Brownian motion. In addition, at high power levels, nonlinear beam self-focusing is also observed, leading to a dual-exponential probability distribution associated with the formation of multiple soliton-like spots. Such rogue wave events should also exist in environments with cells of other species such as swimming bacteria, and understanding of their underlying physics may lead to unexpected biophotonic applications. Rogue waves are ubiquitous in nature, appearing in a variety of physical systems ranging from acoustics, microwave cavities, optical fibers, and resonators to plasmas, superfluids, and Bose–Einstein condensates. Unlike nonlinear solitary waves, rogue waves are extreme events that can occur even without nonlinearity by, for example, spontaneous synchronization of waves with different spatial frequencies in a linear system. Here, we report the observation of rogue-wave-like events in human red blood cell (RBC) suspensions under weak light illumination, characterized by an abnormal L-shaped probability distribution. Such biophotonic extreme events arise mostly due to the constructive interference of Mie-scattered waves from the suspended RBCs, whose biconcave shape and mutable orientation give rise to a time-dependent random phase modulation to an incident laser beam. We numerically simulate the beam propagation through the colloidal suspensions with added disorder in both spatial and temporal domains to mimic random scattering due to Brownian motion. In addition, at high power levels, nonlinear beam self-focusing is also observed, leading to a dual-exponential probability distribution associated with the formation of multiple soliton-like spots. Such rogue wave events should also exist in environments with cells of other species such as swimming bacteria, and understanding of their underlying physics may lead to unexpected biophotonic applications.
Photonics Research
- Publication Date: Oct. 16, 2023
- Vol. 11, Issue 11, 1838 (2023)
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