Nonlinear Optical Modulation Research Articles

224-fs soliton pulses generation at 1μm from ytterbium-doped fiber laser with CoTe2 nanosheets as an ultrafast modulator

Transition metal ditellurides (TMDTs) have numerous attractive properties, making them suitable for a wide range of applications. In this study, cobalt ditelluride (CoTe2) nanosheets, a promising TMDT for photonic applications, were prepared using an ultrasound-enhanced liquid phase exfoliation (LPE) method. A novel saturable absorber (SA) employing CoTe2 nanosheets was then fabricated by optically depositing them on microfiber. The nonlinear optical modulation properties of the CoTe2 SA were investigated. A high-performance 1 μm ultrafast fiber laser was demonstrated by incorporating newly developed CoTe2 nanosheets-based SA in a ring cavity ytterbium-doped fiber laser (YDFL). The dynamical behaviour of the proposed passively mode-locked YDFL in response to variations in pump optical power was investigated. The findings reveal that the device achieved a modulation depth of 2.5 %, and saturation light intensity of 30.6 MW/cm2. Moreover, a stable and robust mode-locked soliton optical pulse sequence with a fundamental repetition frequency of 3.089 MHz, and a pulse duration of 224 fs was generated at 1032 nm. The proposed YDFL, being all-fiber, compact, and cost-effective, is set to find extensive applications in various domains, including optical fiber communication, sensing, and biomedical imaging.

Nonlinear optical research on 2D NbSe2 nanosheets and their ultrafast photonics applications

Two-dimensional (2D) NbSe2 is a new material with a variety of excellent properties. In this article, 2D NbSe2 nanosheets are prepared using liquid phase exfoliation (LPE) and spin coating methods. At the same time, the properties of NbSe2 were calculated by using density functional theory (DFT), exploring the changes in the electronic band structure of NbSe2 with the number of layers, and studying the optical properties of NbSe2. The nonlinear optical properties caused by the Pauli blocking effect and the absorption spectra are studied through typical nonlinear testing techniques and an ultraviolet–visible-near-infrared (UV–VIS-IR) spectrophotometer. In addition, 2 µm solid-state pulse lasers have important applications in a variety of fields. For the first time, 2D NbSe2 nanosheets are prepared as saturable absorbers (SA) and applied them to solid-state lasers as nonlinear optical modulation devices, successfully achieving the generation of ultra-short pulse lasers with a pulse duration of 445.4 ps in 2 µm band. Our research results prove that 2D NbSe2 nanosheets is a promising nanomaterial, can be prepared into nonlinear optical modulation devices with excellent performance, and show great application potential as ultrafast photonic devices. It is beneficial to the miniaturization of solid-state pulse lasers in subsequent applications.

Hollow cylindrical three-dimensional nonlinear photonic crystal for annular beam generation

We present a hollow cylindrical three-dimensional nonlinear photonic crystal for annular beam shaping. By inducing a modification with the near-infrared femtosecond laser inside lithium niobate, we experimentally achieve second-order nonlinear optical coefficient modulation in three dimensions. The center dark spot ratio of the generated annular beam can be adjusted by varying the hollow ratio of the cylindrical structure. To demonstrate the controlled linear variation of the annular distribution, we generate annular beams with center dark spot ratios ranging from 0 to 0.7. Furthermore, we illustrate the feasibility of the generated annular beam in optical trapping by manipulating glass powder particles with diameters of 4–10 μm in water. Our hollow cylindrical structure owns effective control of beam dark spot ratio, while providing a tool for generating annular beam.

Broadband Nonlinear Optical Modulator Enabled by Transition Metal Pentatelluride Nanosheets Towards Mid-Infrared Regime

Broadband Nonlinear Optical Modulator Enabled by Transition Metal Pentatelluride Nanosheets Towards Mid-Infrared Regime

Ultrafast Hot‐Electron Transfer and Plasmonic Coupling Enable Au/MXene Nanohybrids with Broadband Excellent Nonlinear Absorption

AbstractAchieving coupling between plasma oscillators can significantly modulate their intrinsic optical characteristics. In this paper, strong coupling generated by the surface plasma of MXene and Au nanobipyramids (NBPs) for broadband ultrafast nonlinear optical modulation is reported. The femtosecond transient absorption spectra reveal that the ultrafast hot electron transfer occurred in the Au/MXene nanohybrids at <200 fs. Au/Ta4C3Tx nanohybrids outperform the outstanding broadband saturable absorption (SA), with a saturation intensity 106 times less than that of the initial MXene. Laser excitation at 1100 nm results in reverse saturable absorption for Ta4C3Tx nanosheets and a strong SA for Au/Ta4C3Tx nanohybrids, which extends the range of SA. Theoretical calculations indicate that excellent nonlinearity is synergistically achieved via hot electron transfer and plasmon coupling. Femtosecond transient absorption spectra reveal that Au NBPs offer the additional occupied state for carriers through the transfer process and extend the carrier lifetime considerably. This study provides theoretical guidance for the exploration of remarkable novel nonlinear‐active 2D layer‐based materials and candidates for the practical applications of saturable absorbers.

Ternary ReS2(1-x)Se2xalloys of different composition for Q-switched and mode-locked all-fiber laser.

This paper systematically studied the composition-controlled nonlinear optical properties and pulse modulation of ternary ReS2(1-x)Se2xalloys for the first time. The compositionally modulated characteristics of ReS2(1-x)Se2xon the band gap were simulated based on the first principles. We investigated the effect of the band gap on the saturable absorption properties. In addition, we demonstrated the modulation characteristics of different components ReS2(1-x)Se2xon 1.5μm Q-switched pulse performance. The Q-switched threshold, repetition rate, and pulse duration increase as the S(sulfur)-element composition rise. And pulse energy also was affected by the S(sulfur)-element composition. The ReS0.8Se1.2SA was selected to realize a conventional soliton with high energy in the all-fiber mode-locked laser. The pulse was centered at 1562.9 nm with a pulse duration of 2.26 ps, a repetition rate of 3.88 MHz, and maximum pulse energy of 1.95 nJ. This work suggests that ReS2(1-x)Se2xhas great potential in laser technology and nonlinear optics, and widely extends the material applications in ultrafast photonics.

Fundamental frequency and second harmonic mode-locked operations in an erbium-doped fiber laser based on Cr2Sn2Te6 saturable absorbers

With the rapid development of ultrafast photonics, the need for optical modulators is expanding. In particular, the optical modulator with a high damage threshold and the ability to generate multiple soliton states. This has prompted an ongoing search for optical modulators based on two-dimensional (2D) materials. Therefore, in this work, a novel 2D material Cr2Sn2Te6 (CSnT) with modulation depth of 6.17% and saturation intensity of 15.97 MW/cm2 is prepared as saturable absorber (SA). The nonlinear optical absorption characteristics and pulse modulation applications of CSnT are showed in the Erbium-doped fiber laser (EDFL). The fundamental frequency mode-locked operation and the second harmonic mode-locked operation are realized simultaneously in the ring cavity. Moreover, CSnT SA has a high damage threshold and high stability, the damage threshold reaches 467 mW and the signal-to-noise ratio (SNR) is higher than 70 dB. The experimental findings demonstrate that the CSnT-based saturable absorber possesses remarkable nonlinear optical properties, indicating its considerable potential in the realm of ultrafast photonics.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs.

Bimetallic metal-organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

Interfacial Charge Transfer for Enhancing Nonlinear Saturable Absorption in WS2/graphene Heterostructure.

Interlayer charge-transfer (CT) in 2D atomically thin vertical stacks heterostructures offers an unparalleled new approach to regulation of device performance in optoelectronic and photonics applications. Despite the fact that the saturable absorption (SA) in 2D heterostructures involves highly efficient optical modulation in the space and time domain, the lack of explicit SA regulation mechanism at the nanoscale prevents this feature from realizing nanophotonic modulation. Here, the enhancement of SA response via CT in WS2/graphene vertical heterostructure is proposed and the related mechanism is demonstrated through simulations and experiments. Leveraging this mechanism, CT-induced SA enhancement can be expanded to a wide range of nonlinear optical modulation applications for 2D materials. The results suggest that CT between 2D heterostructures enables efficient nonlinear optical response regulation.

Silver sulfide nanoparticles as nonlinear optical modulators for Q-switching and Mode-locking at 2 μm

Silver sulfide nanoparticles as nonlinear optical modulators for Q-switching and Mode-locking at 2 μm

Mapping Light-Dressed Floquet Bands by Highly Nonlinear Optical Excitations and Valley Polarization.

Ultrafast nonlinear optical phenomena in solids have been attracting a great deal of interest as novel methodologies for the femtosecond spectroscopy of electron dynamics and control of the properties of materials. Here, we theoretically investigate strong-field nonlinear optical transitions in a prototypical two-dimensional material, hBN, and show that the k-resolved conduction band charge occupation patterns induced by an elliptically polarized laser can be understood in a multiphoton resonant picture, but, remarkably, only if using the Floquet light-dressed states instead of the undressed matter states. Our work demonstrates that Floquet dressing affects ultrafast charge dynamics and photoexcitation even from a single pump pulse and establishes a direct measurable signature for band dressing in nonlinear optical processes in solids, opening new paths for ultrafast spectroscopy and valley manipulation.

Carbon nanomaterials as nonlinear optical modulators for pulsed laser generation at near-infrared region

In this study, carbon nanoparticles (CNPs) were experimentally investigated as novel saturable absorbers (SAs) capable of delivering strong ultrashort pulses in a passively Q-switched fiber laser. Carbon nanoparticles produced by candle burning and laser ablation can act as saturable absorbers (SAs). In addition, the nonlinear saturable absorption properties of the two synthetic CNPs in telecommunication region (1.5 μm) are investigated. Nonlinear optical measurements show that both SAs have good saturable absorption properties with average modulation depths of about ∼1 and 5 % at 1560 nm. These candle soot carbon nanoparticles (CSC-np) and laser ablation carbon nanoparticles (LAC-np) based SAs, can be used as a building blocker for the generating of stable Q-switched pulses in the near-infrared region. The shortest pulse duration measured with CSC-np and LAC-np are 5.62 and 3.87 μm, respectively. The pulse energy, peak power and SNR were also compared with both SA types at the highest pump power. The damage threshold and long-term stability of the CSC-cn SA and LAC-np were also explored. To the best of the author's knowledge, it is the first comparison of performance and long-term stability of EDFL based on two experimental techniques CSC-np and LAC-np based SAs. These results indicate that LAC-np SA provide have several advantages, including a high damage threshold, good saturable absorption, and optimum stability over a long time compared to CSC-np SA.

Modulation of the NLO properties of p-coumaric acid by the solvent effects and proton dissociation

Solute-solvent interactions and deprotonation effects have been related to second-order nonlinear optical response modulators. This work takes advantage of sequential Monte Carlo/Quantum mechanics together with Time-Dependent Density Functional Theory, Coupled Cluster methods, and the hyper-Rayleigh scattering formalism to investigate how these effects influence the stability and optical response of p-coumaric acid (pCA) and its anionic and diionic forms. The solvent influences the chromophores in different ways, inducing bathochromic and hypsochromic solvatochromism so for the neutral pCA molecule as for its deprotonated derivatives. The results indicate a high sensitivity of the nonlinear optics (NLO) parameters with relation to proton dissociation. Ionization of the carboxyl group produces the lowest values of the first frequency-dependent hyperpolarizability (βHRS), while phenolic deprotonation leads to the highest values. The results show that proton removal can be used as a switch that modulates the NLO response within a wide range of values (159.15≤βHRS≤4393.97 au) greater than those reported for reference NLO chromophores like urea (37.3 au) and p-nitroaniline (74.3 au). Thermochemical analysis of enthalpies and Gibbs free energies indicate that both monoionic forms of the pCA molecule are the most stable in gas or water solvents. Furthermore, these structures represent the limits of NLO modulation in the gas and solvent phases. Analysis of the projected density of states and mapping of the molecular electrostatic potential indicate that increased contributions from conduction electrons found in the aromatic ring are the mechanism by which deprotonation enhances the NLO response. All the results show that ionic pCA forms are promising in the functionalization of optoelectronic devices.

GHz Compact Laser Enabled by GaSb Nanowires as Saturable Absorbers

Owing to the narrow bandgap and excellent optoelectronic properties, III‐Sb nanowires (NWs) enable efficient optical response from near‐infrared to mid‐infrared, making them ideal candidates for broadband optical modulation. Herein, high‐purity GaSb NWs with controlled density are prepared on the transparent substrates of glasses. The phase purity and crystallinity of as‐prepared GaSb NWs are verified by X‐ray diffraction. Z‐scan and I‐scan techniques are adopted to investigate the nonlinear optical modulation properties, displaying a high modulation depth of 40% (at 1 μm wavelength) for the GaSb NWs with growth time of 30 min. Furthermore, the as‐prepared GaSb NWs are used as the saturable absorber elements in a waveguide laser cavity, demonstrating efficient Q‐switched mode‐locked lasers with a repetition rate of 8.2 GHz and a pulse duration of 31 ps (operating at 1 μm wavelength). All results show the great potential of GaSb NWs for the ultrafast laser and nonlinear optical applications.

Stannic oxide saturable absorbers for generating Q-switched erbium-doped fiber lasers

As a kind of transition metal oxides (TMO), stannic oxide (SnO2) has aroused extensive attention due to its direct bandgap N-type semiconductor property. However, few studies have been focused on the nonlinear property and optical modulation. Herein, passively Q-switched erbium-doped fiber lasers based on SnO2 saturable absorber (SA) are constructed and experimentally verified. To our best knowledge, this is the first report on the optical nonlinearity of SnO2 as a Q-switcher for the near-infrared fiber laser. There are two kinds of SAs fabricated by the filmy and D-shaped fiber (DF) deposition methods. A stable Q-switching operation at 1568 nm was achieved induced by the SnO2 film. After replacing SnO2 film with the SnO2-DF SA, Q-switched operations with an operating wavelength of 1532 nm was achieved. To be noted for a comparison, the performance of 1530 nm Q-switched pulses is obviously improved. Our experimental results could further promote the progress of nonlinear optic and pulsed fiber lasers.

Evolution between bright and dark pulses in a MoxW1-xTe2 based fiber laser.

We proposed an erbium-doped fiber laser mode-locked with a MoxW1-xTe2-based nonlinear optical modulator for the first time to our best knowledge. This fiber laser can deliver bright pulses, bright-dark pulse pairs, dark pulses, bright-dark-bright pulses, and dark-dark-bright pulses. The modulation depth and saturation intensity of the MoxW1-xTe2-based saturable absorber were about 7.8% and 8.6 MW/cm2, respectively. When 10% of the laser in the cavity was output, conventional soliton pulses with central wavelength of 1560.1 nm can be obtained in the cavity. When 70% of the laser was output, dual-wavelength domain-wall dark pulses appeared in the laser cavity. This experiment revealed that an appropriate increase in the ratio of output energy can improve the chance of dark pulses in fiber lasers. The mode-locking states in this fiber laser can evolve with each other between bright pulses, bright-dark pulse pairs and dark pulses by adjusting the polarization controller. The results indicated that the MoxW1-xTe2 can be used to make modulators for generating dark pulses. Furthermore, our work will be of great help to improve the chance of the generation of dark pulse in fiber lasers.

Mixed Quantum-Classical Liouville Equation Treatment of Electronic Spectroscopy of Condensed Systems: Harmonic and Anharmonic Electron-Phonon Coupling.

This Review integrates the use of electronic optical response function theory and the mixed quantum-classical (MQC) Liouville equation (MQCLE), thereby leading to electronic spectroscopy in MQC media. It further sheds light on the applicability, utility, and efficiency of the mixed quantum-classical dynamics (MQCD) formalism, which starts off with the MQCLE, in probing spectroscopy and dynamics of condensed systems, whereby quantum mechanics and classical mechanics are combined systematically. The author has been exploring and implementing MQCD to investigate electron-phonon coupling effects on electronic dephasing in harmonic and anharmonic systems by calculating linear and nonlinear optical transition analytically and numerically dipole moment time correlation functions in an MQC environment, thereby presenting an in depth spectral profile analysis and their shape and symmetry. The distinctive capability of the MQC time correlation functions is that ergodicity and stationarity properties are inherently satisfied as part of the mixed quantum-classical dynamics (MQCD) framework, unlike classical correlation functions. While some research groups have applied MQCLE to calculate vibrational spectra to study hydrogen-bonded complexes in a MQC environment and other groups calculated Optical response function to probe electron transfer dynamics using the basis mapping technique, the approach, purpose, rigor, applications, and path to the end results reported herein are different. Finally, the same framework is employed to study dissipative systems in the MQC limit, whereby the zero-phonon line adopts the correct width and eliminates its asymmetry. While the full quantum mechanical model, like the multimode Brownian oscillator (MBO) model, yields the correct width and inaccurate shape in the low-temperature limit, the MQCD formalism seems to produce an accurate zero-phonon profile. Nonlinear optical signals are also reviewed in MQC media to show the applicability and utility of this approach. The vibronic optical response functions developed here will account for geometry change, frequency change, and anharmonicity upon electronic excitation to accurately probe electronic dephasing, electron-phonon coupling, shape, and symmetry of profiles and present differences and similarities to the MBO model on pure electronic dephasing. Frequency change and anharmonicity are vitally crucial for accurately assessing electron-phonon coupling upon electronic excitation. This is an additional unique result obtained by the author to further demonstrate the applicability and utility of this approach over other approximation schemes in probing electronic dephasing including that of the MBO model.

Tunable Fano resonance analysis in plasmonic waveguide side-coupled multiple Taiji resonators

In this paper, we first propose and analyze tunable Fano resonance based on indirect interaction between two Taiji resonators which both side-couple with a MIM (metal–insulator–metal) waveguide. An S-shaped branch waveguide embedded in the Taiji ring can tailor the propagating modes and then varying the number of whispering-gallery (WG) modes in the Taiji resonator, leading to the convenient tuning of Fano resonance lineshape. By covering monolayer graphene on the waveguide, Fano resonance lineshape can be all-optically tuned with relatively low pump intensity because of the optical Kerr effect of graphene; by coating UV-glue on the proposed structure, temperature sensing with high sensitivity of −0.23 nm/°C is obtained because of large negative thermo-optic coefficient of UV-glue. Furthermore, up to 16 Taiji resonators are designed and coupled with a common MIM waveguide to observe and analyze Fano lineshape variation, finally realizing the optical band-stop filter with maximal bandwidth of 49.5 nm and optical band-pass filter with maximal bandwidth of 45.3 nm. This ultra-compact micro-structure of plasmonic waveguide coupling multiple Taiji resonators demonstrates good potential applications in the nonlinear optics, optical modulation, and high-sensitivity biochemical sensors.

Generation of 1.3 µm femtosecond pulses by cascaded nonlinear optical gain modulation in phosphosilicate fiber.

Nonlinear optical gain modulation (NOGM) is a simple and effective approach to generate highly coherent ultrafast pulses with a flexible wavelength. In this work, we demonstrate 34 nJ, 170 fs pulse generation at 1319 nm through a piece of phosphorus-doped fiber by two-stage cascaded NOGM with a 1064 nm pulsed pump. Beyond the experiment, numerical results show that 668 nJ, 391 fs pulses at 1.3 µm can be produced with up to 67% conversion efficiency by increasing the pump pulse energy and optimizing the pump pulse duration. This would offer an efficient method to obtain high-energy sub-picosecond laser sources for applications such as multiphoton microscopy.

Broadband nanosecond pulse generation modulated by zirconium triselenide nanoflakes

Broadband nonlinear optical modulators are necessary for versatile applications in optical communication, laser radar, laser manufacturing, etc. Here, we report that the zirconium triselenide (ZrSe3) nanoflakes exhibit robust broadband nonlinear optical absorption and can modulate the Nd:YVO4 solid-state laser and erbium-doped ZBLAN fiber laser to deliver stable nanosecond pulse experimentally. The ZrSe3 nanoflakes have been prepared by the liquid phase exfoliation method successfully and exhibit broadband nonlinear optical absorption in the near-infrared and the mid-infrared regime. With the nonlinear absorption performance of the ZrSe3 nanoflakes, stable pulsed operation has been achieved with the output pulse width as short as 344.68 ns around 1 µm from the Q-switched Nd:YVO4 solid-state laser and 599 ns around 2.8 µm from the erbium-doped ZBLAN fiber laser successfully. The experimental results suggest that ZrSe3 nanoflakes can act as an excellent nonlinear optical modulator towards the mid-infrared regime and may make inroads toward developing high-performance broadband optoelectronic devices.