Nonlinear Optical Devices Research Articles

Third-order nonlinear optical characteristics of Er3+-doped BaMoO4 nanostructures

We report the third order nonlinear optical properties of Er3+-doped BaMoO4 nanostructures, and its dependence on Er-dopant concentration. BaMoO4 nanostructures with different concentration of Er were synthesized by chemical precipitation method and were characterized by UV–Vis absorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence measurements. The incorporation of Er ions shifted the absorption band of BaMoO4 towards higher wavelength and enhanced the light absorption in the visible region. XRD patterns showed that the powders crystallize in scheelite-type tetragonal structure. The nonlinear optical behavior of the nanostructures was investigated by a Z-scan technique at 532 nm using continuous wave Nd:YAG laser. Experimental results suggested that the addition of Er can considerably enhance the nonlinear absorption coefficient and refractive index of BaMoO4 which could be used as a potential for nonlinear optical device applications.

Graphic-processable deep neural network for the efficient prediction of 2D diffractive chiral metamaterials.

We propose a novel, to the best of our knowledge, graphic-processable deep neural network (DNN) to automatically predict and elucidate the optical chirality of two-dimensional (2D) diffractive chiral metamaterials. Four classes of 2D chiral metamaterials are studied here, with material components changing among Au, Ag, Al, and Cu. The graphic-processable DNN algorithm can not only handle arbitrary 2D images representing any metamaterials that may even go beyond human intuition, but also capture the influence of other parameters such as thickness and material composition, which are rarely explored in the field of metamaterials, laying the groundwork for future research into more complicated nanostructures and nonlinear optical devices. Notably, the rigorous coupled wave analysis (RCWA) algorithm is first deployed to calculate circular dichroism (CD) in the higher-order diffraction beams and simultaneously promote the training of DNN. For the first time we creatively encode the material component and thickness of the metamaterials into the color images serving as input of the graphic-processable DNN, in addition to arbitrary graphical parameters. Especially, the smallest intensity is found in the third-order diffraction beams of E-like metamaterials, whose CD response turns out to be the largest. A comprehensive study is conducted to capture the influence of shape, unit period, thickness, and material component of arrays on chiroptical response. As expected, a satisfied precision and an accelerated computing speed that is 4 orders of magnitude quicker than RCWA are both achieved using DNN. This work belongs to one of the first attempts to thoroughly examine the generalization ability of the graphic-processable DNN for the study of arbitrary-shaped nanostructures and hypersensitive nanodevices.

Aluminium nitride integrated photonics: a review

Abstract Integrated photonics based on silicon has drawn a lot of interests, since it is able to provide compact solution for functional devices, and its fabrication process is compatible with the mature complementary metal-oxide-semiconductor (CMOS) fabrication technology. In the meanwhile, silicon material itself has a few limitations, including an indirect bandgap of 1.1 eV, transparency wavelength of >1.1 μm, and insignificant second-order nonlinear optical property. Aluminum nitride (AlN), as a CMOS-compatible material, can overcome these limitations. It has a wide bandgap of 6.2 eV, a broad transparency window covering from ultraviolet to mid-infrared, and a significant second-order nonlinear optical effect. Furthermore, it also exhibits piezoelectric and pyroelectric effects, which enable it to be utilized for optomechanical devices and pyroelectric photodetectors, respectively. In this review, the recent research works on integrated AlN photonics in the past decade have been summarized. The related material properties of AlN have been covered. After that, the demonstrated functional devices, including linear optical devices, optomechanical devices, emitters, photodetectors, metasurfaces, and nonlinear optical devices, are presented. Last but not the least, the summary and future outlook for the AlN-based integrated photonics are provided.

Resonant Nonlinear Synthetic Metasurface with Combined Phase and Amplitude Modulations

AbstractNonlinear metasurfaces provide a promising platform for integrated nonlinear photonic devices owing to their unprecedented capability of nonlinear wavefront manipulation. However, the previously reported second‐harmonic (SH) metasurfaces are mainly based on the nonlinear Pancharatnam–Berry phase modulation. While this method is quite convenient and robust, it shows limitations of modulation efficiency and the difficulty in extending to multidimensional combined modulations. Here, the resonant nonlinear synthetic metasurface is proposed and experimentally demonstrated for independent phase and amplitude modulations of the SH beam. A high SH modulation efficiency of 75% (with a theoretical limit of 90%) is achieved in the polarization‐dependent SH metalens. Moreover, SH holographic imaging with phase and amplitude (at 2 and 4 levels) combined modulation is realized experimentally. Compared with the pure‐phase modulation, the signal‐to‐noise ratios are increased by 2 and 3 times when 2‐ and 4‐level amplitude controls are introduced. This is not only an important step in the improvement and innovation of holographic display technology, but also paves a distinct avenue toward multifunctional, higher efficiency, and ultracompact nonlinear optical devices.

Nonreciprocal Tamm plasmon absorber based on lossy epsilon-near-zero materials.

Contrary to conventional Tamm plasmon (TP) absorbers of which narrow absorptance peaks will shift toward short wavelengths (blueshift) as the incident angle increases for both transverse magnetic (TM) and transverse electric (TE) polarizations, here we theoretically and experimentally achieve nonreciprocal absorption in a planar photonic heterostructure composed of an isotropic epsilon-near-zero (ENZ) slab and a truncated photonic crystal for TM polarization. This exotic phenomenon results from the interplay between ENZ and material loss. And the boundary condition across the ENZ interface and the confinement effect provided by the TP can enhance the absorption in the ENZ slab greatly. As a result, a strong and nonreciprocal absorptance peak is observed experimentally with a maximum absorptance value of 93% in an angle range of 60∼70°. Moreover, this TP absorber shows strong angle-independence and polarization-dependence. As the characteristics above are not at a cost of extra nanopatterning, this structure is promising to offer a practical design in narrowband thermal emitter, highly sensitive biosensing, and nonreciprocal nonlinear optical devices.

Third-order optical nonlinearity in Ge-Se-Te chalcogenide glasses

We have prepared GexSe10Te90-x glasses with a composition of x from 17.5 to 26.25 and measured their properties using various diagnosis tools. It was found that, all the glasses have a transmittance more than 40% at a wavelength range from 2 to 15 μm, and linear refractive index n0 decreases but optical bandgap energy Eg increases with decreasing Te contents in the glasses. We also analysed the evolution of n2 and β as a function of Ge content, both the evolution of n2 and β are close to the prediction by Sheik-Bahae et al. for optical nonlinearity of semiconductors. In all cases, the nonlinear optical refractive index n2 measured at 3.0 μm is larger than that at 2.5 μm due to the two-photon resonance effect, and a maximum nonlinear index is 2.46 × 10−13 cm2/W at composition of Ge17.5Se10Te72.5. Such larger nonlinearity around 10−13 cm2/W observed in the present paper is one order of the magnitude larger than that in S- and Se-based chalcogenide glasses, demonstrating potentials of Te-based glasses for the applications as mid- and far-infrared nonlinear optical devices.

DFT studies of the structural, chemical descriptors and nonlinear optical properties of the drug dihydroartemisinin functionalized on C60 fullerene

Density Functional Theory (DFT) calculations where performed to study the structural, electronic and nonlinear optical properties, global reactivity descriptors and the solubility of the dihydroartemisinin drug and its functionalization on C60 fullerene. The results of this study show that the geometrical parameters of the studied molecule do not change significantly after its functionalization. Furthermore, the values of the binding and reaction energies are all negative meaning that the binding of dihydroartemisinin to C60 is energetically favorable and the synthesis of our complex structure is possible. By comparing the solvation energies, we found that the functionalization of C60 fullerene improves the solubility of dihydroartemisinin in water. The gap value of functionalized fullerene is about 2.5 eV indicating that it can be considered as a semiconductor material. Finally, the functionalization considerably improves the nonlinear optical properties and the high values of first order hyperpolarizability led us to conclude that our molecules are promising material for nonlinear optical devices.

Local Polarization Reversal by Ion Beam Irradiation in SBN Single Crystals Covered by Dielectric Layer.

Formation of the domain structure by ion beam irradiation was studied in thermally depolarized Ce-doped strontium barium niobate single crystals covered by a dielectric layer. Three types of irradiation regimes were used: dot exposure, stripe exposure, and line exposure. The dependences of the domain size and depth on the irradiated dose were measured. The circular shape of the isolated domains with partially switched broad domain boundary was obtained. Isotropic domain growth was attributed to the step generation at the wall by merging with the residual nanodomains that appeared after thermal depolarization. The obtained linear dose dependence of the switched area was attributed to the screening of the depolarization field by the injected charge. The shape distortion of the domains growing in the neighborhood with already created ones was attributed to the electrostatic interaction of the approaching charged domain walls. The obtained results can be applied for the creation of precise domain patterns with arbitrary orientation and shape to produce nonlinear optical devices with improved characteristics, including electrically tunable diffractive optical elements.

Ultrafast third-order nonlinear optical properties of self-assembled poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa multilayer films

An ultrathin multilayer film with well-defined structure containing anionic Poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa (PCPDTPhSO3Na) and cationic poly(diallydimethyl ammonium chloride) (PDDA) was prepared using layer-by-layer assembly technique. The growth of the film was monitored by UV–Vis absorption spectroscopy, showing regularly consecutive adsorption. The ultrafast third-order nonlinear optical (NLO) properties of the multilayer film were investigated via the 4f coherent imaging measurement with phase object with 190 fs laser pulses at both 400 and 532 nm. The results demonstrate that PCPDTPhSO3Na/PDDA film exhibited excellent self-focusing effect (n 2 ∼2.42 × 10−16 m2/W) and reverse saturable absorption properties (β ∼6.34 × 10−10 m/W) at 400 nm. In contrast, self-focusing effect (n 2 ∼1.81 × 10−16 m2/W) and saturable absorption properties (β ∼−8.02 × 10−10 m/W) are observed when the laser wavelength (532 nm) is near-resonant with the absorption peak (470 nm). Our studies indicate that the PCPDTPhSO3Na/PDDA film is a promising candidate for applications in NLO devices.

Broadband second-harmonic generation from artificial optical nonlinearity.

In this Letter, we present a mechanism for effectively broadening the bandwidth of second-harmonic generation (SHG) with the metamaterial-based artificial optical nonlinearity. As the nonlinear response of the artificial nonlinearity arising from the magnetoelectric coupling constructed by the meta-molecule (MM) structure, the broadband second-order nonlinearity can be built by simply combining the MMs with different geometrical sizes together. The physical model and the numerical simulation fully support the artificial generation and modulation of the broadband second harmonics. Our work suggests a new route for realizing the on-chip custom-designed nonlinear optical devices with broadband operation.

Third-order nonlinear optical properties of CuS/reduced graphene oxide nanocomposites

CuS/Reduced graphene oxide (rGO) nanocomposites can be synthesized using the hydrothermal method. X-ray diffraction and transmission electron microscopy analyses demonstrated that CuS uniformly covered the surfaces of rGO. In this paper, the nonlinear optical (NLO) properties of the CuS/rGO composites with different graphene content were investigated by a Z-scan technique. The results show that while reverse saturable absorption (RSA) is prominent in pristine CuS, saturable absorption (SA) is dominant in pristine rGO. A transition from RSA to SA is seen when the graphene content is increased in the CuS/rGO nanocomposite. The measurements results show that the improvement of nonlinearity is related to the synergistic effect between two or more materials. The research content in this paper can establishes a foundation for further study of CuS/rGO nanocomposites application in NLO devices.

Nonlinear optical property measurements of rhenium diselenide used for ultrafast fiber laser mode-locking at 1.9\xa0\u03bcm

An experimental investigation into the nonlinear optical properties of rhenium diselenide (ReSe2) was conducted at a wavelength of 1.9 μm using the open-aperture and closed-aperture Z-scan techniques for the nonlinear optical coefficient (β) and nonlinear refractive index (n2) of ReSe2, respectively. β and n2 measured at 1.9 μm were ~ − 11.3 × 103 cm/GW and ~ − 6.2 × 10–2 cm2/GW, respectively, which to the best of our knowledge, are the first reported measurements for ReSe2 in the 1.9-μm spectral region. The electronic band structures of both ReSe2 and its defective structures were also calculated via the Perdew–Becke–Erzenhof functional to better understand their absorption properties. A saturable absorber (SA) was subsequently fabricated to demonstrate the usefulness of ReSe2 for implementing a practical nonlinear optical device at 1.9 μm. The 1.9-μm SA exhibited a modulation depth of ~ 8% and saturation intensity of ~ 11.4 MW/cm2. The successful use of the ReSe2-based SA for mode-locking of a thulium–holmium (Tm–Ho) co-doped fiber ring cavity was achieved with output pulses of ~ 840 fs at 1927 nm. We believe that the mode-locking was achieved through a hybrid mechanism of saturable absorption and nonlinear polarization rotation.

Two-Dimensional Bismuthene Showing Radiation-Tolerant Third-Order Optical Nonlinearities.

The ever-increasing space exploration enterprise calls for novel and high-quality radiation-resistant materials, among which nonlinear optical materials and devices are particularly scarce. Two-dimensional (2D) materials have shown promising potential, but the radiation effects on their nonlinear optical properties remain largely elusive. We previously fabricated 2D bismuthene for mode-locking sub-ns laser; herein, their space adaption was evaluated under a simulated space radiation environment. The as-synthesized thin layers of bismuthene exhibited strong third-order nonlinear optical responses extending into the near-infrared region. Remarkably, when exposed to 60Co γ-rays and electron irradiation, the bismuthene showed only slight degradation in saturable absorption behaviors that were critical for mode-locking in space. Ultrafast spectroscopy was applied to address the radiation effects and damage mechanisms that are difficult to understand by routine techniques. This work offers a new bottom-up approach for preparing 2D bismuthene, and the elucidation of its fundamental excited-state dynamics after radiation also provides a guideline to optimize the material for eventual space applications.

Free-Space Nonreciprocal Transmission Based on Nonlinear Coupled Fano Metasurfaces

Optical nonlinearities can enable unusual light–matter interactions, with functionalities that would be otherwise inaccessible relying only on linear phenomena. Recently, several studies have harnessed the role of optical nonlinearities to implement nonreciprocal optical devices that do not require an external bias breaking time-reversal symmetry. In this work, we explore the design of a metasurface embedding Kerr nonlinearities to break reciprocity for free-space propagation, requiring limited power levels. After deriving the general design principles, we demonstrate an all-dielectric flat metasurface made of coupled nonlinear Fano silicon resonant layers realizing large asymmetry in optical transmission at telecommunication frequencies. We show that the metrics of our design can go beyond the fundamental limitations on nonreciprocity for nonlinear optical devices based on a single resonance, as dictated by time-reversal symmetry considerations. Our work may shed light on the design of flat subwavelength free-space nonreciprocal metasurface switches for pulsed operation which are easy to fabricate, fully passive, and require low operation power. Our simulated devices demonstrate a transmission ratio >50 dB for oppositely propagating waves, an operational bandwidth exceeding 600 GHz, and an insertion loss of <0.04 dB.

Four-wave mixing in a triple-core microstructure fiber.

We experimentally demonstrate four-wave mixing (FWM) in a triple-core microstructure fiber for a pump wavelength of 1064 nm. We study the transition between the case where FWM happens primarily in a single core and the case where FWM is distributed among multiple cores. The effective nonlinear coefficient is reduced by a factor of 3 (the number of cores) for distributed-core FWM compared with that for single-core FWM. This effect also leads to a three-fold reduction in the FWM bandwidth for distributed-core FWM. We report on the wavelength and polarization dependence of the core-to-core coupling length, and how those phenomena produce power-dependent coupling among the cores. These are the first reported experimental measurements of FWM in a 3-core microstructure fiber providing critical information for their use as nonlinear optical devices.

Principles to tailor the saturable and reverse saturable absorption of epsilon-near-zero material

Indium tin oxide (ITO) films have recently emerged as a new class of functional materials for nonlinear optical (NLO) devices due to their exotic properties around epsilon-near-zero (ENZ) wavelength. Here, we experimentally investigated and tailored the NLO absorption properties of ITO films. The NLO absorption response of ITO films is investigated by using the femtosecond Z-scan measurement technique at two different wavelengths of 1030 nm (out of ENZ region) and 1440 nm (within ENZ region). Interestingly, we observed conversion behavior from saturable absorption (SA) to reverse saturable absorption (RSA) at 1030 nm with the increasing incident laser intensity, whereas only SA behavior was observed at 1440 nm. We demonstrate that SA behavior was ascribed to ground-state free electrons bleaching in the conduction band, and RSA was attributed to three-photon absorption. Moreover, results reveal that ITO film shows more excellent SA performance at 1440 nm with a nonlinear absorption coefficient of ∼ − 23.2 cm / GW and a figure of merit of ∼ 1.2 2 × 10 − 1 6 esu · cm . Furthermore, we tailored the SA and RSA behaviors of ITO films at 1030 and 1440 nm wavelengths via post-annealing treatment. The modulatable NLO absorption was ascribed to the changing of free-carrier concentration in ITO films via annealing treatment. The experimental findings offered an inroad for researchers to tailor its NLO absorption properties by changing the free-carrier concentration through chemical modification such as annealing, oxidation, or defect implantation. The superior and tunable nonlinear optical response suggests that ITO film might be employed as a new class material with potential applications in novel optical switches or optical limiters to realize the all-optical information process.

Design and Dispersion Control of Microstructured Multicore Tellurite Glass Fibers with In-Phase and Out-of-Phase Supermodes

High nonlinearity and transparency in the 1–5 μm spectral range make tellurite glass fibers highly interesting for the development of nonlinear optical devices. For nonlinear optical fibers, group velocity dispersion that can be controlled by microstructuring is also of great importance. In this work, we present a comprehensive numerical analysis of dispersion and nonlinear properties of microstructured two-, four-, six-, and eight-core tellurite glass fibers for in-phase and out-of-phase supermodes and compare them with the results for one-core fibers in the near- and mid-infrared ranges. Out-of-phase supermodes in tellurite multicore fibers are studied for the first time, to the best of our knowledge. The dispersion curves for in-phase and out-of-phase supermodes are shifted from the dispersion curve for one-core fiber in opposite directions; the effect is stronger for large coupling between the fields in individual cores. The zero dispersion wavelengths of in-phase and out-of-phase supermodes shift to opposite sides with respect to the zero-dispersion wavelength of a one-core fiber. For out-of-phase supermodes, the dispersion can be anomalous even at 1.55 μm, corresponding to the operating wavelength of Er-doped fiber lasers.

Investigation on the growth, structural, optical, thermal and third-order nonlinear optical (NLO) properties of 2,3-dimethyl-N-[(E)-2,4,5-trimethoxybenzylidene] aniline (DTA) organic single crystal

Good-quality organic nonlinear single crystal of 2,3-dimethyl-N-[(E)-2,4,5-trimethoxy benzylidene] aniline (DTA) was synthesized and successfully grown at room temperature by adapting slow evaporation technique using mixed solvent of acetone and methanol. The crystal structure was experimentally confirmed by single-crystal X-ray diffraction, where the DTA crystals crystallize in the centric space group (P $$\overline{1}$$ ) with triclinic crystal system. The surface morphology of DTA was examined by the Field Emission Scanning Electron Microscope (FE-SEM) technique. The presence of various modes of functional groups of the title crystal was analyzed by Fourier-Transform Infra-Red (FT-IR) spectra. Ultraviolet–Visible-Near Infrared (UV–Vis–NIR) spectrum showed high optical transparency of ~ 88% in the Vis and NIR region with a UV–Vis absorption edge of 390 nm. The result of photoluminescence studies suggests that the DTA crystal can be used as source material to exhibit green emission light. From thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, the melting point of the grown crystal was found to be 111 °C. The standard Z-Scan technique was employed to evaluate the third-order nonlinear optical properties of the DTA crystal. The obtained third-order nonlinear parameters were compared with few of the already reported NLO crystals. All these findings indicate that the title crystal may be an attractive material for nonlinear optical device applications.

Gold Nanocluster‐Modified Titanium Nitride for Ultrafast Photonics Applications

AbstractTransition metal nitride materials exhibit unique optical characteristics and have attracted much interest for various applications, including waveguiding, photovoltaics, and nonlinear optical devices. Herein, titanium nitride (TiN), as a typical representative of biocompatible transition metal nitrides, is prepared and modified with gold nanoclusters (Au NCs) for promoting the carrier mobility, and the corresponding physical characteristics are systematically characterized. The TiN‐based saturable absorber (SA) on microfiber is fabricated and its nonlinear optical absorption property is also studied experimentally. Furthermore, the TiN‐decorated SA is applied in an ultrafast fiber laser at the communication bands. The fiber laser can generate the stable ultrashort pulses with a pulse width of 1.66 ps, a fundamental repetition rate of 7.49 MHz, and a spectral bandwidth of 2.61 nm. More importantly, the chaotic multiple pulses can be obtained, which is reported for the first time in the fiber laser based on the TiN SA on microfiber as far as it is known. The chaotic multiple pulses show many interesting characteristics, including high average pulse energy, varying pulse separations, and pulse intensities. These results have proved that the TiN shows great potential in many fields, such as advanced optical‐intensity modulator, ultrafast pulse dynamics, and optical fiber communications.

“Seeing Is Believing”—In-Depth Analysis by Co-Imaging of Periodically-Poled X-Cut Lithium Niobate Thin Films

Nonlinear and quantum optical devices based on periodically-poled thin film lithium niobate (PP-TFLN) have gained considerable interest lately, due to their significantly improved performance as compared to their bulk counterparts. Nevertheless, performance parameters such as conversion efficiency, minimum pump power, and spectral bandwidth strongly depend on the quality of the domain structure in these PP-TFLN samples, e.g., their homogeneity and duty cycle, as well as on the overlap and penetration depth of domains with the waveguide mode. Hence, in order to propose improved fabrication protocols, a profound quality control of domain structures is needed that allows quantifying and thoroughly analyzing these parameters. In this paper, we propose to combine a set of nanometer-to-micrometer-scale imaging techniques, i.e., piezoresponse force microscopy (PFM), second-harmonic generation (SHG), and Raman spectroscopy (RS), to access the relevant and crucial sample properties through cross-correlating these methods. Based on our findings, we designate SHG to be the best-suited standard imaging technique for this purpose, in particular when investigating the domain poling process in x-cut TFLNs. While PFM is excellently recommended for near-surface high-resolution imaging, RS provides thorough insights into stress and/or defect distributions, as associated with these domain structures. In this context, our work here indicates unexpectedly large signs for internal fields occurring in x-cut PP-TFLNs that are substantially larger as compared to previous observations in bulk LN.