Nonlinear Optical Waveguides Research Articles

Coupled Thermal and Power Transport of Optical Waveguide Arrays: Photonic Wiedemann-Franz Law and Rectification Effect.

In isolated nonlinear optical waveguide arrays, simultaneous conservation of longitudinal momentum flow ("internal energy") and optical power ("particle number") of the optical modes enables study of coupled thermal and particle transport in the negative temperature regime. Based on exact numerical simulation and rationale from Landauer formalism, we predict generic photonic version of the Wiedemann-Franz law in such systems, with the Lorenz number L∝|T|^{-2}. This is rooted in the spectral decoupling of thermal and particle current, and their different temperature dependence. In addition, in asymmetric junctions, relaxation of the system toward equilibrium shows apparent asymmetry for positive and negative biases, indicating rectification behavior. This Letter illustrates the possibility of simulate nonequilibrium transport processes using optical networks, in parameter regimes difficult to reach in natural condensed matter or atomic gas systems. It also provides new insights in manipulating power and momentum flow of optical waves in artificial waveguide arrays.

Giant nonlinear optical wave mixing in a van der Waals correlated insulator.

Optical nonlinearities are one of the most fascinating properties of two-dimensional (2D) materials. While tremendous efforts have been made to find and optimize the second-order optical nonlinearity in enormous 2D materials, opportunities to explore higher-order ones are elusive because of the much lower efficiency. Here, we report the giant high odd-order optical nonlinearities in centrosymmetric correlated van der Waals insulator manganese phosphorus triselenide. When illuminated by two near-infrared femtosecond lasers, the sample generates a series of profound four- and six-wave mixing outputs. The near-infrared third-order nonlinear susceptibility reaches near the highest record values of 2D materials. Comparative measurements to other prototypical nonlinear optical materials [lithium niobate, gallium(II) selenide, and tungsten disulfide] reveal its extraordinary wave mixing efficiency. The wave mixing processes are further used for nonlinear optical waveguide with multicolor emission. Our work highlights the promising prospect for future research of the nonlinear light-matter interactions in the correlated 2D system and for potential nonlinear photonic applications.

Motion dynamics of two-dimensional fundamental and vortex solitons in the fractional medium with the cubic-quintic nonlinearity

Motion dynamics of two-dimensional fundamental and vortex solitons in the fractional medium with the cubic-quintic nonlinearity

Highly controllable stabilization and switching of multiple colliding soliton sequences with generic Ginzburg–Landau gain–loss

We investigate propagation of J soliton sequences in a nonlinear optical waveguide array with generic weak Ginzburg–Landau (GL) gain–loss and nearest-neighbor (NN) interaction. The propagation is described by a system of J perturbed coupled nonlinear Schrödinger (NLS) equations. The NN interaction property leads to the elimination of collisional three-pulse interaction effects, which prevented the observation of stable multisequence soliton propagation with J>2 sequences in the presence of generic GL gain–loss in all previous studies. We show that the dynamics of soliton amplitudes can be described by a generalized J-dimensional Lotka–Volterra (LV) model. Stability and bifurcation analysis for the equilibrium points of the LV model, which is augmented by an application of the Lyapunov function method, is used to develop setups that lead to robust and scalable transmission stabilization and switching for a general J value. The predictions of the LV model are confirmed by extensive numerical simulations with the perturbed coupled-NLS model with J=3, 4, and 5 soliton sequences. Furthermore, soliton stability and the agreement between the LV model’s predictions and the simulations are not reduced with increasing value of J. Therefore, our study provides the first demonstration of robust control of multiple colliding sequences of NLS solitons in the presence of generic weak GL gain–loss with an arbitrary number of sequences. Due to the robustness and scalability of the results, they can have important applications in stabilization and switching of broadband soliton-based optical waveguide transmission.

Silicon nanocrystal slab optical waveguide by multi-energy ion implantation: Linear and nonlinear optical properties

Silicon nanocrystals (Si-nc) have gained attention in optics and photonics research areas in recent years due to their advanced optical nonlinear properties. However, a nonlinear integrated optical platform that allows the fabrication of photonic devices with different Si-nc composition is yet under investigation. In this work, we experimentally demonstrated a nonlinear optical waveguide based on ion implantation that offers advantages in terms of material composition, low propagation losses, and enhanced nonlinear optical properties, such as a high nonlinear refractive index. In this work we present the fabrication of Si-nc containing waveguiding structures, and a study of their linear and nonlinear optical properties. Our nonlinear integrated optical platform presents a two-photon absorption coefficient β = 3.17 × 10−6 cm W−1 and a nonlinear refractive index n2 = 1.19 × 10−10 cm2 W−1, which shows potential applications in all-optical signal processing devices, such as single-photon sources.

Simultaneous generation and manipulation of terahertz waves based on nonlinear leaky-waveguide antennas with integrated bianisotropic metasurfaces.

We hereby propose and theoretically investigate a new scheme for simultaneous generation and manipulation of terahertz (THz) waves through difference frequency generation facilitated by a metasurface-assisted nonlinear leaky waveguide antenna. The proposed structure integrates a nonlinear optical waveguide, composed of multiple AlxGa1-xAs layers, with a THz leaky waveguide, wherein a bianisotropic metasurface realizes the radiating aperture. By explicitly utilizing the electric, magnetic, and magnetoelectric coupling responses of the metasurface, we demonstrate that the generated THz wave can be induced as a tightly confined, phase-matched guided mode for efficient generation of the THz wave. Additionally, this approach allows the THz wave to be transformed into a directive beam, radiating at a user-defined leakage rate and direction. Our numerical analyses suggest that THz beams ranging from 2.85 THz to 3.05 THz can be steered from 4 ∘ to 40 ∘, utilizing the inherent beam-steering capabilities of the leaky-waveguide antenna. Within this THz frequency spectrum, the phase matching condition is achieved by adjusting the optical wavelengths between 1.6μm and 1.52μm. In particular, the nonlinear conversion efficiency is 2.9 × 10-5 [1/W] at 3 THz.

High‐Contrast Switching of Light Enabled by Zero Diffraction

Diffraction allows to change the direction of light. Therefore, controlling the diffraction efficiency with high contrast enables controlling the pathway of light within optical systems. However, a high contrast requires that the diffraction efficiency is tunable close to zero. Probably the most prominent example for zero diffraction in a waveguide grating is a bound state in the continuum (BIC). Herein, zero diffraction of two plane waves under symmetric incidence to a leaky symmetric waveguide grating is found. The phenomenon not only occurs at singular spectral positions but on continuous curves in the energy–momentum space. The relative phase of the two waves enables large contrast control over diffraction in a wide spectral range. The practical meaning of this finding for local switching is demonstrated. Light is trapped into a nonlinear optical waveguide and detrapped at a desired position with electric control. A switching contrast exceeding 1000 is experimentally shown.

An elastic luminescent organic single crystal with linear and nonlinear optical waveguide properties

In recent years, organic single crystals combining elastic and photoluminescent (PL) properties have attracted extensive attention due to their promising applications in many fields. However, elastic organic crystals with two-photon luminescence (2 PL) waveguiding properties are still rarely found, which is imperative for various applications, including near-infrared (NIR) bioimaging and nonlinear optical (NLO) photonic devices. This work reports an elastic single crystal with a long needle shape, anthracene-9,10-dicarbaldehyde (An-DC). Its crystal (100) face exhibits highly reversible bending by applying the mechanical force, which is facilitated by the van der Waals (C– H···π), H-bond (C–H⋯O), and π···π interactions among molecules. The crystal emits a strong orange-red fluorescence when excited by blue-violet light. Interestingly, it also exhibits excellent two-photon fluorescence emission when stimulated by near-infrared light. Based on these linear and nonlinear optical characteristics, the waveguide applications of the An-DC crystal were implemented. Notably, in the bending state, the luminescence performance and the crystal structure of the An-DC crystal are maintained well, which can be used as a low-loss material for linear and nonlinear optical waveguide devices, thus expanding the potential use of flexible organic crystals.

Propagation of the ordinary and extraordinary modulated optical pulses in a nonlinear Kerr-type birefringent optical waveguide: Analytical description

The purpose of this work is to describe theoretically the behavior of modulated pulses in nonlinear birefringent optical waveguides and particularly in the optical fibers, by taking into account the anisotropy of the medium as well as the orientation of the optical axis with respect to the propagation direction of an incoming pulse. Firstly, the multiple times scale method is used to describe the behavior of an optical pulse in the waveguide whose optical axis is perpendicular to the direction of propagation of the pulse. It appears that in the nonlinear regime, the optical pulse splits into two different modes in propagation namely an ordinary mode and an extraordinary mode which propagate with different group velocities. These modes are described by the different nonlinear Schrodinger (NLS) equations involving nonlinear Kerr-like responses. Next, we turn attention to the waveguide whose the optical axis is parallel to the direction of propagation of an incoming pulse and found that the two modes continue to exist, and are also described by different NLS equations. In addition, we show that for some parameter regime, the two modes become identical and described by the same NLS equation.

Stabilizing solitons of the cubic–quintic nonlinear Schrödinger equation by frequency-dependent linear gain-loss and delayed Raman response

We demonstrate transmission stabilization against radiation emission by frequency-dependent linear gain-loss and perturbation-induced frequency shifting for solitons of the cubic–quintic nonlinear Schrödinger (CQNLS) equation. We consider soliton propagation in a nonlinear optical waveguide with focusing cubic nonlinearity, defocusing quintic nonlinearity, and dissipative perturbations due to weak frequency-dependent linear gain-loss, cubic loss, and delayed Raman response. The frequency shifting is induced by delayed Raman response. Our perturbation analysis and numerical simulations with the perturbed CQNLS equation show that transmission stabilization with CQNLS solitons is indeed possible, and in this way provide the first demonstration of the stabilization method for solitons of a nonintegrable nonlinear wave model. Moreover, we find that transmission stabilization with energetic CQNLS solitons is realized with significantly smaller frequency shifts and pulse distortion compared with stabilization with energetic solitons of the cubic nonlinear Schrödinger equation. Therefore, our study also demonstrates that stabilization of energetic solitons by the method is significantly improved by the presence of defocusing quintic nonlinearity.

Crystal packing and photoelectric property of bis(2-picolyl)amine-functionalized triarylborane and its complexes

Organic crystalline materials are attracting increasing interest due to their promising applications in the fields of nonlinear optics (NLO), organic lasers, optical waveguides, and light-emitting transistors. In this paper, a photoelectric molecule QB was constructed through combining an electron-withdrawing unit, a triarylborane, and a metal-ligand unit of bis(2-picolyl)amine. The crystallization behavior and crystalline photoelectric properties of QB and its complexes were thoroughly studied. This compound exhibited polymorphism, and a green emitting block-like crystal and blue-emission lamellar crystal were obtained, respectively. Their different photoluminescence mechanisms were clarified through X-ray crystallographic analysis and theoretical calculations. Furthermore, the single-crystal structures of the complexes of QB coordinating with KCN and Zn(ClO4)2 were also determined. Crystal QB-KCN emitted strong blue fluorescence at 445 nm, owing to the formation of rigid 2-to-2 adduct, which could effectively suppress non-radiative transitions. Crystal QB-Zn(ClO4)2 showed very weak cyan emission due to its loose molecular packing. The electrochemical results illuminated that the metal coordination can effectively affect the electron-withdrawing ability of conjugated triarylborane, and further affect the monomolecular luminescent properties due to the intramolecular charge transfer. We believe that polymorphism and metal coordination are available means to obtain excellent crystalline photoelectric materials.

Spatially resolved multimode excitation for smooth supercontinuum generation in a SiN waveguide.

We propose a method of supercontinuum light generation enhanced by multimode excitation in a precisely dispersion-engineered deuterated SiN (SiN:D) waveguide. Although a regularly designed SiN-based nonlinear optical waveguide exhibits anomalous dispersion with the fundamental and first-order multimode operation, the center-symmetric light pumping at the input edge has so far inhibited the full potential of the nonlinearity of SiN-based materials. On the basis of numerical analysis and simulation for the SiN:D waveguide, we intentionally applied spatial position offsets to excite the fundamental and higher-order modes to realize bandwidth broadening with flatness. Using this method, we achieved an SNR improvement of up to 18 dB at a wavelength of 0.6 µm with an offset of about 1 µm in the Y-axis direction and found that the contribution was related to the presence of dispersive waves due to the excitation of TE10, and TE01 modes.

Polygons of quantized vortices in nonlinear photonic waveguides

In a nonlinear optical waveguide with defocusing Kerr-type nonlinearity, we discuss the existence of a type of stationary nonlinear waves with propagation-invariant density profiles, consisting of vortices located at the vertices of a regular polygon with or without an anti-vortex at its center. These polygons rotate around the center of the system and we provide approximate expressions for their angular velocity. We have computed the evolution of the vortex structures and discuss their stability and the fate of the instabilities that can unravel the regular polygon configurations. Such instabilities can be driven by the instability of the vortices themselves, by vortex-antivortex annihilation or by the eventual breaking of the symmetry due to the motion of the vortices.

A collocation-based spectral element method for computing nonlinear optical waveguide

Computation of nonlinear optical waveguide needs to solve nonlinear eigenvalue/ eigenfunction problem mathematically. However, usually the refractive index profiles in the nonlinear optical waveguide are discontinuous, which makes solution of nonlinear eigenvalue/eigenfunction problem not smooth enough. In this work, we mainly discuss how to use high-order collocation-based spectral element method (SEM) to discretize such problem and propose an iterative algorithm for computing nonlinear optical waveguide with discontinuous refractive index profiles. Starting from the linear eigenvalue/eigenfunction problem, we adopt SEM to discretize it and solve the resulting discretized system with Matlab eigen solver; for the nonlinear problem, we first change the nonlinear problem into corresponding linear problems, and then solve the linear problems by usage of the iterative method. The proposed method has advantage of high-order accuracy and lower-order cost. The accuracy and efficiency of the method are tested by several one-dimensional and two-dimensional linear optical waveguide structures. Numerical results for some nonlinear optical waveguide are also presented.

Full-Vector Mode Solver for Nonlinear Optical Waveguides Using Meshfree Finite Cloud Method

A full-vector mode solver based on the meshfree (MF) finite cloud method (FCM) is developed for analysis of nonlinear optical waveguide. Self-consistent solutions are approximated through a simple iterative scheme after the nonlinear eigenvalue matrix equation derived using the quadratic basis function as well as the MF shape function. The proposed mode solver can significantly reduce the computational requirements since major parts of formulations are tackled analytically. Results for two numerical examples are presented and compared with those from the well-known finite element method (FEM) and FEM-based imaginary-distance beam propagation method (FEM-IDBPM), respectively, showing the validity and utility of the proposed method.

Review on optical nonlinearity of group-IV semiconducting materials for all-optical processing

Group-IV semiconductor compounds with intense optical nonlinearity have emerged as a new branch of all-optical processing materials benefiting from the manufacturing compatibility with silicon electronic and photonic integrated circuits. Due to the chemical reforming on the bonding or precipitating feature of the compositional atoms in the membrane matrix, either the orbital hybridization or the quantum self-assembly of interstitial composites can be employed to reform the electronic and optical characteristics. The recent development on enhancing the nonlinear refractive indices of the group-IV semiconductor materials has revealed significant progress to accelerate the all-optical switching logic, which greatly reduces the energy consumption to enable the constitution of the advanced multi-logic gating and the entry-level photonic computing circuits. This work not only overviews the group-IV semiconductor photonic data processing elements but also prospects for the future direction of optical quantum computation and communication. To date, the nonlinear refractive indices of the group-IV semiconductor materials can be obtained as 10−8 to 10−16 cm2/W in the range between 300 and 10 000 nm in 2022. The wavelength conversion and data switching with bit rate beyond 25 Gbps have been achieved via nonlinear photonic waveguide components. By taking the non-stoichiometric SiC-made micro-ring waveguide as an example, the n2 as high as 3.05 × 10−14 cm2/W of the resonant SiC micro-ring gate is retrieved from the pump–probe analysis. The eye-diagram of the wavelength converted data in the micro-ring achieves its signal-to-noise and on/off-extinction ratios (SNR and ER) of 5.6 and 11.8 dB, while up to 25-Gbps all-optical data-format inversion with 4.8-dB SNR and 10.2-dB ER is also performed during an ultrafast switching within rising and falling time of less than 22 ps. Such all-optical data processing including both wavelength switching and format conversion in the highly nonlinear optical SiC waveguide resonator can achieve error-free operation with corresponding bit-error-ratios of lower than 1 × 10−5 at 25 Gbps after forward error correction.

Nonlinear waveguides by femtosecond laser writing of lithium triborate crystals

Nonlinear optical waveguides play a crucial role in the wavelength/frequency conversion of light. Femtosecond laser direct writing is an efficient and flexible technique to produce waveguides in dielectrics. We report on the nonlinear waveguides in LiB3O5 crystals by femtosecond laser writing. The double-line and depressed-cladding structures inscribed by femtosecond laser pulses show excellent guiding properties at 405 nm or 810 nm for both TE and TM polarized light. The investigations of the confocal micro-Raman spectroscopy have indicated that lattice structures in waveguide cores remain almost unchanged compared with those of the bulk. Based on type-I phase matching condition, both second harmonic generation of 810 nm and spontaneous parametric down conversion of 405 nm have been obtained in the laser-written lithium triborate waveguides, suggesting potential applications in integrated nonlinear optics and quantum photonics.

Modulational instability of truncated Airy pulses in cubic–quintic nonlinear optical waveguides with multiphoton absorptions

In this work we study the modulational instability (MI) phenomenon of truncated Airy pulses in a cubic–quintic nonlinear optical waveguide including nonlinear multiphoton absorptions as the two-photon absorption (TPA) and the three-photon absorption (3PA) in the anomalous group-velocity dispersion (AGVD) regime of chromatic dispersion. The investigation is done through a lossless and dimensionless cubic–quintic nonlinear Schrödinger equation (CQNLSE) where we launch a perturbed truncated Airy pulse. The perturbation is defined through the linear analysis of the steady-state of a continuous-wave (CW) in which we have chosen to operate with the optimal frequencies of the MI gain. The data obtained through this analysis led to generate the destabilization of the pulse through its lobes starting with the dominant peak. This MI is improved by the cooperating nonlinearities while its distance of achievement is reduced in this case growing from the main lobe to secondary sides lobes of tail. The MI is avoided in the competing case of nonlinearities for small peak power because the negative quintic Kerr nonlinearity (QKN) reduces or almost cancels the cubic Kerr nonlinearity (CKN) effect. If the peak power of the pulse increases, the deleterious effect of the competing QKN decreases while the AGVD and the CKN take over to bring the MI into existence breaking the Airy pulse into sub-pulses. This feature becomes more and more noised as the peak power increases. The TPA comes as a limiting factor of the MI for both the cases of cooperating and competing nonlinearities. The introduction of 3PA performs this TPA effect in the case of cooperating nonlinearities while in the competing case, the 3PA surprisingly cancels the TPA, increasing the AGVD effect. Since the same feature has already been observed recently in Ref. Heuteu et al, J. Opt. 23, 095503 (2021) for the supercontinuum generation (SCG) of Airy pulses, it is therefore shown that the 3PA could be used for better control the TPA effect even in the MI of this kind of pulses. Moreover, it is also shown that the increase of the Airy pulse duration drastically enhances its MI occurrence with noised outputs for large values of pulse width. However, reducing the pulse width also reduces its input energy, consequently the Airy pulse does not undergo the MI phenomenon but simply manifests the property of acceleration.

Complete conversion between one and two photons in nonlinear waveguides: theory of dispersion engineering

High-efficiency photon-pair production is a long-sought-after goal for many optical quantum technologies, and coherent photon conversion (CPC) processes are promising candidates for achieving this. We show theoretically how to control coherent conversion between a narrow-band pump photon and broadband photon pairs in nonlinear optical waveguides by tailoring frequency dispersion for broadband quantum frequency mixing. We reveal that complete deterministic conversion as well as pump-photon revival can be achieved at a finite propagation distance. We also find that high conversion efficiencies can be realised robustly over long propagation distances. These results demonstrate that dispersion engineering is a promising way to tune and optimise the CPC process.

High-efficiency second harmonic generation of blue light on thin-film lithium niobate.

The strength of interactions between photons in a χ(2) nonlinear optical waveguide increases at shorter wavelengths. These larger interactions enable coherent spectral translation and light generation at a lower power, over a broader bandwidth, and in a smaller device: all of which open the door to new technologies spanning fields from classical to quantum optics. Stronger interactions may also grant access to new regimes of quantum optics to be explored at the few-photon level. One promising platform that could enable these advances is thin-film lithium niobate (TFLN), due to its broad optical transparency window and possibility for quasi-phase matching and dispersion engineering. In this Letter, we demonstrate second harmonic generation of blue light on an integrated thin-film lithium niobate waveguide and observe a conversion efficiency of η0 = 33, 000%/W-cm2, significantly exceeding previous demonstrations.