Phase-matching Condition Research Articles

Optical properties and phase matching conditions of KTiOPO₄ crystals at terahertz frequencies in the temperature range of 5.8 to 300 K

Optical properties and phase matching conditions of KTiOPO₄ crystals at terahertz frequencies in the temperature range of 5.8 to 300 K

Antiferromagnetic Spin Wave Amplification by Scattering in the Presence of Non-Uniform Dzyaloshinskii–Moriya Interaction

In this study, we suggest a method to amplify spin waves (SWs) in antiferromagnets (AFMs). By introducing a non-uniform Dzyaloshinskii–Moriya (DM) interaction, the potential barrier forms a resonant cavity. SWs with an opposite chirality undergo scattering and are resonantly amplified at a phase-matching condition. The calculation is performed in the insulating AFMs where the electric-field-induced DM interaction and pseudo-dipole anisotropy broaden the parabolic-like SW band for multiple resonant modes. Using a transfer matrix method, we also show numerically that scattering between SWs contributes significantly to the SW amplification. Since the electric field selectively amplifies the SWs with resonant frequencies, the proposed device works as an SW transistor and rectifier. This finding will contribute to insulating AFM-based magnon devices where Joule heating is, in principle, avoided.

Optical parametric amplification and oscillation in nonlinear chiral media.

We discuss the nonlinear process of optical parametric amplification inside a chiral crystal. We show that circular birefringence, induced by chirality, leads to two different nonlinear processes with different phase-matching conditions that are associated with the opposite states of circular polarizations. A single nonlinear process occurs only when the states of polarization of the incident pump and signal beams are both circular and orthogonal. When these beams are linearly polarized initially, their state of polarization evolves in an elliptical fashion because of the two competing nonlinear processes taking place in parallel. We also discuss the properties of singly and doubly resonant optical parametric oscillators made by placing a chiral nonlinear crystal inside an optical cavity.

Josephson traveling wave parametric amplifiers with plasma oscillation phase matching

High gain and large bandwidth of traveling-wave parametric amplifier exploiting the nonlinearity of Josephson Junctions can be achieved by fulfilling the so-called phase-matching condition. This condition is usually addressed by placing resonant structures along the waveguide or by periodic modulations of its parameters, creating gaps in the waveguide’s dispersion. Here, we propose to employ the Josephson junctions, which constitute the centerline of the amplifier, as resonant elements for phase matching. By numerical simulations in JoSIM (and WRspice) software, we show that Josephson plasma oscillations can be utilized to create wave vector mismatch sufficient for phase matching as well as to prevent the conversion of the pump energy to higher harmonics. The proposed traveling wave parametric amplifier design has a gain of 15 dB and a 3 GHz bandwidth, which is comparable to the state-of-the-art TWPAs.

Nonlinear optical properties of some nanosized ammonium dihydrogen phosphate crystals incorporated in aluminum oxide nanopores

This study explores the nonlinear optical properties of aluminum oxide (Al2O3) matrices embedded in ammonium dihydrogen phosphate (ADP) nanocrystals using third-harmonic generation (THG) techniques. The successful integration of ADP crystallites within the nanopores of the Al2O3 matrix was confirmed using x-ray structural analysis and electron microscopy. The optical absorption characteristics were examined over a wide wavelength range, revealing that the reflection and transmission spectra were notably affected by pore size and surface scattering effects. THG measurements conducted with a high-intensity infrared laser demonstrated a pronounced third-order nonlinear response, whereas second-harmonic generation was not observed. The absence of SHG can be attributed to phase mismatch and inherent material properties, including centrosymmetry and surface roughness. The comparative and Reintjes models were used to calculate the third-order nonlinear optical susceptibilities. Among these, the Reintjes model provided the most accurate fit for the experimental data. This research underscores the considerable influence of nanopore size on THG efficiency, highlighting the importance of light scattering and phase-matching conditions. These findings contribute to a growing body of knowledge regarding nonlinear optical phenomena in nanocomposite materials and offer valuable insights for future applications in photonic devices. This comprehensive analysis highlights the potential of Al2O3 matrices with embedded ADP nanocrystals to advance the field of nonlinear optics in nanocomposite materials and offers insights for prospective applications in photonic devices.

High-performance and scalable polarization splitter-rotator based on photonic crystal nanobeam reflection

The polarization splitter-rotator (PSR) is a key device for polarization processing in polarization diversity systems, which has wide applications in achieving polarization independence and mixed multiplexing. However, it remains a significant challenge to simultaneously achieve a better balance in bandwidth, crosstalk (CT), polarization extinction ratio (PER), and compact footprint of the PSR. In this article, a photonic crystal nanobeam (PCN) structure is introduced to PSR for large bandwidth and compact size, with a device length of only 104 µm. Additionally, to achieve lower CT, a bridge waveguide is introduced for primary filtering. Simulation results show that the insertion loss (IL) is less than 0.55 dB, CT less than -35 dB, and PER greater than 35 dB within a bandwidth exceeding 110 nm, while maintaining a large process tolerance. Furthermore, the proposed PSR design breaks through the limitations of traditional schemes by extending its functionality effectively. To further improve integration, a novel approach to PSR using mode hybridization followed by spatial beam splitting is proposed. By controlling the phase-matching condition of various modes in different waveguides, the designed spatial beam splitting achieves lower CT and better compactness. Simulation results verify that the IL of the improved scheme is less than 1 dB, CT less than -24 dB, and PER greater than 22 dB within an 85 nm bandwidth, while reducing the overall length to less than 20 µm.

Light bullets under conditions of third harmonics generation

Abstract An analytical study of the possibility of a two-color light bullet forming during generation of the third harmonics in a graded index waveguide with the focusing Kerr nonlinearity is carried out. It is shown that under conditions of phase and group matching, as well as the absence of group velocity dispersion at the third harmonic frequency, a stable light bullet can be formed under certain restrictions. This applies to the lower limit on the temporal duration of the light bullet and to the upper limit on its power. The most stringent condition is the double restriction on the transverse radius of the light bullet.

Topological parametric gain and two-color edge states in equidistant lithium niobate waveguide arrays.

We analyze parametric χ2 processes in equidistant finite-size arrays of thin-film lithium niobate waveguides, where the fundamental harmonic (FH) field supports topological edge states due to the specific interplay between inter- and intra-modal couplings of two families of guided modes, while the second-harmonic (SH) field only supports bulk modes. Regimes of topological parametric gain are identified, where the gain only occurs in the edge states of the FH field, regardless of the spatial distribution of the pump SH field. The topological gain of the FH component generally triggers localization of the SH field near an edge of the array in the optical parametric oscillation dynamics. In small-size arrays, parametric gain at both edges can be observed even when pumped at one side. This process can lead to an anomalous "tunneling" of the SH field to the opposite edge. We also analyze the existence and stability of two-color nonlinear edge states (solitons), in which both FH and SH fields are localized at an edge of the array. Depending on the phase-matching condition, such solitons either emerge from the linear FH edge state without a power threshold or exist above a certain power threshold dictated by the coupling strength in the SH field.

Enhanced high-harmonic generation in a polarization-insensitive all-dielectric metasurface exploiting dual-Fano resonance

Nonlinear optics demands efficacious techniques for nonlinear properties engineering. Metasurfaces, as a flat technology with easy fabrication in various arrangements and without the need for phase-matching conditions, are suitable platforms for nonlinear optics. This study proposes a silicon metasurface with special geometry that provides high conversion efficiency by exploiting Fano resonances and the excitation of magnetic and toroidal dipoles. The results indicate the high efficiencies of third harmonic generation of 5.17×10−3 W−2 and fifth harmonic generation of 7.92×10−9 W−4 under 1 GW/cm2 pump intensity in the near-infrared regime. More specifically, linear and nonlinear optical responses of the structure are completely polarization-independent.

Direct generation of a narrowband EUV vortex with ring Pearcey-Gaussian-vortex-beam-driven harmonics.

The generation of tunable extreme-ultraviolet (EUV) vortex beams is highly sought after for optoelectronic applications in the EUV region. In this study, we investigate the generation of vortex high-order harmonics using a ring Pearcey-Gaussian vortex beam as the driving source. We analyze the beam's spatial structure through phase-matching conditions and simulate high-order harmonic generation by solving the Maxwell wave equations. The beam's self-focusing characteristics and low-diffraction properties after focusing significantly enhance harmonics near the 53rd order, indicating the generation of a narrowband EUV vortex. Our findings underscore the advantages of using a ring Pearcey-Gaussian vortex beam for narrowband EUV vortex generation, paving the way for creating tunable vortex high-order harmonics or attosecond pulses with innovative vortex beams.

Unidirectional and highly dispersive grating emitters for silicon photonic beam steerers.

Grating emitters are the key component used in silicon photonic beam steerers to create light emission and allow dispersion-based steering. Conventional grating emitters are inefficient due to bidirectional emission, and their angular dispersion is only on the order of 0.1°/nm. In this paper, we develop unidirectional grating emitters by choosing a top cladding material with a refraction index higher than that of the bottom cladding. The refractive index difference allows the phase-matching condition to be satisfied only for the upward diffraction. We demonstrate experimentally grating emitters with a directionality of 83% and an angular dispersion of 0.79°/nm. These grating emitters have a simple device structure compatible with the standard silicon photonic platform.

A comprehensive study of optical resonances in metals, dielectrics, and excitonic materials in double interface structures

From an optical perspective, depending on the relationship between the real (n) and imaginary (k) parts of its refractive index, three broad categories of materials can be distinguished: metals (k ≫ n), dielectrics (n ≫ k), and materials in which n ≈ k (termed here excitonic materials). The modes and optical resonances that appear in a thin film bounded by two dielectrics with similar refractive index, what we call here a double interface structure, have been widely studied in the case of metals, but not for dielectrics, or materials with n ≈ k. In this work, we propose a new approach, based on employing the phase matching condition to correlate the resonances that appear in the wavelength versus incident angle color maps of the reflected power with the modal analysis of the cross section of the structure. This analysis is performed, using an attenuated total reflection (ATR) setup, for thin film materials that belong to each of the mentioned categories: a metal (gold, Au), a dielectric (titanium dioxide, TiO2), and a material with n ≈ k (chromium, Cr). The theoretical analysis is supported with experimental results. It is demonstrated that this method enables to identify any resonance at any wavelength or incident angle, being valid for all three types of materials. Therefore, it is considered the suggested approach will help the research in these materials and in the double interface structure in the optics and photonics field.

Signatures of exciton-exciton annihilation in 2DES spectra including up to six-wave mixing processes.

Two-dimensional electronic spectroscopy (2DES) is a powerful spectroscopic tool that allows us to study the dynamics of excited states. Exciton-exciton annihilation is at least a fifth order process, which corresponds to intrachromophoric internal conversion from the double-excited high-energy chromophoric state into the single-excited state of the same chromophore. At high excitation intensities, this effect becomes apparent in standard 2DES and can be inspected via high order nK1⃗-nK2⃗+K3⃗ nonlinear processes. We calculate 2DES based on K1⃗-K2⃗+K3⃗ and 2K1⃗-2K2⃗+K3⃗ wave mixing processes to reveal exciton-exciton annihilation (EEA) induced exciton symmetry breaking, which occurs at high excitation intensities. We present the general theory that captures all these processes for bosonic and paulionic quasiparticles in a unified way and demonstrate that the NEEs can be easily utilized for highly nonlinear two-dimensional spectra calculations by employing phase cycling for separating various phase matching conditions. The approach predicts various excitonic third- to fifth-order features; however, due to high excitation intensities, contributions of different order processes become comparable and overlap, i.e., the signals no longer can be associated with well-defined order-to-the-field contributions. In addition, EEA leads to breaking of the exciton symmetries, thus enabling population of dark excitons. Such effects are due to the local nature of the EEA process.

Topological polarization beam splitter based on directional coupling between asymmetric valley photonic crystal waveguides.

Compared with symmetric directional couplers (DCs), asymmetric DCs constructed by two or over two different parallel waveguides offer a more flexible structure and allow for easier expansion of mode channels. In this Letter, we propose a kind of asymmetric topological DC based on two different valley photonic crystal waveguides (VPCWs). According to the coupled-mode theory, phase matching induces the complete coupling for the guide modes of two different VPCWs, whereas significant phase mismatching indicates no coupling occurs. Furthermore, the asymmetric topological DCs exhibit backscattering immunity and anti-disturbance robustness owing to the topological edge states (TESs), which greatly improve the performance of asymmetric DCs. We further design a new, to the best of our knowledge, kind of topological polarization beam splitter (TPBS) at the communication wavelength of 1550 nm by ensuring that the transverse electric mode satisfies the phase matching condition, while the transverse magnetic mode is phase-mismatched. The simulated results demonstrate that the proposed TPBS exhibits highly effective polarization separation and is robust against defects. This design holds significant potential for applications in optical communication systems.

MEMS‐enabled Ultralow Power Consumption Programmable Arbitrary Order Mode Switch

AbstractMode‐division‐multiplexing (MDM) recently attracted much interest due to its ability to enhance the capacity for optical information communication. To meet growing data transmission demands and enable flexible on‐chip mode manipulation, programmable optical mode converter switches are essential. This work introduces a micro‐electromechanical‐system (MEMS)‐enabled programmable arbitrary order mode switch, capitalizing on the benefits of MEMS technology such as low power consumption, robust modulation capabilities, and seamless large‐scale integration. Employing newly developed MEMS‐tunable mode converter (MTMC) units, the system achieves high conversion efficiencies from the fundamental mode to arbitrary higher‐order modes and supports programmable power distribution among different modes by cascading multiple MTMCs. As a proof‐of‐concept, a programmable TE0–TE0/1/2 mode switch operates in the 3.64 to 3.71 µm wavelength range, achieving maximum crosstalk values of –9.56 and –9.88 dB for TE0 to TE1 and TE0 to TE2 mode conversion, respectively, and a remarkably low power consumption of 67 pW. Furthermore, a programmable mode multiplexer is developed by simultaneously actuating two MEMS actuators to modulate phase matching conditions, enabling arbitrary power splitting ratios among these modes. The demonstrated scalability and flexibility of the proposed system highlight its potential as a foundational component for MDM systems.

Photonic Crystal Fiber Based on Surface Plasmon Resonance Used for Two Parameter Sensing for Magnetic Field and Temperature

This paper presents a photonic crystal fiber (PCF) sensor that can be used to measure the temperature and magnetic field simultaneously, and to monitor the changes in them in the environment. When we designed the fiber structure, two circular channels of the same size were added to the fiber to facilitate the subsequent addition of materials. A gold film is added to the upper channel (ch1), and the channel is filled with a magnetic fluid (MF). The sensor can reflect changes in the temperature and magnetic field strength. The two channels containing MF and PDMS in the proposed fiber are called ch1 and ch2. The structure, mode and properties (temperature and magnetic field) were analyzed and discussed using the finite element method. By using the control variable method, the influence of Ta2O5 or no Ta2O5, the Ta2O5 thickness, the diameter of the special air hole, the distance from the fiber core and the distance between them in the displacement of the loss spectrum and the phase-matching condition of the coupling mode were studied. The resulting maximum temperature sensitivity is 6.3 nm/°C (SPR peak 5), and the maximum magnetic field sensitivity is 40 nm/Oe (SPR peak 4). Because the sensor can respond to temperature and magnetic field changes in the environment, it can play an important role in special environmental monitoring, industrial production and other fields.

Isolated attosecond pulse generation in a semi-infinite gas cell driven by time-gated phase matching

Isolated attosecond pulse (IAP) generation usually involves the use of short-medium gas cells operated at high pressures. In contrast, long-medium schemes at low pressures are commonly perceived as inherently unsuitable for IAP generation due to the nonlinear phenomena that challenge favourable phase-matching conditions. Here we provide clear experimental evidence on the generation of isolated extreme-ultraviolet attosecond pulses in a semi-infinite gas cell, demonstrating the use of extended-medium geometries for effective production of IAPs. To gain a deeper understanding we develop a simulation method for high-order harmonic generation (HHG), which combines nonlinear propagation with macroscopic HHG solving the 3D time-dependent Schrödinger equation at the single-atom level. Our simulations reveal that the nonlinear spatio-temporal reshaping of the driving field, observed in the experiment as a bright plasma channel, acts as a self-regulating mechanism boosting the phase-matching conditions for the generation of IAPs.

Control of a spectral minimum in high-order harmonic generation by adjusting the phase-matching conditions in a gas medium

Control of a spectral minimum in high-order harmonic generation by adjusting the phase-matching conditions in a gas medium

Facile dual-shot measurement of Schmidt number in type-0 and type-2 downconversion

High-dimensional entangled states have now been identified as excellent candidates towards the enhancement of the bandwidth of quantum systems. A variety of methods exist that aim to certify and set the bounds to entanglement. However, rapid and accurate approaches for precise quantification of the dimensions remain a challenge. Here, we report a facile, rapid and robust approach that quantifies a wide range of the spatial dimensions of high-dimensional entangled states using an interferometric technique using only two images. Our process works for a class of pure two-photon states, regardless of its separability and provides a fast and easy way to accurately measure the spatial Schmidt number which is a quantitative measure of dimensionality of entanglement. We apply our method to two-photon states generated by spontaneous parametric down-conversion (SPDC) and show that our results are in excellent agreement with numerical estimates. Since such estimates only exist for collinear phase matching in SPDC crystals, we also derive a noncollinear phase-matching condition applicable for type-2 crystals. In these nonlinear crystals, the commonly applied assumption of degenerate daughter photons no longer holds, leading to deviations from earlier theoretical predictions. Our interferometric technique provides excellent results for both type-0 and type-2 collinear phase-matching conditions, endorsing its wide applicability in quantum photonics. Published by the American Physical Society 2024

Concurrent phase-matchings for multi-wavelength conversion in coupled dual waveguides

Thin film lithium niobate, as a highly promising integrated photonics platform, has emerged as an ideal material platform for wavelength conversion owing to its exceptional second-order nonlinear characteristics. Here, we present the first demonstration of concurrent phase-matchings for multi-wavelength conversion in coupled thin film lithium niobate waveguides without poling technique. In the coupled dual waveguide system, employing modal phase-matching, we validate three effective phase-matching conditions for second harmonic generation, arising from additional momentum compensation due to the coupling of waveguides. Simultaneously, we confirm that phase-matching wavelengths can be tuned by adjusting the gap between waveguides. The concurrent phase-matchings in coupled dual waveguide systems can be readily extended to other nonlinear optical processes, such as difference frequency generation and spontaneous parametric down conversion. Our work contributes to advancing the exploration of efficient on-chip nonlinear optical processes within the realms of nanophotonics and quantum optics.