Effective Nonlinear Coefficient Research Articles

Characterization of Effective Nonlinear Coefficient in Randomly Coupled Multi-Core Fiber

Characterization of Effective Nonlinear Coefficient in Randomly Coupled Multi-Core Fiber

Noncollinear phase matching and effective nonlinear coefficient calculations for biaxial crystal out of the principal plane

Noncollinear phase matching and effective nonlinear coefficient calculations for biaxial crystal out of the principal plane

Circular lattice benzene-core PCFs with flat near-zero dispersion for low-power broad-spectrum supercontinuum generation

A circular photonic crystal fiber infiltrated with benzene with different air-hole diameters is proposed as a new supercontinuum light source. Optical properties related to dispersion, effective mode area, nonlinear coefficient, and attenuation of the fundamental mode are investigated numerically. Two optimized structures are selected and verified against supercontinuum generation (SCG) in detail. The first structure (#F1) possesses all-normal dispersion, while the second (#F2) has a zero-dispersion wavelength. The possibility of coherent, octave-spanning SCG is proved by a 40 fs pulse, 1.064 μm wavelength, and 0.45 kW of power in-coupled into the core of #F1. Otherwise, injecting a 90 fs duration, 1.5 μm wavelength, and 0.555 kW peak power pump pulse into #F2 generates a broad SC spanning 0.76–4.23 μm. With the advantages of flat near-zero dispersion, high nonlinearity, low attenuation, and low input power used for SCG, the proposed fibers may lead to new low-cost all-fiber optical systems.

Porous nano-grained cuprous selenide (Cu2Se) for mid-infrared photonics

Recently, mid-infrared photonics has attracted tremendous attention for various applications. To address the dilemma of the limited variety of materials for mid-infrared photonics, the mid-infrared optical modulation characteristics of the porous nano-grained cuprous selenide (Cu2Se) were investigated for the first time. The large effective nonlinear absorption coefficient, large modulation depth, and low saturation absorption intensity at 2.3 μm indicate that the porous nano-grained Cu2Se were promising saturable absorbers for the generation of Q-switched pulsed laser in the mid-infrared regime. As an application, the Tm:GdVO4 passively Q-switched laser operating on the 3H4 → 3H5 Tm3+ transition was achieved for the first time by using the prepared porous nano-grained Cu2Se as the saturable absorber. The minimum pulse duration and the maximum repetition rate of the stable Q-switched pulse train were 440 ns and 76.9 kHz, respectively. Our results demonstrated that the porous nano-grained Cu2Se was a promising candidate for the mid-infrared photonic applications.

Investigation of hybrid chalcogenide photonic crystal fiber for MIR supercontinuum generation and optical communication

Abstract This study describes a wideband supercontinuum generation (SCG) in the mid-infrared range using a chalcogenide multi-material microstructured fiber design with significant non-linearity under optical communication. The fiber has a single core of As2Se3 and three rings of As2S5 rods arranged in hexagonal pattern in the AsSe2 cladding region. The reported PCF design has effective area and nonlinear coefficients as 59.4174 μm2 and 219.36 W−1 km−1 respectively at 5.3 μm pump wavelength. Additionally, it has a chromatic dispersion profile that is nearly zero and flattened over a large wavelength range of 5–15 µm, which is advantageous for broadband supercontinuum spectrum in the mid-infrared region. Specifically, with pulse width and pulse peak power of 200 fs and 10 kW, respectively, for a 100 mm fibre length, this research work illustrates the SCG that expands from 1000 nm to over 15,000 nm. These extremely nonlinear PCFs are robust contenders for applications that are nonlinear in nature, such as the generation of slow-light and supercontinuum.

Nonlinear optical properties of lanthanum titanate glasses prepared by levitation melting

Lanthanum titanate glasses (17 La2O3-83 TiO2) are fabricated via aerodynamic levitation melting. Nonlinear refraction and absorption were measured with the Z scan technique using ∼550 ps optical pulses at 532 nm wavelength with peak intensities in the range of 0.25–2.5 GW/cm2. The two-photon absorption coefficient (β) and the effective nonlinear refraction coefficient (n2eff) are found to be, respectively, 2.19 cm/GW and 152 × 10−16 cm2/W (85 × 10−13 esu). The Raman gain is measured to be 106 × 10−11 cm/W. The nonlinearity strength is found to be nearly 60 times larger in lanthanum titanate glasses relative to silica.

Numerical investigation of effective nonlinear coefficient model for coupled third harmonic generation

In this paper, the optimal solution of effective nonlinear coefficient of quasi-phase-matching (QPM) crystals for coupled third harmonic generation (CTHG) was numerically investigated. The effective nonlinear coefficient of CTHG was converted to an Ising model for optimizing domain distributions of aperiodically poled lithium niobate (APPLN) crystals with lengths as 0.5 mm and 1 mm, and fundamental wavelengths ranging from 1000 nm to 6000 nm. A method for reconstructing crystal domain poling weight curve of coupled nonlinear processes was also proposed, which demonstrated the optimal conversion ratio between two coupled nonlinear processes at each place along the crystal. In addition, by applying the semidefinite programming, the upper bound on the effective nonlinear coefficients deff for different fundamental wavelengths were calculated. The research can be extended to any coupled dual χ(2) process and will help us to understand better the dynamics of coupled nonlinear interactions based on QPM crystals.

Structural dependence of transmission characteristics for photonic crystal fiber with circularly distributed air-holes

Abstract In this study, design and transmission characteristics of a special type of photonic crystal fiber (PCF) geometry namely, circular-lattice photonic crystal fiber (C-PCF) structure are presented. The cladding of the structure consists by a cylindrically symmetrical distribution of air-holes in the silica background and the core is created by omitting one air-hole at the center. The structure provides high degree of flexibility in the fiber design and hence tailorable modal properties. Structural dependence of transmission characteristics of the geometry is numerically investigated by using finite difference mode convergence algorithm. The wavelength responses of fiber parameters, such as effective refractive index, chromatic dispersion, mode-effective area, and nonlinear coefficient of the structure are systematically investigated. Besides, effective V-parameter and single-mode operation of the fiber are also evaluated and discussed. The simulation results show the possibility of large negative dispersion and dispersion flattened nature of the geometry.

Effect of π-extension and halogenation on the optical limiting properties of meso-pyrenylBODIPYdyes

The lack of suitable optical limiters that cover the entire UV-visible-NIR region has motivated research to identify novel efficient and stable optical limiting materials. There has been a strong focus on attenuating the second harmonic of Nd:YAG pulsed lasers at 532 nm on the nanosecond timescale. The photophysicochemical processes of a series of mono- and di-(4-dimethylamino)styryl-meso-pyrenylBODIPY and mono- and di-(4-dimethylamino)buta-1,3-dienyl-meso-pyrenylBODIPY dyes were studied by UV-visible absorption and fluorescence emission spectroscopy, and by determining the fluorescence and triplet state lifetimes. Z-scan measurements were carried out at a fixed concentration of 10 [Formula: see text]M so that the effective nonlinear coefficients, third-order susceptibilities, second-order hyperpolarizabilities and limiting fluences of the dyes can be compared and trends in the structure-property relationships for these optical limiting parameters can be identified.

Optical properties of circular photonic crystal fibers filled with carbon tetrachloride

In this work, the dispersion properties and nonlinear properties of circular photonic crystal fibers were improved by a combination of carbon tetrachloride infiltration into the core and modification of the air hole diameters d1 and d2 of rings in the cladding. The quantities such as dispersion, effective mode area, nonlinear coefficient, and low confinement are analyzed in detail. Based on the survey results, two photonic crystal fibers with optimal optical properties were proposed which are beneficial for supercontinuum generation. The first fiber with Ʌ = 1.0 µm, d1/Ʌ = 0.6, has an all-normal dispersion of –10.785 ps/nm.km at a pump wavelength of 0.985 µm. The high nonlinear coefficient of 581.795 W–1.km–1 and the low confinement loss of 3.904 dB/m are also achieved with this fiber. SC broadband under the influence of soliton is expected to be generated when using the second fiber (Ʌ = 2.0 µm, d1/Ʌ = 0.3) with flat and low anomalous dispersion at the pump wavelength of 1.3 µm.

Angular non-critical phase-matching second harmonic generation with the Ba3(ZnB5O10)PO4 crystal

The angular non-critical phase-matching (A-NCPM) second-harmonic-generation (SHG) properties of Ba3(ZnB5O10)PO4 (BZBP) crystal were investigated. Based on the small signal solution formula of SHG, the effective nonlinear coefficient deff along z-axis was corrected to 1.43 p.m./V. Combining the theoretical SHG PM conditions, BZBP crystal can be achieved type-I A-NCPM with the fundamental wavelength of 750 nm on y-axis, and 1012 nm on z-axis. Using an OPO laser as pump source, the BZBP crystal could realize the 506 nm and 375 nm SHG lasers with the conversion efficiencies of 35 % and 45.5 % respectively. The acquired results demonstrated that BZBP is a promising NLO crystal for A-NCPM frequency conversion applications in the output spectral regions of Ti:sapphire laser and near-infrared lasers.

Optical Kerr nonlinearity of dielectric nanohole array metasurfaces with different hole shapes near the anapole state

At present, optical anapole resonances in nanostructures have attracted increasing attention due to the strong field confinement and substantially suppressed scattering. This study provides the results of three-dimensional finite-difference time-domain simulations exhibiting the possibility of the anapole state in high refractive index dielectric nanohole array metasurfaces having different profiles of the holes (square, hexagon, and octagon). Behavior of the effective optical Kerr nonlinearity of the metasurfaces in the vicinity of the anapole state is investigated. Depending on the geometry, the absolute value of the effective nonlinear Kerr coefficient of the metasurface may be up to three orders of magnitude greater than that of the unstructured film. A square transverse section of the nanohole is preferable for the optical Kerr effect in the holey metasurfaces. The effect of the random rotation of the square holes representing the metasurface irregularity on the optical nonlinearity is examined. As a result, the dielectric nanohole array metasurfaces display a concrete possibility to have the anapole state with large enhancement of the optical nonlinearity.

Modifying optical nonlinearities of ionic liquid crystal glass by adding gold and carbon nanoparticles

Future disruptive photonics technologies depend on the development of new types of nonlinear-optical glass composites containing nanoparticles. In this paper, we report the synthesis, structural characterization, spectral and nonlinear-optical properties of overlooked yet very promising glass nanocomposites made of glass forming ionic liquid crystals (cadmium caprylate) and two types of nanoparticles (gold and carbon). Nonlinear-optical properties of the prepared nanocomposites are studied by means of a standard Z-scan method and using visible (532 nm) nanosecond laser pulses. By exciting glass nanocomposites within their absorption band, an interplay between several nonlinear-optical mechanisms can be revealed. A simultaneous use of two types of nanoparticles (i.e. carbon and gold) enables a better control over effective optical nonlinearities of nanocomposites. More specifically, by changing an intensity of a laser beam, it is possible to vary the magnitude of the effective nonlinear refractive index and of the effective nonlinear absorption coefficient. In addition, even the sign of the effective nonlinear absorption coefficient can be changed. The proposed strategy to create novel nonlinear-optical materials using metal-alkanoates based glass-forming ionic liquid crystals and several types of nanoparticles will benefit rapidly growing nanophotonics and plasmonics technologies.

Chiral Hybrid Germanium(II) Halide with Strong Nonlinear Chiroptical Properties.

Due to the pronounced anisotropic response to circularly polarized light, chiral hybrid organic-inorganic metal halides have been regarded as promising candidates for the application in nonlinear chiroptics, especially for the second-harmonic generation circular dichroism (SHG-CD) effect. However, designing novel lead-free chiral hybrid metal halides with large anisotropy factors and high laser-induced damage thresholds (LDT) of SHG-CD remains challenging. Herein, we develop the first chiral hybrid germanium halide, (R/S-NEA)3 Ge2 I7 ⋅H2 O (R/S-NGI), and systematically investigated its linear and nonlinear chiroptical properties. S-NGI and R-NGI exhibit large anisotropy factors (gSHG-CD ) of 0.45 and 0.48, respectively, along with a high LDT of 38.46 GW/cm2 ; these anisotropy factors were the highest values among the reported lead-free chiral hybrid metal halides. Moreover, the effective second-order nonlinear optical coefficient of S-NGI could reach up to 0.86 pm/V, which was 2.9 times higher than that of commercial Y-cut quartz. Our findings facilitate a new avenue toward lead-free chiral hybrid metal halides, and their implementation in nonlinear chiroptical applications.

Softening/hardening dynamics of beam resting on generalized nonlinear foundation with a linear stiffening effect

An asymptotic study of softening/hardening dynamics of beam on a generalized nonlinear foundation is presented, by focusing on its linear stiffening effect on quadratic/cubic nonlinearities. It is found that, though linear stiffening simultaneously weakens both quadratic and cubic nonlinearities, they decrease at different rates, leading to complex competing dynamics in sequel, such as enhanced hardening/weakened softening, weakened hardening, and quenched nonlinearity in the limit, among which softening–hardening transition dynamics is of particular interest when quadratic and cubic nonlinearities ‘balance’ with each other (i.e., a vanishing effective nonlinear coefficient). Close to transition, standard third-order perturbation fails and the predicted responses turn invalid in mediate/high amplitude ranges, which critically depends on transition inclination when transversally crossing the line of vanishing effective nonlinear coefficient. In parallel, linear stiffening effects on softening/hardening dynamics are also investigated from a methodology viewpoint, i.e., it reduces differences between discretization and direct perturbations, with the former becoming more reliable by an increased linear stiffness.

Phase‐Coherent Optical Frequency Up‐Conversion with Millimeter‐Size Zn(3‐ptz)2 Metal‐Organic Framework Single Crystals

AbstractMetal‐organic frameworks (MOFs) have emerged as candidate materials for nonlinear optics due to their enhanced optical and chemical stability in comparison with conventional organic crystals. However, producing large single crystals that support perfect phase matching conditions for frequency conversion is a long‐standing challenge due to the highly metastable conditions in which MOF crystals tend to self‐assemble in solution. By modulating the synthesis and growth conditions, this limitation is overcome to produce millimeter–sized Zn(3‐ptz)2 uniaxial MOF single crystals. Optimized MOF crystals with large birefringence in the visible Δn ≈ −0.3 and high transparency allow for the observation of strong second‐harmonic (SHG) and third‐harmonic generation (THG) signals for the first time, using femtosecond near‐infrared pump pulses. For conditions of type‐I SHG phase‐matching, the measured effective nonlinear coefficient of Zn(3‐ptz)2 is deff ≈ 0.10 pm V−1, the largest measured nonlinearity for MOF materials to date. The experiments quantitatively agree with first‐principles simulations based on the crystal lattice structure. The damage threshold is estimated on the order of 0.2 TW cm−2 for raw single crystals, which can be further increased with additional crystal engineering steps. The demonstration of efficient frequency up‐conversion of light with long‐range phase coherence establishes MOF single crystals as promising materials for nonlinear optical devices.

Optical properties of a Moiré-lattice photonic crystal fiber with controllable magic angle

Inspired by the unique electrical properties of bilayer-twisted graphene with moiré superlattice, the light manipulation using photonic moiré structures has attracted tremendous research interest. In this paper, the moiré-lattice arrangement is introduced into the cladding of fiber to construct the moiré-lattice photonic crystal fiber (PCF) with two identical triangular-lattice or square-lattice layers of air holes rotated by a certain angle. The optical properties of the moiré-lattice PCF are studied in detail by varying the rotation angle with regards to the dispersion, effective mode field area, nonlinear coefficient and bending loss. Numerical results show that the optical properties of guiding mode can be flexibly regulated and optimized by the rotation angle. Moreover, the fiber can maintain single-mode transmission and low bending loss at different rotation angles. This moiré-lattice PCF provides a new way of regulating the structure for optimizing the fiber properties and offers a guidance for engineering moiré-lattice fiber devices.

Performance analysis of the fiber coils combining hybrid polarization-maintaining fiber designs and symmetrical winding patterns.

Research on the performance of polarization-maintaining fiber (PMF) for fiber coils is significant for the precision improvement of an interferometric fiber optic gyroscope (IFOG) working in harsh environments. In this paper, we firstly report analytical models of the fiber polarization theory and present two types of hybrid PMF structures by a collaboration of geometry and stress effects: a Panda-type horizontal-elliptical core PMF (Panda-type HE-PMF) based on a superposition of geometry and stress, and a Panda-type longitudinal-elliptical core PMF (Panda-type LE-PMF) with geometry offset stress effect, achieving enhanced and suppressed modal performance by adjusting geometric anisotropy of elliptical-core in different directions. Then, the influence mechanisms of the geometric birefringence on the modal performance of both PMFs as the variation of fiber structural parameters are investigated via numerical simulations to determine the target fiber designs. The other significant attribute, including effective mode area (Aeff), nonlinear coefficient (γ), and chromatic dispersion (D), and their tolerance to PMF parameter fluctuations are also evaluated. Finally, both target PMFs with structural optimization are practically fabricated and wound into four fiber coils with quadrupolar (QAD) and 16-polar symmetrical winding patterns, respectively. The polarization ability and thermal performance are further demonstrated by experiments conducted on both PMFs, wound fiber coils, and built IFOGs under static and dynamic environments (over a wide temperature range of -40 °C to 70 °C), and compared with a conventional PMF. The testing results suggest that designed HE-PMF coils both achieve high birefringence, static extinction ratio (ER) values of up to 30.80 dB and 31.93 dB, respectively, corresponding to an almost one-fold increase over conventional coils. Remarkably, the ER property of the HE-PMF coil by combining this HE-PMF design and a 16-polar winding pattern consistently remains above 29.5 dB with a minimal fluctuation in ER of only 3.0 dB across the entire variable temperature conditions. The bias stability of the IFOG assembled with this coil is strongly enhanced to 0.0019 °/h and 0.082 °/h under static and dynamic conditions, respectively, which is a significant improvement over conventional coils of 0.136 °/h. Also, the static angle random walk performance of the improved IFOG is reduced to 0.000624 °/√h. In contrast, the LE-PMF as a comparison is shown to limited polarization characteristics with a low birefringence and ER due to the suppression effect of the geometric birefringence, and the applied IFOG output also exhibits larger drift, indicating a poor thermal ability. Experimental results show great agreement with theoretical analysis and numerical simulations, confirming the validity of design principles. The advances in both designs are instructive for the engineering applications of PMFs for IFOGs and for improving the accuracy of fiber sensors.

一种逐级超分子组装策略用于显著提高簇合物的三阶非线性光学响应

Developing practical optical materials with strong third-order nonlinear optical (NLO) responses attracts increasing attention. Efforts in this area extend to the activation of appropriate materials and the magnification of their low NLO responses. Herein, we propose a stepwise assembly-amplification strategy to enhance the NLO responses of low NLO-active metal sulfide clusters. Through a self-assembly process, W/Cu/S cluster-based tetrahedral and octahedral cages are successfully obtained, both exhibiting weak NLO responses in solution that are not apparent for the unassembled components. Their incorporation into polyvinyl alcohol (PVA), followed by spin-coating, results in the formation of cluster@PVA composite membranes with controlled thicknesses. Remarkably, the effective nonlinear absorption coefficients β for 12-layered membranes are 104 times higher than those of the respective cage solutions. The octahedral cage delivers a stronger response than the tetrahedral cage, which likely reflects the higher degree of aggregation of the clusters. This work showcases a new approach for amplifying NLO responses, greatly facilitating the development of integrated photonic devices.

Comparison of high average-power femtosecond green and ultraviolet laser emissions generated by K3B6O10Br and K3B6O10Cl nonlinear crystals

We investigate the second harmonic generation (SHG) and third harmonic generation (THG) processes of femtosecond (fs) laser that occurred in type Ⅰ phase-matched K3B6O10X (X = Cl, Br; KBOC and KBOB) crystals. The high average power of 515 nm green and 343 nm ultraviolet (UV) fs lasers output were efficiently generated from these two crystals with an incident fundamental 773 fs 1030-nm laser source. Experimental results show that the highly effective nonlinear coefficient of the KBOC crystal causes higher harmonic conversion efficiency than that of KBOB crystal in the same fundamental laser parameters. The average power of 10.4 W 515 nm green and 4.6 W 343 nm UV lasers output were obtained from two pieces of 4.5 mm KBOC crystals, corresponding to 42.3 % and 19.7 % high optical conversion efficiency respectively, without temporal pulse walk-off time compensation between 1030 nm and 515 nm laser pulses. Our research will stimulate in-depth research on nonlinear frequency conversion in nonlinear optical systems and have potential applications in future applications.