Bulk Second-order Nonlinearity Research Articles

Surface vs bulk contribution to the second-harmonic generation in AlGaAs nanoresonators

We address the surface vs bulk origin of the second-order optical nonlinearity in AlGaAs nanocylinders through polarization-resolved measurements. By comparing numerical simulations accounting just for bulk second-order nonlinearity with experimental results, we show that the surface contribution to second-harmonic generation (SHG) cannot be neglected and depends on the resonant conditions of the nanocylinder. Additionally, our analysis suggests that bulk and surface SHG are competing effects, and that their interference might influence the overall efficiency.

Engineered second-order nonlinearity in silicon nitride

The lack of a bulk second-order nonlinearity (χ(2)) in silicon nitride (Si3N4) keeps this low-loss, CMOS-compatible platform from key active functions such as Pockels electro-optic (EO) modulation and efficient second harmonic generation (SHG). We demonstrate a successful induction of χ(2) in Si3N4 through electrical poling with an externally-applied field to align the Si-N bonds. This alignment breaks the centrosymmetry of Si3N4, and enables the bulk χ(2). The sample is heated to over 500°C to facilitate the poling. The comparison between the EO responses of poled and non-poled Si3N4, measured using a Si3N4 micro-ring modulator, shows at least a 25X enhancement in the r33 EO component. The maximum χ(2) we obtain through poling is 0.30pm/V. We observe a remarkable improvement in the speed of the measured EO responses from 3 GHz to 15 GHz (3 dB bandwidth) after the poling, which confirms the χ(2) nature of the EO response induced by poling. This work paves the way for high-speed active functions on the Si3N4 platform.

Dynamically tunable second-harmonic generation using hybrid nanostructures incorporating phase-change chalcogenides

Abstract Nonlinear metasurfaces with high conversion efficiencies have been vastly investigated. However, strong dynamic tunability of such devices is limited in conventional passive plasmonic and dielectric material platforms. Germanium antimony telluride (GST) is a promising phase-change chalcogenide for the reconfiguration of metamaterials due to strong nonvolatile changes of the real and imaginary parts of the refraction index through amorphous-crystalline phase change. The orderly structured GST has an even higher potential in tunable second-harmonic generation (SHG) with a non-centrosymmetric crystal structure at the crystalline phase, while the amorphous phase of GST does not exhibit bulk second-order nonlinearity. Here, we experimentally demonstrate SHG switches by actively controlling the crystalline phase of GST for a GST-based hybrid metasurface featuring a gap-surface plasmon resonance, and a quarter-wave asymmetric Fabry–Perot (F–P) cavity incorporating GST. We obtain SHG switches with modulation depths as high as ∼ 20 dB for the wavelengths at the on-state resonance. We also demonstrate the feasibility of multi-level SHG modulation by leveraging three controlled GST phases, i.e., amorphous, semi-crystalline, and crystalline, for the gap-surface plasmon hybrid device, which features stronger light–matter interaction and has higher resonant SHG efficiencies than the asymmetric F–P cavity device at respective GST phases. This research reveals that GST-based dynamic SHG switches can be potentially employed in practical applications, such as microscopy, optical communication, and photonic computing in the nonlinear regime.

Atomic layer deposited second-order nonlinear optical metamaterial for back-end integration with CMOS-compatible nanophotonic circuitry

We report the fabrication of artificial unidimensional crystals exhibiting an effective bulk second-order nonlinearity. The crystals are created by cycling atomic layer deposition of three dielectric materials such that the resulting metamaterial is noncentrosymmetric in the direction of the deposition. Characterization of the structures by second-harmonic generation Maker-fringe measurements shows that the main component of their nonlinear susceptibility tensor is about 5 pm/V, which is comparable to well-established materials and more than an order of magnitude greater than reported for a similar crystal [Appl. Phys. Lett.107, 121903 (2015)APPLAB0003-695110.1063/1.4931492]. Our demonstration opens new possibilities for second-order nonlinear effects on CMOS-compatible nanophotonic platforms.

Second-order nonlinearities of lead borate glasses poled with different electrodes

Abstract The second-order nonlinearities in thermally poled lead borate glasses were studied. After poling with different electrodes, both bulk and near surface second-order nonlinearities were obtained. The second harmonic generation signal from near surface effect was two orders of magnitude larger than the bulk effect. By simulating the poling process with a multiple carrier model, we concluded that the bulk second-order nonlinearity was caused by the deficiency of Pb2+ in a thick layer after poling, and the near surface second-order nonlinearity was caused by the depletion of H+ in a thin layer when H+ injection from the atmosphere was blocked.

Bulk and near-surface second-order nonlinearities generated in a BK7 soft glass by thermal poling

Bulk second-order nonlinearity was generated in BK7 glass at a higher temperature and with a longer poling time than near-surface second-order nonlinearity. The temporal decay of the bulk second-order nonlinearity was slower than that of the near-surface second-order nonlinearity. The thickness of the near-surface nonlinear layer increased with poling time. Poled BK7 glass was also measured by x-ray photoelectron spectroscopy. Depletion of Na at the anodic surface and its accumulation at the cathodic surface was observed. At the cathodic surface, a higher-energy peak near O (1s) appeared, which shows peroxy-radical defects. At the anodic surface, a lower-energy peak near Si (2p) appeared, which may be attributed to E′ centers or to two-coordinated Si defects. The mechanisms of generation of these defects and of the second-order nonlinearities are discussed.

Threshold Conditions for Bulk Second-Order Nonlinearity and Near-Surf ace Second-Order Nonlinearity in Thermally Poled Infrasil Silica

Generation of bulk second-order nonlinearity in silica glass requires higher poling temperature or longer poling time than that of near-surface second-order nonlinearity. The threshold conditions for initiating the bulk second-order nonlinearity are studied on Infrasil fused silica glass. The threshold poling time is strongly dependent on the poling temperature. The near-surface second-order nonlinearity is also studied, especially the dependence of thickness of the nonlinear layer on the poling temperature, poling voltage and poling time. Secondary-ion mass-spectroscopy measurement showed depletion of Na+ ions at the anodic surface. We assume there is an ionic wave during poling traveling from the anodic surface to generate the dipolar electric field that induces the near-surface second-order nonlinearity.

Erratum: “Double fitting of Marker fringes to characterize near-surface and bulk second-order nonlinearities in poled silica” [Appl. Phys. Lett. 76, 3346 (2000)

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Nonuniform bulk second-order optical nonlinearity in PbO/B2O3 glass

Second-order nonlinearity (SON) of thermally poled PbO/B2O3 glass was investigated. The SON distribution within the glass was obtained by repeatedly grinding the poled glass and measuring its Maker fringes. After grinding away up to one third of the thickness of the poled sample, i.e., about 300 μm, clear fringes with the interference minimum not equal to zero could still be observed, indicating that the area of SON was not confined within thin layers near the two surfaces. Cathode side grinding and anode side grinding had quite different influences on the SON of the poled sample. A model of the anode-charge-layer dependent bulk electric field distribution was proposed and this electric field was regarded as playing a key role in the generation of a nonuniform bulk SON distribution in PbO/B2O3 glass.

Double fitting of Maker fringes to characterize near-surface and bulk second-order nonlinearities in poled silica

An experimental analysis of the distribution and thickness of the bulk nonlinearity induced in poled silica is reported. The second-order susceptibility decreases exponentially from the anodic interface. Maker fringe patterns showing a double structure are interpreted in relation to the presence of two nonlinear profiles, one concentrated near the anodic surface and another extending into the bulk of the sample. The Maker fringe theory is properly generalized and a double fitting technique reproducing well the experimental results is used to characterize the induced nonlinearities. The dependence of the second-harmonic signal on the poling temperature is given, which is different from that of sol-gel silica.

Incorporation of a Stilbazole Derivative in the Hydrogen-Bonded Chain of l-Tartrate: Toward a One-Step Optimization of Molecular and Bulk Second-Order Nonlinearities

The syntheses and crystal structures of dimethylaminostilbazole (DAS) and dimethylamino-N-methyl stilbazolium hydrogen l-tartrate (DAS-H+Ta-) are described. Crystal data for DAS: monoclinic, P21/c, a = 6.0443(9) A, b = 7.6616(8) A, c = 26.376(4) A, β = 93.66(1)°, Z = 4. Crystal data for DAS-H+Ta-: monoclinic, P21, a = 7.518(1) A, b = 7.528(1) A, c = 16.376(2) A, β = 92.67(1)°, Z = 2. In the latter compound, the anions create infinite chains through intermolecular O−H···O hydrogen bonds, whereas the stilbazolium cations are hydrogen bonded to the chains. INDO calculations and spectroscopic studies show that hydrogen bonding greatly enhances the molecular hyperpolarizability of the stilbazole derivative, while crystal engineering with tartaric acid is achieved into the acentric space group. Therefore, an efficiency of 8 times that of urea in second-harmonic generation has been measured at 1.907 μm for this material.

Difference-frequency generation and sum-frequency generation near the band gap of zincblende crystals

We present recent experimental results of difference-frequency generation (DFG) and sum-frequency generation (SFG) from zincblende materials. We measure the radiation field of difference-frequency generation and the radiation intensity of sum-frequency generation versus crystallographic orientation and fundamental photon energy. The simultaneous measurement of the angular dependence of polarized DFG and SFG is well characterized by the bulk second-order nonlinearity calculation. Pronounced resonant behaviors near the GaAs band gap for both radiations (DFG and SFG) are compared.