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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Suppression of Propagation Losses in TC SAW Resonators Using Thin Plates of LiTaO3 Bonded to Quartz Substrates
摘要： Suppression of Propagation Losses in Thin-Film Lithium Niobate Optical Waveguides
关键词： Lithium Niobate,Thin-Film,Optical Waveguides,Quasi-Phase Matching,Propagation Losses
更新于2025-09-19 17:15:36
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Tailored Spontaneous Four-Wave Mixing in Sinusoidally-Tapered Fibres
摘要： Quasi-phase-matching periodically-tapered waveguides (PTWs) can enable efficient on-demand third-order parametric interactions using right combinations of the tapering period and modulation amplitude. Similar to periodically-poled ferroelectric crystals, this new technique eliminates the stringent constraints imposed by conventional methods on the frequencies, mode profiles, and polarisations of the interacting photons. An example of PTWs is the sinusoidally-tapered fibres that have been exploited in manipulating supercontinuum generation and modulation instability. In this work, I have developed a rigorous quantum model to investigate spontaneous four-wave mixing (SFWM) inside these tapered waveguides. The right combinations between the modulation amplitude ?d and tapering period ΛT that enhances the expected number of photons N?s at the targeted wavelengths are portrayed in Fig.1(a), for fibres with same number of periods M. The values of N?s are normalised to the case when ?d=0, to quantify the enhancement in photon-pairs generation using the PTW-technique in comparison to uniform fibres. For only M=50, N?s is remarkably enhanced by 35dB. The output spectrum of the photon-pairs is featured as a narrow sinc-function with very weak sidelobes that are significantly diminished for large number of periods, as depicted in Fig.1(b). The 2D representation of the spectrum as a function of the photon-pairs wavelengths (λs, λi) is shown in panel (c). In this plot, the pump is assumed to be a monochromatic at a frequency satisfies the energy conservation. The corresponding N?s for a Gaussian-pulse pump source with an input energy 1nJ and a full-width-half-maximum 4ps is portrayed in analysis, Fig.1(d). Using the Schmidt decomposition, the spectral-purity is 0.74. This shows the ability of the PTW-technique in producing highly-efficient relatively-pure single photons at any on-demand frequencies without applying any bandpass filters. This work will also open a new direction of research to investigate how the tapering patterns can be fully optimised to tailor the spectral properties of the output photons in third-order nonlinear guided structures.
关键词： spectral-purity,Quasi-phase-matching,spontaneous four-wave mixing,periodically-tapered waveguides,photon-pairs generation
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Quasi-Phase-Matched Third Harmonic Generation in Periodic Stacks of Polymer Bilayers
摘要： Quasi-phase-matching (QPM) is widely used for nonlinear frequency conversion with quadratic media, in which QPM is achieved by periodically reversing the signs of the nonlinear optical coefficients. Although efficient third harmonic generation (THG) can be realized by cascading two quadratic processes, direct QPM THG with isotropic media is of fundamental interest. For an isotropic cubic medium, however, reversal of the sign of the nonlinearity is not possible. Recently, we reported the first experimental realization QPM THG in isotropic polymer films with alternatingly deposited multilayers of a highly nonlinear organic material and a passive resin up to four periods [1]. Here, we investigated the QPM characteristics by measuring the THG output while tuning the fundamental wavelength around the QPM condition.
关键词： Quasi-phase-matching,third harmonic generation,isotropic polymer films,nonlinear optical coefficients
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Highly Efficient Ultra-Broadband Entangled Photon-Pair Generation using a Chirped PPSLT Ridge Waveguide
摘要： As some of the most promising quantum applications such as high resolution quantum optical coherence tomography (QOCT) with dispersion cancellation as well as quantum key distribution require frequency entanglement. Therefore, frequency entanglement light sources are an essential importance for implement of many quantum optical applications. So Far, the most prominent method used for the entangled photon pair generation is spontaneous parametric down-conversion (SPDC) in nonlinear crystals. Recently, with adopting chirp quasi-phase matching (QPM) PPSLT (periodically poled stoichiometric lithium tantalate) has been used as source of entangled photons with large bandwidth. However, improving the overall system ef?ciency is still remain challenging. One realistic approach is improving the generation ef?ciency of the entanglement source, we developed a source for highly ef?cient frequency entangled photon pairs generation utilizing type-0 PPSLT by adopting chirp QPM technology together with ridge waveguide structure. In experiments, we use 10 mm long waveguides with chirp rate of 0%, 3% and 6.7%. After coupling 405 nm CW pump light into a waveguide we fed the collinearly emitted photons into a single mode ?ber then observed its spectrum with a spectroscope. During experiments, temperature of all waveguides were set to 70.8?C with an accuracy of 0.1?C to ensure the degenerated phase matching condition of fundamental modes for signal, idler and pump lights is met in our multi-mode waveguides. As results are shown in Fig.1 (a), we observed a ～ 20 nm bandwidth sinc function-like spectrum emitted from the 0% chirp waveguide (blue dots), moreover, with increasing device chirp rate we also managed to obtain the broadening of spectra. The measured result of a 3% chirp rate device shows a spectrum with ～ 240 nm bandwidth, as well as ～ 340 nm bandwidth (orange dots) spectrum generated via the 6.7% one. In order to properly evaluate the generation ef?ciency of collinearly emitted photons we separate them with a 50:50 ?ber beam splitter, since signal and idler photons share the same spatial mode (fundamental mode of ridge waveguide) and identical in both frequency and polarization degree of freedom. Fig.1 (b) is the power dependency measurement results measured with a 3% chirp rate waveguide, signal and idler counts are the recorded counting rate of events from two SSPDs. We estimate the generation ef?ciency as 3.2×106 pairs/s·μW. This result appears 1000 times higher compared to our previous result (2×103 pairs/s·μW) observed using a chirped bulk QPM device.
关键词： ridge waveguide structure,frequency entanglement,quantum optical coherence tomography,quantum key distribution,PPSLT,chirp quasi-phase matching,spontaneous parametric down-conversion
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Periodic Poling with Short Period for Thin Film Lithium Niobate Waveguides
摘要： Lithium niobate (LN) is a favourable material for many applications, especially in integrated optics, due to its excellent electro-optic, acousto-optic, and nonlinear optic properties. One promising application of LN is second-harmonic generation (SHG). For enhancing the efficiency of SHG, phase matching between the interacting waves is needed, which is often realized by employing quasi-phase matching (QPM). QPM is typically realized by periodic poling of LN, i.e. the periodic flipping of the crystal orientation. The needed period is determined by the wavelengths as well as by the wave vectors of the fundamental- and the second-harmonic waves (FW and SH, respectively). For the case of backward SHG with a fundamental wavelength of 1.55 μm, where the SH wave travels in the opposite direction to the FW, typically sub-micrometer periods of the poled LN are required. Here, we demonstrate the realization of short-period QPM structures in LN-on-insulator (LNOI) thin-film substrates with a thickness of 600 nm. We aim to fabricate periodically poled LNOI (PPLNOI) waveguides with a periodicity as small as 1 μm, facilitating efficient nonlinear interaction due to the strong mode confinement.
关键词： periodic poling,second-harmonic generation,integrated optics,Lithium niobate,quasi-phase matching
更新于2025-09-12 10:27:22
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Formation Rules and Dynamics of Photoinduced χ <sup>(2)</sup> Gratings in Silicon Nitride Waveguides
摘要： Silicon nitride has emerged as a prominent platform for building photonics integrated circuits. While its nonlinear properties based on third-order effects have been successfully exploited, an efficient second harmonic generation in standard stoichiometric silicon nitride (Si3N4) waveguides can also be achieved after all-optical poling as was recently shown. The root of such phenomenon has been attributed to the inscription of a self-organized periodic space-charge grating along the waveguide, allowing an effective χ(2) and automatic quasi-phase-matching of pump and second harmonic. However, the different parameters and their role in increasing the efficiency of the process are still not fully comprehended. In this work, we use optical means to identify the general conditions of mode matching occurring during all-optical poling. The overlap integral between pump and second harmonic optical modes is shown to be the governing parameter in determining the features of the χ(2) gratings. Two-photon microscopy measurements of the χ(2) gratings reveal the presence of a secondary periodicity in some of the waveguides used in the study. According to overlap integral simulations such effect can occur due to mode mixing in the waveguide bends. From a study of poling dynamics, we observe that poling efficiency and rate increase as a function of optical pump power and waveguide length. However, in order to initiate poling, a critical pump intensity, which is lower for longer waveguides, must be coupled into waveguide. Temporal and thermal stability tests reveal the nature of charge traps responsible for grating inscription. After applying thermally activated hopping as conductivity mechanism in our samples, we show that only shallow traps seem to be activated during the all-optical poling process.
关键词： stoichiometric silicon nitride,nonlinear optics,all-optical poling,second harmonic generation,quasi-phase-matching
更新于2025-09-12 10:27:22
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Quasi-Phase-Matching Method Based on Coupling Compensation for Second Harmonic Generation in GaN Waveguides
摘要： We report a novel quasi-phase-matching method based on coupling compensation for second harmonic generation in GaN/AlGaN waveguides on sapphire substrates. The proposed method can overcome limitations of periodically oriented GaN waveguides because of spatial periodic modulation of the light intensity along the propagation direction, rather than the conventional spatial periodic modulation of the nonlinear optical coefficients of GaN. The method can be realized by using a dual-planar or dual-ridge waveguide frequency doubler structure. This concept has the potential to open a new range of applications for broadband on-chip nonlinear frequency conversion.
关键词： second harmonic generation,directional couplers,GaN and AlGaN waveguides,quasi-phase-matching,supermode dispersion,integrated optics
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Broadband Infrared (2.7–20 μm) Generation Via Random Quasi-Phase-Matched Intra-Pulse Difference-Frequency Generation
摘要： Coherent mid-infrared (MIR) light has a plethora of important applications ranging from life-science to industrial processes. Simultaneous coverage of this region will enable the parallel detection of various chemicals and enhance the specificity of their detection [1]. One of the most popular broadband infrared generation methods is nonlinear down-conversion from the near-infrared. An effective conversion can be achieved by using phase-matching and quasi-phase-matching in birefringent crystals and crystals with periodically poled structure respectively. Random quasi-phase-matching (RQPM) in poly-crystals is an alternative method that has recently shown great promise [2,3], which results in a gradual growth of the generated signal linear to the propagation length. Compared to generic phase-matching schemes, RQPM offers an unparalleled phase-matching bandwidth that is insensitive to incident angle. In addition, unlike single-crystals, poly-crystals can easily be grown into larger dimensions to enable longer interaction lengths. Here we describe the generation of octave-spanning MIR continuum at over 20 mW of average power based on RQPM driven by a Ho:YAG thin-disk oscillator at 2.1 μm [4]. To the best of our knowledge, this is the first time RQPM has been implemented for intra-pulse difference-frequency generation (DFG). A 1 μm laser system based on a Yb:YAG thin-disk oscillator [5] was also tested as the driving source in this scheme.
关键词： ZnS,mid-infrared,Broadband infrared,random quasi-phase-matching,intra-pulse difference-frequency generation,ZnSe
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Optically Engineered Nonlinear Photonic Structures in Ferroelectrics
摘要： Performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of the materials. This modulation ensures, via the quasi phase matching (QPM), an efficient energy exchange between optical waves at different frequencies. The QPM structures, also known as the nonlinear photonic crystals, offer a variety of novel properties and functionalities that cannot be obtained in uniform nonlinear crystals. Typically, such nonlinear structures have been fabricated via electric-poling. However, this technique is restricted to particular crystallographic geometries, and does not allow to create isolated structures inside the nonlinear material. This means that one cannot realize fully 3-dimensional nonlinear structures via traditional electrical poling. In this work we discuss our novel technique capable of engineering quadratic nonlinearity, based on all-optical poling of ferroelectrics. This new approach, is similar to traditional laser writing in optical media. It involves a tight focusing of femtosecond infrared beam and subsequent its two photon absorption which heats locally the medium. The large temperature gradient induces thermoelectric field which, if sufficiently high, inverts locally direction of spontaneous polarization, changing the sign of nonlinearity. The method is extremely flexible, can be applied to different crystallographic orientations and enables formation of localised spatially modulated nonlinear response inside optical media. Here, we demonstrate its application to create structures for efficient frequency conversion in Lithium Niobate waveguides and transverse second harmonic generation. Moreover, we provide here the first ever experimental evidence of the 3D Nonlinear Photonic Crystal, fabricated in ferroelectric barium calcium titanate. Finally we show formation of multiple nonlinear photonic crystals in form of fork structures inside the bulk of ferroelectric calcium barium niobate, and demonstrate their application for wave-shaping in frequency doubling process, directly creating second harmonic optical vortices and conical beams.
关键词： frequency conversion,nonlinear photonic structures,ferroelectrics,all-optical poling,second harmonic generation,quasi phase matching
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Quasi-Phase Matching in High Harmonic Generation using Structured Plasmas
摘要： High harmonic generation (HHG) is an important process in attosecond science. Its efficiency is, however, limited to values below 10-5 of the incident power into a single harmonic. Phase matching can increase the efficiency but deals with low ionization rates. Furthermore HHG from laser-produced plasmas has shown some promising advantages in increasing the response of the conversion. These are the appearance of resonantly enhanced harmonics or the efficient generation in carbon or nanoparticle containing plasmas. On the contrary laser-produced plasmas inherently possess a high degree of ionization which hampers any phase-matching scheme with these sources. This dilemma can be circumvented by quasi-phase matching (QPM). In this case the conversion process is suppressed when the harmonics are generated out of phase leading to a quadratic growth of the harmonic intensity with interaction distance. Experimentally QPM can be achieved e.g. by applying a structured conversion medium in a focused driving beam geometry. Here, we show how such a scheme is realized with laser-produced plasmas. The idea of using a structured plasma for QPM is not new [1], but in none of these earlier studies QPM has been optimized for maximum efficiency nor controlled for different regions of the harmonic spectrum.
关键词： laser-produced plasmas,quasi-phase matching,attosecond science,High harmonic generation
更新于2025-09-11 14:15:04