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Generation of optical signal and terahertz idler photons by spontaneous parametric down-conversion
摘要： Frequency-angular characteristics of signal and idler photons generated under spontaneous parametric down-conversion are studied in a strongly frequency nondegenerate regime, without paraxial approximation, accounting for possible inherent absorption of idler waves in a nonlinear crystal, classical thermal field fluctuations, and the multimode character of parametric interaction induced by transverse spatial limitation of the pump beam. Spatial limitation is shown to lead to a huge increase in angular divergence of the idler photons generated at terahertz frequencies. General expressions are obtained for the frequency-angular sensitivity function of the nonlinear-optical terahertz wave detector and for power densities of the signal and idler photon fluxes. The absorption-induced difference in the parametric conversion coefficients for the noise and externally incident radiation of the idler frequency is shown to be described by approximately the same loss factor for all active spatial idler modes. Two different parametric contributions of the internal thermal noise to the number of output idler photons were revealed with different dependence on the idler-wave absorption. Expressions for the loss factors, which describe absorption-induced effects in signal and idler channels, are obtained and shown to be turning into one another by changing the sign of the absorption coefficient. Relative contribution of thermal and quantum field fluctuations into the intrinsic radiation of a nonlinear crystal at signal and idler frequencies is analyzed accounting for the crystal absorption properties.
关键词： nonlinear optics,thermal fluctuations,terahertz,quantum fluctuations,absorption,spontaneous parametric down-conversion
更新于2025-09-23 15:22:29
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Design and Simulation of Novel Perovskite/Mg <sub/>2</sub> Si Based Monolithic Tandem Solar Cell With 25.5% Conversion Efficiency
摘要： We investigate wavefront engineering of photon pairs generated through spontaneous parametric down conversion in lithium niobate-based nonlinear photonic crystals (NPCs). Due to the complexity of domain structures, it is more convenient to describe photon interaction based on the nonlinear Huygens–Fresnel principle than conventional quasiphase matching regime. Analytical expressions are obtained to describe the transverse properties of down-converted photon states. The convenience of domain engineering in LiNbO3 crystals provides a potential platform for flexible wavefront manipulation of multiphoton states. The generation of N00N state with orbital angular momentum in a twisted NPC is studied utilizing this method. The obtained state is of great value in quantum cryptography, metrology, and lithography applications.
关键词： N00N state,wavefront engineering,spontaneous parametric down-conversion,nonlinear photonic crystal
更新于2025-09-19 17:13:59
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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) - Characterization of Broadband Spontaneous Parametric Down-Conversion in Periodically Poled Materials
摘要： Spontaneous parametric down-conversion (SPDC) is one of the most important sources for entangled or correlated photon pairs, which are the foundation of the emerging fields of quantum-optical imaging and spectroscopy. Using periodically poled materials as an SPDC-source allows broad emission spectra in widely tunable wavelength ranges in an efficient and walk-off-free process. For applications that employ nonlinear interference setups [1,2], maximum interferometric contrast is only achieved when signal and idler modes are overlapped precisely in the second crystal. Thus, accurate knowledge of the spectral-angular characteristic of SPDC is crucial for designing such devices. In our work, we extend an analytic approach introduced by Byer and Harris [3] and develop an application- oriented model for the signal power density of broadband SPDC. For spectrally broad emission, non-collinear phasematching has to be described properly. Here, the finite pump diameter is taken into account by introducing an angular dependent effective interaction length. As an exemplary case, we calculate the angular characteristics, the spectral power density and the total signal power for SPDC in periodically poled lithium niobate pumped at 532 nm. For verification, we compare the calculations to experimental results obtained with a 2 cm long, 5 % MgO-doped lithium niobate crystal at 40 °C crystal temperature. The crystal contains 11 poling channels with periods ranging from 8.2 μm to 11.2 μm. It is pumped by a narrowband laser with 2 W power at 532 nm wavelength focused to a beam waist of 120 μm. Using the different poling periods, we cover a signal wavelength range of 613 nm to 750 nm, which corresponds to correlated idler wavelengths ranging from 4 μm to 1.8 μm. In figure 1a, the calculated spectral power density for different poling channels (solid lines) is compared to measured spectra. To account for the angular-dependent coupling efficiency to the spectrometer fiber input, each measured spectrum is scaled with a constant factor to the best fit with the calculated power density and thus only allows a qualitative comparison. The quantitative comparison of the calculated (solid lines) and measured (black dots) total signal power for the different channels as a function of the collinear (peak) signal wavelength in figure 1b) further verifies our calculations. The presented analytical model is easily applicable to a wide range of experimental configurations for SPDC in periodically-poled crystals, without the need for time-consuming numerical simulations. The exact knowledge of the spatial and spectral structure of SPDC emission allows predictions on design criteria for functionalized devices that employ SPDC as a photon pair source.
关键词： spectroscopy,periodically poled materials,SPDC,Spontaneous parametric down-conversion,quantum-optical imaging
更新于2025-09-16 10:30:52
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Microscale Generation of Entangled Photons without Momentum Conservation
摘要： We report, for the first time, the observation of spontaneous parametric down-conversion (SPDC) free of phase matching (momentum conservation). We alleviate the need to conserve momentum by exploiting the position-momentum uncertainty relation and using a planar geometry source, a 6 μm thick layer of lithium niobate. Nonphase-matched SPDC opens up a new platform on which to investigate fundamental quantum effects but it also has practical applications. The ultrasmall thickness leads to a frequency spectrum an order of magnitude broader than that of phase-matched SPDC. The strong two-photon correlations are still preserved due to energy conservation. This results in ultrashort temporal correlation widths and huge frequency entanglement. The studies we make here can be considered as the initial steps into the emerging field of nonlinear quantum optics on the microscale and nanoscale.
关键词： quantum optics,spontaneous parametric down-conversion,phase matching,lithium niobate,frequency entanglement,momentum conservation
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) - Mid-Infrared Sensing by Induced Coherence in a Single Nonlinear Waveguide
摘要： Induced coherence (IC) between two spatially separated but indistinguishable spontaneous parametric down conversion (SPDC) processes underpins the recent revival of nonlinear interferometry and has led to new applications in quantum imaging and mid-infrared (MIR) spectroscopy [1,2]. These applications exploit induced coherence and the spectral or spatial correlations between signal and idler photons generated through SPDC. Here, we theoretically describe the phenomenon of IC in a general way by making use of a quantum-mechanical approach based on the classical Green’s function (GF) of the system [3,4]. Our formalism is well suited for treating generic linear optical properties of a system, including loss, and studying their influence on the IC phenomena. Moreover, our approach can account for arbitrary spatial profiles of the nonlinearity and hence can be used to describe generalized IC experiments with different number of photon-pair sources. Here we propose a sensing experiment using a single nonlinear waveguide [5] and investigate IC using our formalism. We find that in this case a substance under test inside or surrounding the waveguide can affect the IC during the generation stage along the nonlinear waveguide, making this a compact scheme for MIR spectroscopy without the need for MIR detectors.
关键词： spontaneous parametric down conversion,quantum imaging,nonlinear interferometry,mid-infrared spectroscopy,induced coherence
更新于2025-09-11 14:15:04
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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) - Integrated Semiconductor Quantum Photonics
摘要： For fundamental tests of quantum physics as well as for quantum communications, non-classical states of light are an important tool. In this talk, we will present our work on developing nonlinear AlGaAs waveguides into a platform for quantum photonics in semiconductors. Most III-V semiconductors exhibit a large second-order optical nonlinearity, but phase-matching the nonlinear interaction is notoriously difficult. As a solution Bragg-reflection waveguides allow efficient creation of photon pairs through spontaneous parametric down-conversion. They have the potential to be homogeneously integrated with a pump laser and passive and active components on the chip. In our waveguides, we can create high-fidelity polarization [1] and time-bin entangled [2] photon pairs, which cover a large frequency band in the low-loss telecommunication window, suitable for serving multiple users through wavelength division multiplexing. For all our applications, it is important that we can design the desired linear and nonlinear properties, which in turn makes precise characterization necessary. For this purpose, we have developed a Fourier-transform Fabry-Perot spectroscopy technique [3], which yields the relevant device parameters with superior accuracy. We will further present our results on devices that integrate electrically injected lasers and the nonlinear conversion. A layer of quaternary quantum dots acts as the gain medium in a Fabry-Perot waveguide laser, which lases at room temperature in the Bragg mode, i.e. the pump mode for creating photon pairs. We will close with an outlook on further device integration towards a complete semiconductor quantum photonics platform.
关键词： AlGaAs waveguides,photon pairs,Bragg-reflection waveguides,quantum photonics,Fourier-transform Fabry-Perot spectroscopy,spontaneous parametric down-conversion
更新于2025-09-11 14:15:04
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Dispersion measurement method with down conversion process
摘要： Proper characterization of nonlinear crystals is essential for designing single photon sources. We show a technique for dispersion characterization of a nonlinear material by making use of phase matching in the process of parametric down conversion. We use our procedure to improve the Sellmeier coefficients measured by another methods. Our method is demonstrated on an exemplary periodically poled potassium titanyl phosphate KTiOPO4 crystal phase-matched for 396 nm to 532 nm and 1550 nm. We show a procedure to characterize the dispersion in the range of 390 to 1800 nm by means of only one spectrometer for the UV–visible range.
关键词： second order nonlinear optical processes,single photon sources,spontaneous parametric down-conversion,dispersion measurement
更新于2025-09-09 09:28:46
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Generation of narrow-band single-photon states via spontaneous parametric down-conversion for quantum memories in doped crystals
摘要： We present experimental results on the generation of narrow-band single-photon states via cavity-enhanced spontaneous parametric down-conversion in a PPLN crystal and demonstrate the feasibility of conditional preparation of single 867-nm photons with a 70-MHz linewidth, compatible with optical quantum memory devices based on Nd3+-doped isotopically pure Y7LiF4 crystals.
关键词： single-photon source,cavity,spontaneous parametric down-conversion
更新于2025-09-04 15:30:14