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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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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