We experimentally demonstrate a polarization-entangled photon source at 810 nm using a type-II phase-matched periodically poled potassium titanyl phosphate (PPKTP) crystal pumped by a low-cost, broadband laser diode with a central wavelength of 405 nm and a typical bandwidth of 0.53 nm. The PPKTP crystal is placed in a Sagnac loop to realize the compact size and high stability. The downconverted biphotons, the signal and the idler, have typical bandwidths of 5.57 and 7.32 nm. We prepare two Bell states | Ψ + ⟩ and | Ψ − ⟩ with the fidelities of 0.948 ± 0.004 and 0.963 ± 0.002 . In the polarization correlation measurement, the visibilities are all higher than 96.2%, and in the Bell inequality test, the S value can achieve 2.78 ± 0.01 . This high-quality and low-cost entangled photon source may have many practical applications in quantum information processing.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
Abstract Tightly focused Bessel beams exhibit significantly higher intensity and non-diffractive three-dimensional micro-scale features compared to conventional fundamental Gaussian beams under the same optical power. These unique characteristics make Bessel beams particularly advantageous for enhancing photon pair generation in periodically poled nonlinear crystals. In this work, we experimentally demonstrate a compact pumping system using an asymmetric convex-convex lens and a plano-convex lens to generate Bessel beams. A broadband continuous-wave (CW) laser diode with a full-width at half-maximum (FWHM) of
0.54 (nm) 0.54 ( n m ) is used to pump a periodically poled potassium titanyl phosphate (PPKTP) crystal configured in a type-II phase-matched dual-path Sagnac loop. Our setup achieves a record-high coincidence-to-single-photon (CSP) ratio of 25% for type-II phase-matched spontaneous parametric down-conversion (SPDC) processes using broadband laser diodes. The degenerate polarization-entangled photon pair source, operating at
810 (nm) 810 ( n m ) , demonstrates exceptional performance metrics, including a brightness of
9.3 (kcps/mW) 9.3 ( k c p s / m W ) and a coincidences-to-accidentals ratio (CAR) of approximately 1091. Furthermore, the entanglement quality is verified through high visibility measurements: 99.2% in the horizontal/vertical (H/V) basis and 94.3% in the diagonal/ anti-diagonal (D/A) basis. In a Bell inequality test, we achieve an S value of
(2.7±0.04) ( 2.7 ± 0.04 ) , corresponding to a state fidelity of 0.95. In comparison, the Gaussian-pumped configuration yields a CSP ratio of 11.27%, a brightness of
4.46 (kcps/mW) 4.46 ( k c p s / m W ) , and a CAR of approximately 500. Measured polarization visibilities are 99.1% in the H/V basis and 96.7% in the diagonal (±45 ∘ ) basis, with a Bell parameter of
S=2.6±0.03 S = 2.6 ± 0.03 . These comparative results underscore the substantial advantages of utilizing Bessel beams for high-performance entangled photon pair generation.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
We experimentally demonstrate a source of polarization entangled photon-pairs based on a single periodically poled potassium titanyl phosphate crystal pumped with a broadband, free running laser diode. The crystal is placed within a linear beam-displacement interferometer and emits photon-pairs based on type-0 spontaneous parametric downconversion. We observe pair rates of 0.56 Mpairs/s/mW in a single spatial mode with a polarization visibility of 97.7% over a spectral range of 100 nm. This experiment demonstrates a pathway toward observing gigacount rates of polarization entangled photon pairs by using high-power free-running laser diodes with fast multiplexed detectors.
Polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum communications, quantum computation and high precision quantum metrology. We report on the generation of a continuous-wave pumped 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II periodically poled KTiOPO(4) (PPKTP) crystal in a Sagnac interferometer. Hong-Ou-Mandel (HOM) interference measurement yields signal and idler photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The source can be tuned over a broad range against temperature or pump power without loss of visibilities. This source will be used in our future experiments such as generation of orbital angular momentum entangled source at telecom wavelength for quantum frequency up-conversion, entanglement based quantum key distributions and many other quantum optics experiments at telecom wavelengths.