Photon entanglement has appeared to play a crucial role in the foundation of quantum physics and in the ever-increasing requirements of quantum information processing, quantum communication, quantum sensing and quantum computing. Thus, the industrial development and the characterization of practical entangled photon sources at telecom wavelengths are key element for the deployment of emerging quantum applications, such as Quantum Key Distribution.
The photon source is based on a 775 nm pumped type II Periodically Poled Lithium Niobate wave guide (PPLN_WG) designed for generation of orthogonally polarized photon pairs at 1550 nm. Picometer tunability of the converted central wavelength is achieved by using an accurate temperature control of both the PPLN_WG and the laser diode. All optical and electronics elements are embedded in a compact module. This practical photon source is driven by a USB communication port compatible with computer. The main characteristics of the photon source, Coincidence-to-Accidental-Ratio (CAR), brightness, bi-photon spectrum, heralded efficiency, purity, and indistinguishability are measured by using integrated optical benches and a 2-channels very-low-noise InGaAs single photon avalanche counters (G-SPAD). The proposed photon source measurements protocol is also available for the characterization of other photon sources technologies, such as for the Quantum Dots and semiconductor photon sources.
We performed two experimental Bell inequality violations by creating polarization entanglement or by using the natural frequency entanglement of our source. Violation by more than five standard deviations Bell inequalities with our setups demonstrate that our photon source is a promising tool for the realization of various distances quantum information experiments.
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