We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell’s inequality by up to 10 standard deviations of measurement uncertainty.

In this letter, we present a source of quantum-correlated photon pairs based on parametric fluorescence in a fiber Sagnac loop. The photon pairs are generated in the 1550-nm fiber-optic communication band and detected with InGaAs-InP avalanche photodiodes operating in a gated Geiger mode. A generation rate > 10/sup 3/ pairs/s is observed, which is limited by the detection electronics at present. We also demonstrate the nonclassical nature of the photon correlations in the pairs. This source, given its spectral properties and robustness, is well suited for use in fiber-optic quantum communication and cryptography networks.

We demonstrate greatly improved results for the production of correlated photon-pairs using the four-photon scattering process in silica fiber. We achieve a true-coincidence-count to accidental-coincidence-count ratio greater than 10, when the photon-pair production rate is about 0.04/pulse. This represents a four-fold improvement over our previous results. The contribution of spontaneous Raman scattering, the primary cause of uncorrelated photons that degrades the fidelity of this source, is reduced by decreasing the wavelength detuning between the correlated photons and the pump photons and by using polarizers to remove the cross-polarized Raman-scattered photons. Excess Raman scattering could be further suppressed by cooling the silica fiber. Even without cooling the fiber, the achieved 10 to 1 ratio of true-coincidence to accidental-coincidence makes the fiber source of correlated photon-pairs a useful tool for realizing various quantum-communication protocols.

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Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production.