Daniel Barry Ostrowsky

PPLN waveguide for quantum communication

Abstract:We report on energy-time and time-bin entangled photon-pair sources based on a periodically poled lithium niobate (PPLN) waveguide. Degenerate twin photons at 1 314 nm wavelength are created by spontaneous parametric down-conversion and coupled into standard telecom fibers. Our PPLN waveguide features a very high conversion efficiency of about 10-6, roughly 4 orders of magnitude more than that obtained employing bulk crystals [#!Tanzilli01a!#]. Even if using low power laser diodes, this engenders a significant probability for creating two pairs at a time - an important advantage for some quantum communication protocols. We point out a simple means to characterize the pair creation probability in case of a pulsed pump. To investigate the quality of the entangled states, we perform photon-pair interference experiments, leading to visibilities of 97% for the case of energy-time entanglement and of 84% for the case of time-bin entanglement. Although the last figure must still be improved, these tests demonstrate the high potential of PPLN waveguide based sources to become a key element for future quantum communication schemes.

On the genesis and evolution of Integrated Quantum Optics

Applications of Integrated Optics to quantum sources, detectors, interfaces, memories and linear optical quantum computing are described in this review. By their inherent compactness, efficiencies, and interconnectability, many of the demonstrated individual devices can clearly serve as building blocks for more complex quantum systems, that could also profit from the incorporation of other guided wave technologies.

Independent control of index and profiles in proton-exchanged lithium niobate guides

We demonstrate the possibility of controlling, practically independently, the form and indices of proton-exchanged lithium niobate guides by means of guide annealing and proton exchange in lithium-rich solutions. Experimental results are presented that indicate how one can realize specific guide designs.

Fabrication and characterization of Titanium Indiffused Proton Exchanged (TIPE) waveguides in lithium niobate

Abstract We report the fabrication and characterization of optical waveguides realized in LiNbO 3 by a combined titanium indiffusion proton exchange (TIPE) process. These guides provide several unique advantages which include permitting tailorong of guide birefringence, realizing proton exchanged Y -cut plates of good optical quality, and the realization of imbedded TM guides due to a lowering of n o caused by proton exchange.

Nd:MgO:LiNbO 3 waveguide laser and amplifier

We report efficient operation of a channel waveguide laser and a channel waveguide amplifier in Nd:MgO:LiNbO(3). For the laser a cw output power of 2.9 mW was obtained for 23.6 mW of absorbed pump power. The absorbed pump power at threshold was 1.5 mW, and a slope efficiency of 13% was achieved. For the amplifier a small-signal gain of 7.5 dB was achieved for 22 mW of coupled pump power.

Entanglement-enabled delayed choice experiment

Delaying Quantum Choice Photons can display wavelike or particle-like behavior, depending on the experimental technique used to measure them. Understanding this duality lies at the heart of quantum mechanics. In two reports, Peruzzo et al. (p. 634) and Kaiser et al. (p. 637; see the Perspective on both papers by Lloyd) perform an entangled version of John Wheelers delayed-choice gedanken experiment, in which the choice of detection can be changed after a photon passes through a double-slit to avoid the measurement process affecting the state of the photon. The original proposal allowed the wave and particle nature of light to be interchanged after the light had entered the interferometer. By contrast in this study, entanglement allowed the wave and particle nature to be interchanged after the light was detected and revealed the quantum nature of the photon, for example, it displays wave- and particle-like behavior simultaneously. Quantum entanglement is used to probe the nature of the photon. Wave-particle complementarity is one of the most intriguing features of quantum physics. To emphasize this measurement apparatus–dependent nature, experiments have been performed in which the output beam splitter of a Mach-Zehnder interferometer is inserted or removed after a photon has already entered the device. A recent extension suggested using a quantum beam splitter at the interferometer’s output; we achieve this using pairs of polarization-entangled photons. One photon is tested in the interferometer and is detected, whereas the other allows us to determine whether wave, particle, or intermediate behaviors have been observed. Furthermore, this experiment allows us to continuously morph the tested photon’s behavior from wavelike to particle-like, which illustrates the inadequacy of a naive wave or particle description of light.

Soft proton exchange on periodically poled LiNbO3: A simple waveguide fabrication process for highly efficient nonlinear interactions

We report a simple fabrication process for realizing waveguides on periodically poled lithium niobate which preserves both the nonlinearity and the domain inversion. This so-called soft proton exchange has been used to generate highly efficient optical parametric fluorescence in the 1.48–2.01 μm region using a pump around 830 nm. The measured normalized efficiency is 130% W−1 cm−2 for an effective interaction length of 1.3 cm. This experimental figure is very close to the maximum theoretically predicted value of 140% W−1 cm−2.

A polarization entangled photon-pair source based on a type-II PPLN waveguide emitting at a telecom wavelength

We report the realization of a fiber-coupled polarization entangled photon-pair source at 1310 nm based on a birefringent titanium in-diffused waveguide integrated into periodically poled lithium niobate. By making use of a dedicated and high-performance setup, we characterized the quantum properties of the pairs by measuring two-photon interference in both Hong–Ou–Mandel and standard Bell inequality configurations. For the two sets of measurements we obtained interference net visibilities reaching nearly 100%, which represent important and competitive results compared to those for the similar waveguide-based configurations already reported. These results prove the relevance of our approach as an enabling technology for long-distance quantum communication.

Quasi-phase-matched parametric interactions in proton-exchanged lithium niobate waveguides

We present a review of parametric fluorescence with bulk and guided geometries in quasi-phase matched lithium niobate. Whereas bulk experiments have yielded results close to theoretical predictions, waveguided versions have shown strongly reduced efficiencies. Attributing the observed conversion efficiency reductions to a loss of the material nonlinearity, to a destruction of the inverted domains during the waveguide fabrication, or to both, we carefully studied the influence of the proton-exchange process on the nonlinear and structural properties of the periodically poled lithium niobate. We found that an annealed proton-exchange process can essentially conserve the nonlinearity but will erase the periodic domain structure. This erasure can be avoided by use of a highly diluted proton-exchange melt. This direct proton-exchange process perfectly preserves all the nonlinear optical and structural properties of periodically poled LiNbO3.

Extension of second-harmonic phase-matching range in lithium niobate guides

An extension of the fundamental wavelength phase-matching range for second-harmonic generation based on titanium-indiffused proton-exchanged lithium niobate guides has been demonstrated. Both the theoretical basis and experimental verification are presented.