Entanglement-enabled delayed-choice experiment.

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.

Integrated optical source of polarization entangled photons at 1310 nm.

We report the realization of a new polarization entangled photon-pair source based on a titanium-indiffused waveguide integrated on periodically poled lithium niobate pumped by a CW laser at 655 nm. The paired photons are emitted at the telecom wavelength of 1310 nm within a bandwidth of 0.7 nm.

Increased pump acceptance bandwidth in spontaneous parametric downconversion process using Bragg reflection waveguides.

In this paper we show that by suitably tailoring the dispersion characteristics of a Bragg reflection waveguide (BRW) mode, it is possible to achieve efficient photon pair generation over a large pump bandwidth while maintaining narrow signal bandwidth. The structure proposed consists of a high index core BRW with a periodically poled GaN core and periodically stratified cladding made up of alternate layers of Al(0.02)Ga(0.

Experimental observation of longitudinal modulation of mode fields in periodically segmented waveguides.

We present what is to our knowledge the first experimental observation by fluorescent visualization, of the evolution of the mode field profile in a periodically segmented waveguide. The experimental observations are then compared with the numerical results obtained by a finite-difference beam propagation method. Good agreement between experimental and numerical results is observed.

Spectral Measurement of the Film-Substrate Index Difference in Proton-Exchanged LiNbO(3) Waveguides.

We report the spectral characterization of proton-exchanged lithium niobate (PE:LiNbO(3)) waveguides in terms of the variation of the refractive-index difference between the waveguiding layer and the substrate. The dispersion of the extraordinary refractive-index increase (deltan(e)) is measured from 405 to 1319 nm with several light sources. Two types of proton-exchanged waveguide, prepared under different conditions, are studied.

Ray analysis of parabolic-index segmented planar waveguides.

A ray analysis of periodically segmented waveguides with parabolic-index variation in the high-index region is presented. We carried out the analysis using ray transfer matrices, which is convenient to implement and which can be extended to study different types of graded-index segmented waveguide. Results of this ray tracing approach clearly illustrate the waveguiding properties and the existence of stable and unstable regions of operation in segmented waveguides.

Cascading phase shift and multivalued response in counterpropagating frequency-nondegenerate parametric amplifiers.

We propose and analyze a novel geometry for all-optical processing of low-power signals that is based on a frequency-nondegenerate counterpropagating parametric amplifier. The stationary response in the cascading regime exhibits multivalued solutions with enhanced nonlinear phase shifts. Implementation in a quasi-phase-matched LiNbO(3) waveguide is discussed.

High-performance guided-wave asynchronous heralded single-photon source.

We report on a guided-wave asynchronous heralded single-photon source based on the creation of nondegenerate photon pairs by spontaneous parametric downconversion in a periodically poled lithium niobate wave-guide. We show that, by use of the signal photon at 1310 nm as a trigger, a gated detection process permits announcement of the arrival of single photons at 1550 nm at the output of a single-mode optical fiber with a high probability of 0.37.

Modeling of parametric amplification in the Cerenkov-idler configuration in planar waveguides.

We present theoretical modeling of a novel configuration for quasi-phase-matched parametric amplification in which the pump and the signal fields form guided waves of a planar waveguide while the idler is radiated into the substrate. We follow a coupled-mode approach to study the parametric amplification in periodically domain-reversed proton-exchanged LiNbO(3) waveguides upon a Z-cut substrate and present numerical results relevant to the amplification process. In particular, for given pump and signal wavelengths we have studied the dependence of the gain coefficient on the periodicity of a grating formed by domain inversion.

Erbium-doped silica fibers for intrinsic fiber-optic temperature sensors.

The variation in the green intensity ratio ((2)H(11/2) and (4)S(3/2) energy levels to the ground state) of Er ions in silica fibers has been studied as a function of temperature. The different processes that are used to determine the population of these levels are investigated, in particular 800-nm excited-state absorption in Er-doped fibers and 980-nm energy transfer, in Yb-Er-codoped fibers. The invariance of the intensity ratio at a fixed temperature with respect to power, wavelength, and doped fiber length has been investigated and shown to permit the realization of a high-dynamic-range (greater than 600 °C), autocalibrated fiber-optic temperature sensor.

1.2-µm transitions in erbium-doped fibers: the possibility of quasi-distributed temperature sensors.

We propose the principle of a high-dynamic, quasi-distributed temperature sensor based on the behavior of the 1.13- and the 1.24-µm emission lines in erbium-doped silica fibers.

Quasi-phase-matched parametric fluorescence in room-temperature lithium tantalate waveguides.

We report what is to our knowledge the f irst observation of quasi-phase-matched parametric fluorescence in the 1.2-2.3-microm region, at ambient temperature, in lithium tantalate waveguides, using a pump wavelength between 805 and 845 nm.

Fabrication parameter optimization of a low-threshold high-efficiency proton-exchanged waveguide laser in Nd:LiTaO(3).

Knowing the correlation between the Nd(3+) excited-state lifetime in proton-exchanged waveguides and the phase diagram of the H(x)Li(1-x)TaO(3) compound permits optimized waveguide fabrication parameters to be found. These have been used to produce a Nd:LiTaO(3) waveguide laser with a threshold of 2.9 mW and a slope efficiency of 33%, in good agreement with the best predicted values.

Characteristics of hybrid modes in proton-exchanged lithium niobate waveguides.

A rigorous numerical model, verified by experimental results, gives an explanation of the particular electromagnetic behaviors observed in x-cut proton-exchanged lithium niobate waveguides. This approach, which allows an exact calculation of the weights of the coupled ordinary and extraordinarywaves that make up the hybrid modes, provides deeper insight into the study of the strains induced by the proton-exchange process in the waveguide itself, showing that the optical axis of the exchanged layer is not parallel to the waveguide plane.

Thermalization effects between upper levels of green fluorescence in Er-doped silica fibers.

We present a spectroscopic study of the green fluorescence resulting from pump excited-state absorption in Er-doped silica fibers excited in the 800-nm range. The absorption and emission bands are selectively attributed to the (4)S(3/2) and (2)H(11/2) levels. The fluorescence response at two excitation wavelengths, the temperature behavior, and lifetime measurements demonstrate a fast thermalization between the (4)S(3/2) and (2)H(11/2) levels.

Fluorescence in rare earth-doped fluorozirconate fibers.

Spontaneous fluorescence bands of erbium-, holmium-, and thulium-doped fluorozirconate fibers are studied experimentally and theoretically. From experimental data and for each trivalent ion we identify the set of optical transitions that gives rise to the observed linear fluorescence and upconversion process. Fiber perturbation theory and density matrix formalism are used to model fluorescence spectra with particular attention to modal structure, loss, and mode coupling in the fiber.

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.

Fluorescence and saturated absorption in a neodymium doped silica fiber.

We report the study of absorption and fluorescence in neodymium doped silica fibers with excitation pulses much shorter than the fluorescence lifetime. Fluorescence and absorption saturation are observed for pump powers well below the damage threshold of the fiber. The saturation process is described using the density matrix method for the light absorption and the normal mode formalism for the propagation.

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In this paper, we study the optical Kerr effect theoretically in multimode birefringent optical fibers in connection with the characteristics of the fiber and excitation conditions. We observe experimentally, for a pump power 2 W in the fundamental mode, 70% modulation depth for the probe light with multimodal coupling.

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.

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.