We demonstrate optically stable amorphous silicon nanowires with both high nonlinear figure of merit (FOM) of ~5 and high nonlinearity Re(γ) = 1200W −1 m −1. We observe no degradation in these parameters over the entire course of our experiments including systematic study under operation at 2 W coupled peak power (i.e. ~2GW/cm 2) over timescales of at least an hour.

We demonstrate a technique for generating tunable all-optical delays in room temperature single-mode optical fibers at telecommunication wavelengths using the stimulated Brillouin scattering process. This technique makes use of the rapid variation of the refractive index that occurs in the vicinity of the Brillouin gain feature. The wavelength at which the induced delay occurs is broadly tunable by controlling the wavelength of the laser pumping the process, and the magnitude of the delay can be tuned continuously by as much as 25 ns by adjusting the intensity of the pump field. The technique can be applied to pulses as short as 15 ns. This scheme represents an important first step towards implementing slow-light techniques for various applications including buffering in telecommunication systems.

.We experimentally study the generation of correlated pairs of photons through four-wave mixing (FWM) in embedded silicon waveguides. The waveguides, which are designed to exhibit anomalous group-velocity dispersion at wavelengths near 1555 nm, allow phase matched FWM and thus efficient pair-wise generation of non-degenerate signal and idler photons. Photon counting measurements yield a coincidence-to-accidental ratio (CAR) of around 25 for a signal (idler) photon production rate of about 0.05 per pulse. We characterize the variation in CAR as a function of pump power and pump-to-sideband wavelength detuning. These measurements represent a first step towards the development of tools for quantum information processing which are based on CMOS-compatible, silicon-on-insulator technology.

We present a fiber based source of polarization-entangled photon pairs 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 the signal or the idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the CHSH form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.

Abstract-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 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.Index Terms-Fiber four-wave mixing, parametric amplifiers, photon counting, quantum communication, quantum cryptography. EFFICIENT generation and transmission of quantum-correlated photon pairs, especially in the 1550-nm fiber-optic communication band, is of paramount importance for practical realization of the quantum communication and cryptography protocols [1]. The workhorse source employed in all implementations, thus far [2] has been based on the process of spontaneous parametric down-conversion in second-order [ ] nonlinear crystals. Such a source, however, is not compatible with optical fibers as large coupling losses occur when the pairs are launched into the fiber. This severely degrades the correlated photon-pair rate coupled into the fiber, since the rate depends quadratically on the coupling efficiency. From a practical standpoint, it would be advantageous if a photon-pair source could be developed that not only produces photons in the communication band but also can be spliced to standard telecommunication fibers with high efficiency. Over the past few years, various attempts have been made to develop more efficient photon-pair sources, but all have relied on the down-conversion process [3]- [6]. Of particular note is [4], in which the effective of periodically poled silica fibers was used. In this letter, we report the first, to the best of our knowledge, photon-pair source that is based on the Kerr nonlinearity ( ) of standard fiber. Quantum-correlated photon pairs are observed and characterized in the parametric fluorescence of four-wave mixing (FWM) in dispersion-shifted fiber (DSF).The FWM process takes place in a nonlinear-fiber Sagnac interferometer (NFSI), shown schematically in Fig. 1. Previ- ously, we have used this NFSI to generate quantum-correlated twin beams in the fiber [7]. The NFSI consists of a fused-silica 50/50 fiber coupler spliced to 300 m of DSF having zero-dispersion wavelength nm. It can be set as a reflector with proper adjustment of the intraloop FPC to yield a transmission coefficient 30 dB. When the injected pump wavelength is slightly greater than , FWM in the DSF is phase matched [8]. Two pump photons of frequency scatter into a signal photon and an idler photon of frequencies and , respectively, where . Signal-idler separations of 20 nm can be easily obtained with use of commercial DSF [7]. The pump is a mode-locked train of 3-ps-long pulses that a...

We present the first experimental demonstration of anomalous group-velocity dispersion (GVD) in silicon waveguides across the telecommunication bands. We show that the GVD in such waveguides can be tuned from -2000 to 1000 ps/(nm*km) by tailoring the cross-sectional size and shape of the waveguide.

We demonstrate an all-optical tunable pulse delay scheme that utilizes the power-dependent variation of the refractive index that accompanies stimulated Raman scattering in an optical fiber. Using this technique, we delay 430-fs pulses by up to 85% of a pulse width. The ability to accommodate the bandwidth of pulses shorter than 1 ps in a fiber-based system makes this technique potentially viable for producing controllable delays in ultra-high bandwidth telecommunication systems.

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