Jay E. Sharping

Broad-band optical parametric gain on a silicon photonic chip

Developing an optical amplifier on silicon is essential for the success of silicon-on-insulator (SOI) photonic integrated circuits. Recently, optical gain with a 1-nm bandwidth was demonstrated using the Raman effect, which led to the demonstration of a Raman oscillator, lossless optical modulation and optically tunable slow light. A key strength of optical communications is the parallelism of information transfer and processing onto multiple wavelength channels. However, the relatively narrow Raman gain bandwidth only allows for amplification or generation of a single wavelength channel. If broad gain bandwidths were to be demonstrated on silicon, then an array of wavelength channels could be generated and processed, representing a critical advance for densely integrated photonic circuits. Here we demonstrate net on/off gain over a wavelength range of 28 nm through the optical process of phase-matched four-wave mixing in suitably designed SOI channel waveguides. We also demonstrate wavelength conversion in the range 1,511–1,591 nm with peak conversion efficiencies of +5.2 dB, which represents more than 20 times improvement on previous four-wave-mixing efficiencies in SOI waveguides. These advances allow for the implementation of dense wavelength division multiplexing in an all-silicon photonic integrated circuit. Additionally, all-optical delays, all-optical switches, optical signal regenerators and optical sources for quantum information technology, all demonstrated using four-wave mixing in silica fibres, can now be transferred to the SOI platform.

Tailored anomalous group-velocity dispersion in silicon channel waveguides.

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.

Wide bandwidth slow light using a Raman fiber amplifier

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.

Optical-fiber source of polarization-entangled photons in the 1550 nm telecom band.

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 Bells inequality by up to 10 standard deviations of measurement uncertainty.

Generation of correlated photons in nanoscale silicon waveguides

.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.

All-fiber photon-pair source for quantum communications

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.

All-optical slow-light on a photonic chip

We demonstrate optically tunable delays in a silicon-on-insulator planar waveguide based on slow light induced by stimulated Raman scattering (SRS). Inside an 8-mm-long nanoscale waveguide, we produce a group-index change of 0.15 and generate controllable delays as large as 4 ps for signal pulses as short as 3 ps. The scheme can be implemented at bandwidths exceeding 100 GHz for wavelengths spanning the entire low-loss fiber-optics communications window and thus represents an important step in the development of chip-scale photonics devices that process light with light.

Resonant optical interactions with molecules confined in photonic band-gap fibers

We investigate resonant nonlinear optical interactions and demonstrate induced transparency in acetylene molecules in a hollow-core photonic-band-gap fiber at 1.5 mum. The induced spectral transmission window is used to demonstrate slow-light effects, and we show that the observed broadening of the spectral features is due to collisions of the molecules with the inner walls of the fiber core. Our results illustrate that such fibers can be used to facilitate strong coherent light-matter interactions even when the optical response of the individual molecules is weak.

All-optical, wavelength and bandwidth preserving, pulse delay based on parametric wavelength conversion and dispersion

We demonstrate an all-optical tunable delay in fiber based on wavelength conversion, group-velocity dispersion, and wavelength reconversion. The device operates near 1550 nm and generates delays greater than 800 ps. Our delay technique has the combined advantages of continuous control of a wide range of delays from picoseconds to nanoseconds, for a wide range of signal pulse durations (ps to 10 ns), and an output signal wavelength and bandwidth that are the same as that of the input. The scheme can potentially produce fractional delays of 1000 and is applicable to both amplitude- and phase-shift keyed data.

Optical parametric oscillator based on four-wave mixing in microstructure fiber

We demonstrate, for the first time to our knowledge, optical parametric oscillation based on four-wave mixing in microstructure fiber. The measured wavelength-tunability range of the device (40 nm) and the threshold-pump peak power (34.4 W) are in good agreement with the theory of four-wave mixing in optical fibers. The ellipticity of the fibers polarization modes allows the device to be implemented in a relatively simple Fabry-Perot configuration. Spectral peaks that are due to cascaded-mixing processes are easily observed in our setup, which may provide a way to extend the tunability range of existing high-power lasers.