Chronic amphetamine enhances visual input to and suppresses visual output from the superior colliculus in withdrawal.

Heightened distractibility is a core symptom of Attention Deficit Hyperactivity Disorder (ADHD). Effective treatment is normally with chronic orally administered psychostimulants including amphetamine. Treatment prevents worsening of symptoms but the site of therapeutic processes, and their nature, is unknown.

Repeated intermittent oral amphetamine administration results in locomotor tolerance not sensitization.

Background: The phenomenon of locomotor sensitization to injected amphetamine is well-characterised. The increased locomotor activity found acutely is enhanced with repeated intermittent treatment. This effect arises due to hypersensitization of the dopaminergic system and is linked to drug addiction.

Chronic amphetamine treatment affects collicular-dependent behaviour.

Distractibility can be defined as an attention deficit where orientation toward irrelevant targets cannot be inhibited. There is now mounting evidence that the superior colliculus is a key neural correlate of distractibility, with increased collicular-activity resulting in heightened distractibility. Heightened distractibility is reduced by amphetamine, which acutely suppresses collicular responsiveness.

Ultra-low power parametric frequency conversion in a silicon microring resonator.

We demonstrate parametric wavelength conversion via four-wave mixing using ultra-low peak pump powers of a few milliwatts in a micrometer-scale silicon device. The response time of our device is 100 ps allowing for implementation in high-bandwidth optical communications. At these ultra-low power levels and microscale sizes, it should be possible to realize hundreds of these devices operating simultaneously on a single chip.

Nonlinear optics in photonic nanowires.

We review recent research on nonlinear optical interactions in waveguides with sub-micron transverse dimensions, which are termed photonic nanowires. Such nanowaveguides, fabricated from glasses or semiconductors, provide the maximal confinement of light for index guiding structures enabling large enhancement of nonlinear interactions and group-velocity dispersion engineering. The combination of these two properties make photonic nanowires ideally suited for many nonlinear optical applications including the generation of single-cycle pulses and optical processing with sub-mW powers.

Optical time lens based on four-wave mixing on a silicon chip.

We propose a new technique to realize an optical time lens for ultrafast temporal processing that is based on four-wave mixing in a silicon nanowaveguide. The demonstrated time lens produces more than 100 pi of phase shift, which is not readily achievable using electro-optic phase modulators. Using this method we demonstrate 20x magnification of a signal consisting of two 3 ps pulses, which allows for temporal measurements using a detector with a 20 GHz bandwidth.

Broad-band continuous-wave parametric wavelength conversion in silicon nanowaveguides.

We demonstrate highly broad-band frequency conversion via four-wave mixing in silicon nanowaveguides. Through appropriate engineering of the waveguide dimensions, conversion bandwidths greater than 150 nm are achieved and peak conversion efficiencies of -9.6 dB are demonstrated.

All-optical regeneration on a silicon chip.

We demonstrate optical 2R regeneration in an integrated silicon device consisting of an 8-mm-long nanowaveguide followed by a ring-resonator bandpass filter. The regeneration process is based on nonlinear spectral broadening in the waveguide and subsequent spectral filtering through the ring resonator. We measure the nonlinear power transfer function for the device and find an operating peak power of 6 W.

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.

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.

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.