Stuart G. Murdoch

Widely tunable optical parametric generation in a photonic crystal fiber

We report on the observation of widely tunable optical parametric generation in a photonic crystal fiber. The frequency shift of the generated sidebands that arise from modulational instability is strongly dependent on the detuning of the pump from the fibers zero-dispersion wavelength. We are able to demonstrate experimentally more than 450 nm of sideband tunability as we tune the pump wavelength over 10 nm. Excellent agreement has been found between the experimentally measured and theoretically predicted shifts.

Ultraweak long-range interactions of solitons observed over astronomical distances

Recirculating temporal optical cavity solitons in a coherently driven passive optical fibre ring resonator allows pairs of solitons to interact over distances 8,000 times their width. This finding highlights the extreme stability, robustness and coherence of the process, and of solitons in general.

High-conversion-efficiency widely-tunable all-fiber optical parametric oscillator

A high-conversion-efficiency widely-tunable all-fiber optical parametric oscillator is described. It is based on modulation instability in the normal dispersion regime near the fibers zero-dispersion wavelength. A 40 m long dispersion-shifted fiber is used in a synchronously pumped ring cavity. We demonstrate continuous sideband tuning from 1300 to 1500 nm and 1600 to 1860 nm by tuning the pump wavelength between 1532 and 1556 nm. Internal conversion efficiencies of up to 40% are achieved.

Generation of Coherent Multicarrier Signals by Gain Switching of Discrete Mode Lasers

The authors demonstrate the generation of a highly coherent multicarrier signal that consists of eight clearly resolved 10.7-GHz coherent sidebands generated within 3 dB of the spectral envelope peak and with an extinction ratio in excess of 45 dB by gain switching a discrete mode (DM) laser. The generated spectral comb displays a corresponding picosecond pulse train at a repetition rate of 10.7 GHz with a pulse duration of 24 ps and a temporal jitter of ~450 fs. The optical spectra and associated pulses of the gain-switched DM laser are subsequently compared with a gain-switched distributed feedback (DFB) laser that generates a spectrum with no discernible sidebands and corresponding pulses with ~3 ps of temporal jitter. By means of external injection, the temporal jitter of the gain-switched DFB laser is then reduced to <; 1 ps, resulting in visible tones on the output spectrum. Finally, a nonlinear scheme is employed and initially tailored to compress the optical pulses, after which, the setup is slightly altered to expand the original frequency comb from the gain-switched DM laser.

High performance mode locking characteristics of single section quantum dash lasers.

Mode locking features of single section quantum dash based lasers are investigated. Particular interest is given to the static spectral phase profile determining the shape of the mode locked pulses. The phase profile dependence on cavity length and injection current is experimentally evaluated, demonstrating the possibility of efficiently using the wide spectral bandwidth exhibited by these quantum dash structures for the generation of high peak power sub-picosecond pulses with low radio frequency linewidths.

Polarization modulation instability in weakly birefringent fibers

Modulation instability generated by the coherent interaction of two polarization modes in a weakly birefringent optical fiber has been observed in the normal dispersion regime. In contrast to previous observations of crossphase-modulation instability in the visible, the two generated sidebands have the same polarization, which is orthogonal to that of the pump, and their frequency shift is readily controlled by variation of the birefringence of the fiber. The frequency of the modulation and its qualitative features agree with those theoretically predicted.

Combined effect of Raman and parametric gain on single-pump parametric amplifiers.

We investigate the combined effect of Raman and parametric gain on single-pump parametric amplifiers. The phasematched parametric gain is shown to depend strongly on the real part of the complex Raman susceptibility. In fused silica fibers this results in a significant reduction in the available parametric gain for signal detunings beyond 10 THz. We are able to experimentally measure this effect for signal detunings ranging from 7 to 22 THz. Finally we discuss the implications of these results for the design of broadband optical parametric amplifiers.

Photon pair generation using four-wave mixing in a microstructured fibre: theory versus experiment

We develop a theoretical analysis of four-wave mixing used to generate photon pairs useful for quantum information processing. The analysis applies to a single mode microstructured fibre pumped by an ultra-short coherent pulse in the normal dispersion region. Given the values of the optical propagation constant inside the fibre, we can estimate the created number of photon pairs per pulse, their central wavelength and their respective bandwidth. We use the experimental results from a picosecond source of correlated photon pairs using a micro-structured fibre to validate the model. The fibre is pumped in the normal dispersion regime at 708 nm and phase matching is satisfied for widely spaced parametric wavelengths of 586 and 894 nm. We measure the number of photons per pulse using a loss-independent coincidence scheme and compare the results with the theoretical expectation. We show a good agreement between the theoretical expectations and the experimental results for various fibre lengths and pump powers.

Characterization of chromatic dispersion in photonic crystal fibers using scalar modulation instability

A simple and accurate method is proposed for characterizing the chromatic dispersion of high air-filling fraction photonic crystal fibers. The method is based upon scalar modulation instability generated by a strong pump wave propagating near the zero-dispersion wavelength. Measuring the modulation instability sideband frequency shifts as a function of wavelength gives a direct measurement of the fibers chromatic dispersion over a wide wavelength range. To simplify the dispersion calculation we introduce a simple analytical model of the fibers dispersion, and verify its accuracy via a full numerical simulation. Measurements of the chromatic dispersion of two different types of high air-filling fraction photonic crystal fibers are presented.

Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers

The effect of dispersion fluctuations on the conversion efficiency of large frequency shift parametric sidebands is studied by numerical simulation and experiment. Numerical results based on periodic and random dispersion models are used to fit the experimental results. The fitting parameters provide a measure of the uniformity of the photonic crystal fiber used in the experiment. This allows us to place limits on the required uniformity of a photonic crystal fiber for strong frequency conversion.