P. Millar

Nonlinear propagation effects in an AlGaAs Bragg grating filter

We present experimental observations of nonlinear propagation effects in an integrated AlGaAs waveguide filter. We demonstrate pulse shaping, pulse compression, and the production of gap solitons within the stop band of the grating for switching powers of approximately 130 W . This nonlinear behavior is associated with the counterbalancing effects of self-phase modulation and the large dispersion effects introduced by the grating itself.

Diffraction and transmission of light in low-refractive index Penrose-tiled photonic quasicrystals

We report the measurements of the diffraction pattern of a two-dimensional Penrose-tiled photonic quasicrystal, obtained by etching air cylinders in a silica substrate, and the modelling of the light propagation and dispersion relations of photons inside such a structure. The calculated transmission spectra exhibit dips whose positions are insensitive to the direction of propagation and whose depth increases with increasing structure length. An approach is developed for the calculation of the dispersion relations which is based on a set of reciprocal vectors defined by the diffraction pattern. The dispersion curves exhibit gap-like features at frequencies corresponding to the dips in the transmission spectra.

Two-dimensional Penrose-tiled photonic quasicrystals: from diffraction pattern to band structure

We report measurements of the diffraction pattern of a two-dimensional photonic quasicrystal structure and use the set of plane waves defined by the diffraction pattern as the basis of a theoretical approach to calculate the photonic band structure of the system. An important feature of the model is that it retains the essence of the rotational and inflational properties of the quasicrystal at all levels of approximation: properties lost in approximate models which artificially introduce elements of periodicity. The calculated density of modes of the quasicrystals is found to display a weakly depleted region analogous to the bandgap that occurs in a periodic system. The calculated transmission spectra for different polarizations and directions of propagation show features that correlate with the behaviour of the density of modes.

Two-dimensional Penrose-tiled photonic quasicrystals : diffraction of light and fractal density of modes.

Abstract We report measurements of the diffraction pattern of a two-dimensional photonic quasicrystal structure. Using a set of plane waves defined by the diffraction pattern we introduce a theoretical approach for the calculation of the band structure which captures the rotational and inflational properties of the quasicrystal. Based on this model we find that the density of modes of the quasicrystal displays a fractal character and a depleted region analogous to the band gap in a periodic system.

Second-harmonic generation from a first-order quasi-phase-matched GaAs/AlGaAs waveguide crystal

We demonstrate, for the first time to our knowledge, the generation of second-harmonic pulses by use of a novel methodology for achieving first-order quasi-phase matching in a semiconductor waveguide crystal. This methodology is based on a periodic modulation of the susceptibility coefficient along the direction of light-beam propagation in which advantage is taken of the fact that chi((2))(GaAs)>chi((2))(Al(x)Ga(1-x)As) . Efficient second-harmonic generation at 975 nm of a pump wavelength of 1950 nm has been demonstrated for a crystal with a nonuniform domain dimension (duty cycle, ~39/61).

The design of two-dimensional photonic quasicrystals by means of a fourier transform method

Abstract We report a method of designing aperiodic photonic quasicrystals. The method is based on the recognition that the Fourier transform of the dielectric structure has a direct influence on the mode spectrum, and can be chosen to enhance the properties of the system. The diffraction of light by, and the band structure of, such modified photonic quasicrystals is investigated and compared to the properties of conventional photonic quasicrystals.

Soliton effects in an AlGaAs Bragg grating

Experimental and theoretical research exploring the nonlinear properties of periodic structures has intensified over the past decade within a diverse range of materials utilizing both second and third order effects. Recently we studied the nonlinear transmission characteristics of high intensity pulses propagating through 4-10 mm long gratings etched into ridge waveguides formed in AlGaAs.

Nonlinear propagation in an integrated AlGaAs Bragg grating

Summary form only given. We have examined nonlinear propagation in integrated AlGaAs gratings. Significant nonlinear switching was observed at powers below the damage threshold of AlGaAs and this was due to the formation of gap solitons within the gratings bandgap.