ABSTRACTThe growth and characterisation of a number of organic single crystals, e.g. benzil, 2–methyl–4– nitroaniline and 2–N,N–dimethylamino–5–nitroacetanilide, in silica capillary has become fairly well established over recent years. [1–6 ] However the growth of these same compounds in glass capillary with a much higher refractive index than silica has received little interest. Crystal cored fibres, ccf's, in which there is a close match of the refractive index of the cladding to that of the core allows the possibility of fabricating single mode waveguides with useful dimensions for crystal growth. There is a better overlap integral between phase matched fundamental and second harmonic modes in a low moded structure than in a structure with more allowable modes and thus a rise in the conversion efficiency can be expected if the correct dimensions of waveguide are chosen. If a ccf of high conversion efficiency, 10% at 0.1 mW average power, could be made then the promise of fabricating an organic optical nonlinear device, e.g. parametric amplifier, might be realised. In this paper we will describe how the growth method adopted for silica clad organic crystals has been adapted for their growth in a range of Schott glasses which are better matched in refractive index, RI, than silica to the organic material. The linear and nonlinear optical properties of these crystal cored fibres will be given in terms of; the orientation of the crystal axes with respect to the fibre direction; the sideways scattering characteristics from defects; the throughput of the fundamental beam; the polarisation states of both the fundamental and the second harmonic outputs; and the overall efficiency of second harmonic generation.
Efficient forward second-harmonic generation from planar archimedean nanospirals
