A holey optical fibre for supporting propagation of light of a wavelength .lamda.,comprises a plurality of cylinders (10) each having a longitudinal axis, the cylinders (10) being separated from each other by regions of a matrix material (20) and having their longitudinal axes substantially parallel to each other. Each cylinder (10) has a diameter, in the plane perpendicular to the longitudinal axis, that is small enough for the composite material of the ensemble of cylinders and matrix material to be substantially optically homogenous in respect of light of wavelength .lamda..