a liquid or a gas into a template solid having substantially continuous porosity throughout its extent this is followed by solidifying the fluid and then removing the template solid the resulting structure is formed such that its solid portion is substantially in the positions of the continuous porosity of the template solid and its pores are substantially in the positions of the solid members of the template solid in more particular embodiments the colloidal crystal template technique can be used which includes the following general steps a generally the utilization of colloidal crystal templating for the fabrication of inverse opal photonic crystals involves three main steps firstly the 3 dimensional synthetic opal is fabricated by the self assembly of monodisperse colloidal polymer spheres e g monodisperse poly methylmetacrylate pmma colloids into an face centered cube fcc lattice along the fcc 111 plane a pbg should open in the opaline structure resulting in the reflection of a range of wavelengths depending on the diameter of the sphere across the electromagnetic spectrum second a sol gel of a dielectric material infiltrates the pore spacing in the colloidal crystal template subsequent hydrolysis and condensation reactions lead to the formation of a network solid the solid semi conductive material e g tio 2 formed can then be hydrated to an amorphous form and will have a higher overall refractive index than that of single crystals hence the material must be dried in air after which time calcination is used to remove the colloidal crystal template this leaves behind an inverse opal structure with a periodically modulated refractive index in.