JPH0546522B

PURPOSE:To form a desired refractive index distribution extending over a wide range of a base material extending from the center to the outside circumferential part by setting a characteristic value related to a refractive index of a monomer for forming the base material and a monomer diffused in the inside of the base material, to a specified relation. CONSTITUTION:A base material 7 having a self-shape is formed by executing an incomplete polymerization of a monome Ma, a monomer Mb is diffused to its inside, and at least an initial stage of the subsequent heating polymerization is executed in an atmosphere containing a monomer Mc which is the same as the monomer Mb or different from it. In case the monomer Mc which is different from the monomer Mb is used, the monomer Mb in a liquid phase diffusion chamber 9 is not bubbled but used only for a liquid phase diffusion, and a gaseous or fog-like monomer Mc is led into a gaseous phase chamber 13 from a vapor generator, etc. In any case, however, in case a refractive index of a single polymer of the monomers Ma, Mb and Mc is denoted as Na, Nb, Nc, respectively, a combintion is selected so that Nc is also larger than Na in case Nb is larger than Na, and on the contrary, Nc is also smaller than Na in case Nb is smaller than Na.