Abstract: The invention provides an optical switching method and apparatus by which the response time of a variation in refractive index of light can be further reduced. An electric field applied to a light passing element made of a substance containing conjugated system electrons is controlled to vary the condition of electrons of the substance of the light passing element to vary the refractive index of the light passing element. Then, the outgoing direction of light introduced into the light passing element is controlled to deflect the outgoing light from the light passing element, and the deflected outgoing light is introduced so as to be irradiated upon a selected control object element to control the control object element.

Abstract: In order to selectively reduce the etching rate of the polyimide resin layer, ion implantation is carried out thereto. Preferably, the impurity ion such as As.sup.+, P.sup.+, B.sup.+, BF.sub.2.sup.+ is implanted with dosage of 1.times.10.sup.14 cm.sup.-2 or more. As a result, the polyimide resin layer has a resistivity to etching by the etchant containing hydrazine. This method can be used for preventing generation of unwanted etching in the process of forming the via hole in case of using the polyimide resin as the interlayer insulator for multiwiring structure.