WAVEGUIDE TYPE OPTICAL BRANCHING CIRCUIT

摘要

PURPOSE:To decrease the propagation loss of a main route by eliminating the intersection of waveguides and connecting directly an optical fiber to the side face of the main route for taking out branched light. CONSTITUTION:A photolithographic technique is applied for a quartz optical waveguide film to form an optical circuit; for example, the optical circuit is formed by a reactive ion etching method using amorphous Si as a mask and a gaseous mixture composed of C2F6 and C2H4 as an etching gas. A clad layer is further formed on the side face of the waveguide by a CVD method. A transparent material having a suitable refractive index is put into a reflecting channel 5 in order to function the optical branching circuit. The refractive indices of a main optical waveguide 2'a on the input side and the matching oil in the channel 5 are different in this stage and therefore the propagated light causes a Fresnel reflection at the end face 5a of the waveguide and a part of conducted light I1 is reflected and is made incident I3 on an optical fiber 7c. The remaining light I2 is made incident on a main optical waveguide 2'b on the output side. Only some part of the light propagating in the main optical waveguides 2'a, 2'b is made incident on the fiber 7c and is thus monitored.