Integrated optical interferometer with a stacked waveguide structure

An integrated optical interferometer consisting of Al(2)O(3) waveguides placed upon an oxidized Si substrate is presented. The two waveguides forming the branches of the interferometer are stacked on top of each other with a SiO(2) buffer layer in between. The interferometer further contains two directional couplers which are realized by bending the upper waveguide toward the lower one. A masked evaporation technique is introduced to fabricate the directional couplers. The operation of the interferometer is confirmed in temperature-sensing experiments while the application of the interferometer to humidity measurement is discussed.