Planarization of Film Deposition and Improvement of Channel Structure for Fabrication of Anti-Resonant Reflecting Optical Waveguide Type X-crossing Vertical Coupler Filter

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Abstract
To realize a low-sidelobe narrow-band Anti-resonant reflecting optical waveguide (ARROW)-type vertical coupler filter, the dependence of the refractive index and thickness profiles of compound glass films, deposited by a magnetron RF sputtering technique, on the mixture ratio of Ar and O2 gases was investigated. First, the depth profile of the refractive index of SiO2 films was planarized using pure O2 gas. Next, the lateral profiles of the refractive index and thickness of compound glass films were planarized by optimizing the gas mixture ratio of Ar and O2. When the mixture ratio was Ar : O2 = 1 : 3, the index variation of the Corning 7059 glass film was vastly improved from 0.3% to 0.05%, and the thickness variation was also improved from 9.0% to 4.0%. A similar improvement was also achieved for SK1 glass (from SCHOTT) and the Ta2O5–SiO2 binary glass system. A low sidelobe ARROW-type vertical coupler filter (VCF) with Corning 7059 glass and SK1 glass cores was demonstrated, using these deposition techniques and a wet chemical etching technique. In addition, the planarization technique of stripe-lateral-confinement (SLC)-ARROW waveguide was developed using a lift-off technique. A narrow band ARROW-type vertical coupler filter with Ta2O5–SiO2 cores was achieved by the lift-off and reactive ion etching (RIE) techniques.