Fabrication and characterization of As2S3/Y3Fe5O12 and Y3Fe5O12/SOI strip-loaded waveguides for integrated optical isolator applications

We report two novel strategies to integrate magneto-optical oxides on oxidized silicon and SOI platforms based on strip-loaded waveguide structures. By using conventional waveguide fabrication and thin film deposition techniques, strip-loaded waveguides for magneto-optical non-reciprocal phase shift (NRPS) applications can be integrated on a silicon platform. As a demonstration, two structures, i.e. As2S3/Y3Fe5O12 (YIG) and YIG/SOI waveguides are fabricated. Using pulsed-laser deposition followed by rapid thermal annealing, yttrium iron oxide films in which more than 95 vol.% had crystallized into the YIG phase were achieved on both substrates. The optical loss of the As2S3/Y3Fe5O12 waveguide was characterized by a cut-back method to be similar to 10 dB/cm at 1550 nm, while the optical loss of a 450nm wide YIG/SOI waveguide was determined to be 41 dB/cm at 1550 nm by measuring the quality factor Q of a pulley-type ring resonator consisting of such waveguides. The propagation loss of polycrystalline YIG on a SiO2/Si substrate was around 50 dB/cm at 1550 nm wavelength. The NRPS and figure of merit of both waveguides were simulated. It is suggested that a Bi:YIG or Ce:YIG layer may be integrated in these waveguide structures to achieve a higher NRPS and figure of merit for optical isolator applications. These waveguide fabrication techniques offer a compact, low cost and etch-free route for integrating magneto-optical materials on a silicon platform, which may be useful for making future integrated optical isolators and other magneto-optical components.