Fabrication of Integrated Magneto-Optic Isolator

Abstract

ABSTRACTIn optical applications, especially in optical communications, protecting light sources from harmful reflected energy is very important. With magneto-optic isolators, these light sources can be protected to extend their lifetimes and performance by blocking back-reflected light. The active element in these optical isolators is a magneto-optical garnet. However, garnet is difficult to integrate with semiconductors due to the high thermal budget usually required to obtain the garnet crystal structure. For example, current isolator garnets cannot be integrated monolithically into a photonic integrated circuit due to the growth process, liquid phase epitaxy, which requires growth temperatures of >900 °C and also garnet substrates. In this work, magneto-optical garnets were grown monolithically by low-temperature reactive RF sputtering, followed by an ultra-short (<15 sec) anneal. The refractive indices of the resulting garnets were measured using Fourier transform infrared (FTIR) spectroscopy. Various rib waveguides were fabricated by both wet etching and reactive ion etching (RIE). The width of the waveguides varied from 2 to 12 μm and the heights were varied from 0.5 to 1.0 μm. Sm-Co thin films were used for integrated biasing magnets. They were deposited on top of claddings of both magnesium oxide and yttrium oxide, all using the same sputtering system that was used to deposit the garnet films. These magnetic films had high enough remanent fields to saturate the garnet waveguides, and they had coercivities of 700 Oe. The Faraday rotations and waveguide losses of the subsequent isolators were measured to be 10 degrees and 0.1 dB/μm at 632 nm, respectively. Although this prototype is promising, optimization of the device designs is ongoing. In summary, this work succeeded in providing the first comprehensive report on etching YIG by RIE, in developing all of the steps required for integrating isolators on non-garnet substrates, and in proving the feasibility of these isolators.