In this study, crystalline cobalt ferrite thin films with large Faraday rotation (FR) coefficient were deposited on silicon by radiofrequency magnetron sputtering. An (100)-oriented MgO buffer layer was employed to solve the film/substrate discrepancy. A giant FR coefficient of 25 600 deg cm−1 was achieved for a cobalt ferrite film deposited at a substrate temperature (ST) of 600 °C. Moreover, the magnetic easy axis of the films switched from in-plane (IP) to out-of-plane orientation with increasing ST. This switching in the easy axis could be attributed to induced IP stress in the films with high deposition temperatures.
The photoluminescence (PL) evolution of SiQDs respect deposition and annealing temperatures is studied in a combined manner. The PL identified changes are associated to changes in thin film composition. 150 °C is identified as an important threshold.
We experimentally demonstrated a silicon optical isolator using a monolithically integrated cobalt ferrite (CFO) film as magneto-optical material, achieving an isolation ratio of 9.6 dB near 1550 nm wavelength. By virtue of the large Faraday rotation coefficient of CFO, the device has a compact footprint comparing to the current yttrium iron garnet-based isolators. Furthermore, we demonstrated self-biased isolation by the strong remanence of CFO films, eliminating the tedious demand of an external magnet. Cobalt ferrite represents a potential alternative approach to yttrium iron garnets to realize a practical device for on-chip isolation in silicon photonic integrated circuits because of the small footprint.
In this study, we present the design of an integrated transverse electric mode isolator realized by the epitaxial growth of a cobalt ferrite (CFO) film on a silicon micro-ring resonator structure. Exploiting the large magneto-optical activity of CFO along with the good characteristics of resonator structures, we numerically demonstrated isolator designs with ultra-compact sizes. The use of ring resonator structures with the reduced size is appealing because of lower insertion loss values. The nonreciprocal phase shift was maximized by optimizing the ring cross-section and was further studied in terms of the ring radius employing a transformation optics theory. Finally, we analyzed the optical isolator characteristics in terms of ring size and ring-waveguide power coupling ratio. The computed results pointed out that decreasing the ring size improves the device performance and can ease the device design and fabrication process.
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