TE-mode nonreciprocal propagation in passive Fe50Co50–InGaAsP/InP semiconductor optical isolators

Abstract

We report on optical isolation of TE-mode passive Fe50Co50/InGaAsP/InP semiconductor optical isolators for integration with semiconductor ring lasers and unidirectional lasing devices. The target optical isolation was set at 5 dB/mm for unidirectional semiconductor ring lasers. We calculated the optical isolations for devices with waveguide widths, w, of 1.5, 2, and 2.5 µm, and Al2O3 buffer layer thicknesses, d, of 15–40 nm. The optical isolations were calculated to be 13.2 dB/mm for w = 1.5 µm, 5.7 dB/mm for w = 2 µm, and 2.9 dB/mm for w = 2.5 µm, all with d = 30 nm, which satisfy the target optical isolation. On the basis of calculations, we fabricated TE-mode passive Fe50Co50/InGaAsP/InP semiconductor optical isolators and characterized their optical isolations. We obtained optical isolations of 1.3 dB/mm for w = 2.5 µm and 3.3 dB/mm for w = 2 µm. We compared them with the calculated results and discussed the origin of the differences. The experimentally obtained optical isolations in this study and our investigation of their dependence on the device structure will lead the way to practical unidirectional semiconductor ring lasers and should be useful for realizing low-operating-current unidirectional semiconductor ring lasers for all-optical flip-flop memories using semiconductor optical isolators.