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We report on reduced threshold current and enhanced extinction ratio of a magnetically controllable Fe50Co50–InGaAlAs/InP nonreciprocal semiconductor laser. The improved device performance was consistent with calculated results for the modified layer structure and the use of ferromagnetic metal (Fe50Co50). The fabricated laser showed a threshold current 2.0 times smaller than our previous device having Fe. The extinction ratio, defined as the change in light intensity upon magnetization reversal, increased upon the appearance of the first-order transverse mode and reached 46% at a current of 100 mA. The reduced threshold current and enhanced extinction ratio should be useful for realizing low-operating-current, all-optical, robust signal processing devices using nonreciprocal semiconductor lasers.

We report on optical isolation of TE-mode passive Fe 50 Co 50 /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 Al 2 O 3 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 Fe 50 Co 50 /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.