In our earlier research, we found the MOKE signal incident from 45 degree would cause perpendicular signal to couple with the longitudinal one. To distinguish the signal from one to another, we arranged 45 degree and 0 degree optical setup for the measurement of longitudinal and perpendicular respectively. However, hysteresis loops are only observed in the longitudinal direction. To measure smaller signal in our experiment, we reduced the noise level by one order and thus improved the signal to noise ratio. It¡¦s ten times better then previous result. Under smaller signal or worse S/N ratio condition, we still measured the MOKE signal. In order to quantitatively analyze the current-induced field, we made a metal coil and try to measure the bias produced by the field. And we injected the reverse current-induced field, , try to counteract the bias of hysteresis loop which is induced by sample current. Besides, we also dosed oxygen on the sample and measured the MOKE signal. There was no change comparing with which is measured in gas-free condition. But we found the coercivity became larger after annealing to 300K, and the current-induced bias in oxygen become smaller.

This research investigated the characteristics of single-mode optical pulses generated with orthogonal-polarization optical feedback (OPF) in Fabry-Perot type semiconductor lasers. Single-mode pulse trains with a pulse frequency of 470 MHz and 3.76 GHz were observed. A modified model was proposed to solve the inconsistency between the experimental results and the computer simulations of Otsuka and Chern¡¦s model. These results also solve the problem of a round-trip feedback distance that is too short to enable the feedback system to be implemented, making this technology accomplishable in currently working systems. Furthermore, this investigation recovered and maintained a stable oscillation of every missing longitudinal mode in a hysteresis type mode-hopping gap of a semiconductor laser. A special feature of this method is that both the laser power and spectral purity are preserved during mode recovery and mode switching. The experimental results also reveal that the OPF effectively suppressed mode-hopping in semiconductor lasers and drove the laser into a stable single-mode state. Finally, this research employed OPF to suppress the intensity noise stimulated by coherent optical feedback in a semiconductor laser. At a coherent-feedback level as strong as ¡V14 dB, an OPF ratio of ¡V29 dB could return the laser to its primitive single mode from the multimode, yielding a spectral purity and relative intensity noise (RIN) even better than the solitary values. These discoveries constitute an important contribution to our understanding of applications of semiconductor lasers.