Optical feedback (OF) system plays an important role in nonlinear dynamics because of low cost, less complexity, and well-maintained. Rich nonlinear characteristics of semiconductor laser under optical feedback are investigated, including period-one oscillation (P1), period-two oscillation (P2), quasi-period (QP), and chaotic oscillation (CO) states. However, the stability of the states generated is the most important issue to be solved and improved. In this paper, the polarization rotated feedback is purposed to be an alternative approach that possesses the characteristic of improving the signal quality compared to optical feedback. We focused on the generation of P1 states and on the performance of the noise reduction of the P1 states by utilizing incoherent OF. The polarization rotated feedback system is built up by OF systems under the orthogonally polarized feedback. The optical components that we used in the scheme for generating of the polarization rotated feedback are Faraday rotator (FR) and polarizer to provide the incoherent optical feedback, rich dynamics is obtained compared to those observed in traditional feedback system. Moreover, noise reduction of the P1 states caused by the delay loop frequencies in feedback scheme is realized by applying the orthogonally polarized feedback to the already-generated P1 states by the traditional scheme. To explore the quality of the generated P1 states, the measurements of the amplitude of side peaks, the spectral linewidths, and amplitude variation of P1 states under traditional OF and polarization rotated feedback in both frequency and time domain observed by electrical power spectrum and oscilloscopes are examined and analyzed, respectively. As a result, effective noise reduction in P1 states is achieved while applying a polarization rotated feedback.
Optoelectronic feedback (OEF) system plays an important role in nonlinear dynamics because of low-cost and easy to generate dynamical states, including regular pulsing (RP), quasi-pulsing (QP), and chaotic pulsing (CP). However, the non-ignored noise naturally generated by delay-loop frequency in the dynamical states is the most important problem to be solved. In this paper, we focused on the generation of RP states and also on the improvement of the noise reduction in the RP states by utilizing the double-delay system. The double-delay system is built up by optical feedback (OF) and OEF systems. When adjusting four controllable parameters of OEF delay time, OEF feedback strength, OF delay time, and OF feedback strength, more complex dynamics are obtained compared to those observed in individual OF and OEF system. Moreover, noise reduction of the RP states caused by the mixing of delay loop frequencies in double-delay scheme is realized by applying an additional OF delay loop to the already-generated RP states by OEF scheme. To explore the quality of the generated RP states, the measurements of amplitude variation in time series and the single-side band phase noise in frequency domain are examined. As a result, effective noise reduction in RP states is achieved while applying a weak OF feedback strength and a short OF delay time. Furthermore, no common factor in these two delays is necessary to observe stabilized RPs and the amplitude variation down to 0 which is equal to 100 percentage noise reduction is achieved while fine-tuning the controllable parameters carefully.