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Abstract A theoretical analysis of the optical feedback from external reflector influence on the Frequency response of GaAs/Al0.45Ga0.55As triple quantum well Quantum Cascade Laser emitting at (l=9 mm) is presented. The employed theoretical model was based on Schrodinger equation. To demonstrate the effects of external cavity, many of the external cavity parameters were controlled such as the length of the external cavity, the proportion of optical feedback and the relative phase difference.

Abstract Effect of optical feedback (O.F) on AlGaInP semiconductor laser properties and intensity modulation has been studied experimentally. Threshold current of semiconductor laser decreased 1mA when O.F equal to 160W , while there is no significant decreases observed in threshold current both when increasing O.F above that value or less than it. Influence of O.F on amplitude modulation spectrum at frequencies modulation (0.123,0.246, 0.546, 1.2)MHz has been studied. Fundamentals harmonic spectrum peaks increased with O.F especially at frequency modulation (1.2)MHz , whereas opposite effect of O.F observed on Fundamentals harmonic spectrum peaks at frequency 132kHz, since it decreased with O.F . O.F participate in decreasing of relative intensity noise (RIN) just at frequencies modulation(0.264, 0.546, 1.2)MHz with appearance of Flicker noise at frequency 132kHz. Signal to noise ratio (SNR) increased with O.F especially at frequency modulation equal to 1.2MHz has been observed.

The experimental investigation of the influence of optical feedback on the pulse analysis of GaAlAs laser diode is represented, with an experimental setup designed for this purpose. Optical feedback was constructed with a plane mirror facing the facet of the laser diode at a distance of ( 16 cm ). Phase control and feedback rate were varied according to the external cavity length with the respect of laser diode cavity. Many benefits can be obtained from this research , to improve laser light output with increasing the external differential quantum efficiency by ( 0.7 %), arid threshold reduction by ( 0,5 mA ) with Optical feedback furthermore the experimental result indict that there was a peak shift of the pulse distribution of the laser output towards high frequency by feedback rale was increased. Laser wavelength tuning can be interpreted from there experimental results in additional to the improvement of spectral characteristics with the reduction of FWHM and increase in the intensity of laser output.