Long wavelength semiconductor lasers, such as InGaAsP/InP lasers emitting at 1.3 and 1.55 mm, are widely used as light sources in optical communication systems. The dynamical behavior of semiconductor lasers is significantly influenced by optical feedback from an external reflector. To achieve the highest static and dynamic performance in semiconductor lasers, it is essential to thoroughly grasp how the strength of optical feedback affects their stability. This knowledge is fundamental for creating innovative designs that meet advanced performance standards. In this work, the instability of semiconductor lasers with external cavities in terms of noise and photon number probability distributions is investigated for the first time over a wide range of optical feedback. We successfully numerically solved improved time-delay rate equations across various optical feedback strengths [1,2]. Our analysis will classify the laser's dynamics based on detailed bifurcation diagrams of the photon number, providing valuable insights into its behavior. The study analyzes the temporal trajectory of photon numbers and intensity noise and statistically examines variations in output photon number fluctuations, probability distributions, and corresponding intensity noise at different optical feedback strengths. The simulations indicate that optical feedback strength significantly affects the intensity noise and photon number probability distributions. Intensity noise is reduced at relatively weak and strong optical feedback regimes. The shape of the photon number probability distributions is strongly influenced by optical feedback strength, transitioning from symmetric to asymmetric at weak to strong optical feedback, respectively. In the moderate optical feedback range (chaotic region), the photon number probability distributions exhibit a peak at low intensity and tail off at several times the average photon number. The authors suggest that operating semiconductor lasers under weak or strong optical feedback regimes may reduce their instability.