There is an increasing need for quantum communication applications, including true random numbers and quantum key distribution. The Amplified Spontaneous Emission (ASE) is a quantum physics process, which can play a significant role in both cases. A physical model for detecting and acquiring the ASE noise is developed. The photon probability is calculated, and the relationship with system parameters is presented. Experimental results quantitatively validate the physical model; the simulation results all significantly fit the corresponding experimental data well.