Random thermal motion of electrons in a resistor manifests as a fluctuating current even in the absence of an applied voltage. There are several types of noise that can affect optical systems, including: These types of noise can be broadly classified into two categories: additive noise. This chapter provides a detailed analysis of the noise performance of the single-mode fiber (SMF) SCIIB sensor system, including both the electronic noise and the optical noise. Based on the analysis results, performance improvement measures are proposed. However, they introduce noise into the signal due to the spontaneous emission of photons.