Noise can be classified into different categories based on different criteria. From the perspective of noise generation, it can be classified as thermal noise, shot noise, flicker noise, 1/f noise, quantum noise, etc. Regarding the frequency band of noise, it can be divided into low frequency noise, intermediate frequency noise, and high frequency noise, with further subcategories as microwave noise, millimeter-wave noise, terahertz noise. When considering the elements of electromagnetic waves, noise can be divided into phase noise, amplitude noise. Moreover, based on power spectral density, noise can be categorized into white noise, colored noise.