Noise Formalism in Photodetectors: Understanding Detection Limits

This lecture covers the formalism of noise in photodetectors, focusing on the relationship between input power and output current. It begins by defining the average measured value and the concept of noise, which represents fluctuations around this mean value. The instructor explains the noise equivalent input, particularly the noise equivalent power (NEP), and how it relates to the signal-to-noise ratio (SNR). The lecture includes examples illustrating the SNR and its implications for signal transmission. The detectivity of detectors is introduced, emphasizing the importance of low NEP for high detectivity. The instructor discusses the spectral dependence of detectivity and the characteristics of thermal and photonic detectors. The lecture also delves into root-mean-square (RMS) noise, variance, and the spectral behavior of noise through Fourier transforms. Finally, the relationship between autocorrelation and noise spectral density is explored, providing a comprehensive understanding of noise in optical detection systems.