chapter 3, Photon Transfer Noise Sources

Excerpt

When photons strike a detector, interactions immediately produce a signal variance or noise from pixel-to-pixel. This chapter introduces four fundamental noise sources important to PT work. The first two sources, signal shot noise and Fano noise, are related to photon interaction. The third noise source, fixed pattern noise, is associated with pixel-to-pixel sensitivity nonuniformity. The fourth source, read noise, encompasses all other noise sources that are not dependent on signal strength. Shot noise increases by the square root of signal, whereas FPN increases proportionally with signal. Fano noise increases by the square root of photon energy (or quantum yield).

3.1 Photon Shot Noise

Signal shot noise is fundamentally connected to the way photons spatially arrive on a detector. For example, Fig. 3.1 shows a Monte Carlo simulation where 200 photons are randomly interacting with a 20 × 20 pixel region. As can be seen, the number of photon interactions varies from zero to four interactions per pixel. The standard deviation (or rms) for the number of interactions per pixel is called photon shot noise.

Photon shot noise—a spatially and temporally random phenomenon described by Bose-Einstein statistics—is expressed by

Figure 3.2 plots Eq. (3.1) as a function of wavelength (μm) and the temperature of the semiconductor. For wavelengths greater than 10 μm, photons couple with phonons (i.e., lattice vibrations in a solid) that increase the shot noise. As the operating temperature is reduced, the semiconductor produces less coupling action and variance as seen in the plot.