Focal plane arrays (FPA) are detectors which consist of a linear or two-dimensional matrix of individual elements. They are used at the focus of imaging systems. There are two basic types of focal plane arrays: linear and area. Linear focal plane arrays consist of a single line of pixels. Area focal plane arrays consist of rows and columns of pixels. Product specifications such as horizontal pixels, vertical pixels, and pixel size are important parameters to consider when selecting focal plane arrays. Horizontal pixels are the number of pixels in a row. Vertical pixels are the number of pixels in a column. Pixel size is the largest dimension of a pixel. Although most pixels are square, some are rectangular. Some suppliers refer to pixel size as pitch. 

Focal plane arrays differ in terms of spectral range and application. Choices for spectral range include: X-Rays, ultraviolet (UV), visible, near-infrared (NIR), mid-infrared, far-infrared (FIR), and microwave. X-rays are electromagnetic rays with wavelengths from .01 nm to 10 nm. Ultraviolet light or UV light has wavelengths from 10 nm to 400 nm. Visible light has wavelengths from 400 nm to 750 nm. NIR light has wavelengths from 750 nm to 2.5 µm, mid-infrared light has wavelengths from 2.5 µm to 10 µm, and FIR light has wavelengths from 10 µm to 1 mm. Focal plane arrays with other, unlisted wavelengths are also available. In terms of applications, FPAs are used in astronomical imaging, aerial reconnaissance, aerial mapping, spectrographic analysis, star tracking, machine vision, X-ray diffraction, and measurement applications. 

Specialized focal plane arrays include avalanche focal plane arrays, adaptive focal plane arrays, high-speed focal plane arrays, and industrial focal plane arrays. Avalanche diameters are small enough to allow products to use pixel sizes of tens of microns. Adaptive focal plane arrays (AFPA) are high-performance device that are widely tunable across various wavebands in the infrared (IR) spectrum. They enable multi-spectral imaging across the short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR) bands. Industrial focal plane arrays includes special features such as low-light levels, anti-blooming, integration control, correlated double sampling, and extended blue response. Cooled FPAs are used to reduce noise and improve detection.