Modulation transfer function of infrared focal plane arrays

Fast Fourier transformation of a spatial impulse response of an electro-optical imaging system provides the optical transfer function or the modulation transfer function (MTF) of the system in the spatial frequency domain. The MTFs of the sub-systems in the spatial frequency domain could be multiplied to get the overall MTF of an imaging system. This is much more convenient than the repeated convolutions that would be required for a spatial domain analysis and that produces a quick understanding of the performance limitations of the overall system in terms of individual subsystems in the complete system. The MTF of an imaging system quantifies the ability of the system to resolve or transfer spatial frequencies [1]. Consider a bar pattern with a cross-section of each bar being a sine wave. Since the image of a sine wave light distribution is always a sine wave, the image is always a sine wave independent of the other effects in the imaging system such as aberration. Usually, imaging systems don't have any difficulty in reproducing a bar pattern when the bar pattern is closely spaced. However, an imaging system reaches its limit when the features of a bar pattern get closer and closer together as shown in Fig. 1.