The information capacities of two-dimensional optical low-pass channels are discussed. Coherent and incoherent systems operating under finite optical power and area constraints are characterized in terms of two criteria: space–bandwidth product (SBP; the number of pixels required for achieving maximum information capacity) and resolution (; the smallest spot size capable of supporting positive capacity gain). A coherent system operating with an initial signal-to-noise ratio (SNR) of 5 can achieve a 48% capacity gain by operating at an optimal SBP that is 3.4 times that of the nominal system. The same system has a resolution that is 0.31 times nominal. Incoherent systems experience additional SNR loss, and with an initial SNR of 5 they achieve capacity gains of 29% at the optimal SBP of 2.8 times nominal. The incoherent system resolution is found to be 0.4 times nominal.
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