Improving photon count and flat profiles of multiplex imaging systems with the odd-symmetric quadratic phase modulation mask

The odd-symmetric quadratic (OSQ) phase mask is examined as a candidate for reduction of working distance and enhancement of light collection in multiplex imaging systems. The knowledge gained from the exact mathematical representation of the optical transfer function of the OSQ phase mask imager is exploited to explain the limits of system performance and quantify the upper bound on the magnitude of defocus within which this wavefront coding imager can successfully operate. The sensitivity of this imaging system to defocus about the special imaging condition that yields an enhanced dynamic range is examined, and it is shown that the modulation transfer function (MTF) degradation when the magnitude of misfocus is increased past this condition is much more gradual than the degradation of a conventional imager past a zero-misfocus state. The condition required for the spatial frequency and angular resolution of this OSQ phase mask imager to exceed that of its counterpart scaled imager is established, and results of simulated imaging under a reduced working distance configuration are presented.