Diffractive optics allow achromatic correlation

Researchers at the Universitat de Valencia (Burjassot, Spain), the Universitat Jaume I (Castelló, Spain), and the Univeraität Erlangen-Nüremburg (Erlangen, Germany) have developed an all-incoherent optical correlator that produces a point-spread function (PSF) whose scale is independent of wavelength over much of the visible spectrum. This allows a wide variety of color optical operations to be performed using white light.

The hybrid diffractive-refractive imaging system contains two continuous-relief diffractive elements constructed using half-tone mask technology. One of the diffractive elements must be placed beyond the traditional output plane; an additional refractive element is then required to produce a real image. As in most achromatic optical systems, a low residual scaling chromatic error remains in this correlator: over a wavelength range of 480—660 nm the PSF changes in scale by 2.5%.This compares to an uncorrected scale change of at least 30%. When illuminated by white light from a xenon lamp, the device produces high autocorrelation signals for objects of varying colors.