An improved optical convolution process in spiral phase contrast imaging based on FrFT

Spiral phase contrast (SPC) imaging proves to be an important and convenient approach for edge enhancement in image processing. Due to the limited size of the spiral phase filter and other optical elements, convolution kernel involved may be about the same size as the object image, which leads to serious degradation in resolution especially when the object is small in size. In this letter, a fractional Fourier transform (FrFT) optical setup is proposed to allow a kernel with arbitrarily small size, and hence to an enormous degree improves the brightness, contrast and resolution of the SPC imaging method.