By steering wanted diffraction orders within a concentrated angular region and steering all unwanted diffraction orders outside that region, a wavelength selective switch achieves high port isolation and densely spaced ports. N inputs receive an optical signal. Optics spatially separate and direct wavelength channels from the signal. A phased array switching engine comprising cells steers a wanted diffraction order of each spatially separated wavelength channel from each cell at an angle within a concentrated angular region relative to the PASE, and steers all unwanted diffraction orders of spatially separated wavelength channels from cells outside the concentrated angular region. Optics direct each wanted diffraction order to one of N outputs in accordance with the steering of the wanted diffraction orders by the PASE. The concentrated angular region is defined by a largest and smallest steering angle wherein the largest steering angle is a margin less than the smallest steering angle.