Described herein is a wavelength selective switch (WSS) type optical switching device (1) configured for switching input optical beams from input optical fiber ports (3, 5 and 7) to an output optical fiber port (9). Device (1) includes a wavelength dispersive grism element (13) for spatially dispersing the individual wavelength channels from an input optical beam in the direction of a second axis (y-axis). The optical beams propagate from input ports (3, 5 and 7) in a forward direction and are reflected from a liquid crystal on silicon (LCOS) device (11) in a return direction to output port (9). The input optical beams are transmitted through a port selecting module (21), which provides polarization diversity to device (1) and provides capability to restrict optical beams returning from LCOS device (11) from being coupled back into input ports (3, 5 and 7).