THE INFLUENCE OF APERTURE SIZE AND SHAPE ON CROSSTALK LEVEL IN FREE-SPACE GRATING DEMULTIPLEXERS FOR WDM NETWORKS

A simple method is presented to calculate crosstalk caused by aberrati ons and diffraction at the aperture edges in free-space grating demult iplexers for wavelength-division multiplexed (WDM) communication syste ms, The influence of circular and square aperture sizes is described f or ideal and aberrated optical systems, It is shown that aperture enla rgement is not critical to aberrations whilst providing significant cr osstalk reduction, The minimum crosstalk value is obtained when the di spersion plane is parallel to the diagonal of the square aperture, -60 dB crosstalk is attainable for moderately aberrated systems with 80 c hannels (0.5 nm spacing) in the range 1530-1570 nm.