Virtually imaged phased array with graded reflectivity

A virtually imaged phased array (VIPA) can produce large angular dispersion, i.e., change in output angle with change in wavelength. The insertion loss and crosstalk of the VIPA demultiplexer are analyzed. It is shown that both characteristics are significantly improved by modifying the reflectivity on the VIPA element. With a graded reflectivity instead of a uniform reflectivity, the mode coupling efficiency to the output fiber is improved from 80%99.5% and the crosstalk Is reduced from -23 to -59 dB.