the light arriving into the two waveguides of the directional coupler 114 interfere with a different phase fig5 b shows the field coming from the awg as the frequency changes the awg translates the image of the output waveguide fig6 a shows the superposition of the two previous figures at the center frequency 194 thz the image coming from the array is well coupled to the image coming from the mzi in a symmetric way it remains well coupled from 193 8 thz to 194 02 thz as the two fields superpose themselves roughly fig6 b shows the resulting transmission which has wide passband and good crosstalk due to process variations the mzi may not be tuned correctly to the awg in this instance the image of the mzi will not be synchronized correctly to the image coming from the awg as shown for example in fig7 a the resulting transmission seen at fig7 b becomes asymmetric and the passband and crosstalk degrades placing heaters 11 on top of the mzi arm 110 110 u2032 enables to tune the mzi to the awg and correct for the process variation by heating one or the other heaters one can generate a phase shift from 0 to pi to correct the phase difference between the two arms 110 and 110 u2032 other known phase shifters such as electro optic phase shifters can also be substituted in this invention we found it advantageous to be able to use either of the two inputs 106 and 106 u2032 to reduce the maximum amount of heat needed to.