Abstract: The present invention introduces a novel and simple method to adjust the MZ filter channels to those of the ITU grid. This is done through inducing an optical path length difference by using a UV light source to create a change in the index of refraction of the fiber arms after the device is packaged. The UV light is launched into the MZI filter through one of its input ports in order to achieve the phase adjustment. Since the exposure length is the entire length of one of the arms of the MZI, the required refractive index change is much smaller than the localized UV tuning of the previous methods. This allows for a weaker UV source power and shorter treatment times, thus reducing the chances of localized fiber damage.