How the monitoring curve is affected by the thermal shift of a filter during deposition.

The thermal shift of dense-wavelength-division-multiplexing (DWDM) filters that is caused by nonconstant temperature during fabrication invokes a spectrum shift and an error in the optical thickness of the layer before the matching layer. The relation between the thermal shift and the optical thickness of the layer before the matching layer was calculated. Five kinds of narrow-bandpass filters were fabricated, and their thermal shifts were measured and compared with the theoretical model. By using this technique, we were able to predict the thermal shift of DWDM filters from the abnormal behavior of the layer before the matching layer during deposition.