Figure 1
From: Programmable wavelength filter with double ring loaded MZI
Schematic drawing of the single ring loaded MZI is shown in (a), schematic drawing of double ring loaded MZI is shown in (b), schematic drawing of coupled ring loaded MZI is shown in (c). The main difference between our design given in (c) and the ring loaded MZI given in (b) is that the two rings are connected with a tunable coupler, it is obvious that the design in (c) could be configured to a MZI with delay length of twice the ring circumference, which is not straightforward with the design in (b). The phase shifter is shown as a pink box, the tunable coupler is shown as a normal directional coupler with a pink dot in the middle, the single add drop ring is constructed by connecting the input and output port of the tunable coupler on the same side.
