Hello Dr. Roy,
I have observed NOR-gate and mzi-output.png. It is clear these designs will not function as NOR gate. These structures both have two couplers. To function as a NOR gate, both couplers must be lossless 3dB couplers. However, after BPM simulation it is clear these couplers are very far from the 3dB lossless spec. It is clear from nor-trial.png that the first coupler encountered transfers almost all optical power to the lower waveguide of the MZI. In order to acheive the NOR function, the power of the lower wavguide must cancel the power in the other one. This is not possible in the given design, almost all power transfers to the lower waveguide. Since there is no power in the upper waveguide, no cancellation is possible in the second coupler. function cannot be achieved. One can also see a great deal of radiation loss from the S Bend waveguides. The corners are too sharp for a diffused waveguide. Diffused waveguides are very weakly guiding and cannot tolerate much curvature
Regards, Steve