The number of time steps is most likely not large enough for the optical signal to reach the detector. Place an Observation Point at the same distance and view the time domain signal. The gaussian pulse should be completely recorded, if not increase the number of time steps in the simulation settings to allow the simulation to run longer.
Technically this is possible, but in practice I am not so sure. You could script the generation of numerous Observation Areas, that are all offset by 1 mesh point. This would capture the slices of the volume in different observation areas, which you could then export the fields using the scripting language as well.
However, if you are measuring the absorption of a waveguide you would probably be fine with only having a couple observation areas and interpolating the data in between the areas. If you are exciting propagating modes then the field distribution should be changing very slowly over the length of the waveguide.
You can use Observation Areas to detect the amount of power flow through each arm in a coupler and compare that to the input power. See our TE planar waveguide coupler splitter tutorial in the OptiFDTD installation folder.
Yes you can. If you apply the same voltage to both arms both optical signals will accumulate a phase shift proportional to the applied voltage. If the voltage varies in time you will have a phase modulated signal.
I am not familiar with OTSB, but I think you are talking about Optical Dual Sideband Suppressed carrier and Optical Single Sideband Suppressed Carrier. We have a sample of ODSB found in the samples folder->Microwave and RF optical Systems that you could take as a building block.
There is an absolute maximum for the time step size, but no formula for directly calculating what minimum is the correct choice. The default choice of OptiFDTD is the aforementioned maximum. This at least guarantees a stable simulation.
I think your issue might be the number of time steps and not the individual time step size. Resonators and cavities trap light within them and it takes time for the light to leak out (Q-factor). This means that you will need to check to see if the energy in the resonator has had time to leave. You can do this by using an observation point placed inside the resonator or at on of the ports. You should see the electric field decaying with something similar to an exponential envelope. Check to see if the electric field has diminished to an appropriately small value by the end of the simulation.
You will not be able to convert the .fdt file to .bpd, so you will have to create your design in OptiBPM. OptiBPM is focused on guided optics and so there is no tool that will automatically generate photonic crystals. You can use the scripting functionality to generate your required shapes.