Single Photon Detector detecting faster than dead time

[Scott Johnstun]

I have a layout very similar to the Lesson 1 Transmitter – External modulated laser with the following changes:

– I changed the psuedorandom bit generator to a bit generator that repeats the sequence 0101…
– I added an SPD to the output of the Mach-Zehnder Modulator, with an Oscilloscope Visualizer connected to the SPD output

The primary parameters should be the same, but just in case:
– Bit rate: 2.5e9
– Sequence length: 128
– Samples per bit: 64
– Sample rate: 1.6e11
– Number of samples: 8192
– Symbol rate: 1e10
Time window: 5.12e-8

I ran the simulation and found, in the oscilloscope readout, alternating periods of 0.4 ns of signal followed by 0.4 ns of no signal. This makes sense given the modulation choice. However, I checked the SPD dead time, the time during which the detector cannot read the number of photons, and the value was 95 ns, which is far greater than the 0.8 ns on-off cycle I see. Why is the detector dead time not coming into play?

[Ahmad Atieh]

Dear Scott,
Could you please email me your project as Zip file to ahmad.atieh@optiwave.com and we’ll check the issue? You can’t load the project to the forum.
Please note that you could set the SPD capture time though the parameter “Collection time” in the Detection Conditions tab of the component properties window.
Let me know if you’d like to discuss further. Also, you may use the Component View feature that you can access by right click on the SPD to view results and 2D Graphs of different plots.
Regards,
Ahmad

[Author]

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