error when I simulated a bidirectional system

Hi Joseph,

There are a couple problems I saw with your project file. You need to either add signal delay to every bidirectional component manually or check the Initial Delay box in Layout Parameters->Signals. For more information on how we model bidirectional devices please review our tutorial at:

Lesson 5: Bidirectional Simulation — Working with Multiple Iterations

1. The power meter should calculate the average power over all wavelengths.

2. Yes, it should include the modulated part in the signal.

Finally, for a bit rate of 10 Gbps simulating a time window of 1 second will require a lot of memory. For a samples per bit value of 64, the total number of samples required is ~640e9, and so using a 8 byte double as an estimate the total memory required is roughly 5120 GB’s!

Set the bit rate to the experiment or design you want to test, usually anywhere from 1-2 Mbps to 100 Gbps. The samples per bit determines the accuracy of the simulation, generally 32-64 is perfectly fine. Finally set the sequence length to determine how many bits you will simulate. A larger number of bits will make BER calculations more accurate, but generally 1024, is a good number to start with.

There might be another way to simulate what you want. Is there a specific reason you want to simulate a time window for 1 s?

Hi,

From my point of view you should not need to simulate the system for a full second, and in fact it will just not be possible. The time scale difference between gigahertz (10^-9 seconds) and even megahertz (10^-6 seconds) is just too gigantic. If you are looking at a transient part of the system you could just set the remote signal to be activated at say around 0.1 microsecond.

A time delay simulates the physical effect of time lag. In effect it will shift the optical signal right in the optical time domain visualizer. You could use it to model the estimated time it takes light to travel through a fiber or say through free space.

An optical delay on the other hand is a simulation tool used in bidirectional components. It aids in initializing bidirectional components. There is a better explanation of how bidirectional systems are simulated at:

Lesson 5: Bidirectional Simulation — Working with Multiple Iterations

Cheers

I just did a quick compare of the optical time domain and it seems to be working correctly to me. What is the problem you have with the results?

Hi Joseph,

The issue here is that the output power of the electrical signal is very low compared to the input so you can’t even see the output signal. Try zooming into the microWatt range to view the second signal or incorporate a electrical gain component so that they are of comparative size.

Hi Joseph,

You are using the time delay correctly!

1) Noise bins are a convenient signal representation for noise. Each “bin” is given a bandwidth and amplitude, thus a wide range of frequencies can be modeled and makes calculating SNR much easier. A sampled signal will need a much higher sample rate to model a wider range of frequencies and it is not quite as easy to determine the power of the noise.

What the convert noise bins option does is when a sampled signal overlaps the noise bin signal the noise in the noise bins is converted to a sampled signal and added. Normally I would suggest using the convert noise bins (in OptiSystem 13.0 this option is now set by default), because you are not working with a WDM type network, which would benefit from the large frequency representation. That being said since you are interested in the electrical SNR value, you will HAVE to use noise bins. Our WDM Analyzer can calculate the SNR of a sampled optical signal but the electrical carrier analyzer is not able to yet.

Another reason why you would choose to convert noise bins is because some types of models don’t modify noise bins, because they might be a time domain effect, like nonlinearity, so converting the noise bins will increase the accuracy of the simulation, although since noise power is usually quite low it has a minimal impact. Let me know if this was a sufficient explanation!

3) You can use this component fine and it will compare noise bins to the signal power to calculate the SNR. There are two frequencies simply to allow you to compare values. You need a filter to be able to define the power of a frequency signal. Other wise the “power” is given by W/Hz.

Hope this clarifies the issues!

No you should not have to set them manually. OptiSystem will automatically re-size them to preserve the most accurate version of the noise bins after adding them.

There is a default center frequency for most components. Components like Lasers set the noise center at the lasing frequency, whereas the Erbium doped fiber has an explicit parameter in the Noise tab to set the center frequency.