Modelling PM-BPSK signals

[abhishek136]

I intend to implement the IEEE paper “Modelling PM-BPSK Signals for Coherent Optical Transmission over Single-Mode
Fiber” but on implementation of the layout, the BER always comes to be 1.

I’ve tried varying the system parameters but still BER is always 1.

Hope anyone could help pointing out what could be the mistake in the layout.

[Damian Marek]

You will need to use a dual driven modulator to modulate the phase correctly. Try looking at the example files in your samples folder. DP-BPSK back to back.osd would be a good start.

Cheers

[abhishek136]

I have been using optisystem 7.0 and there is no file by the name DP-BPSK back to back.osd.

It would be kind of you if you could share that

[abhishek136]

And what are the possible reasons that i am getting a BER=1, because the circuit given in this paper has been drawn as per its given but the values are nowhere matching.

[Damian Marek]

I can’t speak for the article, but the main problem is that using our simplified single driven modulator does not allow you to modify only the phase. It modifies the amplitude.

Since older versions of OptiSystem cannot open newer project files I cannot attach the project file. However, take a look at the attached screenshot and try to build the modulator schematic. I’m actually not sure what types of components are available in OptiSystem 7.0, but any dual driven modulator should do. The intensity of the signal should not change for BPSK format. You will also need to design a coherent detection system. A simple PIN diode will not be sufficient to detect the signal.

Regards

[abhishek136]

Is the above diagram complete since i cannot observe the input and output to the Modulator (i.e the green arrows starting from and ending to)

And im attaching the IEEE paper that i intend to implement.

[Damian Marek]

The green line is just the optical signal. You could use a polarized CW Laser for that.

[abhishek136]

So if you could guide me accordingly how should i approach the above paper to obtain the appropriate output.

[Damian Marek]

I looked at the article attached and I don’t think I trust it! Unless I am missing something here I don’t think their results show any phase modulation, so I am little confused by that. Here is a quick introduction to BPSK:

http://www.eng.auburn.edu/~troppel/courses/TIMS-manuals-r5/TIMS%20Experiment%20Manuals/Student_Text/Vol-D1/D1-08.pdf

You should be fine using the double driven modulator, or you could also use the straight phase modulator component, which would make it much simpler. Look at how they do the receiver, you will need a local oscillator (another CW Laser) and couple it to the incident signal.

Regards

[abhishek136]

Thank you Sir!
I shall now try implement considering these changes.

[abhishek136]

Sir

I have tried implementing a coherent detector for the dual driven modulator you had given before but I fail to get the output.

So if you could share a layout of how should a coherent detector for a bpsk modulator which you had shown should be like it shall be of great help Sir.

[Damian Marek]

If you modulate both electrical ports with the same voltage signal it should act as a phase modulator. Look at the attached pic.

[abhishek136]

Thanks a lot! It worked!!

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