Module 4

Modulation Schemes

(1) Use the Existing Modules / Components for Your Research Papers, Research Projects, Theses and Lab Simulation Experiments.
(2) Modify the Modules / Components to the Next Level for Your Research Papers, Research Projects and Theses.
(3) Integrate Different Modules / Components in the OCSim Package to Realize Your Own Fiber Optic Communication Systems.
(4) Modify the Modules for Co-Simulations with the Third Party Commercial Optical Communication Systems Softwares.

Source Code: Optical_tx_ook.m

NRZ-OOK transmitter that uses dual drive Mach-Zehnder modulator (MZM) is simulated. The MZM is driven by polar NRZ signal. The pulse shape is assumed to be raised-cosine.

This source code calls the following functions:
(1) power_meter.m – calculates the average optical power in dBm units.
(2) tx_nrz_ook.m – modulates the output of the laser with OOK data using dual drive Mach-Zehnder modulator.
(3) eye_diagram.m – plots the eye diagram of the optical power.

Explore Further this Module:

4.1 Roll-off factor alpha (defined in tx_nrz_ook.m) determines the steepness of the pulse edge. Modify the source code by changing alpha from 0 to 0.9 with a step of 0.1 and plot the time diagram, eye diagram and spectrum.

4.2 Change the pulse shape to Gaussian and change the duty cycle of the electrical signal to 50% and plot the eye diagram and spectrum. Compare the bandwidth of the 50% duty cycle (RZ) and 100% duty cycle (NRZ) pulses.

4.3 Change the variances of transmitter electronic noise and optical noise and observe how the eye diagram provides the visual information about the noise. Also observe how the noise floor in the spectrum increases as optical and/or electronic noise variance increases.

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Source Code: Optical_tx_psk.m

NRZ-PSK transmitter that uses dual drive Mach-Zehnder modulator (MZM) is simulated. The MZM is driven by polar NRZ signal The pulse shape is assumed to be raised-cosine.

This source code calls the following functions:
(1) power_meter.m – calculates the average optical power in dBm units
(2) tx_nrz_psk.m – modulates the output of the laser with PSK data using a dual drive Mach-Zehnder modulator
(3) eye_diagram.m – plots the eye diagram of the optical power.

Explore Further this Module:

4.4 Modify the source code by changing the roll-off factor, alpha from 0 to 0.9 with a step of 0.1 and plot the time diagram, eye diagram and spectrum.

4.5 Change the variances of transmitter electronic noise and optical noise and observe how the eye diagram provides the visual information about the noise. Also observe how the noise floor in the spectrum increases as optical and/or electronic noise variance increases.

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Source Code: Optical_tx_qpsk.m

NRZ-QPSK transmitter that uses two dual drive Mach-Zehnder modulators (MZM) is simulated. The MZMs are driven by two polar NRZ signals corresponding to in-phase and quadrature data. The pulse shape is assumed to be raised-cosine.

This source code calls the following functions:
(1) power_meter.m – calculates the average optical power in dBm units
(2) tx_nrz_qpsk.m – modulates the output of the laser with QPSK data using two dual drive Mach-Zehnder modulators
(3) eye_diagram.m – plots the eye diagram of the optical power.

Explore Further this Module:

4.6 Repeat 4.4, 4.5 by changing BPSK to QPSK.
4.7 Modify the source code to realize 16-QAM.

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Source Code: Optical_tx_qpsk_nyquist.m

QPSK transmitter that uses raised-cosine pulses in frequency domain is simulated. It is assumed that MZM nonlinearity is compensated by transmitter DSP so that the real part of (imaginary part of) complex optical field envelope is directly proportional to the in-phase (quadrature) component of the driving voltage.

This source code calls the following functions:
(1) power_meter.m – calculates the average optical power in dBm units
(2) raised_cosine_freq.m – modulates the output of the laser with raised-cosine pulse in frequency domain
(3) eye_diagram.m – plots the eye diagram of the optical power.

Explore Further this Module:

4.8 Change the roll-off factor from 0.3 to 1 and observe the spectral width change.

4.9 Change the noise variances of optical and electrical components and observe the constellation diagram.

4.10 Modify the code to realize 16-QAM.

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