1：Experimental Design and Method Selection:

The phase noise characterization of a tunable laser source is performed using a delayed self-homodyne configuration. The measured FM-noise PSD is reproduced by simulations to investigate the impact of EEPN in a coherent transmission system.

2：Sample Selection and Data Sources:

The tunable laser source is capable of tuning to 103 channels in a 50 GHz grid between 1527.6-1568.36 nm. The phase noise characterization is performed for channels 13, 45, 95, and

3：6-36 nm. The phase noise characterization is performed for channels 13, 45, 95, and List of Experimental Equipment and Materials:

103. 3. List of Experimental Equipment and Materials: The measurement setup includes a tunable laser under test, a fiber optic isolator, a 3 dB power splitter, a polarization controller (PC), a coherent receiver, and a real-time scope.

4：Experimental Procedures and Operational Workflow:

The measurement consists of the tunable laser under test; a fiber optic isolator, to avoid reflections back into the laser; a 3 dB power splitter, with the first branch connected to a polarization controller (PC) and afterwards to the coherent receiver; and the second branch connected to a 27 km delay fiber, assuring that the coherence length of the laser is exceeded, then connected to a PC and finally to the coherent receiver. From the coherent receiver, the in-phase and quadrature signals are recovered and digitized by the real-time scope at 20 GS/s.

5：Data Analysis Methods:

The FM-noise PSD and the field spectrum are generated from the measured signal. The linewidth of each channel is calculated by averaging the FM-noise PSD values from the frequency region >1 MHz.