The influence of the power mismatch of two optical sources on the system performance has been
evaluated. In the simulation, two optical sources with the wavelength of 1551 nm and 1552 nm are
used in the CS, and the length of fiber link between the CS and BS is 10 km. A length of 7.5 km SMF
is placed in BS1 as a dispersive medium, while in BS2, there are no extra dispersive elements, and
the signal from the CS is demultiplexed directly. In this case, if the frequency of the subcarrier is set
to 12 GHz (modulated with 1 Gb/s NRZ data stream), it will be suppressed in BS1 since its located
in the valley frequency, and in BS2, it is at the peak frequency, and therefore, the signal can be well
demultiplexed. Fig. 3 shows the calculated results of the eye diagram in BS1, BS2, and the
corresponding frequency response, when the power ratio of two optical sources are 1 : 0.63 (a)–(c),
1 : 0.79 (d)–(f), and 1 : 1 (g)–(i), respectively. One can see that, as power ratio of two optical
sources gets closer to 1, the notch depth becomes larger, and in turn, the eye diagram of BS1
changes from open to close, while that of BS2 keeps widely open.