Eye Diagrams at 2.5Gb/s
To obtain the Eye diagram, the circuit in Fig. 4. was changed to the one shown in Fig. 13. , where a butterworth filter(LPF_1) is added after the PIN photodetector (PIN_1) to filter out unwanted frequencies. Note that the filter has a matched bandwidth of 0.75* bitrate, which gives a much cleaner graph as the filter ensures the signal to noise ratio is maximized so sensitivity to noise is reduced. Moreover, the DC source is replaced by a Pseudo-random bitstream(PRBS_1) and Non-return to zero modulation format(NRZ_1) to simulate the transfer of data by modulating the power input of the RSOA. The resulting eye diagram in Fig 14. shows a clear graph, with eye vertical opening at 0.009161 dBm, and horizontal opening at 398.8ns. An optical fibre of 1km was added after the Bragg grating(Wbg_1). The resulting eye diagram is shown in the right of Fig. 14. From the graph, the eye diagram is distorted as the signal-to-noise ratio increases. Since the mask is heavily distorted, it is not possible to define an exact vertical and horizontal opening.