## 4 Dynamic Characterization
### Direct Data Modulation and On-Off Keying (OOK) Transmission  
Next, we carry out direct data modulation of the SG section of the PIC with a 10.7 Gb/s OOK data signal to investigate the potential of usage of the PIC as a transmitter in a short reach network. The experimental setup used is shown in Figure 6a (black wire connections). A pulse pattern generator (PPG) is used to generate a 10.7 Gb/s pseudo random bit sequence (PRBS) with a length of \(2^{15}\)-1. The data signal is combined with a DC bias of 72.8 mA using an internal bias-tee within the device package. The optical output of the device is split using a 90%-10% coupler. The 10% path is connected to a 20 MHz high-resolution OSA, while the 90% path is launched into a 20 GHz PIN photodiode (DSC30S) either B2B or after transmission over 25 km of SSMF. A variable optical attenuator (VOA) is used to vary the received optical power. The photodiode output is connected either to a digital sampling oscilloscope, to generate eye diagrams, or to an error detector, to measure the bit error rate (BER) of the system.  
BER results as a function of the received optical power are presented in Figure 6c. The measurements are taken for both the cases when the master laser was turned off (circles) and on (triangles). For the B2B transmission, the injected case has a power penalty of 2 dB with respect to the non-injected one at \(\text{BER}=4\times 10^{-9}\). This penalty can be attributed to the fact that the optical injection reduces the threshold current of a laser, resulting in a degraded extinction ratio [35]. However, after transmission over 25 km of SSMF, the optically injected laser performs significantly better. The received optical power required to achieve the FEC limit for the injection case is 2 dB lower than that without injection. This can be attributed to a reduction of the chirp due to the applied OIL [36]. For both cases, a BER below the hard decision (7% overhead) forward error correction (FEC) limit (\(\text{BER}=3.8\times 10^{-3}\)) is achieved. The optical spectra recorded using a 0.04 pm resolution OSA (APEX AP2433B) in Figure 6d further verify the reduction in frequency chirp, where the OIL case is represented by the blue line and the non-injected case by the red line. It can be seen that the spectral width of the modulated laser without OIL is significantly broader than when the master laser is turned on. The interplay between the fiber chromatic dispersion and this large spectral width (due to higher value of chirp) causes pulse spreading, leading to intersymbol interference and resulting in a degraded performance (worse BER). The insets in Figure 6d show the recorded eye diagrams at a received optical  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Section** & **SG** & **SR** & **MG** & **MR** \\ \hline Bias point 1 (mA) & 100.18 & 69.7 & 45.35 & 85.15 \\ Bias point 2 (mA) & 98.68 & 56.15 & 65.62 & 87.56 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Bias points for frequency response measurements.  
power of 0.5 dBm for both cases. The reduced eye-opening for the laser without injection is visible and validates the results of the BER measurements.