## 4 System Modeling and Performance
Figure 14: Simulated eye diagram results of eight channels of silicon photonic transmitter with NRZ modulation format of 100 Gb/s. Figure 13: The calculated frequency spectra of the eight-channel modulated optical signals **(a)** with NRZ modulation format. **(b)** with PAM4 modulation format. The BER test simulations were carried out for both NRZ and PAM4 modulation format signal transmission. Figure 16a,b shows the measured curve of BER versus the received optical power (ROP) for 100 Gb/s NRZ and 50 Gbaud/s PAM4 signal transmission, respectively. The ROP is equal to the input laser power minus the total optical loss of the optical transmitter chip. Performance under different transmission lengths is investigated, including back-to-back (0 km), 0.5 km and 2 km single mode fiber. Here, a model of single mode fiber G.652 is utilized with dispersion characteristics. For OOK and PAM4 signal, FEC [49; 50] threshold of \(5\times 10^{-5}\) and \(1\times 10^{-3}\) are assumed for error-free transmission, respectively. Thus, it can be seen that the minimum achievable ROP for 500 m transmission is about \(-1\) dBm and \(-5\) dBm for 100 Gb/s OOK and 50 Gbaud/s PAM4, respectively. The power consumption of the optical transmitter is of great concern in real applications. In our estimation, the total power consumption is divided into three parts. Firstly, the modulators are power hungry devices. According to our simulations, the PN junction capacitance of 2 mm phase shifter length is about 0.44 pF. Since the modulators are working in push-pull differential mode, the capacitance of a single modulator would be doubled as 0.88 pF. According to the equation of modulator power consumption:  
\[E=C\cdot V_{pp}^{2}/4 \tag{19}\]  
Here \(V_{pp}\) of 2 V is utilized in this design. Then the power consumption of a single modulator is estimated to be 0.88 pF/bit. The power consumption of 800 G optical modulation is about 0.704 W. Secondly, the thermal tuning functions are added for setting  
Figure 16: (**a**) Calculated curve of BER versus the received optical power for 100 Gb/s OOK signal transmission. (**b**) Calculated curve of BER versus the received optical power for 50 Gbaud/s PAM4 signal transmission. Figure 15: Simulated eye diagram results of eight channels of silicon photonic transmitter with PAM4 modulation format of 50 Gbaud/s. the operation point of the modulators, which contributes to the total power consumption. Assuming that the length of thermal tuning functions is about 100 \(\upmu\)m, the resistance of TiN thermal heater is about 210 \(\Omega\). At 3 V, the power consumption of single channel thermal tuning is about 43 mW, and the total power consumption of thermal tuning is about 0.35 W (including the possible thermal tuning in the WDM function). Finally, although lasers are not part of silicon photonics chips at present, they contribute to the total power consumption of silicon photonic transmitter as well. According to the datasheet of a DFB laser product of Lumentum corporation, the typical power consumption of a single laser is about 90 mW, which corresponds to an output optical power of 11.5 mW. This is fairly enough for our transmitter power budget. Therefore, the total power consumption of eight lasers is 0.72 W at maximum. The power consumption of the 800 Gbps WDM silicon photonic transmitter is about 1.77 W in total. Other power consumptions for ASICs and TEC are beyond our discussions here. Considering the power consumption standard of 800G silicon photonic transceiver modules is 16 W, the total power consumption of our transmitter chip is acceptable in general.