Impact of Nonlinearity Including Bleaching in $p$-$i$-$n$ Photodetectors on RF-Modulate

We use a drift-diffusion model that includes the effect of bleaching to study the impact of nonlinear distortion in a $p$-$i$-$n$ photodetector (PD) on RF-modulated frequency combs. This work complements a similar study that we carried out for a modified uni-traveling carrier (MUTC) PD. We begin by using experimental responsivity data to develop an empirical model of the bleaching in a $p$-$i$-$n$ PD when operating in pulsed mode. We then incorporate this model of bleaching into a drift-diffusion model. Next, we use this drift-diffusion model to determine the impact of nonlinearity on the second- and third-order intermodulation distortion products IMD2$_n$ and IMD3$_n$ as a function of the comb line number $n$. We then determine the corresponding output intercept points OIP2$_n$ and OIP3$_n$ and distortion-to-signal ratios $\rho _{\mathrm{2}n}$ and $\rho _{\mathrm{3}n}$. In contrast to MUTC devices, we find that bleaching increases $\rho _{\mathrm{2}n}$ and $\rho _{\mathrm{3}n}$ at all comb line numbers. However, these distortion products change little as $n$ increases, in contrast to MUTC devices where they grow rapidly as $n$ increases.