Comparison of the impact of nonlinearity in a p-i-n and an MUTC photodetector on electro-optic frequency combs

We calculate the impact of nonlinearity in both a p-i-n photodetector (PD) and a modified uni-traveling carrier (MUTC) PD on an RF-modulated frequency comb generated using 100-fs optical pulses with a 50-MHz repetition rate. We take into account bleaching (nonlinear saturation) that is due to the high peak-to-average-power ratio and contributes to the device nonlinearity. Nonlinear impairment of an RF-modulated continuous wave is typically characterized by the second- and third-order intermodulation distortion products (IMD2 and IMD3). In contrast, an RF-modulated frequency comb must be characterized by a distinct IMD2_n and IMD3_n for each comb line n. We calculate IMD2_n and IMD3_n in both p-i-n and MUTC PDs and compare the results. We also calculate the ratio of the IMD2_n power and the IMD3_n power to the fundamental power S_in in both p-i-n and MUTC PDs. We find that nonlinear distortion has a greater impact at high frequencies in the MUTC PD than in the p-i-n PD.