Optimum design for RF-to-optical up-converter in coherent optical OFDM systems
Yan Tang, William Shieh, Xingwen Yi, Rob Evans
IEEE PHOTONICS TECHNOLOGY LETTERS | IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC | Published : 2007
In this letter, we conduct analysis on the optimum design for RF-to-optical up-converter in coherent optical OFDM systems using an optical I/Q modulator. We first derive closed-form expressions for the nonlinearity in the optical I/Q modulator, represented by two-tone intermodulation products as a function of the bias point and modulation index. Additionally, we perform a numerical simulation to identify Q-penalty and the excess modulation insertion loss under various transmitter conditions. We find that in contrast to the direct-detected system, the optimal modulator bias point for the coherent system is π, where the Q-penalty and excess loss are minimized. © 2007 IEEE.