An FPGA-Based Optical Transmitter Design Using Real-Time DSP for Advanced Signal Formats and Electronic Predistortion

Abstract

Advances in the performance and flexibility of future optical networks will be brought about through the use of high-speed digital signal processing (DSP) for the generation of advanced optical signal formats and the compensation of transmission impairments. The use of field-programmable gate arrays (FPGAs) to implement experimental transceivers employing novel DSP techniques is attractive, as they are of low cost and are reprogrammable. In this paper, the design of a reprogrammable FPGA-based 10-Gb/s optical transmitter using real-time DSP is described and assessed through simulation. Using a single Xilinx Virtex-4 FPGA, digital filtering based on lookup tables with up to 12-bit addressing could be implemented. We also present, for the first time, a simulation technique using industry-standard digital design simulation tools (mentor graphics modelsim) in combination with a simulation of analog microwave components, optical transmission, and bit-error-rate estimation to assess the performance of the full transmission system. This simulation technique is used to demonstrate 10-Gb/s transmission over 550 km of standard single-mode fiber (SSMF) using electronic predistortion (EPD) and the generation of optical single sideband signals. A proof-of-principle experiment is described in which a single 10.7-Gb/s Mach-Zehnder modulator drive signal with 4-bit amplitude resolution and 1-sample/bit temporal resolution was generated. This was used as the input to Monte Carlo simulations to assess EPD transmission performance over SSMF links of up to 640 km.