A Novel analog broadband RF predistortion circuit in directly modulated lasers for radio-over-fiber systems

For radio-over-fiber (RoF) systems, the laser is a major source of nonlinearity. A CMOS analog broadband RF predistortion circuit to improve the nonlinearity in RoF systems is firstly described in this letter. It is shown by simulation that the predistortion circuit shows a significant reduction of about 20 dBc in the third-order intermodulation distortion (IMD3) in the optical fiber system over the frequency range of 1~2 GHz. The predistortion lineariser is being fabricated using the TSMC 0.18-μm CMOS technology.