Abstract

In radio over fiber (RoF) systems there are two popular optical subcarrier modulations (SCMs) which are single side band (SSB) modulation and tandem single side band (TSSB) modulation. In TSSB modulation one optical carrier carries half of radio frequency (RF) signal tones to lower sideband (LSB) and the reminder to upper sideband (USB); while in SSB modulation all multiple RF signal tones in either LSB or USB. We analyze the impact of nonlinear distortion considering one wavelength carrying two RF signals. For small modulation depth TSSB and SSB SCMs lead to similar and very small nonlinear distortion. Because harmonic distortions (HDs) and inter-modulation distortion (IMDs) are strongly dependent on modulation depth, TSSB and SSB SCMs lead to different nonlinear distortion if modulation depth is not small, depending on two RF difference. To reduce nonlinear distortion for high modulation depth the two RF difference of 1GHz is preferred for both TSSB and SSB SCMs because some nonlinear distortions are dependent on the difference and sum of the two RFs and transmission fiber. However for the larger RF difference, either small modulation depth or medium modulation depth combined with minimum RF of 6GHz has to be used. Comparison of TSSB and SSB SCMs in DWDM RoF systems with 12.5GHz channel spacing and two subcarriers uniformly distributed in the optical spectrum shows that better performance is obtained using SSB SCM when small modulation depth is used. On the contrary, TSSB SCM is better than SSB SCM when large modulation depth is used.