I. Introduction
Nonlinear crosstalk in wavelength-division multiplexing (WDM) analog-fiber cable television (CATV) systems can Schematic diagram of the complete complementary modulation of twin carriers and balanced detection (TC-BD) technique. The lines above the axes represent intensity modulation. be so severe as to prevent satisfactory operation, even with just a few wavelengths [1], [2]. Since Raman gain-induced crosstalk can be very large at low frequencies, it is desirable to find techniques providing high degrees of suppression at low RF frequencies. Recently, we achieved a 35-dB crosstalk reduction at low frequencies by using complementary modulation of twin carriers (TCs) [3]. However, it was only an experimental measurement that demonstrated the feasibility of suppressing nonlinear crosstalk in an analog link, but not a complete system due to the asymmetry between the twin carriers and the probe (i.e., we used two carriers on the modulated channel but only one carrier on the probe channel). Here we report on a system using a realistic set of wavelengths. By using complementary modulation of twin carriers and balanced detection (TC-BD), we were able to obtain up to 50-dB crosstalk reduction at low frequencies. The implementation of TC-BD is only marginally more complicated than that of the previous technique of [3]. Thus, it may be of practical interest.