Abstract

Optical fiber communication systems having a linear transfer characteristic are of interest for rf to millimeter wave applications. Among these is the distribution of amplitude modulated cable television signals. In that application typically 40-60 channels in the frequency range of 50-500 MHz are multiplexed for transmission, which consequently places stringent requirements on linearity and SNR and constrains the per channel optical modulation depth (OMD) to ~4%.^1,2 None of the standard types of waveguide electrooptic modulator inherently provides the necessary linearity. For example, at 4% OMD the two-tone third-order intermodulation products of the Mach-Zehnder modulator, the directional coupler switch, and the y-fed directional coupler are calculated to be −74, −72, and −73.6 dBc,³ whereas the requirement is about −100 dBc Here we investigate the use of active feedforward compensation⁴ to reduce the distortion from an integrated optic transmitter. We demonstrate signal suppression ratios of >15 dB over the range of 50-300 MHz and >25 dB from 300 to 500 MHz.

© 1990 Optical Society of America