MODULATION SYSTEM AND METHOD FOR ATTENUATION OF TERTIARY INTERMODULATION DISTORTION

摘要

PURPOSE: To provide a system for attenuating a third intermodulation distortion(IMD) in a light signal modulated by two frequencies. CONSTITUTION: Optical beams in a first waveguide 2 are electric/opto-modulated and are connected to second waveguide 4. The beams of opposite phase are guided into the second waveguide 4. A second optical coupler 8 is provided so that the beams are mutually connected to the two waveguides 2 and 4 in down stream from the first optical coupler 6. An optical connection coefficient, coupler length and the difference of the optical transmission coefficients between the two waveguides 2 and 4 in the first coupler 6 are selected so that tertiary IMD is substantially invalidated. The difference of the optical transmission coefficients is established by the DC bias of the demodulation signal. Extended linearity is obtained by guiding correction phase shift to the second coupler 8 or a space between the fist optical coupler 6 and the second coupler 8.