Modulation system and method with third order intermodulation di

Details Modulation system and method with third order intermodulation di Modulation system and method with third order intermodulation di

1992-06-03

1994-11-29

Moskowitz, Nelson

Optical: systems and elements

Optical frequency converter

Harmonic generator

385 3, 359238, 359279, G02F 1313, H04B 1014

Patent

active

053695224

ABSTRACT:
When an optical signal is modulated at two modulation frequencies, third order intermodulation distortion (IMD) is eliminated by inducing an out-of-phase signal that is complementary to the modulated signal, and cross-coupling the two signals with each other to remove the third order terms. An optical beam in a first waveguide is electro-optically modulated and coupled with a second waveguide to induce the out-of-phase complementary beam therein. A second optical coupler is provided that cross-couples the beams in the two waveguides downstream from the first optical coupler. The optical coupling coefficients, the coupler lengths, and the differential between the optical propagation coefficients of the two waveguides within the first coupler are selected empirically to substantially negate third order IMD. The differential in propagation coefficients is established by the DC bias of the modulation signal. Enhanced linearity can be obtained by inducing a compensating phase shift either in the second optical coupler, or between the first and second optical couplers.

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