Cable system incorporating highly linear optical modulator
AssigneeHoechst Celanese Corporation
InventorsDonald Raskin, Kophu Chiang, James B. Stamatoff
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Abstract
A system incorporating a pair of Mach-Zehnder modulators (164,166) for performing amplitude modulation of an optical carrier is disclosed. Each of the modulators is designed to suppress even order distortion products and develop third order distortion products of opposite sign and equal magnitude. The outputs of the two modulators are combined in a directional coupler (155) resulting in substantially suppressing second through fourth order distortion products.
Claims13
In an optical cable television distribution system having a light source means operative to generate an optical carrier signal for information to be transmitted over said system and having an electrical driver means for providing an electrical signal defining information to be transmitted over said cable system, the combination comprising:
- (a) a first modulator optically coupled to said light source means and having an output port for light therefrom modulated in accordance with said electrical signal and having the characteristic of substantially eliminating even order distortion products, said first modulator having a characteristic that third order intermodulation distortion products are of a first sign;
- (b) first coupling means for coupling said electrical signal to said first modulator;
- (c) a second modulator optically coupled to said light source means and having an output port for light therefrom modulated in accordance with said electrical signal and having the characteristic of substantially eliminating even order distortion products, said second modulator having a characteristic that third order intermodulation distortion products are of a sign opposite to said first sign;
- (d) second coupling means for coupling said electrical signal to said second modulator;
- and
- (e) an optical adder to receive the outputs of said first and second modulators and producing at its output a modulated light signal characteristic of the combination of the outputs from said first and second modulators.
In a device for modulating the output of light source means in accordance with an electrical signal containing information to be transmitted, the combination comprising:
- (a) a first modulator coupled to receive light from said light source means, said first modulator having an output port for modulated light and having the characteristic of substantially eliminating even order distortion products, said first modulator having a characteristic that third order intermodulation distortion products are of a first sign;
- (b) first coupling means for coupling said electrical signal to said first modulator;
- (c) a second modulator coupled to receive light from said light source means, said second modulator having an output port for modulated light and having the characteristic of substantially eliminating even order distortion products, said second modulator having a characteristic that third order intermodulation distortion products are of a sign opposite to said first sign;
- (d) second coupling means for coupling said electrical signal to said second modulator;
- and
- (e) an adder optical coupled to receive the output of said first and second modulators and producing at its output a modulated output light signal characteristic of the output of said first and second modulators.
Dependencies are inferred from the claim text.