Ortel Corporation

John S Frame

Henry A Blauvelt

Amnon Yariv

David B Huff

Howard L Loboda

Noise and distortion due to scattering and reflection in a fiber-optic communications system are suppressed by modulating the optical frequency of (chirping) a laser light source to broaden the spectrum of the laser light output. The broader spectrum spreads the noise produced by an unchirped source over a broader band. A noise and distortion suppression system includes a chirp signal generator coupled to the signal path of an RF input signal carrying information to modulate the laser optical output. In some cases, the frequency of the chirp generating signal may result in second-order intermodulation products falling within the information band. In such cases, the RF input signal is predistorted to offset the expected distortion products.

Suppression of noise and distortion in fiber-optic systems

An electronic circuit provides a linear output from an amplitude modulated transmission device such as a semiconductor laser which has inherent distortion. The distortion of the nonlinear device is compensated by applying a predistorted signal equal in magnitude and opposite in sign to the distortion introduced by the nonlinear device. The input signal is split into two or three paths with primary part of the signal applied directly to the device, with a time delay to compensate for delays in two secondary paths. One secondary path generates even order intermodulation products and the other generates odd order intermodulation products. These are recombined with the primary signal in proper phase and amplitude for cancelling distortion in the output device. A distortion generator in each secondary path generates adjustable amplitude intermodulation signals. A tilt adjustment is made to compensate the amplitude of the predistortion for frequency dependence of the amplitude of the distortion. Phase of the distortion signal is adjusted to be in proper phase relation with the distortion of the device. In the even order path there are means for adjusting predistortion at an intermediate frequency so that the distortion is cancelled near the upper, lower and intermediate portions of the frequency range of the device.

Growing community of inventors

Torrance, CA, United States of America

John S Frame