Circuit for suppressing noise and distortion in linear fiber optic links
AssigneesAgere Systems Inc., Emcure Corporation
InventorHenry A. Blauvelt
Life of this patent
Estimating the term…
Abstract
The quality of a multi-channel signal launched into an optical fiber may be degraded by active device distortion as well as non-linear fiber effects. Active device distortion in the form of clipping distortion and interferometric noise are reduced by a laser bias control circuit that does not require significant delay of the main RF signal. An information carrying signal, with periodic high amplitude peaks, drives the RF input of a laser as well as the input of a laser bias control circuit. The laser bias control circuit directly modulates the laser with a low frequency signal that is proportional to the frequency of occurrence and intensity of peaks in the information carrying signal that are likely to cause the laser to clip.
Claims46
An optical transmission system for transmitting information with reduced interferometric noise and clipping distortion in linear fiber optic links comprising:
- a laser having an RF input for receiving an information carrying signal, wherein the information carrying signal includes amplitude peaks that cause the laser to clip;
- and
- a laser bias control circuit that monitors said information carrying signal to detect a first amplitude peak in said information carrying signal that causes said laser to clip and adjusts laser bias current to prevent subsequent amplitude peaks within a predetermined period in said information carrying signal from causing said laser to clip as a function of the detection of said first peak.
An optical transmission system for transmitting information with reduced interferometric noise and clipping distortion in linear fiber optic links comprising:
- a laser having an RF input for receiving an information carrying signal, wherein the information carrying signal includes amplitude peaks that cause the laser to clip;
- a laser bias control circuit that detects a first amplitude peak in said information carrying signal that causes said laser to clip and adjusts laser bias current prior to occurrence of a second amplitude peak in said information carrying signal that would cause said laser to clip as a function of the detection of said first peak;
- and
- wherein said laser bias control circuit comprises a peak detector which generates a laser bias control signal that is proportional to frequency of occurrence and intensity of the amplitude peaks in the information carrying signal that cause said laser to clip;
- and wherein said peak detector comprises a resistor connected in series with a shunt device and a parallel RC network, wherein the shunt device conducts current when there is a voltage peak in the information carrying signal that exceeds a preset voltage level.
An optical transmission system for transmitting information with reduced interferometric noise and clipping distortion in linear fiber optic links comprising:
- a laser having an RF input for receiving an information carrying signal, wherein the information carrying signal includes amplitude peaks that cause the laser to clip;
- and
- a laser bias control circuit that detects a first amplitude peak in said information carrying signal that causes said laser to clip and adjusts laser bias current prior to occurrence of a second amplitude peak in said information carrying signal that would cause said laser to clip as a function of the detection of said first peak;
- a diode signal limiter which restricts maximum amplitude of the laser bias control signal to a preset level, wherein said diode signal limiter further comprises,
- a forward biased diode with a positive bias voltage level for restricting maximum positive voltage levels output by the laser bias control circuit;
- and
- a reverse biased diode with a negative bias voltage level for restricting maximum negative voltage levels output by the laser bias control circuit.
An optical transmission system for transmitting information with reduced interferometric noise and clipping distortion in linear fiber optic links comprising:
- a laser having an RF input for receiving an information carrying signal, wherein the information carrying signal includes amplitude peaks that cause the laser to clip;
- and
- a laser bias control circuit that monitors said information carrying signal to detect a first amplitude peak in said information carrying signal that causes said laser to clip and adjusts laser bias current to prevent subsequent amplitude peaks within a predetermined period in said information carrying signal from causing said laser to clip as a function of the detection of said first peak;
- and
- wherein the laser bias control circuit amplitude modulates transmitted RF carriers.
A method of suppressing clipping distortion and interferometric noise in a linear fiber optic link comprising the steps of:
- inputting an information carrying RF signal with amplitude peaks into an RF input of a laser;
- monitoring said information carrying signal to detect a first peak in said information carrying signal that causes said laser to clip;
- and
- increasing laser bias as a function of the detection of said first peak to prevent subsequent peaks within a predetermined period in said information carrying RF signal from causing said laser to clip.
A method of suppressing clipping distortion and interferometric noise in a linear fiber optic link comprising the step of
- inputting an information carrying RF signal with amplitude peaks into an RF input of a laser;
- detecting first peak in information carrying signal that causes laser to clip;
- anticipating occurrence of a second peak in information carrying signal that would cause the laser to clip as a function of the detection of said first peak;
- increasing laser bias by directly modulating the laser bias with the signal that is substantially proportional to the frequency of occurrence and intensity of amplitude peaks in the information carrying signal prior to the occurrence of said second peak;
- and
- amplitude modulating RF carriers in the information carrying signal in a manner that is equal in amplitude and opposite in sign to the modulation of the laser bias.
An optical transmission system comprising:
- a laser bias control circuit that monitors a characteristic of an information carrying laser input signal prior to inputting said information carrying laser input signal into said laser and increases laser bias to prevent clipping of said information carrying laser input signal as a function of said characteristic, without delaying input of said information carrying signal into a laser.
An optical transmission system comprising:
- a laser bias control circuit that increases laser bias to prevent clipping of an information carrying signal, wherein the laser bias control circuit amplitude modulates transmitted RF carriers;
- a voltage variable attenuator for modulating the amplitude of the RF carriers in a manner that is substantially equal in amplitude and opposite in sign to modulation of RF carriers created by the laser bias control circuit.
An optical transmission system comprising:
- a laser bias control circuit that adjusts laser bias to prevent a laser from clipping an information carrying signal;
- and
- wherein said laser bias control circuit comprises a peak detector comprising a resistor connected in series with a shunt device and a parallel RC network, wherein the shunt device conducts current when there is a voltage peak in the information carrying signal that exceeds a preset voltage level.
Dependencies are inferred from the claim text.