Variable sensitivity compensation network for Mach-Zender optical modulator
First Claim
1. A compensation network for a Mach-Zender optical modulator comprisingfirst and second pilot signal sources emitting first and second pilot signals f1 and f2, respectively,a signal coupler for combining the first and second pilot signals with an RF information-bearing signal and producing a modulating signal having both information and pilot components, said modulating signal being input to a bias-controlled Mach-Zender optical modulator, wherein a bias control fixes an operating point for said modulator, said optical modulator having a modulated lightwave output comprising the information signal and the sum frequency f1 +f2,a variable sensitivity feedback loop comprising an optical detector for detecting the pilot signals from the modulated lightwave output of the optical modulator, the output of said detector being the input to a bandpass filter for passing the sum frequency f1 +f2, said sum frequency comprising the input to a voltage variable attenuator for adjusting the sensitivity of the feedback loop, a logarithmic compression circuit for compressing the f1 +f2 signal level output from the variable attenuator, means for measuring the compressed f1 +f2 signal from the compression circuit, means for controlling the variable attenuator, and means for producing an analog bias signal for controlling the operating point of the optical modulator, said bias signal being input to the modulator.
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Accused Products
Abstract
A variable sensitivity compensation network for a Mach-Zender optical modulator comprising first and second pilot signal sources f1 and f2, a signal coupler for combining the pilot signals with an RF information signal for modulating a bias-controlled Mach-Zender optical modulator, a variable sensitivity feedback loop comprising an optical detector for detecting the pilot signals from the modulator output, a bandpass filter for selecting the sum frequency f1 and f2, a voltage variable attenuator for adjusting the sensitivity of the loop, a logarithmic compression circuit for compressing the f1 and f2 signal level from the variable attenuator, means for measuring the signal level, means for controlling the variable attenuator and means for producing an analog bias signal for controlling the operating point of the Mach-Zender modulator. The measuring and controlling means include a microprocessor.
34 Citations
13 Claims
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1. A compensation network for a Mach-Zender optical modulator comprising
first and second pilot signal sources emitting first and second pilot signals f1 and f2, respectively, a signal coupler for combining the first and second pilot signals with an RF information-bearing signal and producing a modulating signal having both information and pilot components, said modulating signal being input to a bias-controlled Mach-Zender optical modulator, wherein a bias control fixes an operating point for said modulator, said optical modulator having a modulated lightwave output comprising the information signal and the sum frequency f1 +f2, a variable sensitivity feedback loop comprising an optical detector for detecting the pilot signals from the modulated lightwave output of the optical modulator, the output of said detector being the input to a bandpass filter for passing the sum frequency f1 +f2, said sum frequency comprising the input to a voltage variable attenuator for adjusting the sensitivity of the feedback loop, a logarithmic compression circuit for compressing the f1 +f2 signal level output from the variable attenuator, means for measuring the compressed f1 +f2 signal from the compression circuit, means for controlling the variable attenuator, and means for producing an analog bias signal for controlling the operating point of the optical modulator, said bias signal being input to the modulator.
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7. A compensation network for a Mach-Zender optical modulator comprising
a variable sensitivity feedback loop comprising an optical detector and a filter, said detector having as its input a small portion of a modulated lightwave from a bias-controlled optical modulator, the output of said detector comprising the input to the filter, said filter being tuned to pass a second-order signal product detected from the modulator output, a variable attenuator for adjusting the loop sensitivity to changes in the second-order signal level received from the filter output, said attenuator having a control input, a means for scaling the second-order signal connected to the output of the variable attenuator, a means for measuring the second-order signal connected to the output of the scaling means, and a means for producing a bias control signal for setting the bias control of the modulator to its most linear operating point.
Specification