Optical Transmitter Error Reduction via Receiver Feedback
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Solution Overview
Problem
Optical transmitter errors such as quadrature error, carrier leakage, and IQ timing error in optical communications networks impair signal quality and are difficult to detect and correct, leading to performance degradation and increased costs.
Innovation Solution
A method that processes the optical signal to generate a digitally-equalized signal, determines nonlinear characteristics indicative of transmitter errors, and uses a control signal to adjust transmitter parameters, reducing impairments like quadrature error and IQ timing error through a system comprising a digital signal processor, memory module, and control module.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If bias control is used to reduce quadrature error and control gain, then transmitter error is reduced, but nonlinearities in drive controls and chirp in MZ modulators introduce additional errors
Solution Approach 1:
The patent implements a feedback mechanism where the receiver detects transmitter errors (quadrature error, carrier leakage, IQ timing error, IQ gain error) and sends control signals back to the transmitter to adjust bias voltages and other parameters, thereby reducing the errors while compensating for introduced nonlinearities
Solution Approach 2:
The patent replaces complex expensive transmitter-side error detection hardware with a simpler receiver-side detection system that uses digital signal processing to identify errors and communicate them back to the transmitter for correction
2Object-generated harmful factors
If MZ modulator bias voltage is adjusted to achieve extinction, then carrier leakage is reduced, but detection of bias voltage errors at the transmitter is difficult and expensive
Solution Approach 1:
Instead of detecting errors at the transmitter as conventionally done, the patent inverts the approach by having the receiver detect the errors in the transmitted signal and communicate the error information back to the transmitter for correction
Solution Approach 2:
The receiver measures carrier leakage and other transmitter errors, then sends feedback control signals to the transmitter to adjust bias voltages and minimize these errors, creating a closed-loop error correction system
3Reliability
If IQ timing error is not corrected, then sampling phase errors occur and BER degrades, but precise timing synchronization increases system complexity
Solution Approach 1:
The receiver detects IQ timing errors in the received signal and sends feedback control signals to the transmitter to adjust the timing of the I and Q channel signals, thereby reducing sampling phase errors and improving BER without requiring complex timing synchronization hardware at the transmitter
Solution Approach 2:
The patent uses digital signal processing and control signals as intermediaries to transmit timing error information from the receiver to the transmitter, enabling precise timing adjustment without direct complex timing synchronization mechanisms
Data Source
AI summary
Described is a method of reducing transmitter error in an optical communications channel. An optical signal transmitted from an optical transmitter that has impairment due to transmitter error is processed to generate a digitally-equalized signal. A nonlinear characteristic of the digitally-equalized signal that relates to the transmitter error is determined. An optical control signal comprising data that are based on the nonlinear characteristic is transmitted to the optical transmitter. The optical transmitter modifies a transmitter parameter in response to the optical control signal to change the nonlinear characteristic and thereby reduce the impairment.