Optical Modulator I/Q Imbalance Compensation
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Solution Overview
Problem
Coherent optical communication systems face challenges with I/Q imbalances, which can lead to phase shifts and amplitude differences between the I and Q components of optical signals, affecting data transmission accuracy, especially at higher symbol rates and larger symbol constellations.
Innovation Solution
An apparatus and method for measuring and compensating I/Q imbalances at the optical output of an optical data modulator without a remote coherent optical receiver, using an optical source, data modulator, and receiver to alternately measure and adjust the phase and amplitude of the components during calibration, allowing for simpler digital processing and improved data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital compensation of I/Q imbalance is performed at the coherent optical receiver via DSP processing, then I/Q imbalance can be compensated, but the digital processing complexity increases and measurement precision is affected by receiver-induced imbalances
Solution Approach 1:
The patent performs I/Q imbalance measurement and compensation at the transmitter before optical signal transmission, rather than compensating at the receiver after transmission. The transmitter measures the I/Q imbalance characteristics of its own modulator using training sequences and performs digital compensation on the transmitted signal in advance, eliminating the need for complex receiver-side compensation and avoiding receiver-induced measurement errors.
2Measurement precision
If I/Q imbalance measurement is performed at a remote coherent optical receiver, then measurement can be conducted, but measurement precision is degraded by I/Q imbalances produced in the receiver itself
Solution Approach 1:
The patent extracts the I/Q imbalance measurement function from the remote coherent optical receiver and relocates it to the optical transmitter. By measuring the I/Q imbalance characteristics at the transmitter using a local receiver and training sequences, the system eliminates the harmful effect of receiver-induced I/Q imbalances on measurement precision.
3Productivity
If coherent optical communication operates at higher symbol rates and larger symbol constellations, then data transmission capacity increases, but I/Q imbalances worsen and affect data transmission accuracy
Solution Approach 1:
The patent performs I/Q imbalance measurement and compensation before high-rate data transmission by using training sequences transmitted in dedicated time slots. The transmitter measures its own I/Q imbalance characteristics and applies digital compensation to the data signal, enabling accurate transmission at higher symbol rates and larger constellations without being limited by I/Q imbalance degradation.
Data Source
AI summary
An apparatus includes an optical source of an optical wavelength carrier, an optical modulator to receive the optical wavelength carrier, and an optical data receiver. The optical data modulator is configured to produce, from the optical wavelength carrier, an optical signal to carry separate data on different first and second components thereof in individual modulation periods during data transmission and to carry a training sequence on one of the components during time slots for calibration. The first component is relatively phase offset from the second component in the optical signal. The optical data modulator alternates the one of the components between the first and second components over the time slots for calibration. The optical receiver is connected to receive a portion of the optical signal and to temporally interleave a measurement of a characteristic of the first component and a measurement of a characteristic of the second component over the time slots for calibration. The optical receiver is configured to feedback information to the optical data modulator based on the measured characteristics. The optical data modulator is configured to reduce an imbalance between the two components of the optical carrier during data transmission based on the information.