Optical IQ Modulator Imbalance Estimation via Phase Retrieval
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Solution Overview
Problem
Existing optical modulator evaluation systems face challenges in estimating frequency-dependent IQ imbalance and bias shift, particularly in high-order multi-level modulation schemes, due to the complexity and cost of existing monitoring techniques, and the limitations of current methods in integrating with transceivers and supporting in-service monitoring.
Innovation Solution
A system and method that formulate the estimation of IQ imbalance between in-phase and quadrature channels as a phase retrieval problem, using a simple optical power detector and analog-digital converter, allowing for the estimation of frequency-dependent IQ imbalance and bias shift without requiring an expensive coherent receiver, enabling integration into transceivers and in-service monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical coherent receiver is used to evaluate IQ imbalance, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts only the necessary intensity information measurement function from the complex coherent receiver system. By using a simple photodetector to measure only the intensity of optical signals rather than full coherent detection, the system achieves sufficient IQ imbalance estimation accuracy without requiring the complex local oscillator and phase detection hardware of a coherent receiver.
Solution Approach 2:
The patent replaces expensive, complex coherent receiver hardware with a simple, low-cost photodetector and digital signal processing system. This substitution uses inexpensive components that can be easily integrated into transceivers, making the solution economically viable for deployment.
2Measurement precision
If a coherent receiver is deployed close to the modulator for monitoring, then measurement precision is improved, but ease of operation and integration are worsened
Solution Approach 1:
The patent creates a universal monitoring solution using a simple photodetector that can be integrated into various transceiver configurations without requiring dedicated coherent receiver hardware. This multi-functional approach allows the same simple detector to evaluate different modulator types and operating conditions, facilitating easy integration into existing transceiver systems.
3Measurement precision
If existing monitoring methods are used, then measurement precision is improved, but adaptability to frequency-dependent IQ imbalance is worsened
Solution Approach 1:
The patent implements dynamic adaptation by using digital signal processing algorithms that can adjust to different frequency characteristics of IQ imbalance. The system processes intensity measurements across multiple frequencies and adaptively estimates frequency-dependent imbalance parameters, allowing the monitoring solution to handle varying imbalance characteristics without hardware changes.
Data Source
AI summary
A system for estimating an imbalance between electrical-optical responses of an in-phase (I) channel and a quadrature (Q) channel in an optical amplitude and phase modulator (optical IQ modulator) includes an optical detector (PD), an analog-digital converter (ADC), and an imbalance operation unit that estimates an imbalance between electrical-optical responses of an I channel and a Q channel in the optical IQ modulator, wherein the imbalance operation unit includes an input signal information receiving unit that receives information regarding a first modulation signal, and an intensity information receiving unit that receives intensity information of the digitalized output signal from the ADC, and the imbalance operation unit estimates an imbalance between electrical-optical responses of an I channel and a Q channel in the optical IQ modulator using information regarding a first modulation signal and intensity information of the digitalized output signal.