Optical Receiver FSR Phase Compensation for ISI Mitigation
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Solution Overview
Problem
Intersymbol interference (ISI) in optical systems with differentially encoded phase shift keyed receivers causes signal distortion and reduces decision quality, leading to increased bit error ratios, which existing technologies fail to adequately mitigate by relying on a fixed delay difference equal to the symbol time.
Innovation Solution
An optical receiver with a signal processor that includes a delay line interferometer, a free spectral range (FSR) phase controller, and a gain imbalancer, allowing for adjustable FSR and gain settings to control constructive and destructive transfer functions, thereby reducing ISI distortion and optimizing signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed delay difference equal to the symbol time is used in the DLI, then the FSR is maximized and the demodulated signals at constructive and destructive outputs are maximized, but ISI distortion occurs and decision quality deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of the delay difference between the two arms of the DLI, transitioning from a fixed delay equal to symbol time to a variable delay that can be optimized in real-time. The delay is adjusted based on measured signal characteristics (such as FSR phase) to dynamically compensate for ISI distortion while maintaining adequate FSR, thereby resolving the contradiction between maximizing signal strength and minimizing distortion
Solution Approach 2:
The patent changes the critical parameter of delay difference from a fixed value (symbol time) to an adjustable parameter. By modifying this parameter based on measured FSR phase and signal characteristics, the system optimizes the balance between FSR magnitude and ISI reduction, improving decision quality without sacrificing signal strength
2Object-affected harmful factors
If the delay difference is adjusted to reduce ISI, then ISI distortion is reduced, but the FSR decreases and the difference between constructive and destructive output signals is reduced
Solution Approach 1:
The patent employs feedback mechanisms where the FSR phase is measured from the received signal, and this measurement is used to adjust the delay difference in the DLI. The system continuously monitors signal characteristics and adjusts the delay parameter to maintain optimal performance, ensuring that ISI reduction does not come at the cost of excessive FSR degradation or signal strength loss
3Device complexity
If a DLI with delay difference equal to symbol time is used, then the system structure is simple and fixed, but the system cannot adapt to varying signal conditions and ISI varies
Solution Approach 1:
The patent transforms the static DLI structure into a dynamic system where the delay difference can be adjusted based on signal conditions. This is achieved by adding control mechanisms that measure FSR phase and automatically adjust the delay parameter, enabling the system to adapt to varying signal conditions without fundamentally redesigning the overall DLI architecture
Solution Approach 2:
The patent introduces adjustability to the delay parameter while maintaining the fundamental DLI structure. By allowing the delay difference to vary based on measured signal characteristics rather than being fixed at symbol time, the system gains adaptability to different signal conditions while preserving the core interferometer design
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces ISI distortion, improving signal quality and minimizing bit error ratios by dynamically adjusting the FSR and gain settings relative to the carrier frequency, even when the delay difference is not equal to the symbol time, thus enhancing the performance of differentially encoded phase shift keyed modulation systems.
Implementation Method 1
The interferometer works on the principle that two waves that coincide with the same phase will add to each other while two waves that have opposite phases will tend to cancel each other
Data Source
AI summary
An optical receiver apparatus and methods for mitigating intersymbol interference (ISI) in a differentially-encoded modulation transmission system by controlling constructive and destructive transfer functions. The receiver includes a bandwidth control element for controlling transfer function bandwidth, a transfer phase controller for controlling transfer function phase and/or an imbalancer for imbalancing the transfer functions for compensating for intersymbol interference and optimizing the quality of the received optical signal.