Optical Receiver ISI Compensation via FSR Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optical systems with differential encoding face significant challenges in reducing intersymbol interference (ISI) caused by filters, which distort signals and increase bit error ratios, affecting the accuracy of data detection in receivers.
Innovation Solution
An optical receiver with a signal processor that includes a delay line interferometer (DLI), a free spectral range (FSR) phase controller, and a gain imbalancer, which adjusts the transit time difference and gain between signal paths to control constructive and destructive transfer functions, optimizing the FSR bandwidth and phase to minimize ISI distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filters are used in optical systems, then signal processing is enabled, but intersymbol interference (ISI) is induced causing signal distortion and increased bit error ratios
Solution Approach 1:
The patent applies differential encoding (DPSK modulation) to convert the harmful effect of ISI into a beneficial differentiating mechanism. By encoding data as phase differences between consecutive symbols rather than absolute phases, the system exploits the ISI-induced signal variations to enhance rather than degrade detection accuracy, effectively transforming the harmful interference into a useful signal characteristic
Solution Approach 2:
The patent changes the detection parameter from absolute phase detection to differential phase detection. By measuring the phase difference between consecutive symbols rather than the absolute phase, the system adapts to the distorted signal conditions caused by filters and ISI, maintaining reliable detection despite signal degradation
2Reliability
If differential encoding is used, then signal robustness is improved, but complexity of the receiver increases due to additional processing requirements
Solution Approach 1:
The patent replaces complex electronic differential detection circuits with an optical domain solution using a delay line interferometer. The interferometer performs the differential detection function optically by interfering the current symbol with the previous symbol, eliminating the need for complex electronic processing and reducing receiver complexity while maintaining signal robustness
3Measurement precision
If delay line interferometer is used for differential decoding, then decoding accuracy is improved, but device complexity increases due to additional components
Solution Approach 1:
The patent merges the delay line interferometer with the detection architecture by integrating it directly into the receiver signal path. This consolidation allows the interferometer to perform both the differential decoding and the signal detection functions in a unified structure, reducing overall system complexity while maintaining high decoding accuracy through optical interference
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
This solution effectively reduces ISI distortion, improving signal quality and reducing bit error ratios by optimizing the transfer functions relative to the carrier frequency, thereby enhancing the accuracy of data detection in optical receivers.
Implementation Method 1
The interferometer has an input port for receiving the optical signal and two output ports—a constructive output port for issuing the waves that add and a destructive output for issuing the waves that tend to cancel
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.