Digital Coherent Optical Receiver Distortion Mitigation
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Solution Overview
Problem
Single-ended photo-detection in digital coherent optical receivers suffers from high local-oscillator-to-signal power ratio (LOSPR) leading to distortion and increased relative intensity noise, which degrades performance in chromatic dispersion compensation, polarization recovery, and polarization mode dispersion compensation.
Innovation Solution
A novel digital signal processing (DSP) algorithm is employed to estimate and subtract time-dependent random variables introducing distortion in the coherent detection process, reducing the LOSPR and mitigating distortion in the received signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-ended photo-detection is used in digital coherent optical receivers, then device complexity is reduced, but distortion increases due to high local-oscillator-to-signal power ratio
Solution Approach 1:
The patent converts the harmful effect of high LOSPR-induced distortion into a beneficial outcome by using digital signal processing to estimate and subtract the distortion from the received signal. The distortion that would normally degrade performance is instead calculated and removed, allowing single-ended detection to achieve performance comparable to balanced detection systems.
Solution Approach 2:
The patent introduces digital signal processing as an intermediary between the photo-detection stage and the final signal output. This intermediary processes the distorted signal by estimating the distortion component based on known system parameters and subtracting it, thereby mediating between the simple single-ended detection structure and the requirement for low-distortion signal recovery.
2Measurement precision
If high local-oscillator-to-signal power ratio is used in single-ended photo-detection, then detection sensitivity is improved, but relative intensity noise increases and degrades performance
Solution Approach 1:
The patent converts the harmful relative intensity noise into a manageable parameter by modeling its statistical characteristics and using digital signal processing to mitigate its effects. The high LOSPR that generates the noise is maintained for sensitivity, while the resulting noise is processed and reduced through estimation and subtraction techniques.
Solution Approach 2:
The patent implements a feedback mechanism where the received signal is processed to estimate the distortion and noise components, which are then subtracted from the original signal. This feedback loop continuously refines the signal quality by removing the harmful effects of high LOSPR, allowing the system to maintain both high sensitivity and low noise.
3Ease of manufacture
If single-ended photo-detection is used instead of balanced detection, then ease of manufacture is improved, but performance in chromatic dispersion compensation and polarization recovery deteriorates
Solution Approach 1:
The patent converts the performance deficiency of single-ended detection into an advantage by using the simplified structure to reduce manufacturing complexity while compensating for performance losses through digital signal processing. The distortion that would normally harm performance is instead calculated and removed, making the simpler single-ended design perform as well as or better than complex balanced detection systems.
Solution Approach 2:
The patent replaces the mechanical/optical complexity of balanced detection with digital signal processing operations. Instead of using complex optical hardware to achieve performance, the system uses computational methods to estimate and subtract distortion, substituting mechanical simplicity with digital sophistication.
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 DSP algorithm significantly reduces the LOSPR, easing receiver design constraints and minimizing the impact of local oscillator intensity noise, allowing for improved performance comparable to balanced detection systems.
Implementation Method 1
Coherent detection treats optical signals in a manner analogous to RF, with response to the amplitude and phase of each wavelength. In coherent detection, an incoming optical signal is mixed with light from a local oscillator source. When the combined signals are detected by a photo-detector, the photocurrent contains a component at a frequency that is the difference between the signal frequency and the local oscillator frequency.
Implementation Method 2
A receiver employs a photo-detector that converts the light into electric current.
Data Source
AI summary
A method and system for mitigating distortion in coherent single-ended photo-detection is disclosed. The methodology comprises: receiving an optical signal carried on an optical transmission medium and coherently detecting the received optical signal to produce a digitized signal; estimating a time-dependent random variable introducing distortion to the coherently detected signal; and subtracting the distortion from digitized signal to produce a distortion mitigated output signal.