Coherent Optical Receiver Compensation for 16QAM Constellation Distortion
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Solution Overview
Problem
Existing coherent optical reception systems face challenges in compensating for constellation distortion, particularly when the characteristics of the optical modulator cannot be measured in advance or when they change over time, leading to difficulties in compensating for variations in bias voltage and imperfections caused by errors in the automatic bias control circuit.
Innovation Solution
A coherent optical reception device is designed with a local oscillation laser, a coherent optical reception front-end unit, an analog-to-digital converter, a compensation unit for dispersion, a constellation distortion compensation unit that includes DC offset and IQ crosstalk compensation, and an error correction decoding unit, enabling adaptive compensation for constellation distortion on the reception side without requiring prior measurement of the optical modulator characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If incoherent light sources (LEDs, VCSELs) are used for optical communication, then device complexity and cost are reduced, but spatial coherence is lost causing signal degradation over distance
Solution Approach 1:
The patent introduces a spatial light modulator (SLM) as an intermediary device between the incoherent light source and the optical fiber. The SLM spatially modulates the incoherent light to generate coherent light signals, enabling long-distance transmission while maintaining the simplicity of using incoherent light sources like LEDs or VCSELs.
2Reliability
If coherent light sources (lasers) are used, then spatial coherence is maintained for long-distance transmission, but device complexity and cost increase
Solution Approach 1:
The patent changes the spatial parameters of incoherent light through the spatial light modulator, transforming it into coherent light without requiring complex coherent light sources. This parameter transformation approach achieves laser-like coherence properties using simpler incoherent light sources.
3Device complexity
If incoherent light is transmitted without spatial modulation, then device complexity is minimized, but transmission distance is limited to short ranges
Solution Approach 1:
The patent applies preliminary spatial modulation to the incoherent light before transmission using the SLM. This preliminary action of spatially modulating the light creates coherent light signals that can maintain signal quality over long transmission distances, preventing signal degradation before it occurs.
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 compensates for constellation distortion, reducing bit error rates and improving data transfer reliability even with multi-level modulation schemes like 16QAM, and can adapt to gradual changes in constellation distortion over time, particularly excelling in 16QAM or higher multi-level modulation.
Implementation Method 1
spatially modulating the incoherent light with a spatial light modulator to generate coherent light signals
Implementation Method 2
coherent light-receiving device that receives coherent light signals from an optical fiber
Data Source
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AI summary
A coherent optical reception device includes a local oscillation laser that supplies laser light, a coherent optical reception front-end unit that receives a multi-level modulated optical signal, demodulates the optical signal on the basis of the laser light, and converts a demodulated optical signal into an electrical analog signal, an analog-to-digital converter that converts the analog signal into a digital signal, a compensation unit that compensates for an influence of dispersion due to a wavelength or a polarized wave of the optical signal and recovers a carrier phase of the digital signal, a constellation distortion compensation unit that compensates for constellation distortion of the multi-level modulation included in the digital signal in which an influence of dispersion is compensated for by the compensation unit, and an error correction decoding unit that performs error correction of the digital signal in which the constellation distortion is compensated for.