DSBSC Optical Demodulation with Costas Loop for Phase Noise Reduction
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Solution Overview
Problem
Coherent low data rate laser communication systems between satellites are limited by laser phase noise, which affects the accuracy of Doppler frequency shift tracking.
Innovation Solution
The use of double sideband suppressed carrier (DSBSC) modulation and demodulation, combined with a Costas loop circuit, to reduce phase noise and improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional laser communication systems are used, then communication functionality is achieved, but laser phase noise limits tracking accuracy
Solution Approach 1:
The patent extracts and removes the carrier component from the optical signal, using DSBSC modulation to suppress the carrier and retain only the sidebands. This extraction of the problematic carrier element eliminates the source of phase noise while preserving the information-carrying sidebands, directly resolving the contradiction between tracking accuracy and phase noise
Solution Approach 2:
The patent changes the modulation parameter by transitioning from conventional modulation schemes to DSBSC modulation with suppressed carrier. This parameter change in the signal structure fundamentally alters the phase characteristics, eliminating phase noise flaring while maintaining the Doppler frequency shift information needed for accurate tracking
2Reliability
If DSBSC modulation with Costas loop is used, then phase noise is reduced, but device complexity increases
Solution Approach 1:
The patent employs a Costas loop feedback mechanism that automatically tracks and compensates for residual phase variations. The feedback loop continuously adjusts the local oscillator phase to match the incoming signal, providing automatic phase error correction that maintains signal quality without requiring complex manual intervention or additional hardware
Data Source
AI summary
A method for operating an optical demodulator includes receiving a double sideband suppressed carrier (“DSBSC”) optical signal. The method further includes passing the DSBSC optical signal through a Costas loop circuit. The method further includes outputting a radio frequency (“RF”) signal from a quadrature port of the Costas loop circuit.