Digital Delay Interferometer Phase Compensation for Coherent Optical Receivers
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Solution Overview
Problem
Optical communication systems face challenges in compensating for phase noise and frequency offset in coherent detection, particularly with high baud rates and expensive low phase noise oscillator lasers, which limits system performance and increases costs.
Innovation Solution
A method and system that uses a digital delay interferometer with adaptive equalization and phase distortion compensation to handle phase noise without carrier phase recovery, enabling the use of less expensive local oscillator lasers by tracking and compensating for local oscillator frequency offset through a phase de-rotation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent detection with carrier phase recovery (CPR) is used to recover amplitude and phase information, then measurement precision of the received signal is improved, but device complexity increases and CPR bandwidth is limited by hardware feasibility
Solution Approach 1:
The patent extracts the CPR function from the coherent detection system and replaces it with a digital delay interferometer (DDI) that performs differential decoding. This removes the complex hardware-based CPR module while maintaining phase information recovery through digital signal processing, directly resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent replaces the hardware-based CPR mechanism with a software/digital-based differential decoding approach using DDI. This substitution of mechanical/hardware systems with digital processing systems eliminates bandwidth limitations and implementation complexity while preserving phase detection capability
2Reliability
If conventional CPR (feed forward or backward) is used to compensate for phase distortion, then phase noise compensation is provided, but the bandwidth is insufficient to handle high phase noise with wide bandwidth
Solution Approach 1:
The patent implements a dynamic phase compensation mechanism where the DDI continuously adapts to phase variations through digital signal processing. The system dynamically tracks and compensates for phase noise without being constrained by fixed hardware bandwidth, enabling effective compensation of high phase noise with wide bandwidth
3Measurement precision
If low phase noise oscillator lasers are used to reduce laser phase noise and frequency offset, then measurement precision is improved, but system cost increases significantly
Solution Approach 1:
The patent enables the use of inexpensive, higher phase noise oscillator lasers by compensating for their deficiencies through digital signal processing. The DDI and differential decoding technique effectively remove the need for expensive low phase noise lasers, dramatically reducing system cost while maintaining acceptable performance
Solution Approach 2:
The patent converts the harmful effect of high phase noise from inexpensive lasers into a manageable parameter through digital compensation. Rather than requiring perfect hardware, the system uses software-based phase tracking to compensate for laser imperfections, turning a disadvantage into an acceptable trade-off that reduces cost
Data Source
AI summary
An optical signal receiver tracks local oscillator frequency offset (LOFO) and compensates for the phase distortion introduced in the received signals as a result of utilizing the local oscillator within a coherent detection scheme. This phase distortion is basically a constant phase rotation caused by the LOFO and implementation of the receiver using coherent detection and a digital interferometer instead of a conventional (yet complex) carrier phase estimation or recovery scheme. With an optical receiver implemented in this manner, the requirement of using a precise local oscillator laser with low frequency offset is less important.