Coherent Receiver Frequency Offset Compensation Without Wavelength Lockers
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Solution Overview
Problem
Conventional coherent optical communication systems require expensive wavelength lockers for frequency stability, making them costly and unsuitable for metropolitan or access domain applications, and existing DSPs cannot compensate for the large frequency offsets when using low-cost lasers without wavelength lockers.
Innovation Solution
A coherent receiver system with a frequency offset estimation unit and compensation unit that uses photoelectric detectors and an etalon to measure and adjust the frequency offset between signal and local oscillator lights, allowing for compensation without wavelength lockers, thereby reducing system costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wavelength lockers are used in lasers to ensure frequency stability, then frequency offset control is improved, but system cost increases
Solution Approach 1:
The patent extracts the frequency stabilization function from the expensive wavelength locker component and relocates it to the DSP through digital signal processing. The wavelength locker is removed from the laser assembly, and its frequency control function is implemented algorithmically in the digital domain, thereby reducing hardware complexity and cost while maintaining frequency offset control capability
Solution Approach 2:
The patent replaces the optical/mechanical wavelength locker system with a digital electronic system. Instead of using optical feedback mechanisms and mechanical tuning elements in a wavelength locker, the frequency control is achieved through digital algorithms in the DSP that process the optical signals electronically, substituting a complex optical-mechanical system with a simpler digital system
2Device complexity
If low-cost lasers without wavelength lockers are used, then system cost is reduced, but frequency offset compensation capability deteriorates
Solution Approach 1:
The patent introduces an intermediary frequency offset estimation and compensation mechanism between the low-cost lasers and the DSP. This intermediary layer measures the frequency offset between signal and local oscillator lights and provides compensation control signals to adjust the local oscillator laser frequency, enabling the use of inexpensive lasers while maintaining acceptable frequency offset compensation through the intermediary control system
Solution Approach 2:
The patent implements a feedback control system where the frequency offset is continuously estimated by comparing signal light and local oscillator light characteristics, and the compensation amount is adjusted based on the estimated offset. This closed-loop feedback mechanism enables low-cost lasers to achieve acceptable frequency stability through active digital compensation rather than passive hardware stabilization
3Device complexity
If DSP compensation capability is limited to +/â5 GHz, then device complexity is constrained, but adaptability to different laser types deteriorates
Solution Approach 1:
The patent applies preliminary frequency offset compensation before the main DSP processing. By estimating and compensating for the majority of the frequency offset in advance using the dedicated frequency offset compensation unit, the remaining offset that requires DSP compensation is reduced to within the +/â5 GHz capability range, enabling compatibility with low-cost lasers that have larger initial frequency deviations
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
Enables frequency offset estimation and compensation within the coherent system, reducing costs by using low-cost lasers while maintaining system performance, as the frequency offset value is adjusted to meet the system requirements, aligning with the DSP's compensation capability.
Implementation Method 1
receive signal light, wherein the signal light is received by a first photoelectric detector after passing through an etalon
Implementation Method 2
a first current intensity value is obtained; the signal light is received by a second photoelectric detector, and a second current intensity value is obtained
Data Source
AI summary
Embodiments of the present disclosure disclose a coherent receiver, including: a frequency offset estimation unit and a frequency offset compensation unit, where the frequency offset estimation unit is configured to receive signal light and local oscillator light, where the signal light is received by a first photoelectric detector, and a first intensity value is obtained, the signal light is received by a second photoelectric detector, and a second intensity value is obtained, the local oscillator light is received by a third photoelectric detector, and a third intensity value is obtained, and the local oscillator light is received by a fourth photoelectric detector, and a fourth intensity value is obtained; and the frequency offset compensation unit is configured to obtain a frequency offset value between the signal light and the local oscillator light according to a difference between a first ratio and a second ratio.