Multi-bandwidth Carrier Phase Estimator for Cycle Slip Reduction
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Solution Overview
Problem
Cycle slip, characterized by undesired rotation of the received symbol constellation in coherent optical communication systems, occurs due to increased bandwidth of the carrier phase estimator, laser phase-noise, and noise from Amplified Spontaneous Emission (ASE) and Cross Phase Modulation (XPM), hindering effective forward error correction decoding.
Innovation Solution
A multi-bandwidth carrier phase estimator is employed, performing parallel first and second carrier phase estimation operations to track fast and slow phase variations, with a difference computation and low-pass filtering to detect and correct cycle slips by applying phase rotations when the difference exceeds a threshold, thereby reducing cycle slip occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bandwidth of the carrier phase estimator function is increased to track fast phase variations, then the tracking speed is improved, but the cycle slip rate increases
Solution Approach 1:
The patent divides the single carrier phase estimation function into two separate functions with different bandwidths: a first carrier phase estimation function with higher bandwidth for tracking fast phase variations, and a second carrier phase estimation function with lower bandwidth for tracking slow phase variations. This segmentation allows each function to operate optimally within its designated bandwidth range, resolving the contradiction between tracking speed and cycle slip rate.
2Power
If laser phase-noise is increased at the transmitter, then the transmission power is improved, but the cycle slip rate increases
Solution Approach 1:
The dual-stage carrier phase estimation approach segments the phase noise compensation task into two stages: the first stage handles fast phase variations with higher bandwidth, and the second stage handles slow phase variations with lower bandwidth. This segmentation enables effective compensation of laser phase-noise even at higher power levels, maintaining reliability while allowing improved transmission power.
3Power
If Amplified Spontaneous Emission (ASE) noise is increased, then the signal amplification is improved, but the cycle slip rate increases
Solution Approach 1:
The patent employs a feedback mechanism where the output of the second carrier phase estimation function (with lower bandwidth) is used to correct the output of the first carrier phase estimation function. This feedback loop allows the system to detect and correct cycle slips that occur in the first stage, maintaining reliability even when signal amplification and associated ASE noise are increased.
4Productivity
If Cross Phase Modulation (XPM) noise is increased, then the channel capacity is improved, but the cycle slip rate increases
Solution Approach 1:
The dual-stage carrier phase estimation function segments the noise handling process: the first stage with higher bandwidth addresses fast phase variations including XPM noise effects, while the second stage with lower bandwidth provides refined phase estimation. This segmentation enables the system to maintain reliability in high-capacity channels where XPM noise is present.
Data Source
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AI summary
Carrier phase estimation techniques are provided for processing a received optical signal having a carrier modulated according to a modulation scheme. First and second carrier phase estimation operations are performed on a digital signal derived from an optical carrier obtained from the received optical signal using coherent optical reception. The first carrier phase estimation operation tracks relatively fast phase variations of the optical carrier of the received optical signal to produce a first carrier phase estimation and the second carrier phase estimation operation tracks relatively slow phase variations of the optical carrier of the received optical signal to produce a second carrier phase estimation. A difference between the first and second carrier phase estimations is computed. Occurrence of a cycle slip is determined when the difference is greater than a threshold. A correction is applied to the first carrier phase estimation when the low pass filtered difference exceeds the threshold.