Polarization Calibration for Multichannel Optical Transport Networks
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Solution Overview
Problem
High-speed optical signal transmission in OTN protocols faces challenges due to polarization errors introduced during transmission, making it difficult to recover serial streams from parallel streams, especially with complex envelope signals like QPSK, where the state of polarization at the receiver differs from the transmitter.
Innovation Solution
A method and system for calibrating orthogonal polarity in a multichannel OTN receiver by separating and controlling polarization ambiguity, applying transformations to Ix, Qx, Iy, and Qy signals to adjust their magnitudes and phases, and using training and Forward Error Correction (FEC) to resolve potential ambiguities, allowing complex envelope signals to be restored to their original form.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polarization multiplexing is used to increase bandwidth efficiency, then the data rate is improved, but polarization errors are introduced making signal recovery difficult
Solution Approach 1:
The patent applies preliminary action by introducing training sequences before the actual data transmission. These training sequences allow the receiver to estimate and compensate for polarization rotation effects before decoding the actual signal, thereby maintaining signal recovery accuracy while utilizing polarization multiplexing for high data rates
Solution Approach 2:
The patent implements feedback mechanisms where the receiver monitors signal quality and uses this information to adjust polarization compensation parameters. This closed-loop approach enables continuous optimization of polarization alignment, resolving the contradiction between high data rate transmission and accurate signal recovery
2Productivity
If complex envelope signals like QPSK are used to increase bandwidth efficiency, then the data rate is improved, but polarization ambiguity and errors increase
Solution Approach 1:
Training sequences are transmitted beforehand to establish accurate polarization state information before the complex envelope signals are decoded. This preliminary calibration enables precise measurement of polarization states even when using bandwidth-efficient modulations like QPSK
Solution Approach 2:
The patent dynamically adjusts polarization compensation parameters based on received signal characteristics. By continuously adapting these parameters, the system maintains high polarization state accuracy while utilizing complex envelope signals for maximum bandwidth efficiency
3Reliability
If polarization adjustment is performed in the optical domain prior to photodiode detection, then polarization errors are minimized, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary processing stage that bridges optical and electrical domains. This intermediary layer performs polarization compensation using electrical signal processing techniques, achieving polarization error minimization without requiring complex optical adjustment mechanisms, thus balancing reliability improvement with device complexity control
Data Source
AI summary
A system and method are provided for calibrating orthogonal polarity in a multichannel optical transport network (OTN) receiver. The method accepts a composite signal and separates the polarization of the signal into a pair of 2n-phase shift keying (2n-PSK) modulated input signals via Ix and Qx optical signal paths, where n≧1. Likewise, a pair of 2p-PSK modulated input signals are accepted via Iy and Qy optical signal paths where p≧1. Polarization-adjusted I′x, Q′x, I′y, and Q′y signals are generated. An average magnitude is compared to either 2×the absolute magnitude of (I′x and Q′x), or 2×the absolute magnitude of (I′y and Q′y). The average magnitude value can be used that is either 2×(a predetermined peak signal amplitude), or the sum of the absolute magnitudes of (I′x and Q′x) and (I′y and Q′y). The polarization-adjusted I′x, Q′x, I′y, and Q′y signals are modified until the magnitude comparison is about zero.