Optical Modulation Unit Timing Adjuster for Polarization Multiplexing
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Solution Overview
Problem
Existing optical modulation units using polarization multiplexing face challenges in addressing large timing differences between polarized waves, which degrade signal properties, particularly in DP-QPSK and DP-16QAM modulation schemes, as described in Japanese Patent Applications Laid-Open No. 2011-044906 and No. 2015-052670.
Innovation Solution
An optical modulation unit comprising a data generator, timing adjuster, optical modulators, phase adjusters, synthesizers, and a peak detection circuit, which generates test-data streams with repeated 2N-bit marks and spaces to adjust timing differences between polarized waves, allowing for the synthesis of orthogonal or co-polarized waves to maximize intensity peaks and effectively address timing differences up to nearly N bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a timing adjuster is used to reduce timing difference between polarized waves, then signal properties are improved, but the device complexity increases
Solution Approach 1:
The patent extracts the timing adjustment function from the main modulation path by using a separate timing adjuster that processes data streams before they enter the modulators. This allows timing synchronization to be handled independently, improving signal properties without fundamentally changing the core modulation architecture.
Solution Approach 2:
The timing adjuster performs timing alignment preliminarily before the data streams are modulated and combined. By adjusting the timing of data streams in advance (shifting bits in the data stream), the system ensures proper synchronization is established before the complex modulation process begins, preventing timing differences from degrading signal properties.
2Loss of time
If the intensity of synthesized output is detected to control timing, then timing difference is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent implements a feedback mechanism where the intensity of the synthesized optical output is detected and used to control the timing adjuster. The system continuously monitors the output intensity and adjusts the timing of data streams accordingly, creating a closed-loop control system that automatically optimizes timing alignment without requiring manual calibration or high manufacturing precision.
3Productivity
If polarization multiplexing is used to modulate light with multiple data streams, then productivity is improved, but timing synchronization becomes more difficult
Solution Approach 1:
The patent segments the modulation process by separating the handling of different polarized waves into distinct modulation units. Each polarized wave (X and Y polarization) is modulated independently with its own data streams, allowing timing adjustment to be applied separately to each stream before combination. This segmentation makes timing synchronization more manageable despite the increased productivity from parallel data transmission.
Data Source
AI summary
A timing adjuster shifts a timing between a first data-stream group and a second data-stream group in accordance with a timing setting. A data generator in first test mode generates a first test-data stream repeating 2N-bit marks and 2N-bit spaces as each of a first data stream and a third data stream, and generates a second test-data stream that is N-bit shifted from the first test-data stream, where N denotes a natural number. A first phase-difference setting and a second phase-difference setting are rendered zero. The timing adjuster adjusts the timing setting so as to maximize a detected value from a peak detection circuit.