Pilot Tone Modulation by Data Bias in Optical Transmitters
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Solution Overview
Problem
Existing optical communication systems face challenges in efficiently implementing pilot tone modulation, particularly in dense wavelength division multiplexing (DWDM) systems, due to increased complexity and cost associated with hardware requirements and calibration needs for internal data drivers and external variable optical attenuators, which hinder effective power monitoring and higher frequency modulation.
Innovation Solution
The implementation of pilot tone modulation by data bias, where bias bits are inserted into optical signals to carry channel identification information and facilitate power monitoring, eliminating the need for additional hardware and calibration through accurate modulation depth control, and allowing for lower-cost and simplified system integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pilot tone modulation is added through data drivers, then wavelength identification and power monitoring are facilitated, but additional hardware is required and system complexity increases due to feedback control and calibration needs
Solution Approach 1:
The data driver itself generates the pilot tone modulation by varying its driving amplitude based on data patterns, eliminating the need for separate pilot tone generation hardware. The driver serves both its primary data modulation function and the additional pilot tone function, reducing overall system complexity while maintaining power monitoring capability
Solution Approach 2:
The data driver is designed to perform multiple functions: primary data signal modulation and pilot tone modulation for wavelength identification and power monitoring. By making the data driver universal, the patent eliminates the need for dedicated pilot tone hardware, reducing system complexity while maintaining all required functions
2Reliability
If pilot tone modulation is added through external variable optical attenuators (VOAs), then power monitoring is enabled, but cost increases and achieving higher frequency modulation becomes difficult
Solution Approach 1:
The patent extracts the pilot tone modulation function from external VOAs and relocates it to the data driver's amplitude control capability. This removes the need for expensive external VOA hardware while maintaining the power monitoring function through the same amplitude variation mechanism that the data driver already possesses
3Adaptability or versatility
If additional hardware is used for pilot tone modulation, then modulation function is achieved, but cost increases
Solution Approach 1:
The patent merges the pilot tone modulation function with the data driver's existing amplitude control functionality. Instead of combining separate hardware components, the solution integrates both modulation functions within the single data driver, eliminating redundant hardware and reducing cost while maintaining full modulation capability
Data Source
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AI summary
Embodiments are provided for applying pilot tone modulations to optical signals by introducing bias bits to data frames carried on the optical signals. Since the modulation is done by modifying data, the modulation depth is accurate, and there is no need for calibration or feedback control, which can improve power monitoring accuracy and simplify implementation. In an embodiment, a transmitter determines a period of a pilot tone modulation for tracking or identifying an optical channel. The transmitter inserts a sequence of bias bits, periodically according to the determined period, in a plurality of frames comprising original data bits. The amplitudes of the optical signals carrying the frames are modulated at a higher frequency than the pilot tone modulation. The optical signals are then transmitted including the bias bits within the frames.