Optical Transmitter Linearity Control via Dynamic Gain Adjustment
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Solution Overview
Problem
In high-speed long-distance optical transmission, the quality of optical signals deteriorates due to changes in the output of the DAC and gain of the driving circuit over time, influenced by temperature and power supply voltage, leading to decreased noise immunity and non-linearity in the input-output characteristic of optical modulators.
Innovation Solution
An optical transmitter system that includes a processor for rotating the polarization state or phase of the optical output signal, a digital-to-analog converter, a driving circuit, and a monitoring control circuit to adjust the output of the DAC and gain of the driving circuit based on monitored optical output power, using a rotation dither to maintain linearity and suppress noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the output of the DAC and gain of the driving circuit are increased to improve optical signal output power, then the optical signal transmission distance is extended, but the input-output characteristic of the optical modulator enters a nonlinear range causing signal distortion
Solution Approach 1:
The patent implements dynamic adjustment of DAC output and driving circuit gain during operation based on real-time monitoring of optical output power. The system continuously adapts the operating point to maintain linearity while maximizing output power, transitioning from a static fixed-gain design to a dynamic adaptive system that responds to environmental changes and component aging.
Solution Approach 2:
The patent introduces a feedback mechanism where the optical output power is monitored and used to adjust the DAC output and driving circuit gain. This closed-loop control ensures that the system operates within the linear range of the optical modulator while maintaining maximum output power, preventing signal distortion caused by nonlinear operation.
2Manufacturing precision
If the optical transmitter operates with a margin in the linear range to maintain signal quality, then the input-output characteristic linearity is preserved, but the optical signal output power decreases and noise immunity deteriorates
Solution Approach 1:
The system dynamically adjusts the operating point rather than maintaining a fixed conservative margin. By continuously monitoring optical output power and adapting the DAC output and driving circuit gain, the system can operate closer to the optimal point on the linear range boundary, maximizing output power while maintaining acceptable linearity and noise immunity.
Solution Approach 2:
The patent changes the operating parameters (DAC output level and driving circuit gain) based on monitored optical output power. This allows the system to optimize the balance between output power and linearity by adjusting parameters in real-time, rather than being constrained by a fixed design margin.
3Device complexity
If the gain of the driving circuit and output of the DAC are fixed at initial optimized values, then the device complexity is reduced, but the input-output characteristic fluctuates due to temperature and power supply voltage changes
Solution Approach 1:
The patent implements a feedback control system that monitors optical output power and adjusts DAC output and driving circuit gain accordingly. This feedback mechanism compensates for temperature and power supply voltage variations, maintaining stable input-output characteristics without requiring complex pre-compensation circuits or multiple optimization stages.
Solution Approach 2:
The system performs self-adjustment by using its own optical output as the reference for correction. The monitoring control circuit automatically detects deviations from optimal operation and adjusts the DAC and driving circuit gain without external intervention, enabling the system to self-correct for environmental changes and component aging.
4Reliability
If the DAC output and driving circuit gain are readjusted during operation to maintain optimal performance, then the noise immunity is improved, but the device complexity and control difficulty increase
Solution Approach 1:
The patent uses a straightforward feedback mechanism where optical output power is monitored and used to adjust DAC output and driving circuit gain. This simple closed-loop approach improves noise immunity without requiring complex control algorithms or additional hardware, making the readjustment process manageable despite the increased functionality.
Solution Approach 2:
The monitoring control circuit serves multiple functions: it monitors optical output power, determines linearity status, and adjusts both DAC output and driving circuit gain. This multi-functional approach consolidates control operations into a single circuit, reducing overall system complexity despite the multiple adjustment tasks.
Data Source
AI summary
An optical transmitter includes, a processor that receives an input data signal from an outside and performs rotation processing for periodically or repeatedly rotating a polarization state or phase of the optical output signal upon the input data signal, an optical modulator that modulates light transmitted from a light source based on the input data signal, a digital-to-analog converter that converts an output of the processor into an analog electric signal, a driving circuit that amplifies an output of the digital-to-analog converter and drives the optical modulator, and a monitoring control circuit that monitors an optical output signal output from the optical modulator and adjusts at least one of an output of the digital-to-analog converter and a gain of the driving circuit based on a result of monitoring of the optical output signal.