Optical Transmitter Phase Bias Control via Phi Scan
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Solution Overview
Problem
In optical communication systems, the automatic bias control (ABC) circuit of Mach-Zehnder type optical modulators experiences phase bias pull-in uncertainty, leading to potential distortion and inaccurate demodulation, especially when the phase bias is not at 90°, affecting the quality of the transmitted signal.
Innovation Solution
The optical transmitter employs a ϕ scan method to determine and set the pull-in phase of the ϕ bias to either 90° or 270° by monitoring changes in optical output power during phase rotation, ensuring accurate bias control and minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the pilot tone superimposing method is used to control bias voltages, then the ABC circuit can automatically adjust biases, but the pull-in phase becomes uncertain and may not be at the optimal 90° position
Solution Approach 1:
The patent implements a feedback mechanism where the optical output is detected and used to adjust the phase bias. The system continuously monitors the optical signal and modifies the phase bias to maintain the optimal 90° position, resolving the phase uncertainty caused by automated pilot tone superimposition.
Solution Approach 2:
The patent changes the phase bias parameter dynamically to achieve the optimal operating point. By adjusting the phase bias to specifically 90° based on detected optical output characteristics, the system overcomes the fixed or uncertain phase positions resulting from automated control methods.
2Productivity
If phase bias is not accurately controlled at 90°, then signal transmission can occur, but distortion increases and demodulation accuracy decreases
Solution Approach 1:
The detection of optical output provides feedback that enables real-time adjustment of phase bias, ensuring it remains at the optimal 90° position. This continuous feedback loop maintains signal quality and prevents distortion that would otherwise occur with inaccurate phase bias.
3Productivity
If high-degree QAM modulation is used to increase capacity, then transmission capacity increases, but detection sensitivity is compromised and phase bias control becomes more difficult
Solution Approach 1:
The patent uses an intermediary detection mechanism that monitors optical output characteristics to indirectly determine and control phase bias. This intermediary approach allows accurate phase bias control even in high-degree QAM systems where direct detection sensitivity is compromised.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise determination and setting of the pull-in phase, enhancing signal quality and preventing data inversion at the receiving device, even in high-degree QAM modulation schemes, where detection sensitivity is compromised.
Implementation Method 1
an optimal modulator configured to have a voltage-to-light-intensity characteristic in which intensity of output light changes in response to an applied voltage, and to generate a light signal that corresponds to the drive signal
Data Source
Figure 1
Figure 2A~2D
Figure 3A~3D
AI summary
There is provided an optical transmitter including a signal generator to generate an electric signal, an optical generator to generate light, an optical modulator to modulate the light with the electric signal to create an optical signal, a first voltage electrode to apply a first voltage to the optical signal, a second voltage electrode to apply a second voltage to the optical signal to which the first voltage is applied, and a detector to detect an optical power of the optical signal to which the second voltage is applied, wherein the signal generator stops generating the electric signal, controls the first voltage electrode to change the first voltage after the stop of generating the electric signal, and controls the second voltage electrode to change the second voltage according to the detected optical power after the change of the first voltage.