LiNbO3 Modulator Bias Point Control via First Harmonic Detection
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Solution Overview
Problem
Current methods for determining the bias point of optical phase modulators, such as LiNbO3 modulators, are complex and lack accuracy due to sensitivity to temperature and pressure, and existing control methods introduce pilot signals or harmonic noise, leading to high complexity and poor control accuracy.
Innovation Solution
A method and apparatus that add pilot signals to the bias voltages of the modulator, adjust the bias point in predetermined steps, and detect the first harmonic amplitude in the backlight detection current signal to determine the optimal bias point, reducing control complexity and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pilot signals of different frequencies are added to two arms of the DQPSK LiNbO3 modulator and backlight detection signal is collected to filter difference frequency signal, then the LiNbO3 modulator can be locked to normal bias point, but the control loop becomes high complexity and very difficult to implement
Solution Approach 1:
The patent extracts and eliminates the complex difference frequency signal filtering process by directly detecting the first harmonic amplitude of the backlight detection signal. This simplifies the control loop while maintaining bias point control accuracy, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
Instead of filtering difference frequency signals to find the bias point, the patent inverts the approach by directly detecting the first harmonic amplitude and using its maximum value to determine the optimal bias point. This inversion simplifies the control mechanism while achieving the same control objective.
2Device complexity
If backlight detection signal is directly sampled to judge whether it contains RF harmonic signal, then no pilot signal is required, but control accuracy is diminished due to harmonic signal noise from non-ideal data signal
Solution Approach 1:
The patent applies preliminary action by adding pilot signals to the bias voltages before detecting the backlight detection signal. This preliminary modification enables clear identification of the first harmonic component, improving control accuracy while maintaining simple control circuitry without requiring complex filtering.
Solution Approach 2:
The patent introduces pilot signals as intermediaries that modify the bias voltages, creating a detectable first harmonic component in the backlight detection signal. This intermediary approach enables accurate bias point determination without requiring complex signal processing or filtering, resolving the contradiction between device complexity and measurement precision.
3Reliability
If LiNbO3 modulator is used for DQPSK modulation, then phase modulation performance is improved, but sensitivity to temperature and pressure requires periphery control circuit to ensure precise phase control
Solution Approach 1:
The patent enables the LiNbO3 modulator to self-adjust its bias point by detecting the first harmonic amplitude of its own output and automatically locking to the optimal bias point. This self-service mechanism reduces the complexity of external control circuits while maintaining reliable phase modulation performance and compensating for temperature and pressure effects.
Data Source
AI summary
The disclosure discloses a method and an apparatus for determining a bias point of a modulator, wherein the method includes: adding pilot signals to the bias voltages of the modulator; adjusting the bias point of the modulator at a predetermined step and acquiring a first harmonic amplitude value corresponding to each bias point in a backlight detection current signal output by the modulator; and determining a bias point corresponding to the maximum value of the first harmonic amplitude values associated with multiple bias points as the bias point of the modulator. By virtue of the disclosure, the detection of a difference frequency signal can be eliminated, thereby reducing the complexity and cost of a periphery control circuit while ensuring the control accuracy, effectively improving the stability and reliability of the control process, and improving the modulation and transmission performance of optical signals in the whole system.