Optical Module Operating Point Control via Dither Frequency Adjustment
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Solution Overview
Problem
In optical transmission devices, the detection of dither signal components becomes difficult due to low amplitude, especially when the control voltage approaches the maximum or minimum point of the optical output characteristic curve, leading to decreased detection accuracy and difficulty in determining the optimum operating point.
Innovation Solution
An optical module configuration that includes a voltage controller applying a dither signal with a known frequency, a monitor unit, a multiplier, and a filter unit to extract a direct-current component, with the option to change the frequency of the dither or reference signal to twice the original frequency when the direct-current component meets a predetermined condition, enhancing detection accuracy by increasing the amplitude of the reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amplitude of the dither signal is decreased to reduce phase and amplitude fluctuations of transmission symbols, then transmission property is improved, but detection accuracy of the dither signal component decreases
Solution Approach 1:
The patent applies periodic dither signal superimposition at specific frequency ranges (100 Hz to 10 kHz) to enable operating point detection while maintaining transmission integrity. The periodic nature allows detection through frequency-selective filtering without causing excessive symbol fluctuations.
Solution Approach 2:
The patent introduces a monitor signal as an intermediary that carries the dither signal component information. By monitoring the optical output and extracting the dither component through band-pass filtering, the system can detect operating points without directly measuring the control voltage, thus maintaining transmission property while enabling detection.
2Reliability
If the amplitude of the dither signal is decreased to improve transmission property, then phase and amplitude fluctuations are reduced, but the dither signal component in the monitor signal becomes difficult to distinguish from noise
Solution Approach 1:
The monitor signal serves as an intermediary that amplifies and transports the dither signal component information. Even when the dither amplitude is small, the monitor signal captures the optical intensity variations caused by the dither, making the component detectable through frequency-selective filtering.
Solution Approach 2:
The system uses feedback through the monitor signal to detect the dither signal component and determine the operating point. The feedback loop allows the system to identify when the operating point is optimal based on the presence and characteristics of the dither component in the monitor signal.
3Measurement precision
If the control voltage is regulated to the optimum operating point where the optical output characteristic curve has maximum or minimum intensity, then desired optical output characteristic is achieved, but the inclination of the curve becomes close to zero making dither signal detection difficult
Solution Approach 1:
The patent uses periodic dither signal superimposition at frequencies where the system response is maximized (100 Hz to 10 kHz range). This periodic excitation creates detectable oscillations in the optical output even at operating points where the static curve inclination is zero, enabling detection through dynamic response rather than static slope.
Solution Approach 2:
The dither signal acts as a controlled vibration or oscillation applied to the control voltage. By superimposing this high-frequency small-amplitude vibration, the system creates dynamic variations in optical output that can be detected even when the static operating point is at a maximum or minimum where the first derivative is zero.
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 improves the detection accuracy of the dither signal component, allowing for precise determination of the optimum operating point even when the amplitude is low, thereby maintaining desired optical output characteristics.
Implementation Method 1
a multiplier that multiplies the monitor signal by a reference signal having a frequency corresponding to the dither signal
Implementation Method 2
a filter unit that extracts a direct-current component included in a multiplication result of the multiplier
Data Source
AI summary
An optical module includes an optical device that outputs an optical signal corresponding to a control voltage, a voltage controller that applies the control voltage on which a dither signal is superimposed to the optical device, a monitor unit that monitors the optical signal output from the optical device, and outputs a monitor signal, a multiplier that multiplies the monitor signal by a reference signal corresponding to the dither signal, a filter unit that extracts a direct-current component included in a multiplication result, and a controller that causes the voltage controller to change the control voltage in accordance with the direct-current component. The controller changes the frequency of the dither signal or the reference signal such that the frequency of the reference signal is twice as large as that of the dither signal, when the direct-current component satisfies a predetermined condition.