Mach-Zehnder Optical Modulator Bias Reversal for DC Drift Control
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Solution Overview
Problem
Mach-Zehnder optical modulators using lithium niobate films suffer from DC drift, causing the optical output to change over time, making it difficult to maintain a constant optical output, which complicates the control and implementation of XR glasses.
Innovation Solution
An optical modulator with a control unit that independently applies pixel voltages to multiple Mach-Zehnder optical modulation units, alternating the polarity of the pixel voltage every predetermined period to compensate for DC drift, using a ferroelectric thin film like lithium niobate and controlling the power supply to apply pixel voltages with specific widths and shift voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant bias voltage is applied to a Mach-Zehnder optical modulator, then the initial optical output is stable, but the optical output changes over time due to DC drift
Solution Approach 1:
The patent applies periodic polarity reversal to the pixel voltage applied to the Mach-Zehnder optical modulator. The control unit alternates the polarity of the pixel voltage at predetermined intervals, which periodically compensates for the DC drift effect and maintains stable optical output over long-term operation.
Solution Approach 2:
The patent implements a control unit that monitors the optical output and adjusts the pixel voltage polarity accordingly. This feedback mechanism detects changes in optical output caused by DC drift and automatically compensates by reversing the voltage polarity to restore the operating point.
2Reliability
If feedback control is performed on bias voltage based on average intensity of output light, then the operating point voltage can be followed within limited range, but the control system becomes more complex
Solution Approach 1:
Instead of continuous feedback control, the patent uses periodic polarity reversal of the pixel voltage. This simpler approach leverages the periodic nature of the modulation signal to automatically compensate for DC drift without requiring complex continuous monitoring and adjustment circuits.
Solution Approach 2:
The control unit uses the existing pixel voltage signal and its own control logic to compensate for DC drift, rather than requiring separate bias voltage control circuits. The system serves itself by utilizing the polarity reversal of the pixel voltage to maintain the operating point.
3Reliability
If the polarity of pixel voltage is alternated every predetermined period, then DC drift is compensated and optical output remains stable, but the voltage control becomes more complex
Solution Approach 1:
The patent combines the DC drift compensation function with the existing pixel voltage control. The polarity reversal of the pixel voltage serves dual purposes: maintaining the image signal integrity and compensating for DC drift, thereby achieving compensation without adding separate control circuits.
Solution Approach 2:
The control unit changes the polarity parameter of the pixel voltage at predetermined intervals. This parameter change approach allows simple implementation through digital control logic that flips the voltage polarity, avoiding complex analog circuit modifications.
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
The solution effectively suppresses or compensates for DC drift, ensuring stable optical output and continuous color reproduction in XR glasses by alternating the polarity of pixel voltages, thereby maintaining consistent image quality.
Implementation Method 1
Mach-Zehnder optical modulation units (1-1, 1-2, 1-3), each having a Mach-Zehnder optical waveguide (11) and an electrode (12) for applying an electric field to the Mach-Zehnder optical waveguide (11)
Data Source
AI summary
The optical modulator of the present disclosure includes: Mach-Zehnder optical modulation units with optical waveguide and an electrode; a power supply for applying a pixel voltage to Mach-Zehnder optical modulation units independently; and a control unit controlling the power supply, wherein the control unit controls the power supply to apply the pixel voltage with a predetermined applied voltage width, the control unit is configured to repeat a set of a step 1 and a step 2, in the step 1, application of the pixel voltage having one polarity to Mach-Zehnder optical modulation units being continued during a predetermined pixel voltage application continuation period, and in the step 2, a shift voltage that is an even multiple of a half-wavelength voltage being applied to Mach-Zehnder optical modulation units and application of the pixel voltage having other polarity being continued during the pixel voltage application continuation period after the step 1.