Lithium Niobate Ridge Modulator Using Alternating Polarity to Curb DC Drift
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Solution Overview
Problem
Lithium niobate-based Mach-Zehnder-type optical modulators experience DC drift, leading to fluctuations in optical output over time, making it difficult to maintain constant optical outputs over a long period.
Innovation Solution
A Mach-Zehnder-type optical modulator with a control circuit that alternately applies positive and negative voltages as a square wave signal to offset DC drift, maintaining optical output within a predetermined range using a lithium niobate ridge optical waveguide and a control circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control with respect to bias voltage is performed based on average intensity of output light to follow change in operating point voltage caused by DC drift, then optical output stability is improved, but device complexity increases due to requiring operating point voltage detection means and two-system reference voltages
Solution Approach 1:
The patent extracts and eliminates the complex operating point voltage detection means and two-system reference voltage comparison circuitry from the feedback control system. Instead, it uses a simplified approach where the drive voltage is directly modulated with alternating positive and negative square wave signals, removing the need for complex detection and comparison hardware while maintaining optical output stability.
Solution Approach 2:
The patent inverts the conventional feedback control approach by not trying to detect and correct drift through complex circuitry, but rather by proactively applying alternating polarity square wave signals that inherently counteract DC drift. This inversion transforms the problem from detection-and-correction to prevention-through-opposite-action.
2Reliability
If conventional feedback control is used to compensate for DC drift, then optical output stability is improved, but manufacturing and mounting difficulty increases due to complex control circuit requirements
Solution Approach 1:
The patent removes the complex operating point detection means and reference voltage comparison circuitry from the system, significantly simplifying the control circuit architecture. This extraction of unnecessary components directly improves ease of manufacture and mounting while maintaining the ability to compensate for DC drift through the alternating square wave signal approach.
3Reliability
If alternating positive and negative square wave voltages are applied to offset DC drift, then optical output stability is improved, but energy consumption increases due to continuous voltage switching
Solution Approach 1:
The patent employs periodic alternating square wave signals with alternating positive and negative polarities to continuously counteract DC drift. This periodic action ensures that the modulator operates at its optimal operating point throughout the modulation range, maintaining optical output stability. The energy consumption increase is justified by the significant improvement in optical output stability and elimination of complex feedback circuitry.
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 curbs DC drift, ensuring stable optical output by canceling out drift effects, allowing for consistent performance over time.
Implementation Method 1
Lithium niobate has a large electro-optic constant, can be used to form optical modulators, optical waveguides, optical switches, optical filters, and the like
Data Source
AI summary
Provided is an optical modulator in which DC drift is curbed at all times. An optical modulator of the present invention includes a Mach-Zehnder-type lithium niobate ridge optical waveguide, an electrode for applying an electric signal to the ridge optical waveguide, an electric signal source generating an electric signal in which a set of voltages having a positive value and a negative value is repeated periodically, and a control circuit controlling the electric signal source. The control circuit sets a set of voltages having the positive value and the negative value such that light output from the ridge optical waveguide is continuously maintained in a range of a predetermined value.