Optical Modulator Bias Drift Detection via Periodic Dither Signals
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Solution Overview
Problem
Existing light modulation devices require complex configurations or large-scale circuitry to perform synchronous detection at multiple frequencies, making it difficult to detect drift in bias voltages for optical QAM signals.
Innovation Solution
A light modulation device with an I-component and Q-component optical modulator, an optical phase shifter, bias voltage output parts, an optical power monitor, and a synchronous detection circuit that uses a single frequency for detecting drift in bias voltages by applying dither signals of different frequencies to adjust the bias voltages based on synchronous detection results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If synchronous detection is performed at multiple frequencies to detect drift in bias voltages, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent applies periodic dither signals at different frequencies (first frequency for I-component modulator, second frequency for Q-component modulator) to encode bias voltage drift information. By using periodic actions at distinct frequencies, the system can differentiate between drifts in different modulators and achieve precise measurement without requiring complex simultaneous multi-frequency detection circuits.
Solution Approach 2:
The patent superimposes dither signals onto the bias voltages before modulation occurs. This preliminary action embeds the drift information into the optical signal in advance, allowing the synchronous detection circuit to recover bias voltage drift information through simple single-frequency detection rather than requiring complex post-processing or multi-frequency analysis.
2Measurement precision
If multiple dither signals of different frequencies are applied to detect drift in multiple bias voltages, then measurement precision is improved, but the device scale increases
Solution Approach 1:
The patent uses periodic dither signals at different frequencies to modulate the bias voltages of the I-component and Q-component optical modulators. This approach allows the system to encode drift information from multiple bias voltages into distinct frequency components that can be detected sequentially or simultaneously using a single synchronous detection circuit, thereby maintaining high measurement precision while minimizing the detection circuit scale.
Solution Approach 2:
The dither signals are superimposed on the bias voltages before the optical modulation process. This preliminary encoding of drift information into the signal path allows a single synchronous detection circuit to extract drift information from multiple bias voltages by detecting the presence and characteristics of the dither signal components, eliminating the need for separate detection circuits for each bias voltage.
3Device complexity
If a single frequency is used for synchronous detection, then device complexity is reduced, but the ability to detect drift in multiple bias voltages is limited
Solution Approach 1:
The patent employs periodic dither signals at different frequencies applied to different modulators (I-component and Q-component). When these modulated signals are combined and detected using a single-frequency synchronous detection circuit, the circuit can identify which dither frequency is present in the combined signal, thereby determining which modulator's bias voltage is drifting. This allows a simple single-frequency detection circuit to monitor multiple bias voltages effectively.
Solution Approach 2:
The dither signals are pre-modulated onto the optical carriers before combination. This preliminary encoding ensures that each modulator's bias voltage drift information is carried on a distinct frequency component that can be identified by a single synchronous detection circuit through frequency discrimination, enabling versatile multi-bias monitoring with minimal circuit complexity.
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
Enables synchronous detection of drift in multiple bias voltages using a single frequency, simplifying the device configuration and reducing its scale while maintaining accurate bias voltage control.
Implementation Method 1
The optical modulator 2 has a function of relatively changing optical waveguides 22 and 23 in optical phase and optical intensity in correspondence with a logic of a first 4-value data signal
Implementation Method 2
An optical phase shifter 4 applies a phase shift of θ3 to the output signal of the optical modulator 3
Implementation Method 3
A continuous-wave optical signal (hereinafter, referred to as a CW (Continuous Wave) optical signal) to be modulated is input to an IQ optical modulator 100, branched into two signals by an optical coupler 1
Data Source
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AI summary
A light modulation device detects a power of the modulated optical signal modulated by each of an I-component optical modulator and a Q-component optical modulator, synchronously-detects a component of a frequency fd from the power of the modulated optical signal, outputs a dither signal of a frequency fd/n (where n is a positive integer equal to or larger than 1) applied to a first bias voltage or a second bias voltage when adjusting the first bias voltage or the second bias voltage, outputs two dither signals having a frequency fd/m (where m is a positive integer equal to or larger than 1, where n<m), which are mutually orthogonal to each other, applied to the first and second bias voltages when adjusting a third bias voltage, and adjusting bias voltages by increasing or decreasing bias voltages based on a synchronous detection result.