Bias Voltage Control for High Extinction Ratio Modulators
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Solution Overview
Problem
High extinction ratio optical modulators require precise bias voltage control to achieve desired extinction ratios, which is challenging with generic AD converters/control boards, often leading to local lock-in operations at incorrect minimum or maximum points.
Innovation Solution
Implementing a method where the bias voltage is adjusted by comparing optical intensities at neighboring bias voltages with a step voltage of less than or equal to 0.1 of the half-wave voltage, shifting the bias voltage towards the lower output, and repeating the process to avoid local lock-in, allowing for simple and easy control of the desired extinction ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high extinction ratio optical modulator is used to achieve high optical SN ratio, then the extinction ratio reaches 60 dB or higher, but the allowable range for bias control becomes extremely narrow making it difficult to control with generic AD converters
Solution Approach 1:
The patent implements a feedback mechanism where the optical output intensity is continuously monitored and used to adjust the bias voltage. The control unit measures the optical output and automatically adjusts the bias voltage to maintain the optimal operating point (minimum or maximum), eliminating the need for manual precision control and enabling generic AD converters to achieve the desired extinction ratio.
2Reliability
If conventional bias control methods are used with high extinction ratio modulators, then optical minimum/maximum points are sought, but the system may lock into local minimum/maximum points due to the narrow control range
Solution Approach 1:
The patent applies preliminary action by performing a coarse bias voltage adjustment in broader steps before transitioning to fine adjustment. This two-stage approach allows the system to first locate the general region of the optimal bias point without risking local lock-in, then refine the position with smaller steps to achieve the desired extinction ratio reliably.
3Measurement precision
If precise bias control is attempted with generic AD converters, then control resolution of 0.1 mV or less is required, but the search for optimum point continues without reaching it
Solution Approach 1:
The patent employs dynamic adjustment where the bias voltage control transitions from coarse steps to fine steps based on the convergence state. The control unit automatically adapts the adjustment step size: using larger steps when far from the optimum point to accelerate convergence, and smaller steps when approaching the optimum to achieve precise control, thereby improving both speed and accuracy.
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 effective control of bias voltage for high extinction ratio modulators using generic AD converters/control boards, avoiding local lock-in operations and maintaining desired extinction ratios, even with coarse adjustments.
Implementation Method 1
a high extinction ratio optical modulator (having a high SN ratio) is needed
Data Source
AI summary
To provide a method whereby a bias voltage capable of easily realizing a required extinction ratio can be controlled by utilizing a high-extinction ratio modulator even when a generic AD converter/control board is used, and a device for realizing the method. In the present invention, the step quantity (variation quantity) ΔV of a control voltage is no more than 0.1 times the half-wave voltage Vπ [V]. For example, in the case of searching for the minimum point, the light intensity is measured when a bias that is larger by the step voltage ΔV and a bias that is smaller by the step voltage ΔV are applied, the current bias voltage being used as a reference, and the bias voltage is moved toward the smaller of the measured light intensities. The process of setting the moved bias voltage as a reference, comparing the light intensities for the bias points in both neighboring positions, and changing the reference bias voltage is then repeated. A configuration may be adopted whereby ΔV then gradually decreases in accordance with a predetermined algorithm.