QPSK Modulator Optical Power Control via Bias Adjustment
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Solution Overview
Problem
Conventional Dual Polarization-Quadrature Phase Shift Keying (DP-QPSK) modulators face challenges in precisely controlling the optical power output, particularly in ensuring even contribution from both X-polarization and Y-polarization QPSK modulators in optical communication systems.
Innovation Solution
The implementation of semiconductor optical modulators with waveguides exhibiting Quantum Confined Stark Effect (QCSE) and an electrode bias system, where a power controller adjusts biases to eliminate optical output from one modulator, allowing precise control of optical signal contributions using power monitors and Mach-Zender interferometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional DP-QPSK modulators are used, then the system can transmit optical signals with phase modulation, but the optical power output cannot be precisely controlled and the contribution of two QPSK modulators cannot be evenly adjusted
Solution Approach 1:
The patent implements a feedback control mechanism where power monitors continuously detect the optical power output from each QPSK modulator and the total output power. These detected values are fed back to a control mechanism that adjusts the bias voltages applied to each modulator, enabling automatic balancing of the contribution from X-polarization and Y-polarization modulators and precise control of total optical power output.
Solution Approach 2:
The patent controls the optical power output by dynamically adjusting the bias voltage parameter applied to each QPSK modulator. By changing the bias voltage, the operating point of the modulator is shifted, which directly controls the optical power contribution from each modulator. This allows independent adjustment of X-polarization and Y-polarization modulator contributions to achieve even balance.
2Ease of operation
If bias is applied to waveguide to control optical output, then power control is achieved, but additional control mechanisms and monitoring systems are required
Solution Approach 1:
The control system uses power monitors to detect optical power from each modulator and the total output, feeding this information back to a control mechanism that automatically adjusts bias voltages. This closed-loop feedback system simplifies operation by eliminating the need for manual adjustment while maintaining precise control.
Solution Approach 2:
The system performs self-adjustment by using the detected optical power information to automatically modify its own bias voltages. The control mechanism monitors the output power and autonomously adjusts the bias to maintain the desired power distribution between modulators, reducing the need for external intervention.
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 enables precise and easy control of optical power output from both QPSK modulators, ensuring balanced contributions and stabilizing the optical transmitter's performance by adjusting biases to match target output power.
Implementation Method 1
Each of QPSK modulators outputs an optical signal and includes a waveguide made of semiconductor material showing the Quantum Confined Stark Effect (QCSE)
Data Source
AI summary
An optical transmitter implemented with two QPSK (Quadrature Phase Shift Keying) modulators is disclosed. Each of the QPSK modulators provides a waveguide made of semiconductor material inducing the QCSE (Quantum Confined Stark Effect) by a bias supplied thereto. The optical performance of one of the QPSK modulators is determined by supplying a deep bias to the other of the QPSK modulator to eliminate the optical output therefrom.