Digital Bias Control Circuit for Optical Modulator Drift
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Solution Overview
Problem
Existing bias control circuits for optical transmitters, particularly in digital coherent optical transmission systems, face challenges in downsizing and power saving due to the use of analog components like oscillators, amplifiers, and filters, which are not suitable for compact and low-power operation.
Innovation Solution
A bias control circuit that includes a bias generator, differential amplifier, and controller, utilizing a dither signal with a predetermined frequency to adjust bias voltages in optical waveguides, allowing for digital signal processing and reduced component size and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If analog components (oscillator, amplifier, mixer, filter) are used to constitute a control circuit for generating dither signal and performing synchronous detection, then the control function is achieved, but the circuit size and power consumption increase
Solution Approach 1:
The patent replaces analog components (oscillator, amplifier, mixer, filter) with digital signal processing operations. The dither signal generation and synchronous detection are implemented through digital computation in the controller, eliminating the need for physical analog circuits and thereby reducing circuit size and power consumption while maintaining the bias control function
Solution Approach 2:
The patent changes the operational mode from analog to digital domain. By performing signal processing operations in the digital domain rather than using analog circuits, the system achieves the same control function with reduced hardware requirements, directly addressing the contradiction between functional reliability and circuit compactness
2Reliability
If analog components (oscillator, amplifier, mixer, filter) are used to constitute a control circuit for generating dither signal and performing synchronous detection, then the control function is achieved, but the power consumption increases
Solution Approach 1:
The patent replaces power-hungry analog components with digital signal processing operations. Digital processing in the controller consumes significantly less power than analog oscillators, amplifiers, mixers, and filters, thereby reducing overall power consumption while maintaining the essential bias control function
Solution Approach 2:
The patent transitions the system from analog to digital operation, changing the energy efficiency characteristics. Digital signal processing operations require less power than their analog counterparts, directly resolving the contradiction between achieving reliable bias control and minimizing power consumption
3Productivity
If multi-level phase modulator is used for QPSK modulation in digital coherent optical transmission, then the transmission capacity is improved, but the bias voltage drift phenomenon occurs
Solution Approach 1:
The patent applies preliminary action by superimposing a dither signal on the bias voltage before the drift phenomenon fully develops. This proactive approach allows the system to detect and correct bias voltage deviations before they significantly impact modulation performance, maintaining both high transmission capacity and bias stability
Solution Approach 2:
The patent implements feedback control by monitoring the optical power of the modulated signal and using this information to adjust the bias voltage. The controller detects the dither signal component in the feedback path and automatically adjusts the bias voltage to compensate for drift, ensuring stable operation while maintaining high transmission capacity
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 enables compact and low-power operation, effectively maintaining bias voltages at optimum values, compensating for drifting phenomena and enhancing the density and efficiency of communication channels in optical transmission systems.
Implementation Method 1
a power monitor to receive the modulated signal and to generate a monitor signal according to an intensity of the modulated signal
Implementation Method 2
a differential amplifier to receive the monitor signal and a reference signal, and to generate an amplified signal corresponding to a difference between the monitor signal and the reference signal
Implementation Method 3
a controller to detect frequency components contained in the amplified signal. The frequency components originates from the dither signal
Implementation Method 4
The bias generator provides a bias signal to one of the optical waveguides. The bias signal includes a dither signal having a predetermined frequency
Data Source
AI summary
A bias control circuit for an optical modulator including a pair of optical waveguides and a power monitor is disclosed. The bias control circuit includes a bias generator, a differential amplifier, and a controller. The bias generator provides a bias signal to one of the optical waveguides. The bias signal includes a dither signal having a predetermined frequency. The differential amplifier receives a monitor signal from the power monitor and a reference signal, and generates an amplified signal corresponding to a difference between the monitor signal and the reference signal. The controller detects frequency components contained in the amplified signal. The frequency components originates from the dither signal. The controller generates a control signal according to intensity of the frequency components. The bias signal is adjusted according to the control signal provided from the controller.