Optical Transmitter DC Bias Control Without Dither Signal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical communication systems require expensive optical detectors or high sampling rate analog to digital converters to adjust bias voltages in Mach-Zehnder modulators, increasing costs and complexity.
Innovation Solution
An optical transmitter system that includes a light source, optical modulators, a DC component detector, and a controller to apply specific bias voltages based on the detected DC component of the modulated optical signal, eliminating the need for a dither signal and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If automatic bias control is implemented using a low frequency dither signal, then operation point fluctuation is suppressed, but the amplitude of voltage applied to the optical modulator changes and optical signal quality deteriorates
Solution Approach 1:
The patent extracts and removes the dither signal component from the bias control system. Instead of using a low frequency dither signal that causes amplitude modulation, the invention directly detects the DC component of the optical signal to determine the operation point, thereby eliminating the harmful amplitude variations while maintaining operation point stability
Solution Approach 2:
The patent introduces a DC component detector as an intermediary element that measures the DC level of the optical signal to infer the operation point. This mediator allows bias control without requiring direct modulation by dither signals, thus avoiding the amplitude modulation problem while achieving reliable operation point stabilization
2Ease of manufacture
If bias voltages are adjusted without a dither signal as in NPL1, then cost is reduced, but clock tone information is required which needs expensive optical detectors or high sampling rate ADCs
Solution Approach 1:
The patent replaces expensive, high-performance detectors or high sampling rate ADCs with a simpler, lower-cost DC component detector. The invention uses a basic detector with low sampling rate that only needs to measure the DC level, eliminating the need for costly high-performance components while achieving the same bias control function
Solution Approach 2:
The patent changes the measurement parameter from requiring full signal waveform analysis (which needs high sampling rate) to only measuring the DC component level. This parameter change allows the use of low sampling rate detectors, significantly reducing system cost while maintaining the ability to control bias voltages effectively
Data Source
AI summary
To carry out automatic bias control to an optical modulator without a dither signal with reduced cost, an optical transmitter comprises a light source configured to output a light, an optical first modulator configured to modulate the light and output a first modulated optical signal, a DC component detector configured to detect a DC component of the first modulated optical signal and a controller configured to apply a first specific bias voltage identified based on the DC component to the optical first modulator.