Directly Modulated Laser Non-Linearity Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Analog optical signals experience non-linearity due to temperature changes, age, internal parameters, and parasitics, leading to frequent and costly replacement of directly modulated lasers, especially in uncontrolled field environments where only digital communication components are 'outside-plant' rated.
Innovation Solution
A compact analog directly modulated laser configuration using electrical feedback to compensate for non-linearity in real-time, incorporating a large bandwidth photo-detector at the back facet to monitor output power and provide feedback for linearization, thereby eliminating the need for regular laser replacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If directly modulated lasers are used for analog optical signal generation, then device complexity is reduced, but non-linearity occurs due to temperature changes, age, and internal parameters requiring frequent replacement
Solution Approach 1:
The patent implements a feedback mechanism where a monitor photodiode detects the optical output power and feeds this information back to adjust the drive current. This closed-loop feedback system automatically compensates for non-linearity caused by temperature changes, aging, and internal parameters, maintaining reliable analog optical signal generation without frequent laser replacement while using a simple directly modulated laser configuration
2Manufacturing precision
If externally modulated lasers are used to compensate for non-linearity, then linearity is improved, but component complexity and cost increase
Solution Approach 1:
The patent introduces a monitor photodiode as an intermediary element that detects the optical output and enables feedback control. This intermediary component allows a simple directly modulated laser to achieve the linearity performance previously requiring complex externally modulated systems, by mediating between the laser output and the drive current control
3Adaptability or versatility
If directly modulated lasers operate in uncontrolled field environments, then deployment flexibility is improved, but non-linearity increases due to uncontrolled temperature and environmental conditions
Solution Approach 1:
The patent implements a self-service mechanism where the laser system automatically monitors its own output through the monitor photodiode and self-adjusts its drive current via feedback control. This enables the directly modulated laser to maintain signal linearity in uncontrolled field environments without external intervention, combining deployment flexibility with environmental robustness
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 significantly reduces component complexity and cost by maintaining a substantially linear transfer function, effectively compensating for non-linearity and relative intensity noise, allowing the laser to operate effectively close to threshold without frequent replacements.
Implementation Method 1
a photo-detector device disposed adjacent to the back facet of the laser device, wherein the photo-detector device is operable for measuring the optical output power of the laser device
Data Source
AI summary
The present invention provides a compact analog directly modulated laser configuration that is suitable for use in the field that uses electrical feedback to compensate for non-linearity in real time, such that no matter how the LI curve changes, the electrical feedback compensates for non-linearity by amplifying a portion of the output analog optical signal and combining it with the input analog electrical signal using the standard control method of negative feedback. When the gain of the feedback loop is relatively high, the overall transfer function of the system is primarily dependent on the feedback loop gain block, which is substantially linear. This is accomplished by incorporating a relatively large bandwidth photo-detector at the back facet of the laser that both monitors the output power of the system and provides a feedback signal to the linearization control circuit, as well as an amplifier. The amplified signal from the relatively large bandwidth photo-detector is used to correct for various undesirable effects, such as non-linearity and relative intensity noise (RIN) of the laser. The signal from the relatively large bandwidth photo-detector also allows the laser to operate effectively close to threshold.