Optical Transmitter Temperature Compensation via Faraday Rotator
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Solution Overview
Problem
Optical transceivers using directly modulated lasers (DMLs) face quality deterioration at low temperatures due to the increased ratio of optical output power to driving current, leading to decreased pulse mask characteristics and communication quality.
Innovation Solution
An optical transmitter configuration that includes a semiconductor laser chip with increasing light power at lower temperatures, a Faraday rotator to adjust polarization, and an optical isolator with increased insertion loss at lower temperatures, ensuring stable operation and communication quality across a wide temperature range without the need for temperature regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a DML is used at low temperatures with automatic power control (APC), then the optical output power remains the same, but the driving current decreases and communication quality deteriorates
Solution Approach 1:
The patent applies preliminary anti-action by introducing an optical isolator with temperature-dependent insertion loss characteristics that counteracts the laser's temperature-dependent power characteristics in advance. The optical isolator's insertion loss increases as temperature decreases, which compensates for the laser's increased optical output power at low temperatures, thereby preventing communication quality deterioration before it occurs.
Solution Approach 2:
The patent utilizes parameter changes by selecting an optical isolator whose insertion loss parameter varies with temperature. This temperature-dependent insertion loss parameter change is leveraged to automatically compensate for the laser's power fluctuations across different operating temperatures, eliminating the need for active temperature regulation or complex control circuits.
2Power
If the optical output power increases at low temperatures, then the laser operates efficiently, but the pulse mask characteristic deteriorates
Solution Approach 1:
The patent converts the harmful effect of increased optical output power at low temperatures into a beneficial compensation mechanism. By using an optical isolator whose insertion loss increases at low temperatures, the system transforms the potential harm (excessive power causing pulse mask deterioration) into a benefit (automatic power normalization that maintains pulse mask characteristics across temperature ranges).
3Reliability
If a temperature regulating function is added to the semiconductor laser module, then the operating temperature range is assured, but the cost increases
Solution Approach 1:
The patent implements self-service by designing a system where the optical isolator automatically compensates for temperature-induced power variations without requiring external temperature regulation. The optical isolator's inherent temperature-dependent insertion loss characteristics enable the system to self-regulate the optical power level across different temperatures, eliminating the need for expensive TECs, heaters, or complex temperature control circuits.
4Illumination intensity
If the driving current decreases to maintain constant optical output power, then the optical output power remains stable, but the communication quality deteriorates
Solution Approach 1:
The patent introduces an intermediary component (optical isolator) between the laser and the optical fiber that mediates the relationship between driving current and optical output power. The optical isolator's temperature-dependent insertion loss acts as a passive mediator that automatically adjusts the optical power level without requiring changes to the driving current, thereby maintaining both power stability and communication quality.
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 maintains consistent optical output power and pulse mask margin across varying temperatures, preventing communication quality degradation and expanding the operating temperature range without additional heating or complexity, thus enhancing communication reliability.
Implementation Method 1
a Faraday rotator configured to rotate a polarization direction of the light in accordance with the temperature
Implementation Method 2
an optical isolator with increased insertion loss at lower temperatures
Data Source
AI summary
An optical transmitter includes a laser configured to emit light, a power of the light increasing with temperature decreasing, a Faraday rotator configured to rotate a polarization direction of the light in accordance with the temperature, and a first polarizer that has a principal axis inclined at a given angle and inputs the light output from the Faraday rotator.