Optical Transceiver Laser Diode Extinction Ratio Control
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Solution Overview
Problem
Existing optical transceivers face challenges in accurately maintaining the extinction ratio of light output from semiconductor laser diodes due to temperature discrepancies between the ambient environment and the laser diode, leading to inaccuracies in look-up-tables used for controlling bias and modulation currents.
Innovation Solution
A method involving pre-installation measurement of the I-L characteristics of the laser diode, followed by a feedback loop to determine and adjust the modulation current based on temperature, with an automatic power control circuit maintaining average optical power, and revising the look-up-table with practical modulation current data to ensure the extinction ratio remains within a preset range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the LUT is created using conventional methods with ambient temperature variation, then the LUT can be generated without complex procedures, but the accuracy of the LUT deteriorates due to temperature discrepancy between ambient environment and LD
Solution Approach 1:
The patent applies preliminary action by measuring the I-L characteristics of the LD at multiple temperatures before installing it in the optical transceiver. This pre-characterization allows the LUT to be created with accurate temperature-dependent data without requiring the LD to reach thermal equilibrium with the ambient environment during normal operation. The pre-measured characteristics are stored and used to determine modulation currents at different operating temperatures.
Solution Approach 2:
The patent implements feedback by using a feedback loop that determines the modulation current based on the measured I-L characteristics and the actual operating temperature. The system continuously monitors the temperature and adjusts the modulation current according to the pre-stored characteristic data, ensuring accurate extinction ratio control despite temperature variations between ambient environment and LD.
2Manufacturing precision
If the modulation current is determined by setting values in LUT based on ambient temperature, then the process is simple, but the extinction ratio control deteriorates due to temperature difference between ambient and LD
Solution Approach 1:
The patent applies preliminary action by pre-measuring and storing the I-L characteristics at multiple temperatures in the LUT before the optical transceiver operates. This eliminates the need for complex real-time temperature control mechanisms while maintaining accurate extinction ratio control. The pre-characterized data allows the system to directly lookup appropriate modulation currents based on measured temperature without requiring complex adjustment procedures.
Solution Approach 2:
The patent implements feedback by using a feedback loop that determines the modulation current based on the actual operating temperature and the pre-stored I-L characteristics. This feedback mechanism ensures accurate extinction ratio control by continuously adapting the modulation current to the actual temperature conditions, eliminating the need for complex temperature control hardware while maintaining precision.
3Manufacturing precision
If the LUT stores data for many temperatures to maintain extinction ratio, then the extinction ratio control is improved, but the LUT size and data requirements increase
Solution Approach 1:
The patent applies parameter changes by measuring and storing the I-L characteristics at multiple discrete temperature points rather than storing exhaustive data for all possible temperatures. This approach efficiently captures the temperature-dependent behavior of the LD using a manageable number of characteristic measurements. The stored parameters include threshold currents and slope efficiencies at different temperatures, which are sufficient to determine modulation currents for extinction ratio control without requiring excessive data storage.
Data Source
AI summary
A method to control an optical transceiver, in particular, to drive an LD installed within the optical transceiver is described. The LD in the bias current thereof is determined by the automatic power control (APC) loop to keep an average of the optical output power. The modulation current is determined by a feedback loop to keep the extinction ratio (ER) in a preset range. The initial condition of the modulation current for the feedback loop is set by T-Im characteristic. The T-Im characteristic is first derived based on data measured in a status of the LD not installed in the transceiver. The T-Im characteristic is revised timely by the modulation current practically obtained for the optical transceiver.