Optical Transmitter Stepwise Current Control for Laser Diode
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Solution Overview
Problem
Conventional automatic power control (APC) operations for semiconductor laser diodes fail to suppress rush currents during power-up, leading to unstable optical output and prolonged stabilization time due to abrupt increases in bias and modulation currents.
Innovation Solution
A method involving a controller with memory that increases bias and modulation currents in stepwise fashion, starting the APC loop only after reaching target values, with integral filtering to prevent abrupt current increases, thereby controlling the power consumption and stabilizing the optical output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional APC operation immediately starts adjusting bias and modulation currents upon powering, then the optical output can be controlled, but rush current and power consumption increase abruptly
Solution Approach 1:
The patent applies preliminary action by pre-setting target values for bias and modulation currents before starting APC operation. The controller first establishes these target values based on initial parameters, then gradually increases currents toward these targets before activating the APC loop. This prevents abrupt current increases and rush current while ensuring the system is ready for stable optical output control.
2Reliability
If conventional APC operation adjusts currents to maintain optical output, then power control is achieved, but stabilization time is prolonged due to overshoots and undershoots
Solution Approach 1:
The patent applies dynamics by implementing a two-stage current control process. First, currents are gradually increased to target values using a controlled ramp function. Second, only after reaching target values does the APC loop activate to maintain optical output. This dynamic sequencing eliminates overshoots and undershoots that occur in conventional immediate APC operation, achieving stable optical output faster.
Solution Approach 2:
The controller performs preliminary action by pre-calculating and setting target current values before APC operation begins. This preliminary setup allows the system to approach the operating point smoothly without the oscillations and delays characteristic of conventional APC that starts immediately upon powering.
3Productivity
If bias and modulation currents are increased rapidly to reach target values, then productivity is improved, but rush current damages the laser diode
Solution Approach 1:
The patent applies beforehand cushioning by implementing a gradual current increase mechanism with predefined step widths and target values. Instead of rapidly switching currents to target levels, the controller increases bias and modulation currents in controlled steps, cushioning the transition to prevent rush current. This protective approach maintains productivity by establishing a predictable, time-bound power-up sequence while protecting the laser diode from damage.
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
This approach prevents abrupt power consumption spikes and stabilizes the optical output quickly by gradually increasing bias and modulation currents, ensuring efficient power management and rapid stabilization of the semiconductor laser diode.
Implementation Method 1
a photodiode (hereafter denoted as PD) to monitor the optical output power from the laser diode
Data Source
AI summary
The present invention discloses an optical transmitter that provides a function to vary the rate of the increase of the bias and modulation currents and their practical values during the APC feedback loop is left unstable without prolonging this unstable period. The optical transmitter of the invention includes a controller configured to read initial parameters from the memory, to increase the bias and modulation currents in stepwise based on thus read initial parameters, and to begin the automatic feedback control to keep the optical output from the laser diode constant after the bias and modulation currents reach their temporarily target values.