SOA Bias Control for Optical Signal Jitter Suppression
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Solution Overview
Problem
Existing methods for controlling semiconductor laser diodes and optical amplifiers in optical communication systems, such as those used in fiber-to-the-home (FTTH) networks, require determining multiple bias currents to maintain optimal operating conditions, which can be challenging to consistently achieve.
Innovation Solution
A method that adjusts the second bias current for the semiconductor optical amplifier based on the waveform of the optical signal after transmission, followed by adjustments to the thermo-electric cooler driving current, the first bias current for the laser diode, and the driving signal to achieve target wavelength, power, extinction ratio, cross point, and pulse mask margin, with the second bias current adjusted in a region where optical signal power shows a negative relation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three currents (bias current for LD, current for TEC, and bias current for SOA) are determined by conventional monitoring methods, then operating conditions can be controlled, but it becomes hard to determine all three currents consistently
Solution Approach 1:
The patent extracts the SOA bias current determination from the conventional three-current control method. Instead of determining the SOA bias current separately through monitoring, the invention uses a fixed relationship where the SOA bias current is set to a predetermined value (e.g., 200 mA) independent of the monitoring-based determination of other currents. This reduces the complexity of consistent determination across all three currents.
Solution Approach 2:
The patent changes the parameter determination strategy by fixing the SOA bias current to a predetermined value rather than dynamically adjusting it through monitoring. This parameter change simplifies the control system by reducing the number of dynamically determined parameters from three to two (LD bias current and TEC current), thereby improving reliability.
2Power
If the second bias current for SOA is adjusted in a region where optical signal power shows positive relation, then amplification is enhanced, but transmission performance deteriorates due to chirp effects
Solution Approach 1:
The patent converts the harmful chirp effect into a beneficial one by operating the SOA in a specific current region (e.g., 200 mA) where the chirp characteristics compensate for fiber transmission losses. By adjusting the SOA bias current to a predetermined value in the negative relation region, the invention transforms what would normally be a degradation mechanism into a compensation mechanism that improves transmission performance over long distances.
Solution Approach 2:
The patent changes the operating parameter region of the SOA from the conventional positive relation region (higher amplification) to the negative relation region (lower amplification but better transmission characteristics). This parameter change prioritizes transmission reliability over maximum amplification power, achieving better overall system performance.
3Reliability
If multiple parameters (wavelength, power, extinction ratio, cross point, PMM) are adjusted simultaneously, then transmission performance is optimized, but control complexity increases
Solution Approach 1:
The patent segments the control process into distinct sequential steps: first determining the LD bias current, then the TEC current, and finally setting the SOA bias current to a predetermined value. This segmentation of the control process into manageable stages reduces overall complexity while achieving optimization of multiple parameters including wavelength, power, extinction ratio, cross point, and PMM.
Solution Approach 2:
The patent applies preliminary action by determining the LD bias current and TEC current before setting the SOA bias current to its predetermined value. This sequential determination ensures that each parameter is optimized in the correct order, simplifying the overall control process while achieving transmission performance optimization.
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 simplifies the determination of operating conditions, improves transmission performance by suppressing jitter and maintaining target parameters, and enhances the reliability of optical signals over long distances by compensating for chirp effects in the optical fiber.
Implementation Method 1
The DFB-LD and the SOA are commonly mounted on a thermo-electric cooler (TEC) like a Pertier Elements thereby controlled in temperatures thereof
Data Source
AI summary
A method of controlling a semiconductor element that includes a semiconductor laser diode (LD), a semiconductor modulator, and a semiconductor optical amplifier (SOA) is disclosed. The LD generates CW light supplied with the first bias current. The semiconductor modulator generates a modulated light by modulating the CW light supplied with a driving signal. The SOA generates an optical signal by amplifying the modulated light supplied with the second bias current. The method first sets the second bias current in a region where the output power of the optical signal shows negative dependence of the second bias current. Then, a temperature of the semiconductor element, the first bias current, and the driving signal are adjusted such that the optical signal shows performance in respective preset ranges.