Burst-Mode Tunable EML Biasing for Wavelength Drift Suppression
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Solution Overview
Problem
Tunable optical network units (ONUs) using Electro-absorption Modulated Lasers (EMLs) face significant wavelength drift issues due to self-heating effects during burst operations, leading to increased Bit-Error-Rate (BER) and limited transmission distance in TWDM-PON systems, as existing temperature control methods are insufficient to manage rapid thermal fluctuations.
Innovation Solution
A method involving a laser driving circuit that adjusts bias currents to the gain-section and phase-section diodes of a tunable laser during burst-on and burst-off states, maintaining continuous heating during the burst-off state to minimize thermal fluctuations, thereby stabilizing the wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If TEC control is used to maintain temperature at static states, then wavelength stability is improved, but self-heating effects during burst operations cause large wavelength drifts
Solution Approach 1:
The patent applies preliminary action by pre-heating the laser device during the burst-off state through a bias current delivery mechanism. This prepares the device thermally before the actual burst operation, preventing sudden thermal shocks and wavelength drifts when the burst-on state begins. The bias current is delivered in advance to maintain stable wavelength operation during transitions between burst states.
Solution Approach 2:
The patent implements periodic action by alternately delivering bias current during burst-off states and normal operating current during burst-on states. This periodic current modulation creates controlled thermal cycles that prevent excessive temperature buildup while maintaining wavelength stability. The rhythm of current delivery matches the burst operation pattern, ensuring thermal management throughout the operational cycle.
2Productivity
If burst operations are performed rapidly to reduce overhead and increase bandwidth, then productivity is improved, but wavelength drift increases due to self-heating effects
Solution Approach 1:
The patent applies preliminary action by delivering bias current during the burst-off state to pre-heat the laser device before the next burst operation. This preliminary thermal preparation ensures that when rapid burst operations occur, the device is already at an optimal temperature, preventing wavelength drift and reducing bit error rates even at high speeds.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring the bias current delivery mechanism operates continuously during burst-off states, keeping the laser device in a ready state. This continuous preparation eliminates thermal gaps between bursts, allowing rapid succession of burst operations without compromising wavelength stability or increasing error rates.
3Stability of the object's composition
If bias current is delivered during burst-off state to maintain heating, then wavelength stability is improved, but energy consumption increases
Solution Approach 1:
The patent applies partial action by delivering only a bias current during the burst-off state rather than the full operating current. This partial current delivery provides just enough heating to maintain wavelength stability without excessive energy consumption. The bias current is optimized to be sufficient for thermal stability but minimal enough to conserve energy during non-transmission periods.
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 effectively suppresses wavelength drift, reduces Bit-Error-Rate, and enhances transmission distance by maintaining stable wavelength operation during burst operations, even with rapid temperature changes.
Implementation Method 1
delivering, by the laser driving circuit, a first bias current to an anode of a gain-section diode disposed on a shared substrate of the tunable laser, and delivering, by the laser driving circuit, a second bias current to an anode of a phase-section diode disposed on the shared substrate of the tunable laser
Implementation Method 2
Traditionally, Directly Modulated Lasers (DMLs) have been widely used in the TWDM-PON system with wavelength lengths tuned either through Distributed Bragg Reflector (DBR) current or the temperature by Thermoelectric Cooling (TEC) control
Data Source
AI summary
A method (700) of biasing a tunable laser (310) during burst-on and burst-off states includes receiving a burst mode signal (514) indicative of the burst-on state or the burst-off state and when the burst mode signal is indicative of the burst-on state: delivering a first bias current (IGAIN) to an anode of a gain-section diode (590a) disposed on a shared substrate of the tunable laser; and delivering a second bias current (IPH) to an anode of phase-section diode (590b) disposed on the shared substrate. The second bias current is less than the first bias current. When the burst mode signal transitions to be indicative of the burst-off state, the method also includes delivering the first bias current to the anode of the gain-section diode; and delivering the second bias current to the anode of the phase-section diode wherein the first bias current is less than the second bias current.