Tunable Laser Source with Optical Filter for ASE Suppression
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Solution Overview
Problem
Tunable laser sources in wavelength division multiplexed optical networks face challenges with high costs due to the need for multiple backup laser diodes and trade-offs between output optical power and spectral purity, particularly in reconfigurable networks where dynamic wavelength addition and dropping are required.
Innovation Solution
A tunable laser device is implemented with a tunable transmission optical filter, preferably an asymmetric Mach-Zehnder waveguide interferometer, placed between the laser section and the semiconductor optical amplifier to suppress back-propagating amplified spontaneous emission, thereby enhancing the side mode suppression ratio by doubling ASE suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a semiconductor optical amplifier is added to boost output power, then output optical power is improved, but side mode suppression ratio deteriorates due to amplified spontaneous emission noise
Solution Approach 1:
An optical filter is introduced as an intermediary component between the laser section and the semiconductor optical amplifier. This filter selectively transmits the desired lasing wavelength while blocking amplified spontaneous emission at other wavelengths, thereby preventing ASE noise from degrading the side mode suppression ratio while still allowing the SOA to boost the output power of the fundamental mode.
2Reliability
If multiple backup laser diodes are provided for each wavelength channel, then reliability is improved, but cost increases prohibitively
Solution Approach 1:
The patent implements a single tunable laser source that can dynamically switch between multiple wavelength channels. This universal laser source replaces the need for multiple dedicated laser diodes (one per wavelength channel plus backups), providing both primary and backup functionality through wavelength tuning capability, thereby significantly reducing the total number of laser diodes required while maintaining system reliability.
3Adaptability or versatility
If laser sources are made widely tunable for reconfigurable networks, then adaptability is improved, but spectral purity deteriorates due to coherent crosstalk
Solution Approach 1:
The optical filter serves as a mediator that ensures spectral purity across the entire tuning range. By blocking amplified spontaneous emission and suppressing side modes at all wavelengths within the tuning range, the filter prevents coherent crosstalk with other wavelength channels, thereby enabling widely tunable operation without sacrificing spectral purity.
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 configuration improves the side mode suppression ratio by 10dB, achieving better spectral purity and maintaining sufficient output optical power, essential for wavelength-agile optical networks.
Implementation Method 1
A tunable laser device is implemented with a tunable transmission optical filter, preferably an asymmetric Mach-Zehnder waveguide interferometer, placed between the laser section and the semiconductor optical amplifier to suppress back-propagating amplified spontaneous emission
Implementation Method 2
semiconductor optical amplifier section (SOA) disposed downstream of the tunable transmission optical filter. The SOA section has an amplification band
Data Source
Figure 1A~1C
Figure 1B
Figure 2A~2B
AI summary
A tunable transmission optical filter is optically coupled between a laser section and semiconductor optical amplifier (SOA) section of a tunable laser device. The optical filter may be tuned to provide a high transmission near the lasing peak while suppressing a significant portion of back-propagating amplified spontaneous emission (ASE) of the SOA section. Without the optical filter, the laser output spectrum may develop side lobes of higher intensity after the ASE is amplified and reflected in the forward direction by the laser gain and mirror sections. While lessening the side lobes, the optical filter simultaneously transmits the laser peak for amplification by the SOA section.