ROADM Optical Filters for ASE Suppression
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Solution Overview
Problem
In reconfigurable optical add-drop multiplexers (ROADMs), amplified stimulated emission (ASE) light generated by erbium-doped fiber amplifiers causes noise interference across different optical signal groups, degrading the signal-to-noise ratio (OSNR) and increasing bit error rates, especially over longer transmission distances.
Innovation Solution
Incorporating optical filters with passbands that match the wavelengths of specific optical signal groups to attenuate ASE light outside these bands, reducing noise interference when combining optical signals in a multicast switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If optical amplifiers are used to boost signal power in ROADMs, then signal loss is compensated, but ASE noise is generated that degrades OSNR and increases bit error rate
Solution Approach 1:
The patent divides the optical signal processing into separate segments: one path for amplifying and switching optical signals, and another path for detecting wavelengths and controlling ASE suppression. This segmentation allows independent optimization of signal amplification and noise suppression functions.
Solution Approach 2:
The patent introduces an intermediary control mechanism where detected wavelength information is used to dynamically adjust ASE suppression levels. This intermediary process coordinates between the optical signal path and the noise suppression path, allowing adaptive noise management without directly interfering with signal amplification.
2Adaptability or versatility
If multiple optical signal groups are combined in optical combiners, then system capacity and flexibility are increased, but ASE noise from one group interferes with other groups, reducing OSNR
Solution Approach 1:
The patent applies local quality by implementing ASE suppression that is specific to each optical signal group's wavelength characteristics. Each group receives tailored noise suppression based on its unique wavelength profile, allowing high-capacity multi-group operation while maintaining individual OSNR quality.
Solution Approach 2:
The patent introduces dynamic ASE suppression that adapts to the specific wavelength composition of each optical signal group. The suppression levels and characteristics change dynamically based on the detected wavelengths, enabling flexible system capacity while maintaining signal quality across different grouping configurations.
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 significantly reduces noise levels, leading to lower bit error rates and improved signal quality by isolating ASE noise from the desired optical signal groups, thereby extending the transmission distance and reliability of optical communication systems.
Implementation Method 1
optical amplifiers, such as erbium doped fiber amplifiers, may be provided in the ROADM to boost the power of the optical signals
Implementation Method 2
Erbium doped fiber amplifiers (EDFA) often generate amplified stimulated emission (ASE) light at wavelengths other than the optical signal wavelengths
Implementation Method 3
Incorporating optical filters with passbands that match the wavelengths of specific optical signal groups to attenuate ASE light outside these bands
Data Source
AI summary
Consistent with the present disclosure, optical filters are provided in a reconfigurable optical add-drop multiplexer (ROADM). In one example, groups of optical signals are amplified by corresponding erbium-doped fiber amplifiers (EDFAs) and supplied to each optical filter, which has a passband that includes the wavelengths associated with the received optical signal group. Light at wavelengths outside the passband of each optical filter, such as amplified stimulated emission (ASE) light generated by a respective EDFA, is significantly attenuated. Each optical signal group, after such amplification and filtering may then be switched and combined in a multicast switch before being directed toward a desired optical communication path. When, for example, first and second optical signal groups are combined, however, the first optical signal group is accompanied by little or no ASE light at the second optical signal group wavelengths. In addition, the second optical signal group is not accompanied by significant ASE light at the first optical signal group wavelengths. Accordingly, the first and second optical signal groups have less noise than would otherwise be present in the absence of the optical filters, and bit error rates associated with the optical signal groups are reduced.