Side-lobe Compensation in WSS-based ROADMs
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Solution Overview
Problem
The introduction of reconfigurable optical add-drop multiplexers (ROADMs) with micro-electromechanical systems (MEMS) or liquid-crystal modulators leads to side-lobes that cause an optical signal-to-noise ratio (OSNR) penalty due to uneven ASE noise distribution, which current systems fail to adequately compensate for, resulting in signal power drops and network performance impairment.
Innovation Solution
Implementing a comb filter, such as a thin film filter or interleaver, along with adaptive amplifier control to adjust target power based on side-lobe size and OSNR, ensuring accurate ASE estimation and compensation across WSS-based ROADMs, thereby maintaining signal launching power and reducing OSNR penalties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If reconfigurable optical add-drop multiplexers (ROADMs) with MEMS or liquid-crystal modulators are introduced to enable dynamic wavelength switching, then adaptability and versatility of the optical network are improved, but side-lobes are generated that cause uneven ASE noise distribution and OSNR penalty
Solution Approach 1:
The patent extracts and removes the harmful side-lobes from the optical signal path by inserting comb filters at strategic locations in the ROADM architecture. These filters specifically target and eliminate the side-lobe components while preserving the main signal wavelengths, thereby resolving the OSNR penalty caused by the MEMS-based wavelength selective switches.
Solution Approach 2:
The patent introduces comb filters as intermediary components between the WSS and other network elements. These filters act as mediators that selectively pass the desired wavelengths while blocking the harmful side-lobes, thus improving OSNR without compromising the dynamic switching capability of the ROADM.
2Device complexity
If conventional ASE compensation methods are used that assume even ASE distribution, then device complexity is reduced, but measurement precision of actual ASE conditions deteriorates leading to inaccurate compensation
Solution Approach 1:
The patent implements a feedback mechanism where optical monitors continuously measure the actual OSNR and ASE levels at various points in the network. This measured information is fed back to the control system, which then adjusts the amplifier gain and comb filter settings dynamically to compensate for the uneven ASE distribution caused by side-lobes, achieving accurate compensation without excessive complexity.
3Ease of operation
If amplifier target power is set without considering side-lobe ASE, then ease of operation is improved, but signal power drops occur due to unexpected ASE sharing of total output power
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-compensating for the expected ASE power in side-lobes when setting the amplifier target power. The system determines the side-lobe characteristics in advance and adjusts the amplifier gain accordingly before signal transmission, ensuring that sufficient power is allocated to maintain signal levels despite the presence of side-lobe ASE.
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
The solution effectively reduces passband side-lobes and maintains signal OSNR by accurately estimating ASE noise and adjusting amplifier settings, preventing unexpected signal power drops and improving network performance.
Implementation Method 1
an optical pre-amplifier including an input with multiple wavelengths, a wavelength selective switch connected to the optical pre-amplifier, wherein the wavelength selective switch includes a variable optical attenuator on a connection from the optical pre-amplifier and a filter for each of the multiple wavelengths
Implementation Method 2
wherein the wavelength selective switch includes a variable optical attenuator on a connection from the optical pre-amplifier
Implementation Method 3
an optical pre-amplifier including an input with multiple wavelengths
Implementation Method 4
The WSS 10 includes a MEMS mirror 12 for each of the wavelengths λ1, λ2, . . . λn. The MEMS mirror 12 is a micro-mirror that deflects the optical signal to an appropriate output port 13
Data Source
AI summary
Systems and methods to reduce passband side-lobes associated with WSS-based ROADMs by applying a filter on each channel are provided. In an exemplary embodiment, a comb filter, such as a thin film filter or an interleaver, is utilized. Additionally, the present invention provides systems and methods to adaptively control amplifier target power and per wavelength target power to maintain signal launching power as per design in networks with WSS-based ROADMs. Accordingly, signal OSNR does not collapse faster than other similar configured system without WSS-based ROADM. In order to correct amplifier target power, the present invention utilizes system information about side-lobe size and OSNR at each amplifier.