Optical Circulator WDM Coupling for Low-Loss Spectral Flexibility
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Solution Overview
Problem
Existing optical networks face challenges in extending their capacity and optimizing spectral management with minimal insertion loss and maximum flexibility, particularly in wavelength division multiplexing systems, where conventional methods either lack flexibility or incur high insertion losses.
Innovation Solution
The use of optical circulators with low insertion loss (<1 dB) for directional coupling in wavelength division multiplexing systems, allowing for flexible wavelength management and integration in terminal nodes and inline amplifier nodes, combined with wavelength selective switches and bandpass filters to manage spectral capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If wavelength selective switches (WSS) are used for flexible wavelength selection, then wavelength flexibility is improved, but insertion loss increases significantly (5 to 10 dB)
Solution Approach 1:
The system segments the optical signal path by separating the flexible wavelength selection function (in the electrical domain at coherent receivers/transmitters) from the optical transmission path. This allows the optical path to use simple, low-loss components while flexibility is achieved through digital signal processing and electrical switching at the coherent interfaces.
Solution Approach 2:
The patent replaces traditional mechanical/optical wavelength switching mechanisms (WSS) with electronic/digital wavelength selection through coherent detection and digital signal processing. This substitution eliminates the need for high-loss optical switching components while maintaining full wavelength flexibility through electrical domain operations.
2Loss of energy
If filter-based approaches are used for wavelength selection, then insertion loss is reduced, but wavelength flexibility is lost (fixed controllable)
Solution Approach 1:
The patent replaces fixed optical filters with dynamic electrical filtering through coherent detection and digital signal processing. The coherent receivers convert optical signals to electrical domain where flexible, software-defined filtering and wavelength selection can be performed without the insertion loss penalties of optical filters.
Solution Approach 2:
The system changes the operating domain from optical filtering to electrical/digital filtering. By performing wavelength selection and signal processing in the electrical domain after coherent detection, the system achieves both low loss (characteristic of simple optical paths) and high flexibility (characteristic of software-defined processing).
3Adaptability or versatility
If existing optical networks are extended with additional network elements, then spectral capacity management capability is improved, but hardware requirements and footprint increase
Solution Approach 1:
The patent makes existing coherent optical network elements (receivers and transmitters) perform additional spectral capacity management functions through software-defined processing. These multi-functional elements can handle both traditional coherent communication and advanced spectral management, eliminating the need for dedicated hardware additions.
Solution Approach 2:
The system enables existing network elements to self-manage spectral capacity through integrated digital signal processing and control plane software. The coherent receivers and transmitters automatically perform wavelength assignment, spectral optimization, and capacity management without requiring external dedicated management hardware.
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 provides minimal insertion loss and maximum flexibility in managing spectral capacity, enabling efficient system extensions with reduced hardware requirements and maintaining existing network management solutions.
Implementation Method 1
directional coupling spectral management approach employed by the method and apparatus according to the present invention. The directional coupling provided by the circulator combines the two advantages of low loss coupling of the WDM subsystems
Data Source
Figure 1A~4B
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AI summary
An apparatus (1) for management of a spectral capacity of a wavelength division multiplexing, WDM, system comprising at least one pair of transmission fibers provided for transporting optical signals, wherein each transmission fiber of a transmission fiber pair (3) is connected to a first port of an optical circulator (2) having at least two additional ports and adapted to transmit an incoming optical signal entering one of its ports via its next port, wherein WDM subsystems (A, B) configured with counter-propagating assignable wavelengths are connected to associated ports of the optical circulator (2) of said apparatus (1).