Bidirectional Optical Link Asymmetric Mode Coupling
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Solution Overview
Problem
Existing bidirectional optical links over a single multimode fiber face significant insertion loss and logistical challenges due to the need for wavelength separation optics and complex transceiver labeling, which increase costs and alignment requirements, and are not robust for high-speed or long-distance applications.
Innovation Solution
The use of asymmetric mode-coupling in multimode fibers, where a single transverse mode laser is coupled to a multimode fiber using a tapered coupler to excite high-order modes, resulting in low loss for detector coupling and high loss for laser coupling, allowing for identical transceivers and standard optical connectors, with no stringent fiber alignment requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wavelength separation optics are used to achieve bidirectional communication over a single fiber, then laser coupling is avoided and communication is enabled, but insertion loss increases and cost increases
Solution Approach 1:
The patent uses asymmetric mode coupling where the local coupler at each end couples light differently in opposite directions. The coupler is designed to couple outgoing light efficiently while strongly rejecting incoming light from the opposite direction, creating asymmetric optical paths that eliminate the need for wavelength separation optics and reduce insertion loss.
Solution Approach 2:
The bidirectional coupler is implemented as a local component at each end of the fiber link rather than using distributed wavelength separation optics along the entire link. This local implementation reduces complexity and insertion loss while maintaining laser stability through the asymmetric coupling mechanism.
2Reliability
If wavelength separation optics are used for bidirectional communication, then laser coupling is prevented, but device complexity and alignment requirements increase
Solution Approach 1:
The asymmetric mode coupling approach replaces complex wavelength separation optics with a simpler asymmetric coupler design. The coupler's asymmetric structure inherently provides directionality and laser isolation without requiring additional filters, gratings, or complex optical assemblies, thereby reducing device complexity.
Solution Approach 2:
The patent extracts the wavelength separation function entirely from the system by using asymmetric mode coupling in the multimode fiber itself. Instead of adding separate wavelength separation components, the solution removes the need for them by exploiting the asymmetric coupling properties of the fiber-optic interface.
3Adaptability or versatility
If wavelength multiplexing is used for bidirectional links, then communication is enabled, but logistical challenges and labeling requirements arise
Solution Approach 1:
The asymmetric coupler design enables both ends of the link to use identical transceivers with the same wavelength lasers. Each transceiver can operate in both transmit and receive modes without requiring different wavelength assignments or labeling, making the system universal and simplifying installation and operation.
Solution Approach 2:
Instead of using different wavelengths for different directions (traditional wavelength multiplexing), the patent inverts the approach by using the same wavelength in both directions and achieving directionality through asymmetric spatial mode coupling. This eliminates the need for wavelength-based labeling and simplifies logistics.
4Reliability
If attenuators are used with same wavelength lasers for bidirectional links, then laser coupling is reduced, but link margin is compromised and precision alignment is required
Solution Approach 1:
The asymmetric mode coupling provides inherent directionality where the coupler allows efficient light transmission in the forward direction while strongly rejecting light from the opposite direction. This asymmetric rejection provides laser stability without requiring attenuators that would compromise link margin, as the rejection is achieved through mode mismatch rather than power attenuation.
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 achieves very low loss for transmitter-to-receiver coupling while maintaining laser stability with greater than 40 dB isolation, using identical transceivers and standard connectors, and allows for flexible fiber insertion, reducing costs and complexity.
Implementation Method 1
The use of asymmetric mode-coupling in multimode fibers, where a single transverse mode laser is coupled to a multimode fiber using a tapered coupler to excite high-order modes
Implementation Method 2
A detector coupled to predominantly all the modes of the channel via the waveguide or fiber based bidirectional coupler
Data Source
AI summary
A transceiver for use in a bidirectional optical communication link over a multimode channel is provided. The transceiver includes a single transverse mode light source in a transmitter. A waveguide or fiber based bidirectional coupler projects the transmitter mode to the high modes of the multimode channel. A detector coupled to predominantly all the modes of the channel via the waveguide or fiber based bidirectional coupler.