Optical Mode Converter for Quantum Communication
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Solution Overview
Problem
Conventional quantum key distribution (QKD) technologies are not suitable for use with multimode optical fibres, as they cause significant signal and phase distortions due to the excitation of multiple modes.
Innovation Solution
The implementation of an optical communication system that includes a transmitter optically coupled to a single-mode optical channel and a multimode optical fibre, with an optical mode converter that gradually changes the transverse profile of propagating light to match the target mode of the multimode fibre, ensuring robust signal transmission without significant distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional QKD technologies are used with multimode optical fibres, then the fibre can be deployed for quantum communication, but significant signal and phase distortions occur due to excitation of multiple modes
Solution Approach 1:
The patent applies local quality by designing mode converters with specific spatially varying refractive index profiles that are tailored to the particular multimode fibre being used. Each mode converter has a customized transverse profile that matches the target mode's characteristics, allowing selective excitation of only the desired mode while suppressing others. This local optimization of the converter structure at each position across the fibre cross-section enables high-fidelity mode coupling.
Solution Approach 2:
The patent employs parameter changes by systematically varying the transverse profile parameters of the mode converters to match different target modes. The refractive index distribution, core diameter, and profile shape parameters are adjusted to optimize coupling to specific modes (LP01, LP11, etc.). This parameter optimization ensures that the converter transitions smoothly between the single-mode fibre mode and the target multimode fibre mode, minimizing distortions.
2Quantity of substance
If multiple modes are excited in multimode fibres, then the fibre can transmit more information, but signal and phase distortions increase significantly
Solution Approach 1:
The patent applies the taking out principle by selectively extracting and eliminating unwanted modes from the transmission. The mode converters are designed to couple exclusively to the target mode while rejecting all other modes. By taking out the harmful multi-mode excitation and leaving only the desired single mode, the system achieves both high information capacity (through optimized single-mode transmission) and high signal integrity (by eliminating mode-related distortions).
Solution Approach 2:
The patent applies inversion by reversing the conventional approach: instead of trying to control and manage multiple excited modes, the system inverts the strategy by designing converters that naturally excite only one specific mode from the outset. This inverted approach of selective single-mode excitation rather than multi-mode control simplifies the transmission and eliminates the need for complex mode management while maintaining high information capacity.
3Reliability
If single-mode fibres are used for QKD, then signal transmission is reliable, but the system cannot utilize existing multimode fibre networks
Solution Approach 1:
The patent applies the intermediary principle by introducing mode converters as mediator devices between single-mode fibres and multimode fibres. These converters serve as the intermediate coupling elements that bridge the two different fibre types. The first converter acts as an intermediary to launch light from the single-mode fibre into a specific mode of the multimode fibre, while the second converter acts as an intermediary to couple light from the multimode fibre back into a single-mode fibre at the receiver, thereby enabling reliable transmission through the multimode network.
Solution Approach 2:
The patent applies universality by designing a multi-functional mode converter system that can work with different types of multimode fibres and support various quantum communication protocols. The converters are designed to be adaptable to different fibre parameters and can handle both quantum key distribution and potentially other quantum communication applications, making the system universally compatible with existing multimode fibre networks while maintaining single-mode transmission quality.
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 solution allows for the robust transmission of optical signals over multimode fibres by coupling the signal to substantially only one mode of the multimode fibre, reducing signal and phase distortions and improving the performance of quantum communication systems.
Implementation Method 1
an optical mode converter configured to optically couple the mode of the channel to the target mode of the multimode fibre by gradually changing a transverse profile of propagating light received from the channel to match a transverse profile of the target mode of the multimode fibre
Data Source
AI summary
An optical communication system comprises a transmitter optically coupled to a single-mode optical channel, and a multimode optical fibre configured to support transmission of a plurality of guided modes. The plurality of guided modes comprises a target mode. The system further comprises an optical mode converter configured to optically couple the mode of the channel to the target mode of the multimode fibre by gradually changing a transverse profile of propagating light received from the channel to match a transverse profile of the target mode of the multimode fibre.