Multimode Fiber Intrusion Detection via Modal Power Distribution
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Solution Overview
Problem
Current intrusion detection systems for multimode fiber optic cables are limited by the Base-Rate Fallacy, which leads to false alarms and inability to detect passive optical fiber tapping, as they rely on power loss measurements that cannot detect subtle intrusions before actual power loss occurs.
Innovation Solution
A method that involves launching pulsed light signals into a multimode optical fiber to establish a non-uniform mode field power distribution, detecting changes in modal power distribution, and generating an alarm for any manipulation, allowing for the detection of fiber movement or intrusion before optical power loss, using a combination of time division signal separation and analysis of Rayleigh backscattered components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If power loss measurement methods are used for intrusion detection, then the system can detect obvious fiber manipulation, but it cannot detect passive optical fiber tapping or subtle intrusions before power loss occurs
Solution Approach 1:
The patent changes the detection parameter from optical power loss to modal power distribution. By monitoring how light distributes across different modes in the fiber, the system can detect subtle physical disturbances that precede actual power loss, thereby improving detection sensitivity without increasing false alarms.
Solution Approach 2:
The system performs preliminary detection of fiber manipulation by monitoring modal power distribution changes before they result in measurable power loss. This allows the system to alert operators to potential intrusions early, before the intrusion completes or causes actual data theft.
2Measurement precision
If software-based IDS is deployed to capture and analyze network packets, then intrusion patterns can be detected, but the system complexity increases and processing power is burdened
Solution Approach 1:
The patent replaces software-based packet analysis with a physical layer optical monitoring system. By using optical sensors to detect modal power distribution changes, the system eliminates the need for complex software processing and packet capture, significantly reducing system complexity while maintaining detection capability.
3Ease of operation
If bend couplers are used for fiber tapping, then data stream can be intercepted, but the method introduces detectable light power loss
Solution Approach 1:
The monitoring system performs preliminary detection of fiber manipulation by tracking modal power distribution changes that occur during the tapping process itself. This allows detection of the intrusion attempt before the intruder completes the tap, even if they use sophisticated low-loss methods.
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 effectively detects and locates physical intrusions into multimode fiber optic cables before any optical power loss occurs, minimizing false alarms and ensuring the security of the fiber optic communication network by identifying mechanical disturbances and handling events.
Implementation Method 1
optical fibers are easily tapped and the data stream intercepted. One relatively simple non-interruptive tapping method involves placing a bend coupler on the fiber to be tapped. A controlled bend of a critical radius is placed on the fiber. This causes a small spatial distortion in the core/cladding guiding properties and a fraction of the light escapes the fiber.
Implementation Method 2
detecting the modal power distribution of a series of the light signals from the Rayleigh backscattering components in discrete time steps to generate for each time step data relating to the modal power distribution
Data Source
AI summary
A telecommunications multimode optical fiber is secured against intrusion by detecting manipulation of the optical fiber prior to an intrusion event. Pulses are injected using a launch arrangement which generates a narrow spectral width, under-filled, non-uniform mode field power distribution in the multimode optical fiber and Fresnel reflections and Rayleigh backscattering from the pulse are detected at the transmit end to monitor the modal power distribution in the fiber which changes on manipulation of the fiber. The Rayleigh backscattering time sliced data can be stored in a register until an intrusion event is detected. The detection is carried out by a modal power distribution detection system which includes an optical coupler to tap off a portion of the light which contains the higher order signal modes.