Bidirectional Time Division Multiplexing for Fiber-Optic Time Transfer

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Solution Overview

Problem

Current high-precision time synchronization methods, such as GPS common view and two-way satellite time transfer, face limitations in precision and stability due to external influences, while fiber-optic time transfer methods struggle with Rayleigh backscattering and dispersion issues over long distances, leading to reduced precision and increased complexity and cost.

Innovation Solution

A high-precision fiber-optic time transfer method utilizing bidirectional time division multiplexing over a single fiber with the same wavelength (BTDM-SFSW) is introduced, which pre-adjusts and dynamically synchronizes time signals to mitigate the effects of Rayleigh backscattering and dispersion, ensuring stable and precise two-way time transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If bidirectional WDM transmission method is adopted to suppress Rayleigh backscattering and Fresnel reflection, then the transmitted timing signals are protected, but bidirectional propagation delay asymmetry increases with distance due to fiber dispersion

Engineering Contradiction:

ImproveRayleigh backscattering and Fresnel reflectionVSAvoidpropagation delay asymmetry

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent replaces the WDM wavelength division multiplexing scheme with a TDM time division multiplexing scheme. Instead of using different wavelengths to separate bidirectional signals, the invention uses different time slots, allowing single-wavelength transmission that eliminates dispersion-induced delay asymmetry while still suppressing backscattering and reflection effects.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the transmission parameter from wavelength division (WDM) to time division (TDM). By transmitting signals at different time slots rather than different wavelengths, the system maintains the ability to suppress harmful optical effects while eliminating the propagation delay asymmetry caused by fiber dispersion.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If spread spectrum coding/decoding is used to realize two-way time transfer over single fiber, then Rayleigh backscattering and Fresnel reflection are suppressed, but the system complexity and cost increase

Engineering Contradiction:

ImproveRayleigh backscattering and Fresnel reflectionVSAvoidspread spectrum coding/decoding complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent replaces complex spread spectrum coding/decoding mechanisms with a simpler time division multiplexing approach. The TDM scheme achieves the same goal of suppressing optical backscattering and reflection through time-gated transmission, eliminating the need for complex coding and decoding operations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent adopts a simpler, more cost-effective TDM transmission scheme that does not require expensive spread spectrum equipment. The time-division approach uses standard optical components and simpler control logic, reducing system cost and complexity while maintaining effectiveness in suppressing harmful optical effects.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Stability of the object's composition

If WDM all-optical path is used for two-way fiber-optic time transfer, then path symmetry is maintained, but propagation delay asymmetry increases with distance due to fiber dispersion

Engineering Contradiction:

Improvepath symmetryVSAvoidpropagation delay asymmetry

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent substitutes the WDM all-optical path method with a TDM-based approach. By using time division multiplexing on a single wavelength, the system maintains path symmetry through identical fiber usage while eliminating the propagation delay asymmetry that arises from wavelength-dependent dispersion in WDM systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS10063315B2Method and system for high-precision two-way fiber-optic time transfer

Publication Date: 2018.08.28 SHANGHAI JIAOTONG UNIV

AI summary

A method and system for high-precision two-way fiber-optic time transfer comprising pre-adjusting, including calculating a local timing signal adjustment amount for a first fiber-optic time synchronization unit and a second fiber-optic time synchronization unit, and the corresponding adjusting. and following steps including the two fiber-optic time synchronization units conducting two-way time transfer based on a time division multiplexing transmission over an optical fiber link. The present invention realizes high-precision fiber-optic time transfer by combining two-way time transfer and bidirectional time division multiplexing technique.