Multi-Phase Correlation OTDR for 1 mm Spatial Resolution
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Solution Overview
Problem
Current methods for determining the time-of-flight of an optical signal in optical fibers lack precision and accuracy, especially when the ends of the fiber are at different locations, and are costly to implement for high-precision measurements.
Innovation Solution
The method involves using a correlation OTDR with noise-like statistical properties and multi-phase sampling and slicing to derive multiple receive code sequences from electrical return signals, allowing for improved resolution and accuracy by calculating a multi-phase correlation function, which can identify the reflection point with higher precision than single-phase methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-bit A/D converter is used for low-cost implementation, then device cost is reduced, but measurement precision is limited to the inverse of the data rate
Solution Approach 1:
The patent divides the measurement process into multiple phases by sampling the electrical return signal at different phase positions. This segmentation allows the system to achieve higher precision than the inverse of the data rate by combining multiple low-precision single-bit measurements taken at different phases, effectively overcoming the resolution limit of the single-bit A/D converter while maintaining low device cost.
Solution Approach 2:
The patent employs periodic sampling at multiple phase positions within each bit period. By systematically varying the sampling phase and combining the results through correlation processing, the system achieves time-of-flight accuracy of 10 ps, which is significantly better than what a single-phase single-bit measurement could provide, thus resolving the contradiction between low cost and high precision.
2Measurement precision
If multi-phase sampling and slicing is used to improve resolution, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses the inherent noise-like statistical properties of the optical signal itself to perform the measurement. By correlating the received signal with a known pseudo-random code sequence, the system automatically achieves high-resolution time-of-flight measurement without requiring complex external reference systems or additional hardware, thus improving precision while limiting the increase in device complexity.
Solution Approach 2:
The patent changes the sampling phase parameter systematically across multiple measurement cycles. By varying the phase position and combining the results through correlation processing, the system achieves 1 mm spatial resolution. This parameter-based approach avoids the need for complex hardware modifications, resolving the contradiction between improved resolution and device complexity.
3Measurement precision
If correlation OTDR with broad optical spectrum is used for high precision, then spatial resolution is improved to 82 mm, but the system requires complex hardware implementation
Solution Approach 1:
The patent replaces complex optical hardware (broad spectrum sources, complex correlators) with a simpler electronic implementation. By using a single-bit A/D converter and performing correlation processing in the digital domain, the system achieves comparable or better spatial resolution (1 mm) without requiring complex optical hardware, thus substituting mechanical/optical complexity with simpler electronic/digital processing.
Data Source
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AI summary
The invention relates to a method of determining a time-of-flight of an optical signal between a starting point of an optical path and a reflection point within the optical path, especially an optical fiber, the method comprising the steps of supplying to the optical path (116) at least one binary optical probing signal (Sopt) comprising a sequence of pulses according to a binary transmit code sequence, the sequence of pules having a predetermined bit duration, phase and bit rate; detecting at least one electrical return signal (Rel) according to at least one optical return signal (Ropt) returning from the optical path (116) in response to a corresponding one of the at least one optical probing signals (Sopt) using direct detection; deriving at least one receive code sequence by sampling and slicing the at least one electrical return signal (Rel), wherein a sampling rate corresponding to the bit rate of the sequence of pulses of the at least one optical probing signal (Sopt) is used; determining a correlation function by correlating the transmit code sequence and the at least one receive code sequence; and identifying a main peak of the correlation function that corresponds to the reflection point and a time position of the main peak, and determining the time-of-flight as the time position of the main peak. According to the invention, two or more receive code sequences are derived from one or more electrical return signals (Rel), wherein at least two receive code sequences are generated by sampling and slicing the same one of the one or more electrical return signals (Rel) at different phase positions, and/or from two or more electrical return signals (Rel), wherein at least two receive code sequences are generated by sampling and slicing different ones of the two or more electrical return signals (Rel) at different phase positions. A multi-phase correlation function is determined by calculating, for each receive code sequence that has been determined for a given phase position, values of a discrete correlation function by correlating the respective receive code sequence and the transmit code sequence of the corresponding optical probing signal (Sopt), and interleaving the values of the at least two discrete correlation functions according to their respective phase position, or by, if required, interleaving the receive code sequences that have been determined for different phase positions according to their respective phase position in order to create an interleaved receive code sequence, and creating an interleaved transmit code sequence by interleaving a number of transmit code sequences that corresponds to the number of different phase positions, and correlating the interleaved receive code sequence and the interleaved transmit code sequence. According to the invention, the multi-phase correlation function is used to identify the main peak that corresponds to the reflection point. The invention further relates to a device for determining a time-of-flight of an optical signal between a starting point of an optical path and a reflection point within the optical path, especially an optical fiber, that implements this method.