Highly accurate fiber transfer delay measurement with large dynamic range

Abstract

A novel and efficient method for fiber transfer delay measurement is demonstrated. Fiber transfer delay measurement in time domain is converted into the frequency measurement of the modulation signal in frequency domain, accompany with a coarse and easy ambiguity resolving process. This method achieves a sub-picosecond resolution, with an accuracy of 1 picosecond, and a large dynamic range up to 50 km as well as no measurement dead zone. References and links1. B. Mukherjee, "WDM optical communication networks: progress and challenges," IEEE J. Sel. Areas Comm.18(10), 1810-1824 (2000). 2. B. Lee, "Review of the present status of optical fiber sensors," Opt. Fiber Technol. 9(2), 57-79 (2003).

Accurate and fast fiber transfer delay measurement based on phase discrimination and frequency measurement

“…In the previous method [22], a coarse FTD (tcoarse) measurement using conventional pulse method is employed to resolve this ambiguity. For an operational frequency at 1 GHz, the coarse FTD measurement uncertainty should be below 250 ps.…”

“…Under the FUT length below 50 km, the FTD will not exceed 0.5 ms, resulting in a maximum frequency scanning step of 500 Hz. To eliminate the measurement dead zone, a 5 km long fiber is inserted into the system [22]. …”

“…For the latter, due to the fast frequency locking operation, the time interval could be less than 2 s, making the FTD variation-induced frequency shift not to exceed 3 Hz (corresponding to 10℃/hour temperature variation). According to [22], under the operation frequency of 1 GHz, coarse t  < 250 ps is required for accurate ambiguity resolving. Consequently, for FTD below 0.5 ms (50 km FUT), the frequency scanning range 21 () ff  should be more than 6 MHz.…”

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“…When the microwave signal is frequency-locked to the transmission delay, the time delay measurement can be implemented by a frequency measurement. Figure 4 shows the schematic diagram that consists of a fiber transmission delay (FTD) measurement loop and a system delay control (SDC) loop [14] . The precision of this system is mainly limted by the SDC loop, because compensating the system delay fluctuation by changing the temperature of the internal fiber will lead to uncertainty of 0.5 ps.…”

“…Various optical time delay measurement technologies have been proposed and studied in the last decades, which can be generally divided into three categories: (1) the time domain measurement techniques, such as optical time domain reflectometry (OTDR), chaotic-light-based measurement, and optical femtosecond-pulse-based measurement [8][9][10] ; (2) the frequency domain measurement techniques, such as optical frequency domain reflectometry (OFDR) [11] , mode-locked laser repetition frequency measurement [12] , free-running laser mode-spacing measurement [13] , and phase-locked-loop-based measurement [14] ; (3) the phase-derived range measurement, including direct phase-derived range measurement [15] and indirect phase-derived range measurement.…”